Ventricular tachycardia in the infarcted, Langendorff-perfused human heart: role of the arrangement of surviving cardiac fibers

Comparison of radiofrequency ablation in normal versus scarred myocardium

INTRODUCTION

Reentrant circuits causing ventricular tachycardia are closely associated with previously scarred myocardium. The presence of scar has been blamed for the poor success rate of radiofrequency ablation (RFA) in that context. This article investigates the in vivo effects of radiofrequency ablation in myocardium scarred from acute myocardial infarction.

METHODS AND RESULTS

Anterior myocardial infarction was induced in five dogs by ligating the left anterior descending artery. The mean left ventricular ejection fraction after infarction was 38%. At a mean of 15 weeks following myocardial infarction, 50 RFA lesions were created in random order, 25 in scarred and 25 in normal myocardium using a needle electrode (21 gauge, 5 mm in length) introduced from the epicardium of the left ventricle at thoracotomy. During unipolar temperature-controlled RFA (90 degrees C for 60 seconds), intramural temperatures were measured by thermistors at distances of 1, 2, 3, 4, and 5 mm from the ablating electrode. The margins of the lesions were clearly discernible in scar at histological examination in 64% of ablations where the scarring was patchy. There were no significant differences between lesion sizes, intramural temperatures at different distances, total energy required for ablation, or mean impedance during ablation of normal versus scarred myocardium.

CONCLUSIONS

Scar does not affect lesion size or intramural temperature profile during RFA if electrode size, tissue contact, and tip temperature are controlled. More radiofrequency energy is not required to maintain tip temperature at 90 degrees C in scar compared to normal myocardium.

Isolated Potentials During Sinus Rhythm and Pace-Mapping Within Scars as Guides for Ablation of Post-Infarction Ventricular Tachycardia

OBJECTIVES

The purpose of this study was to identify ventricular tachycardia (VT) isthmus sites by pace-mapping within scar tissue and to identify electrogram characteristics that are helpful in identifying VT isthmus sites during sinus rhythm (SR).

BACKGROUND

Pace-mapping has been used in the scar border zone to identify the exit site of post-infarction VT.

METHODS

In 19 consecutive patients (18 men, mean age 66 +/- 9 years, mean ejection fraction 0.24 +/- 0.12) with post-infarction VT, a left ventricular voltage map was generated during SR. Pace-mapping was performed at sites with abnormal electrograms or isolated potentials. Radiofrequency ablation was performed at isthmus sites as defined by pace-mapping (perfect pace-map = 12/12 matching electrocardiogram leads; good pace-map = 10/12 to 11/12 matching electrocardiogram leads) and/or entrainment mapping.

RESULTS

A total of 81 VTs (mean cycle length 396 +/- 124 ms) were inducible. In 16 of the 19 patients, a total of 41 distinct isthmus areas of 41 distinct VTs were identified and successfully ablated. All but one displayed isolated potentials during SR. Furthermore, 22 of the 81 VTs (27%) for which no isthmus was identified became noninducible after ablation of a targeted VT. The 16 patients in whom > or =1 isthmus was identified and ablated were free of arrhythmic events during a mean follow-up of 10 months.

CONCLUSIONS

During SR, excellent or good pace-maps at sites of isolated potentials within areas of scar identify areas of fixed block that are protected and part of the critical isthmus of post-infarction VT. Shared common pathways might explain why non-targeted VTs might become noninducible after ablation of other VTs.

Structure-Related Initiation of Reentry by Rapid Pacing in Monolayers of Cardiac Cells

This study examines how a zigzag pattern of conduction, a form of structural heterogeneity frequently found in old or diseased hearts, affects the vulnerability to reentry during rapid pacing. A central rectangular island (8×4 mm) containing a predefined zigzag pattern was created in cultured isotropic monolayers of neonatal rat ventricular myocytes. Impulse propagation was optically mapped from 253 sites using voltage-sensitive dye and was anisotropic within the zigzag island. With increasing interval between neighboring transverse connections ( a ), relative to the distance between longitudinal strands ( b ), transverse conduction velocity (CV) decreased to 66±6%, 20±2%, and 15±2% of CV in the surrounding isotropic region, whereas longitudinal CV increased to 102±8%, 113±12%, and 131±23% for a : b ratios of 1:1, 1:5, and 1:9, respectively. During rapid pacing, propagation distal to the island was steered from the side of the island with more transverse connections (“dominant” side) toward the side with fewer connections (“weak” side). Increased asymmetry in the pattern accentuated this effect, and resulted in increased rate-dependent differences in CV on the 2 sides. Consequently, a functional obstacle formed on the weak side, followed by development of single loop reentry. The reentrant wave revolved around a line of block defined by the border of the island. Reentry chirality was determined by the weak side location, and the pacing rate needed to initiate reentry decreased with increased asymmetry in the pattern. In conclusion, reentry is readily induced by rapid pacing in confluent cardiac cell monolayers containing a central and asymmetric island of zigzag conduction.

Relationship Between Successful Ablation Sites and the Scar Border Zone Defined by Substrate Mapping for Ventricular Tachycardia Post-Myocardial Infarction

INTRODUCTION

It is unknown if identification of scar border zones by electroanatomical mapping correlates with successful ablation sites determined from mapping during ventricular tachycardia (VT) post-myocardial infarction (MI). We sought to assess the relationship between successful ablation sites of hemodynamically stable post-MI VTs determined by mapping during VT with the scar border zone defined in sinus rhythm.

METHODS AND RESULTS

Forty-six patients presenting with hemodynamically stable, mappable monomorphic VT post-MI and who had at least one such VT successfully ablated were prospectively included in the study. In each patient, VT was ablated by targeting regions during VT that exhibited early activation, +/- isolated mid-diastolic potentials, and concealed entrainment suggesting a critical isthmus site. Prior to ablation, a detailed sinus-rhythm CARTO voltage map of the left ventricle was obtained. A voltage <0.5 mV defined dense scar. Successful VT ablation sites were registered on the sinus voltage map to assess their relationship to the scar border zone. Of the 86 VTs, 68% were successfully ablated at sites in the endocardial border zone. The remaining VTs had ablation sites within the scar in (18%), in normal myocardium (4%), and on the epicardial surface (10%). There were no significant differences in VT recurrence amongst the different groups.

CONCLUSION

Successful ablation sites of hemodynamically stable, monomorphic VTs post-MI are often located in the scar border zone as defined by substrate voltage mapping. However, in a sizable minority, ablation sites are located within endocardial scar, epicardially, and even in normal myocardium.

Basic mechanisms of cardiac impulse propagation and associated arrhythmias

Propagation of excitation in the heart involves action potential (AP) generation by cardiac cells and its propagation in the multicellular tissue. AP conduction is the outcome of complex interactions between cellular electrical activity, electrical cell-to-cell communication, and the cardiac tissue structure. As shown in this review, strong interactions occur among these determinants of electrical impulse propagation. A special form of conduction that underlies many cardiac arrhythmias involves circulating excitation. In this situation, the curvature of the propagating excitation wavefront and the interaction of the wavefront with the repolarization tail of the preceding wave are additional important determinants of impulse propagation. This review attempts to synthesize results from computer simulations and experimental preparations to define mechanisms and biophysical principles that govern normal and abnormal conduction in the heart.

Detection of the fingerprint of the electrophysiological abnormalities that increase vulnerability to life-threatening ventricular arrhythmias

Reduction of sudden death requires accurate identification of patients at risk for ventricular tachycardia (VT) and effective therapies. The Multicenter Unsustained Tachycardia Trial and Multicenter Automatic Defibrillator Implantation Trials demonstrate that the implantable cardioverter defibrillator impacts favorably on the incidence of VT in patients with myocardial infarction, underscoring the need to detect the electrophysiologic abnormalities required for the development of VT. Methods used for this purpose include: Holter monitoring, ejection fraction, signal-averaged ECG, heart rate variability, T-wave alternans, baroreflex sensitivity, and programmed stimulation. Performance of each method alone has demonstrated high-negative but low-positive predictive values. Recent studies confirm that their use in combination augments performance.A second approach for improving performance has been to reexamine how well each method detects the electrophysiological derangements that lead to VT. Our recent work has focused on the signal-averaged ECG. Judging from transmural maps of ventricular activation during VT and sinus rhythm obtained from patients, late potentials fail to detect completely signals from myocardium responsible for VT. To obviate this limitation we developed an approach based on inferred epicardial potentials in the frequency domain from 190-surface ECGs using individualized heart-torso models. Torso geometry and electrode positions are measured with a 3-armed digitizer. The location of cardiac structures is determined using echocardiography. The pericardial surface is approximated by a sphere that encloses the heart. Epicardial potentials are inferred using the boundary element method with zero-order Tikhonov regularization and the Composite Residual Smoothing Operator over the QRS complex. Studies are underway to determine if analysis of bioelectrical signals enveloping arrhythmogenic tissue improves identification of patients vulnerable to VT.

Catheter ablation of ventricular tachycardia in remote myocardial infarction: substrate description guiding placement of individual linear lesions targeting noninducibility

INTRODUCTION

The aim of this study was to describe the arrhythmogenic substrate in postinfarction patients with ventricular tachycardia (VT) guiding the placement of individual strategic linear lesions transecting all potential isthmuses using target area maps with limited mapping points to allow short procedure times.

METHODS AND RESULTS

In 28 patients with pleomorphic, unstable, and/or incessant VT, electroanatomic voltage mapping was performed in conjunction with limited sinus rhythm mapping, pace mapping, and activation mapping. Radiofrequency (RF) energy was applied directly within the low-voltage areas of the chronically infarcted areas or in the border zone. Ablation lines typically were perpendicular to the course of the presumed central common pathways. The maps consisted of 63 +/- 30 mapping points. An average lesion line length of 46 +/- 21 mm was placed with 17 +/- 7 RF pulses. Twenty-two (79%) of the 28 patients were rendered completely noninducible at the end of the procedure. Procedure time measured 134 +/- 41 minutes. No major complications were observed. Six (27%) of 22 patients who were rendered completely noninducible experienced VT recurrence during follow-up versus 4 (67%) of 6 patients who were still inducible after ablation (P = 0.06).

CONCLUSION

Individually tailored substrate description guiding the placement of linear lesion lines transecting potential isthmuses rendered 80% of the patients completely noninducible. The construction of regional target area maps allowed short procedure times, with a resulting low incidence of complications in these critically ill patients.

Sympathetic nervous system activity and ventricular tachyarrhythmias: recent advances

Sympathetic nervous system activity (SNSA) is believed to participate in the genesis of ventricular tachyarrhythmias (VTA) but understanding has been impeded by the number and complexity of effects and the paucity of data from humans. New information from studies of genetic disorders, animal models, and spontaneous human arrhythmias indicates the importance of the temporal pattern of SNSA in arrhythmia development. The proarrhythmic effects of short-term elevations of SNSA are exemplified by genetic disorders and include enhancement of early and delayed afterdepolarizations and increased dispersion of repolarization. The role of long-term elevations of SNSA is suggested by animal models of enhanced SNSA signaling that results in apoptosis, hypertrophy, and fibrosis, and sympathetic nerve sprouting caused by infusion of nerve growth factor. Processes that overlap short- and long-term effects are suggested by changes in R-R interval variability (RRV) that precede VTA in patients by several hours. SNSA-mediated alterations in gene expression of ion channels may account for some intermediate-term effects. The propensity for VTA is highest when short-, intermediate, and long-term changes are superimposed. Because the proarrhythmic effects are related to the duration and intensity of SNSA, normal regulatory processes such as parasympathetic activity that inhibits SNSA, and oscillations that continuously vary the intensity of SNSA may provide vital antiarrhythmic protection that is lost in severe heart failure and other disorders. These observations may have therapeutic implications. The recommended use of beta-adrenergic receptor blockers to achieve a constant level of inhibition does not take into account the temporal patterns and regional heterogeneity of SNSA, the proarrhythmic effects of alpha-adrenergic receptor stimulation, or the potential proarrhythmic effects of beta-adrenergic receptor blockade. Further research is needed to determine if other approaches to SNSA modulation can enhance the antiarrhythmic effects.

Relationship of slow conduction detected by pace-mapping to ventricular tachycardia re-entry circuit sites after infarction

OBJECTIVES

This study sought to characterize the relationship of conduction delays detected by pace-mapping, evident as a stimulus to QRS interval (S-QRS) delay >or=40 ms, to ventricular tachycardia (VT) re-entry circuit isthmuses defined by entrainment and ablation.

BACKGROUND

Areas of slow conduction and block in old infarcts cause re-entrant VT.

METHODS

In 12 patients with VT after infarction, pace-mapping was performed at 890 sites. Stimulus to QRS intervals were measured and plotted in three-dimensional reconstructions of the left ventricle. Conduction delay was defined as >or=40 ms and marked delay as >80 ms. The locations of conduction delays were compared to the locations of 14 target areas, defined as the region within a radius of 2 cm of a re-entry circuit isthmus.

RESULTS

Pacing captured at 829 sites; 465 (56%) had no S-QRS delay, 364 (44%) had a delay >or=40 ms, and 127 (15%) had a delay >80 ms. Sites with delays were clustered in 14 discrete regions, 13 of which overlapped target regions. Only 1 of the 14 target regions was not related to an area of S-QRS delay. Sites with marked delays >80 ms were more often in the target (52%) than sites with delays 40 to 80 ms (29%) (p < 0.0001).

CONCLUSIONS

Identification of abnormal conduction during pace-mapping can be used to focus mapping during induced VT to a discrete region of the infarct. Further study is warranted to determine if targeting regions of conduction delay may allow ablation of VT during stable sinus rhythm without mapping during VT.

Endocardial mapping of electrophysiologically abnormal substrates and cardiac arrhythmias using a noncontact nonexpandable catheter

INTRODUCTION

In previous studies, we established methodology for reconstructing endocardial potential maps, electrograms, and isochrones from a noncontact intracavitary catheter during a single beat. Recently, we evaluated this approach using a 9-French (3-mm) spiral catheter in a normal heart preparation. Here we extend the approach to hearts with structural disease and examine its ability to detect and characterize abnormal electrophysiologic (EP) substrates and to map ventricular arrhythmias on a beat-by-beat basis.

METHODS AND RESULTS

Reconstruction of endocardial potentials from cavity potentials measured with 82 electrodes mounted on a 9-French spiral catheter was performed in an isolated canine left ventricle (LV). Endocardial potentials were recorded with 91 intramural needles, providing a gold standard for evaluating the noncontact reconstruction. Studies were performed in a normal LV (control) and the same LV 3 hours after left anterior descending coronary artery occlusion and ethanol injection to create an infarct. Abnormal EP characteristics over the infarct were faithfully reconstructed, including (1) low potentials and electrogram derivatives; (2) fractionated electrograms; (3) small deflections on electrograms reflecting local activation; and (4) slow discontinuous conduction transverse to fibers. During arrhythmia, beat-to-beat dynamic shifts of initiation site and activation pattern were captured by the reconstruction.

CONCLUSION

Noncontact, nonexpendable catheter mapping can locate and characterize abnormal EP substrates and can capture the endocardial sequence of an arrhythmia during a single beat.

A novel catheter design for laser photocoagulation of the myocardium to ablate ventricular tachycardia

Nd:YAG laser energy has been proposed as an alternative to radiofrequency energy for ablation of ventricular tachycardia (VT) associated with coronary artery disease (CAD) in an effort to increase lesion size and success rates. However, issues of catheter design to maintain flexibility and ensure adequate tissue contact have hindered development of laser catheters. We developed and tested a prototype 8 Fr. steerable catheter with a flexible and extendible tip (designed to ensure tissue contact and efficient ventricular mapping), which projects the laser beam through a side port containing a lens-tipped optical fiber that rests against the endocardial surface. The catheter has a channel for simultaneous saline irrigation to displace the interceding blood and discharge a laser beam between two electrodes for bipolar mapping and a thermocouple for temperature monitoring. The catheter was tested on bench top using the epicardial surface of freshly slaughtered bovine hearts and in vivo using six anaesthetized closed-chest sheep. In vitro experiments demonstrated that lesion size increased linearly with applied power up to 40 watts. When compared to radio frequency, laser energy penetrated more deeply into the myocardium. In the in vivo studies, using increasing powers of up to 40 watts for application times of 60 to 120 seconds created circular or elliptical lesions with surface dimensions up to 12 mm x 12 mm and depth of 9 mm (full LV wall thickness with a mean lesion diameter of 9.9 +/- 5.2 mm and depth 5.8 +/- 3.2 mm). Most lesions, 16 total in both right and left ventricular walls were transmural or near transmural in thickness. Lesions demonstrated coagulation necrosis with smooth well-demarcated borders. No animal suffered cardiac perforation, hypotension, hemopericardium, damage to cardiac valves, or cavitation effect from any of the ablations. Runs of VT were seen during energy application at the highest laser outputs in two animals. In conclusion, this catheter design provides effective endocardial delivery of laser energy and is capable of creating transmural or nearly transmural lesions in vivo and in vitro, thereby potentially increasing the efficiency of VT ablation in CAD patients.

Characteristics of wavefront propagation in reentrant circuits causing human ventricular tachycardia

BACKGROUND

We investigated the relationship between wavefront curvature and slowing of conduction both within and outside the diastolic pathway of circuits causing ventricular tachycardia (VT) in the infarcted human heart.

METHODS AND RESULTS

Propagation was determined around the reentrant circuits of 11 VT (cycle length, 348+/-75 ms) in 8 patients undergoing high-resolution noncontact mapping. The diastolic pathway had a mean wavefront velocity of 0.82+/-0.49 m/s and occupied 68+/-7% of VT cycle length. Significant changes (>5 degrees/mm) in trajectory of propagation occurred in 8 diastolic pathway segments (10.1+/-3 degrees/mm) in which wavefront propagation slowed to 0.41+/-0.11 m/s compared with the segments immediately preceding (0.91+/-0.16 m/s, P< 0.05) and following (1.07+/-0.33, P<0.05) the change in trajectory. At the turning points of entry (9.3+/-3.9 degrees/mm) and exit (9.0+/-4.8 degrees/mm) of the diastolic pathway propagation, velocity slowed at entry from 1.23+/-0.4 to 0.6+/-0.26 ms (P<0.001) and was more rapid at exit turning points (0.8+/-0.25 m/s) (P<0.05). There was an inverse relationship between wavefront curvature and velocity, both within and outside the diastolic pathway (r=0.46, P=0.0001), and VT cycle length correlated with total curvature multiplied by length of the diastolic pathway (P< 0.01).

CONCLUSIONS

Slowing of propagation in circuits causing VT in the infarcted human heart occurs over regions of wavefront turning, with an inverse relationship between wavefront curvature and velocity, both within and outside the diastolic pathway. Conduction is slower at entry than exit turning points of the diastolic pathway but is slowest during turns within the diastolic pathway.

Noninvasive electrocardiogram imaging of substrate and intramural ventricular tachycardia in infarcted hearts

OBJECTIVES

The goal of this study was to experimentally evaluate a novel noninvasive electrocardiographic imaging modality during intramural reentrant ventricular tachycardia (VT).

BACKGROUND

Myocardial infarction and subsequent remodeling produce abnormal electrophysiologic substrates capable of initiating and maintaining reentrant arrhythmias. Existing noninvasive electrocardiographic methods cannot characterize abnormal electrophysiologic substrates in the heart or the details of associated arrhythmias. A noninvasive method with such capabilities is needed to identify patients at risk of arrhythmias and to guide and evaluate therapy.

METHODS

A dog heart with a four-day-old infarction was suspended in a human shaped torso-tank. Measured body surface potentials were used to noninvasively compute epicardial potentials, electrograms and isochrones. Accuracy of reconstruction was evaluated by direct comparison to measured data. Reconstructions were performed during right atrial pacing and nine cycles of VT.

RESULTS

Noninvasively reconstructed potential maps, electrograms and isochrones identified: 1) the location of electrophysiologically abnormal infarct substrate; 2) the epicardial activation sequences during the VTs; 3) the locations of epicardial breakthrough sites; and 4) electrophysiologic evidence for activation of the Purkinje system and septum during the reentrant beats.

CONCLUSIONS

Electrocardiographic imaging can noninvasively reconstruct electrophysiologic information on the epicardium during VT with intramural reentry, provide information about the location of the intramural components of reentry and image abnormal electrophysiologic substrates associated with infarction.

[Endocardial ablation of substrate of postinfarction ventricular tachycardia during sinus rhythm]

OBJECTIVE

Radiofrequency ablation of ventricular tachycardia requires good tachycardia tolerance during mapping and entrainment, and this limits its application. We present our initial experience with ventricular tachycardia ablation during sinus rhythm in 7 patients with previous inferior myocardial infarction.

METHODS

Seven men, 56-70 years old (mean +/- SD, 65 +/- 4.5) were included in the study. Ventricular tachycardia was unstable in 6 and in 1 it was induced non-sustained. The scar was localized by recording low-voltage, fragmented electrograms (< 2 mV). Ventricular tachycardia "exit" was localized by pace-mapping in sinus rhythm. Radiofrequency lines were made radially, point by point, from normal to scarred tissue. One of the lines crossed the exit area. The objective was to achieve non-inducibility.

RESULTS

Sustained clinical ventricular tachycardia was induced in 6 and non-sustained in 1. Two-four lines were performed per patient with 11-28 (21 +/- 5.4) radio frequency applications. The procedure duration was of 130-280 min (230 +/- 61) and being 49-75 min (63 +/- 7.9) for fluoroscopy. There were no complications. Clinical ventricular tachycardia became non-inducible in 6, although in 4 a rapid (cycle < or = 250 ms), non-clinical ventricular tachycardia remained inducible. Defibrillators were implanted in the patient remaining inducible for clinical ventricular tachycardia and another with > 60 tachycardia episodes the previous week. During 3-22 months (13.8 +/- 5.9) of follow-up, 1 patient died of heart failure at 20 months and another received 3 defibrillator shocks for VT at 13 months. There were no other episodes of ventricular tachycardia, syncope or sudden death.

CONCLUSIONS

This preliminary experience suggests that radiofrequency ablation of post-infarction ventricular tachycardia substrate is possible during sinus rhythm, suggesting that radiofrequency ablation may be applicable in a large proportion of patients with post-infarction sustained ventricular tachycardia.

Noninvasive ECG imaging of electrophysiologically abnormal substrates in infarcted hearts : A model study

BACKGROUND

Myocardial infarction and subsequent remodeling create substrates with altered electrophysiological (EP) properties that are highly arrhythmogenic. Existing ECG methods cannot always detect the existence of such substrates nor provide any detailed information about their EP characteristics. A noninvasive method with such capabilities is greatly needed for identifying patients at risk of arrhythmias and for guidance and evaluation of therapy. Recently, we developed a noninvasive ECG imaging modality that can reconstruct epicardial EP information from body surface potentials. We extended its application to hearts with structural disease and examined its ability to detect and characterize abnormal EP substrates.

METHODS AND RESULTS

Epicardial potentials were recorded with a 490-electrode sock from an open-chest dog. Recordings were obtained from a normal heart and from the same heart 2 hours after left anterior descending coronary artery occlusion and ethanol injection to create an infarct. Body surface potentials were generated from these epicardial potentials in a human torso model. Realistic geometry errors and measurement noise were added to the torso data, which were then used to noninvasively reconstruct epicardial potentials and electrograms (EGMs), with excellent accuracy. EP characteristics associated with the infarct substrate were reconstructed, including (1) a negative region over the infarct, (2) EGMs with large predominant negative deflections (eg, Q-wave EGMs), (3) Q-wave EGMs with superimposed RS deflections reflecting local activation of surviving myocardium within the infarct border zone, (4) reduced magnitudes of EGM negative derivatives, and (5) negative QRS integrals of EGMs over the infarct.

CONCLUSIONS

ECG imaging can noninvasively detect and map abnormal EP substrates associated with infarction and structural heart disease.

Epicardial mapping and radiofrequency catheter ablation of ischemic ventricular tachycardia using a three-dimensional nonfluoroscopic mapping system

Endocardial radiofrequency catheter ablation of ischemic left ventricular tachycardia has been of variable success due to multiple factors. Two such factors include the location of the reentrant circuit in the deep myocardium or on the epicardial surface and the inherent limitations of fluoroscopy as a guide for target localization. We report a patient in whom successful epicardial mapping and radiofrequency catheter ablation of an ischemic left ventricular tachycardia was performed using pericardial access and the CARTO electroanatomic mapping system.

Ventricular tachycardia originating from the posteroseptal process of the left ventricle with inferior wall healed myocardial infarction

Ventricular tachycardia (VT) substrates may form in preferential locations and similar electrocardiographic patterns may be observed when ventricular activation starts from a particular site. We examined the role of the posterior inferior process of the left ventricle in the mechanism of VT occurring after inferior wall myocardial infarction. We reviewed isochronal maps of 40 VTs obtained at surgery in 13 patients, with a 128-electrode system using epicardial sock and endocardial balloon electrode arrays. Based on the epicardial to left endocardial relation we observed 7 tachycardias in 7 patients with onset of activation over the crux of the heart. This activation mimicked excitation through a posteroseptal accessory pathway. Endocardial activation maps showed breakthroughs occurring 6 to 40 ms later and did not give evidence in favor of macroreentry. In all but 1 VT, left-axis deviation was present (-30 to -75 degrees) with a positive concordance from leads V2 to V6 (QRS wave patterns were variable in V1). These tachycardias, which were clinical in 3 of 7 cases, were interpreted as arising from the posterior inferior process of the left ventricle and successfully ablated by left septal and epicardial cryolesions. In another patient, this concept was further validated by percutaneous radiofrequency ablation of a tachycardia with the previously described morphology. In conclusion, VT may originate from the posteroseptal process of the left ventricle with inferior wall healed myocardial infarction. Because these tachycardias can be successfully eliminated, their characteristic morphologies may provide clinical markers for the identification of patient candidates to surgical or nonsurgical ablative therapy.

Mapping and ablation of ventricular tachycardia with the aid of a non-contact mapping system

OBJECTIVE

Treatment of ventricular tachycardia (VT) in coronary heart disease has to date been limited to palliative treatment with drugs or implantable defibrillators. The results of curative treatment with catheter ablation have proved disappointing because the complexity of the VT mechanism makes identification of the substrate using conventional mapping techniques difficult. The use of a mapping technology that may address some of these issues, and thus make possible a cure for VT with catheter ablation, is reported.

PATIENTS AND INTERVENTION

The non-contact system, consisting of a multielectrode array catheter (MEA) and a computer mapping system, was used to map VT in 24 patients. Twenty two patients had structural heart disease, the remainder having "normal" left ventricles with either fasicular tachycardia or left ventricular ectopic tachycardia.

RESULTS

Exit sites were demonstrated in 80 of 81 VT morphologies by the non-contact system, and complete VT circuits were traced in 17. In another 37 morphologies of VT 36 (30)% (mean (SD)) of the diastolic interval was identified. Thirty eight VT morphologies were ablated using 154 radiofrequency energy applications. Successful ablation was achieved by 77% of radiofrequency within diastolic activation identified by the non-contact system and was significantly more likely to ablate VT than radiofrequency at the VT exit, or remote from diastolic activation. Over a mean follow up of 1.5 years, 14 patients have had no recurrence of VT and only two target VTs have recurred. Five patients have had recurrence of either slower non-sustained, undocumented or fast non-target VT. Five patients have died, one from tamponade from a pre-existing temporary pacing wire, and four from causes unrelated to the procedure.

CONCLUSION

The non-contact system can safely be used to map and ablate haemodynamically stable VT with low VT recurrence rates. It is yet to be established whether this system may be applied with equal success to patients with haemodynamically unstable VT.

Intraoperative computerized mapping of ventricular tachycardia: differences between anterior and inferior myocardial infarctions

INTRODUCTION

Although direct ventricular tachycardia (VT) surgery has been shown to be effective for treatment of inferior myocardial infarction (MI), the differences in the arrhythmia substrates compared to anterior MI have not been systematically delineated. We sought to compare operative procedures and VT substrates between anterior and inferior MI locations.

METHODS AND RESULTS

Computerized mapping was performed in 30 patients with a 128-electrode system using epicardial sock and transatrial left ventricular endocardial balloon arrays, followed by combined endocardial resection and cryoablation. At surgery, there were 51 and 34 different VTs in 18 patients with anterior MI and 12 patients with inferior MI, respectively. The proportion of aneurysms was lower in inferior MI (25% vs 78%, P = 0.008). Total activation times accounted for 65% +/- 23% and 50% +/- 22% of the VT cycle length in anterior and inferior infarcts, respectively (P = 0.005). Complete superficial reentry was identified in 12 VTs related to anterior infarcts and in only two VTs associated with inferior infarction (P = 0.038). Involvement of papillary muscles occurred in two patients with inferior MI. Patients with inferior infarcts received more cryolesions and required epicardial cryolesions or mitral valve replacement more frequently, and their operative mortality was greater (2/12 vs 0/18). Noninducibility rate (89.3%) and 2-year survival (76% +/- 8%) did not differ according to infarct location.

CONCLUSION

VT associated with inferior MI can be ablated successfully; however, the substrate is more complex, with frequent participation of intramural layers rendering the ablative procedure more difficult.

Characteristics of sinus rhythm electrograms at sites of ablation of ventricular tachycardia relative to all other sites: a noncontact mapping study of the entire left ventricle

INTRODUCTION

Regions of the diseased ventricle that activate abnormally during sinus rhythm (SR) may be the areas of slow and disorganized conduction that form the diastolic pathway through which reentry may occur during ventricular tachycardia (VT).

METHODS AND RESULTS

We examined features of electrograms recorded during SR that might indicate a site suitable for ablation of VT using a noncontact mapping system, which enables reconstruction of > 3,000 electrograms. Preablation SR electrogram characteristics at sites of successful radiofrequency ablation (RFA) were examined in 13 patients with 53 VTs. Timing of onset, lateness of activity, electrogram duration, and number of baseline crossing events of reconstructed electrograms at the sites of successful RFA were compared with the electrograms of latest onset, latest activity, longest duration, and most baseline crossing events of all ventricular sites. Onset of activation at sites of successful RFA were 26.9+/-25.2 msec (mean +/- SD) earlier than (and 2.9+/-1.7 cm away from) the site of latest onset of SR activation. Electrogram duration at sites of successful RFA was 83%+/-14.6% of (and 4.3+/-1.8 cm away from) the longest electrogram. The baseline crossing events at sites of successful RFA were 53%+/-22% of (and 4.9+/-1.9 cm away from) the most fractionated electrogram. The latest activity at sites of successful RFA was 21.6+/-24.8 msec earlier than (and 4.3+/-1.6 cm away from) the site of latest activity.

CONCLUSION

Although the site of latest onset of endocardial activation during SR proved to be the most sensitive indicator, the characteristics of SR electrograms did not usefully predict successful ablation sites.

Simultaneous endocardial mapping in the human left ventricle using a noncontact catheter: comparison of contact and reconstructed electrograms during sinus rhythm

BACKGROUND

Catheter ablation of ventricular tachycardia is limited in part by difficulty in identifying suitable sites for ablation. A noncontact multielectrode array (MEA) has been developed that allows reconstruction of 3360 electrograms, using inverse-solution mathematics, that are superimposed onto a computer-simulated model of the endocardium. This study assesses the accuracy of timing and morphology of reconstructed unipolar electrograms compared with contact unipolar electrograms from the same endocardial site.

METHODS AND RESULTS

The MEA was deployed in the left ventricles of 13 patients (end-diastolic diameters, 61.7+/-8.4 mm [mean+/-SD]). We recorded contact electrograms at 76 points equatorial and 32 points nonequatorial to the MEA during sinus rhythm using a catheter-locator signal to record direction and distance from the MEA. Morphology (cross-correlation) and timing of maximum -dV/dt of contact and reconstructed electrograms were compared at different distances from the MEA center to endocardium (M-E) and from the MEA equatorial plane. For equatorial data, the M-E was 32.12+/-12.12 mm. The timing of reconstructed with respect to contact electrograms was -1.94+/-7.12 ms for M-E <34 mm and -14.16+/-19.29 ms at M-E >34 mm (P<0.001). Cross-correlation of electrograms was 0.87+/-0.12 (95% CI, 0.84 to 0.91) and 0.76+/-0.18 (95% CI, 0.69 to 0.83) for M-E <34 mm and >34 mm, respectively. Nonequatorial points were 32.33+/-10.81 mm (range, 16.9 to 55.6 mm) from the MEA equatorial plane; electrogram timing difference was -8.97+/-15.75 ms and was unrelated to this distance from the equator.

CONCLUSIONS

This noncontact mapping system accurately reconstructs endocardial unipolar electrograms from the human left ventricle. At M-E distances >34 mm, timing accuracy of reconstruction decreases.

Characteristics of local electrograms with diastolic potentials: identification of different components of return pathways in ventricular tachycardia

BACKGROUND

Diastolic potentials are often sought as a possible site for catheter ablation in post-infarct ventricular tachycardia. However, delivery of energy at such sites is often unsuccessful. The purpose of this study was to determine the characteristics of local electrograms with diastolic potentials and to identify activation pattern which might indicate the critical portion of the return path of the ventricular tachycardia reentry circuit.

METHODS

In 17 patients with post-myocardial infarction ventricular tachycardia, 30 ventricular tachycardias were mapped with an 112 bipolar endocardial balloon at the time of surgery. Diastolic mapping of the return tract in ventricular tachycardia was performed. Four activation patterns were observed (15 figure 8 patterns, 2 circular patterns, 2 biregional patterns and 11 monoregional patterns). Of 3,360 local electrograms, 207 (6.2%) demonstrated a diastolic potential in ventricular tachycardia. They were classified into following four categories, based on the appearance and timing of the systolic component. Type A-1 electrogram: systolic activation was of low amplitude (< 2 mV) and was prolonged (> or = 100 msec), but preceded the onset of the surface QRS in ventricular tachycardia. Type A-2 electrogram: systolic activation was of low amplitude, was prolonged, but followed the onset of the surface QRS. Type B electrogram: systolic electrogram was fractionated, but relatively normal amplitude (2.0-3.6 mV). Type C electrogram: systolic electrogram was almost normal.

RESULTS

Of all electrograms with diastolic potentials, three type A-1 electrograms (1.4%) were located at the exit of the return pathway, 11 type A-1 electrograms (5.3%) were located at the pre-exit site. No type A-1 was found at an entrance/bystander area. 21 type A-2 electrograms (10.1%) were at the pre-exit and 83 type A-2 electrograms (40.2%) were located at the entrance/bystander area, but such electrograms were never found at the exit site. 71 type B electrograms (34.3%) and 18 type C electrograms (8.7%) were located at the entrance/bystander area. To distinguish the type A-2 electrograms at the pre-exit site from those at the entrance/bystander area, the diastolic potential to QRS interval was measured. This interval at the pre-exit was significantly shorter than that at the entrance/bystander area (-47.2 +/- 10.7 vs -96.3 +/- 31.3 msec, p = 0.0001).

CONCLUSION

Type A-1 electrograms indicated the exit or pre-exit site of return pathway. Type A-2 electrograms with diastolic potential to QRS interval < -50 msec indicated the pre-exit site. However, the other types of local electrograms with diastolic potential did not indicate the critical portion of the ventricular tachycardia circuit. These observations may be helpful during catheter mapping and ablation of patients with post-infarct ventricular tachycardia.

CONDENSED ABSTRACT

Diastolic potentials are often sought to direct catheter ablation in post-infarct ventricular tachycardia. We investigated the characteristics of local electrograms showing diastolic activity in an attempt to determine whether critical portions of the ventricular tachycardia circuit could be identified by a typical "signature." In 17 patients with a remote myocardial infarction, 30 ventricular tachycardias were mapped with 112 bipolar endocardial balloon at the time of surgery. Diastolic potentials in association with low amplitude (< 2 mV) and prolonged (> or = 100 msec) systolic electrograms preceding the onset of QRS were found at the exit site and pre-exit site of return pathway. A similar systolic electrogram occurring after QRS onset with a diastolic potential to QRS interval of < -50 msec was found at the pre-exit site. However, other local electrograms with diastolic activity were at sites remote from the exit or pre-exit of the return pathway. These observations may be helpful during catheter mapping and ablation in patients with ventricular tachycardia.

Simulation study of cellular electric properties in heart failure

Patients with severe heart failure are at high risk of sudden cardiac death. In the majority of these patients, sudden cardiac death is thought to be due to ventricular tachyarrhythmias. Alterations of the electric properties of single myocytes in heart failure may favor the occurrence of ventricular arrhythmias in these patients by inducing early or delayed afterdepolarizations. Mathematical models of the cellular action potential and its underlying ionic currents could help to elucidate possible arrhythmogenic mechanisms on a cellular level. In the present study, selected ionic currents based on human data are incorporated into a model of the ventricular action potential for the purpose of studying the cellular electrophysiological consequences of heart failure. Ionic currents that are not yet sufficiently characterized in human ventricular myocytes are adopted from the action potential model developed by Luo and Rudy (LR model). The main results obtained from this model are as follows: The action potential in ventricular myocytes from failing hearts is longer than in nonfailing control hearts. The major underlying mechanisms for this prolongation are the enhanced activity of the Na+-Ca2+ exchanger, the slowed diastolic decay of the [Ca2+]i transient, and the reduction of the inwardly rectifying K+ current and the Na+-K+ pump current in myocytes of failing hearts. Furthermore, the fast and slow components of the delayed rectifier K+ current (I(Kr) and I(Ks), respectively) are of utmost importance in determining repolarization of the human ventricular action potential. In contrast, the influence of the transient outward K+ current on APD is only small in both cell groups. Inhibition of I(Kr) promotes the development of early afterdepolarizations in failing, but not nonfailing, myocytes. Furthermore, spontaneous Ca2+ release from the sarcoplasmic reticulum triggers a premature action potential only in failing myocytes. This model of the ventricular action potential and its alterations in heart failure is intended to serve as a tool for investigating the effects of therapeutic interventions on the electric excitability of the human ventricular myocardium.

Endocardial and epicardial ablation guided by nonsurgical transthoracic epicardial mapping to treat recurrent ventricular tachycardia

INTRODUCTION

An epicardial site of origin of ventricular tachycardia (VT) may explain unsuccessful endocardial radiofrequency (RF) catheter ablation. A new technique to map the epicardial surface of the heart through pericardial puncture was presented recently and opened the possibility of using epicardial mapping to guide endocardial ablation or epicardial catheter ablation. We report the efficacy and safety of these two approaches to treat 10 consecutive patients with VT and Chagas' disease.

METHODS AND RESULTS

Epicardial mapping was carried out with a regular steerable catheter introduced into the pericardial space. An epicardial circuit was found in 14 of 18 mapable VTs induced in 10 patients. Epicardial mapping was used to guide endocardial ablation in 4 patients and epicardial ablation in 6. The epicardial earliest activation site occurred 107+/-60 msec earlier than the onset of the QRS complex. At the epicardial site used to guide endocardial ablation, earliest activation occurred 75+/-55 msec before the QRS complex. Epicardial mid-diastolic potentials and/or continuous electrical activity were seen in 7 patients. After 4.8+/-2.9 seconds of epicardial RF applications, VT was rendered noninducible. Hemopericardium requiring drainage occurred in 1 patient; 3 others developed pericardial friction without hemopericardium. Patients remain asymptomatic 5 to 9 months after the procedure. Interruption during endocardial pulses occurred after 20.2+/-14 seconds (P = 0.004), but VT was always reinducible and the patients experienced a poor outcome.

CONCLUSION

Epicardial mapping does not enhance the effectiveness of endocardial pulses of RF. Epicardial applications of RF energy can safely and effectively treat patients with VT and Chagas' disease.

Mechanisms causing sustained ventricular tachycardia with multiple QRS morphologies: results of mapping studies in the infarcted canine heart

BACKGROUND

Sustained reentrant ventricular tachycardias (VTs) with different QRS morphologies have been observed to occur spontaneously and during programmed stimulation in human hearts. We determined mechanisms that can cause tachycardias with multiple morphologies in a canine model of myocardial infarction by mapping reentrant circuits.

METHODS AND RESULTS

Reentrant VT with multiple QRS morphologies was induced in 11 canine hearts with 4-day-old infarcts. Comparison of activation maps of the reentrant circuits in the epicardial border zone associated with each morphology indicated two basic mechanisms. Less frequently, VTs of different morphologies in the same heart were caused by reentrant circuits in different regions of the infarct. Most commonly, the reentrant circuits associated with different morphologies were in the same region. Three different factors caused different exit routes from circuits in the same region, leading to the multiple morphologies. (1) The reentrant wave front for each morphology rotated around the same line of block but in different directions. (2) Reentrant circuits associated with each morphology were similar, but there were small changes in the extent of the central line of block. (3) Reentrant circuits with completely different sizes and shapes caused different morphologies.

CONCLUSIONS

In this canine model, tachycardias with multiple morphologies most commonly arise from reentrant circuits in the same region of the infarct, suggesting that most often only one area has electrophysiological properties necessary to sustain reentry.

Transcatheter neodymium-yttrium-aluminum-garnet laser coagulation of canine ventricle using a balloon-tipped cardioscope

The feasibility of transcatheter laser ablation of the canine left ventricle (LV) was tested using a newly developed cardioscope. In 17 anesthetized dogs, a combined laser-endoscope catheter, consisting of an endoscope encased in a 7-French flexible catheter with an inflatable and transparent balloon at the distal end, was introduced into the LV via the carotid artery. A 1064-nm neodymium-yttrium-aluminum-garnet (Nd:YAG) laser was delivered by laser optic fiber, which was introduced through the transport channel and positioned inside the saline-filled balloon. In 16 of 17 dogs, the endocardial surface of the LV was clearly observed. Laser energy totaling 500-5,000 J was applied sequentially in 13 dogs and laser irradiation was completed in all but 2 of the dogs. The excised hearts revealed well-demarcated oval-shaped lesions 2.5-9.5 mm deep in 7 of 11 dogs. Histologic sections revealed coagulation necrosis surrounded by a rim of contraction band necrosis. Thus, transballoon laser photocoagulation of the beating LV is feasible. The newly combined laser-endoscope catheter, which is still in its preliminary stages and needs to be improved to increase the success rate of photocoagulation, appears to be a promising alternative modality for catheter ablative therapy for ventricular tachycardia.

Response to pacing at sites of isolated diastolic potentials during ventricular tachycardia in patients with previous myocardial infarction

OBJECTIVES

The goal of this study was to determine whether isolated diastolic potentials (IDPs) recorded during ventricular tachycardia (VT) are generated in zones of slow conduction and whether the arcs of block that bound these zones of slow conduction are functional or anatomic in nature.

BACKGROUND

No previous studies have systematically investigated the response to pacing during VT and sinus rhythm at sites where IDPs are recorded.

METHODS

The study included 11 patients with a previous infarction who underwent radiofrequency catheter ablation of 15 hemodynamically stable, sustained VTs and in whom an IDP that could not be dissociated from the VT was detected during mapping.

RESULTS

Pacing during VT at the site where the IDP was recorded resulted in concealed entrainment in each of the 15 VTs. In 10 of the 15 VTs, an IDP was present during sinus rhythm at the same site at which a diastolic potential was recorded during VT. In nine VTs, the isolated potential occurred early in diastole; in these cases, the QRS configuration during pacing in the setting of sinus rhythm was different from that during VT. In six VTs, the isolated potential occurred later in diastole, and in these cases, the QRS configuration during pacing in the setting of sinus rhythm was the same as that during VT.

CONCLUSIONS

Isolated diastolic potentials may often be generated in an area of slow conduction bounded by arcs of block that are anatomically determined and present during sinus rhythm.

Pathophysiologic substrate for sustained ventricular tachycardia in coronary artery disease

Sustained ventricular tachycardia (VT) in the presence of coronary artery disease (CAD) is almost always associated with prior infarction. Its mechanism is reentrant excitation and it can be initiated > 95% of the time. Disrupted and delayed endocardial activation and prolonged, fragmented electrograms recorded during sinus rhythm distinguish patients with VT from those with normal ventricles and those of prior infarction without VT. The extent of abnormalities of activation and number of abnormal, fragmented and late electrograms are greatest in patients with sustained VT. These abnormalities are associated with scar tissue separating the viable myocytes. Fragmented electrograms are due to discontinuous activation due to nonuniform anisotropy caused by the scar tissue. Patients with CAD demonstrate depressed excitability and prolonged relative refractory periods (ie, an upward shift in the strength-interval curve) at sites of infarction but effective refractory periods measured at 10 mA comparable to normals and dispersion of refractory periods. However the associated abnormalities of conduction and activation produce an abnormal dispersion of recovery. Intraoperative mapping of patients with CAD has shown that most of the abnormalities of endocardial activation and conduction are in the subendocardial layers and subendocardial resection of these areas cures VT and abolishes delayed, fragmented electrograms and split potentials and normalizes the electrograms recorded from the subjacent tissue. This supports the hypothesis that abnormalities of conduction are the critical pathophysiologic substrate of VT in CAD.

Subendocardial and intramural temperature response during radiofrequency catheter ablation in chronic myocardial infarction and normal myocardium

BACKGROUND

The ability of radiofrequency energy to extend across scar tissue is unknown. We investigated the effects of radiofrequency catheter ablation on intramural temperature in experimental chronic myocardial infarction.

METHODS AND RESULTS

Myocardial infarction was induced in eight dogs by a transcatheter coronary artery occlusion-reperfusion technique. The dogs were reanesthetized after 15 to 24 days. Four additional dogs served as controls. The freshly excised preparations were cut and placed in a saline bath at 37 degrees C. Temperature-guided energy applications with a preselected catheter tip temperature of 80 degrees C were performed for 60 seconds with a 7F ablation catheter. Thermoelements were inserted into the ventricular muscle at depths of 2.5 to 3.0 mm ("subendocardial") and 5.5 to 6.0 mm ("intramural"). Surviving muscle fibers were interspersed among the transmural scar tissue. The maximal temperatures did not differ significantly between normal hearts and chronic infarctions at the subendocardial (64.5+/-6.4 degrees C versus 66.7+/-6.6 degrees C) or intramural thermo-element (51.9+/-5.7 degrees C versus 52.3+/-5.7 degrees C). The myocardial temperature rise was slow, and steady-state temperatures had not been reached after 60 seconds. The intramural temperatures in chronic infarctions measured 49.0+/-4.3 degrees C after 40 seconds of energy delivery and were still below the critical tissue temperature of 50 degrees C that is necessary to induce permanent myocardial damage.

CONCLUSIONS

Temperature-guided radiofrequency ablation in a dog model of chronic myocardial infarction may induce tissue temperatures >50 degrees C at a depth of 5.5 to 6.0 mm. The intramural temperature rise was slow, indicating that long energy applications might be necessary if the arrhythmogenic substrate is subepicardial.

Mitral valve prolapse and ventricular arrhythmias: observations in a patient with a 20-year history

INTRODUCTION

Ventricular arrhythmias are a common feature in patients with mitral valve prolapse. In an attempt to determine the origin and underlying electrophysiologic mechanism, we describe a patient with ventricular fibrillation, exercise-induced ventricular tachycardia (VT), and, at the time of diagnosis, prolapse of the posterior mitral valve leaflet without mitral regurgitation.

METHODS AND RESULTS

Treatment with beta-blockade and diphenylhydantoin prevented the occurrence of malignant ventricular arrhythmias for more than 17 years. Discontinuation of the therapy resulted in an immediate reappearance of the VT, which, despite the marked enlargement of the left ventricle (secondary to development of severe mitral valve regurgitation), had a strikingly similar morphology. For hemodynamic reasons, the patient was finally selected for valve replacement. Detailed pre-, peri-, and postoperative studies were performed, including administration of flunarizine, body surface mapping, construction of perioperative epicardial and endocardial maps, and studies of the excised muscles in vitro.

CONCLUSIONS

Delayed afterdepolarization-induced triggered activity is the mechanism of VT in this mitral valve prolapse patient. The trigger is provided by isolated ventricular premature complexes elicited by a different electrophysiologic mechanism, possibly reentry, which is related to stretch and presumably to fibrosis of the papillary muscles.

Epicardial neodymium. YAG laser photocoagulation of ventricular tachycardia without ventriculotomy in patients after myocardial infarction

BACKGROUND

Surgical ablation of ventricular tachycardia (VT) after myocardial infarction has been reported by different endocardial approaches. The ventriculotomy may increase mortality of the procedure.

METHODS AND RESULTS

We report on nine patients who suffered from recurrent VT in the late post-myocardial infarction period. Significant stenoses were detected in all patients. The mean left ventricular ejection fraction was 43.1 +/- 8.3%. Left ventricular scar (n = 9) was seen. The mean NYHA class was 2.2 +/- 0.4. Sustained VT (mean cycle length, 293 +/- 52 ms) occurred spontaneously (n = 9) and could be induced reproducibly. Catheter mapping detected a prematurity of -42 +/- 13 ms in six patients. Clinical VT was inducible during surgery in seven patients. Middiastolic potentials were detected from the epicardial surface (n = 3), and premature potentials were found (n = 8 with prematurity of -108 +/- 46 ms). Application of neodymium/yttrium/argon/ garnet (Nd:YAG) laser energy to early epicardial activation terminated the arrhythmia (n = 7). Ventriculotomy was not performed. Seven patients have been free of VT for a mean follow-up period of 17 +/- 11 months; one patient relapsed and was treated with an implantable cardioverter-defibrillator, as was a second patient with inducible VT after surgery.

CONCLUSIONS

Surgical Nd:YAG laser photocoagulation of VT on the epicardial surface of the heart in post-myocardial infarction patients without ventriculotomy is safe and has a high success rate. At the present time, this method is recommended in patients with sustained and tolerated VT who need bypass surgery. This is the first report on epicardial laser ablation of VT in post-myocardial infarction VT.

Current role and future perspectives for radiofrequency catheter ablation of postmyocardial infarction ventricular tachycardia

The most common substrate for ventricular tachycardia (VT) is a postmyocardial infarction (MI) scar. Radiofrequency catheter ablation (RFCA) in post-MI VT faces clinical, electrophysiologic, anatomic, and methodologic difficulties not found in many other human tachycardias. The pathophysiologic understanding of post-MI VT is incomplete; this influences the process of selecting RFCA target sites, which is time consuming, demands catheter stability, and has low sensitivity and predictive value for VT interruption by RF current. Improving and simplifying the methodology of RFCA in post-MI VT is badly needed. We review the pathophysiology of post-MI VT from the data reported on endocardial, epicardial, and intramural ventricular mapping obtained either intraoperatively or in a Langendorff perfused set-up in hearts from transplanted patients. From these studies we conclude that (1) some post-MI VT cases are not amenable to RFCA (reentry around the scar, VT having a subepicardial or deep intramural substrate, or a wide, extensive, subendocardial intrascar area of slow conduction); and (2) searching for the endocardial exit is advantageous for selecting the RFCA targets. We also comment on a new self-reference mapping catheter that allows the recording of high gain, noise-free, unfiltered and filtered unipolar signals as well as unipolar pacing. Among the unresolved issues in these patients is the meaning of fast nonclinical VT induced after successful RFCA of the clinical VT, which may explain why a substantial number of these patients still receive an implantable cardioverter-defibrillator.

A comparison of unipolar and bipolar electrodes during cardiac mapping studies

Controversy exists as to whether the unipolar or bipolar electrode configuration is superior in detecting local activations during cardiac mapping studies. However, the strengths and weaknesses of each mode suggest that they may provide complementary information. To examine the relative merits of unipolar and bipolar electrode configurations, recordings by each were simultaneously acquired during episodes of ventricular tachycardia in eight consecutive patients undergoing map guided arrhythmia surgery. Unipolar electrograms were classified as either unambiguous or ambiguous according to whether or not they were polyphasic in nature. The activation times from the unambiguous electrograms were compared with activation times from the corresponding bipolar signals where local activation was measured both at the signal's peak amplitude (BI-PK), and at the point at which the waveform's first major, rapid transient crossed baseline (BI-TRN). Occurrences of discrete diastolic activations were also quantified from the unipolar and bipolar tracings. From a total of 415 unipolar electrograms, 301 unambiguous signals were identified as suitable for comparison with the bipolar signals. Both BI-PK and BI-TRN criteria for the determination of local activation were highly correlated with and not significantly different from the local activation from the unipolar electrogram. From 85 ambiguous unipolar electrograms, it was possible to determine local activation from the corresponding bipolar signal in 33% of the occurrences. From the eight patients, 64 diastolic potentials were recorded of which 42 were seen only in bipolar mode, 7 in only unipolar mode, and 15 were evident in both tracings. The prevalence of diastolic potentials was significantly greater in recordings made using bipolar mode. The results demonstrate that complementary information regarding local activations and diastolic potentials can be derived from unipolar and bipolar recordings and suggest that both electrode configurations should be used in multichannel cardiac mapping systems.

Ionic mechanisms of ischemia-related ventricular arrhythmias

The aim of this review is the utmost simplification of the cellular electrophysiologic background of ischemia-related arrhythmias. In the acute and subacute phase of myocardial infarction, arrhythmias can be caused by an abnormal impulse generation, abnormal automaticity or triggered activity caused by early or delayed afterdepolarizations (EAD and DAD), or by abnormalities of impulse conduction (i.e., reentry). This paper addresses therapeutic intervention aimed at preventing the depolarization of "pathologic" slow fibers, counteracting the inward calcium (Ca) influx that takes place through the L-type channels (Ca antagonists), or hyperpolarizing the diastolic membrane action potential, increasing potassium (K) efflux (K-channel openers) in arrhythmias generated by an abnormal automaticity (ectopic tachycardias or accelerated idioventricular rhythms). If the cause enhanced impulse generation is related to triggered activity, and since both EAD and DAD are dependent on calcium currents that can appear during a delayed repolarization, the therapeutic options are to shorten the repolarization phase through K-channel openers or Ca antagonists, or to suppress the inward currents directly responsible for the afterdepolarization with Ca blockers. Magnesium seems to represent a reasonable choice, as it is able to shorten the action potential duration and to function as a Ca antagonist. Abnormalities of impulse conduction (re-entry) account for the remainder of arrhythmias that occur in the acute and subacute phase of ischemia and for most dysrhythmias that develop during the chronic phase. Reentrant circuits due to ischemia are usually Na channel-dependent. Drug choice will depend on the length of the excitable gap: in case of a short gap (ventricular fibrillation, polymorphic ventricular tachycardia, etc.), the refractory period has been identified as the most vulnerable parameter, and therefore a correct therapeutic approach will be based on drugs able to prolong the effective refractory period (K-channel blockers, such as class III antiarrhythmic drugs); on the other hand, for those arrhythmias characterized by a long excitable gap (most of the monomorphic ventricular tachycardias), the most appropriate therapeutic intervention consists of depressing ventricular excit-ability and conduction by use of sodium-channel blockers such as mexiletine and lidocaine. Compared with other class I antiarrhythmic agents, these drugs minimally affect refractoriness and exhibit a use-dependent effect and a voltage dependent action (i.e., more pronounced on the ischemic tissue because of its partial depolarization).

Catheter ablation of the mitral isthmus for ventricular tachycardia associated with inferior infarction

BACKGROUND

Intraoperative mapping studies suggest that an isthmus of myocardium between the mitral valve annulus and the border of inferior myocardial infarction may play a role in the genesis of ventricular tachycardia. We examined the frequency with which a slow conduction zone within the mitral isthmus was critical to the maintenance of ventricular tachycardia associated with remote inferior infarction in patients undergoing catheter ablation.

METHODS AND RESULTS

In 4 of 12 patients, a critical zone of slow conduction was identified within the mitral isthmus. In each of these patients, two characteristic and morphologically distinct tachycardias were induced: a left bundle (rS in V1, R in V6), left superior axis morphology and a right bundle (R in V1, QS in V6), right superior axis morphology (cycle length, 610 to 320 ms). In each patient, a zone of slow conduction, shared by both morphologies, was characterized by diastolic potentials with electrogram-QRS intervals of 85 to 161 ms (21% to 47% of tachycardia cycle length) and entrainment with concealed fusion during pacing associated with stimulus-QRS intervals of 81 to 400 ms (20% to 91% of tachycardia cycle length). In each patient, a single radiofrequency energy application at the shared site of slow conduction eliminated inducibility of both morphologies. During follow-up of 1 to 11 months, no patient had recurrent tachycardia.

CONCLUSIONS

The mitral isthmus contains a critical region of slow conduction in some patients with ventricular tachycardia after inferior myocardial infarction, providing a vulnerable and anatomically localized target for catheter ablation. Characteristic tachycardia morphologies may provide clinical markers for this underlying mechanism.

Cellular mechanisms of ventricular bipolar electrograms showing double and fractionated potentials

OBJECTIVES

This study sought to determine the types of trans-membrane action potentials associated with bipolar electrograms that show double and fractionated potentials.

BACKGROUND

The cellular correlates of ventricular bipolar electrograms showing double potentials and fractionated low amplitude potentials remain poorly defined.

METHODS

A bipolar electrogram (1-cm interelectrode distance [6F, USCI]) and two transmembrane action potentials (within 1 mm of each pole) were recorded simultaneously in 12 isolated canine right ventricular endocardial preparations (2 x 1 cm, 2 mm thick). The long axis of the bipolar electrode was parallel to the long axis of the superficial endocardial fibers, and the recordings were made at 40 to 500 Hz.

RESULTS

The following phenomena were associated with double potentials: 1) an increase in conduction time between the two poles of the bipole during a) the propagation of premature action potentials (7 of 12 tissues in 4 mmol/liter extracellular potassium ion concentration [K+]o); b) rapid pacing and premature stimuli (3 of 6 in 9 mmol/liter [K+]o); and c) the propagation of slow responses induced by barium chloride (4 mmol/liter). There was a positive correlation between conduction time (CT) and interspike interval (IPI) of the double potential (IPI [ms] = 0.5 x CT [ms] + 35) during early afterdepolarizations induced by barium chloride (4 mmol/liter) superfusion (three of six tissues). The following events were associated with fractionated electrograms: 1) propagation of induced graded responses (six tissues) in 4 mmol/liter [K+]o; 2) induced reentry at cycle lengths of 140 to 170 ms in 9 mmol/liter [K+]o (four of six tissues); and 3) asynchronous afterdepolarizations induced by 4 mmol/liter barium chloride (four of six tissues).

CONCLUSIONS

Endocardial double potentials and fractionated electrograms seen on clinically used bipolar electrodes occur under conditions of slowed or discontinuous conduction and induced reentry and during asynchronous automatic firing initiated by afterdepolarizations. Caution must be exercised in interpreting such bipolar electrograms because more than one type of cellular action potential may cause these abnormal electrographic results.

Radiofrequency catheter ablation of sustained ventricular tachycardia in idiopathic dilated cardiomyopathy

BACKGROUND

The feasibility of radiofrequency (RF) catheter ablation for the treatment of sustained ventricular tachycardia (VT) in patients with coronary artery disease and remote myocardial infarction has recently been demonstrated. At present, therapeutic options for VT in patients with idiopathic dilated cardiomyopathy (DCM) include antiarrhythmic drugs and implantable cardioverter/defibrillators (ICD). The purpose of the present study was to investigate the feasibility of RF catheter ablation in patients with idiopathic DCM who could not be adequately treated by conventional treatment modalities because of incessant or frequent, recurrent VT.

METHODS AND RESULTS

RF current application for ablation of 9 VTs (mean cycle length, 402 +/- 78 ms) was attempted in 8 patients with idiopathic DCM (4 men, 4 women; mean age, 54 +/- 6 years; mean left ventricular ejection fraction, 30 +/- 9%). Inclusion criteria for ablation were incessant VT (n = 4) or frequent, recurrent VT reproducibly inducible with programmed electrical stimulation (n = 5). Three patients had suffered aborted sudden cardiac death, and 2 had experienced syncope. Two patients were artificially ventilated and catecholamine dependent for hemodynamic reasons at the time of attempted ablation. Potential target sites for RF current application were identified by detailed endocardial mapping during sinus rhythm, activation and entrainment mapping during VT, and pace mapping. After 7 +/- 5 RF pulses (range, 2 to 18 pulses; median, 6 pulses) applied with 32 +/- 7 W for 39 +/- 9 seconds, 6 of the 9 target VTs (67%) were rendered noninducible (4 of 4 incessant VTs and 2 of 5 chronic recurrent VTs). In 6 patients, VTs with ECG morphologies other than the target VTs were inducible after RF catheter ablation. Seven patients were on antiarrhythmic drugs during the ablation procedure and during the follow-up period of 8 +/- 5 months (range, 2 to 17 months). One patient received an ICD before RF ablation, 4 patients after RF ablation, and 1 patient after ablation of an incessant VT and before attempted ablation of frequent, recurrent VTs. One patient underwent heart transplantation 5 months after ablation in end-stage heart failure. There were no acute complications during the mapping and ablation procedure. During the follow-up period, 1 patient had been resuscitated from ventricular fibrillation 6 weeks after ablation and finally died of congestive heart failure 2 weeks later. No further episodes of incessant VT occurred in the patients who had undergone RF current application for ablation of incessant VT. A complete prevention of VT could be achieved in 2 of 8 patients, whereas in 5 patients, VT episodes were stored in the ICD devices during follow-up.

CONCLUSIONS

The results of the present study indicate that RF current application for ablation of VT in a select group of patients with idiopathic DCM is feasible. The efficacy of RF ablation may be high in patients presenting with incessant VT, whereas the success rate seems to be only moderate in patients with chronic recurrent VT. In all patients, additional treatment options, including antiarrhythmic drugs, ICDs, and/or heart transplantation, were applied after RF ablation, indicating that RF ablation for this indication may be an adjunctive and not a curative treatment option.

Endocardial mapping of ventricular tachycardia in the intact human ventricle. III. Evidence of multiuse reentry with spontaneous and induced block in portions of reentrant path complex

OBJECTIVES

This study was conducted to characterize the functional nature of the reentrant tract responsible for ventricular tachycardia due to ischemic heart disease.

BACKGROUND

A zone of slow conduction forming the return path is though to form a critical component of the reentrant mechanism in ventricular tachycardia. Despite its importance, detailed knowledge of the return path is rare in clinical studies.

METHODS

Multielectrode arrays were used intraoperatively to obtain unipolar and high gain bipolar recordings of left ventricular endocardium in patients undergoing map-directed surgical ablation of ventricular tachycardia. A total of 224 local electrograms were analyzed for each tachycardia.

RESULTS

Of 10 consecutive patients undergoing intraoperative cardiac mapping, detailed recording of the return tracts of eight ventricular tachycardias were obtained in three patients. The recordings demonstrated that return tracts can be complex and extensive, with multiple paths of entry and exit. Potential and actual alternate paths were observed. Spontaneous and induced block occurred within portions of the complex. Intermittent block in one of two paths of entry resulted in intermittent cycle length changes of the tachycardia without a change in configuration. Block in one exit path resulted in a shift to alternative exit paths, with dramatic changes in ventricular activation and tachycardia configuration. Termination of the tachycardia could result from block close to the entrant or exit portion of the return tract. Different tachycardias were seen to share common portions of a return tract.

CONCLUSIONS

These observations enlarge and extend our knowledge of the functional repertoire of complex reentrant tracts that occur in infarct-related ventricular tachycardia. The use of common portions of a reentrant tract by several tachycardias is confirmed. Utilization of alternate pathways can account for changes in configuration and cycle length. Spontaneous and induced block can occur at points of entry and exit in a reentrant tract and may identify optimal targets for ablation attempts. Further advances will require greater emphasis on diastolic activation mapping.

Dispersion of 'refractoriness' in noninfarcted myocardium of patients with ventricular tachycardia or ventricular fibrillation after myocardial infarction

BACKGROUND

Postinfarction ventricular tachycardias (VTs) may degenerate into ventricular fibrillation (VF), but this does not happen in all patients. The underlying mechanism is not exactly known, but dispersion of refractory periods is considered a major factor in both induction and persistence of reentrant arrhythmias in general. Hypertrophied, noninfarcted myocardium has altered electrophysiological characteristics. We hypothesized that noninfarcted ventricular tissue may provide the heterogeneities that cause the transition from VT into VF. Local fibrillation intervals, ie, the average interval between local activations during VF, have previously been shown to correlate well with local refractoriness in human and canine atrium and in porcine and canine ventricle and may therefore be used as an index of local refractoriness. This technique permits simultaneous assessment of refractoriness at multiple sites.

METHODS AND RESULTS

We measured local fibrillation intervals at 32 to 64 sites in the noninfarcted part of the left ventricle in patients undergoing antiarrhythmic surgery for symptomatic, drug-refractory, postinfarction ventricular tachyarrhythmias. The grid of electrodes (interelectrode distance, 7 mm) was attached to the epicardium of the left ventricle remote from the infarcted tissue. Group 1 consisted of 7 patients with hemodynamically tolerable sustained VT (VT group). Group 2 consisted of 7 patients with cardiac arrest and documented VF (VF group). With the patients on cardiopulmonary bypass, VF was induced by multiple premature stimulation. The VF interval was not significantly different in the two study groups (VT group, 136 +/- 5.5 ms; VF group, 129 +/- 3.4 ms, mean +/- SEM). However, spatial dispersion of the VF intervals (remote from the infarcted area) expressed as the coefficient of variation of VF intervals (SD x 100/mean VF interval in each heart) was significantly larger in the VF group. It was 3.63 +/- 0.56 in the VF group and 1.55 +/- 0.40 in the VT group (mean +/- SEM; P < .01). Differences between the shortest and longest VF intervals in one and the same heart and the largest difference between two adjacent sites were also larger in the VF group (P < .02 and P < .05, respectively).

CONCLUSIONS

This study shows larger dispersion in VF intervals and therefore suggests larger dispersion of refractory periods in parts of the myocardium remote from the infarction in patients with postinfarction VF than in patients with postinfarction VT.

Three distinct patterns of ventricular activation in infarcted human hearts. An intraoperative cardiac mapping study during sinus rhythm

BACKGROUND

Comprehensive data based on single-beat analysis of the ventricular activation sequence during sinus rhythm in infarcted hearts are currently not available. It was the aim of our study (1) to measure and analyze these activation sequences on the epicardial surface of the right and left ventricles and on the left ventricular endocardial surface, and (2) to correlate specific activation patterns with the surface ECG.

METHODS AND RESULTS

Isochronal maps were computed from 127 endocardial and epicardial unipolar electrograms recorded simultaneously during sinus rhythm in 45 post-myocardial infarction patients operated on for recurrent ventricular tachycardia (age, 57 +/- 10 years [mean +/- SD], left ventricular ejection fraction, 29 +/- 9%). Patients with bundle-branch block, but not with intraventricular conduction defects, were excluded. Data such as the timing of initial and terminal activation, the number of breakthroughs, the total activation time, and the number of ventricular segments without activation were measured and analyzed according to location of the myocardial infarction. The global epicardial activation was characterized in all patients by a widespread initial breakthrough on the anterior right ventricle (16 +/- 8 milliseconds after QRS onset), which was followed by one or two other breakthroughs in 65% of patients. Subsequently, three characteristic epicardial patterns of the activation spread were found: (1) radial, from the right to the left ventricle, found in all patients with inferoposterior myocardial infarction; (2) counterclockwise rotation, in which posteroseptal crossing preceded the anteroseptal crossing, found in 38% of patients with anterior myocardial infarction; and (3) pincerlike encirclement, in which both septal crossings and/or breakthroughs occurred nearly simultaneously and merged at the left ventricular free wall (typical for apical involvement in anterior and combined myocardial infarction). The simultaneous presence of multiple major activation wave fronts typically found in patients with the pincerlike activation pattern was reflected on the surface ECG by multiphasic, notched QRS complexes. Activation delay was observed in 89% of patients, and terminal activation was topographically related to myocardial infarction in 94% of patients. Delayed activation exceeding the surface QRS was observed in 11% and 31% of cases on the endocardium and epicardium, respectively.

CONCLUSIONS

These results offer a solid basis for a more precise interpretation of a wide range of electrophysiological data and provide a framework for future investigations of surface ECG reflections of endocardial and epicardial activation patterns recorded in patients with chronic myocardial infarction.

Modulation of connexin43 expression: effects on cellular coupling

INTRODUCTION

Gap junctions connect cardiac myocytes allowing propagation of action potentials. They contain intercellular channels formed by multiple different connexin proteins. The arrangement and type of gap junctions and the types, function, and interaction of connexin proteins determine intercellular resistance and can thereby influence conduction velocity and the potential for reentrant arrhythmias. Our goal was to develop genetically manipulable models to test the effects of altering expression of a major cardiac connexin (connexin43) on intercellular coupling and expression of other connexin proteins.

METHODS AND RESULTS

BHK cells that are poorly coupled and BWEM cells that are well coupled were stably transfected with plasmids containing connexin43 cDNA in antisense and sense orientations. RNA blots confirmed expression of the transfected transcripts. Immunoblots showed that connexin43 protein was reduced in the BHK antisense transfectants and increased in the BHK sense transfectants compared to the parental cells. It was not detectably changed in the BWEM antisense transfectant line compared to the BWEM parental cells. Transfection of connexin43 cDNA did not affect production of connexin45 mRNA and protein nor did transfection induce expression of other previously unexpressed connexin mRNAs. Cell coupling was assessed by intercellular diffusion of microinjected Lucifer yellow in confluent cell populations. Lucifer yellow passed to a mean of 3 +/- 3 neighboring parental BHK cells, to 8 +/- 8 neighbors in the sense connexin43 transfected BHK cells, and to only 2 +/- 2 neighbors in the antisense connexin43 transfected BHK cells (P < 0.05). In contrast, dye transfer did not differ significantly between the parental BWEM cells (mean transfer = 19 +/- 14 cells) and the BWEM connexin43 antisense transfectants (mean transfer = 15 +/- 12 cells) (P = 0.20).

CONCLUSIONS

These data demonstrate that stable transfection with connexin43 cDNA constructs can result in detectable changes in connexin43 expression and cellular coupling without inducing compensatory changes in the cell's connexin phenotype and, therefore, may provide a basis for future attempts at specifically modulating connexin expression and intercellular resistance in cardiac tissues.

Ventricular tachycardias with left bundle branch block morphology

The differential diagnosis of VTs with LBBB morphology includes several well-defined syndromes. Although the majority of cases are attributable to acquired structural heart disease, including ischemia, prior infarction, or dilated cardiomyopathy, consideration of specific right ventricular processes is essential to proper evaluation and treatment. The approach to older patients or those with evidence for heart disease should begin with an evaluation for coronary artery disease and an assessment of biventricular function. Careful evaluation for bundle branch reentry should be performed during electrophysiological study, especially when there is underlying conduction system disease. Younger patients, those without overt heart disease, or those with isolated right ventricular disease, should receive a complete noninvasive evaluation of right and left ventricular size and function. An abnormal SAECG or identification of intracardiac late potentials suggest right ventricular dysplasia or cardiomyopathy, whereas responsiveness to adenosine and absence of detectable heart disease support the diagnosis of idiopathic right VT. Newer techniques, including MRI, show promise in identifying subtle right ventricular disease not otherwise detectable even in the setting of presumed idiopathic right VT. Following surgical repair of selected congenital heart defects, particularly tetralogy of Fallot, symptoms of recurrent palpitations, near syncope, syncope, or aborted sudden death may be attributable to recurrent VT, and diagnostic electrophysiological study should be considered for these patients. Finally, SVTs with LBBB morphology, particularly cases associated with right-sided or septal accessory pathways, should always be considered in this differential diagnosis.

Integrative models and responses in cardiac ischemia

This chapter considers the study of electrophysiological changes during ischemia and incorporates mechanoelectric feedback, i.e., mechanical changes affecting electrophysiology. It considers these interactions in the cell, through multicell systems, the intact heart and the intact organism.

Effects of barriers on propagation of action potentials in two-dimensional cardiac tissue. A computer simulation study

A two-dimensional anisotropic model of cardiac ventricular muscle was used to study the effects of discontinuities (barriers), such as dead cells or high-resistance areas, on longitudinal plane-wave propagation. Problems in propagation appear when long barriers become thicker and their spacing closer. Short barriers with large widths and small spacing also cause propagation disturbances and significant delays in their vicinity. If the plane wave front propagates through the barriers, the velocity returns to near normal within one-length constant away from the end of the barrier region. For a funnel-like structure, an opening of 13 cells should exist for longitudinal plane wave propagation. For smaller openings, the ratio of openings required for propagation to occur when traveling from a narrow to a wider area of tissue is proportional to the anisotropy ratio, which can cause unidirectional block. Tortuosity, created by spatial distribution of dead cell barriers, can facilitate propagation by changing the effective impedance the wave front sees, and can create multiple local delays, which may result in discrepancies when measuring propagation velocity.

Why is catheter ablation less successful than surgery for treating ventricular tachycardia that results from coronary artery disease?

Nearly 80% of patients with coronary artery disease who have map-directed surgery for control of ventricular tachycardias require no drug therapy to prevent recurrences, while fewer than 50% of patients undergoing catheter ablation have similar outcomes. Catheter ablation will fail if arrhythmogenic sites are incompletely ablated by lesions that are too small or too far away from the reentrant pathway or if all arrhythmogenic sites are not identified. The underlying assumptions used to guide site selection are that: (a) ventricular tachycardias arise from reentrant mechanisms; (b) monomorphic ventricular tachycardias with similar QRS morphologies arise from the same pathway; (c) the ventricular tachycardia initiated during the procedure represents the patient's spontaneous arrhythmia; (d) the endocardial site that should be ablated can be identified from cardiac activation maps produced during induced ventricular tachycardia or from ancillary techniques; and (e) the patient has only one or two reentrant pathways. Relying on incorrect assumptions may account for the difference in success rates. Patients may have similar appearing ventricular tachycardias that arise from different pathways, and the entire thin layer of viable tissue between the infarct and the endocardium may contain many reentrant pathways. Some ventricular tachycardias may arise from the myocardium away from the endocardium, while others may arise from the epicardium. Small lesions may not be large enough to eliminate all possible reentrant pathways. Catheter ablation may be less successful because the lesions are inadequate, the assumptions guiding the selection of arrhythmogenic tissue are incorrect, or all arrhythmogenic sites are not identified. The primary reason catheter ablation is less successful than surgery in the treatment of ventricular tachycardias is that catheter ablation does not ablate as much tissue as is removed by surgery. The success rate of catheter ablation probably can be improved if the amount of tissue ablated is increased.

Value of body surface mapping in localizing the site of origin of ventricular tachycardia in patients with previous myocardial infarction

OBJECTIVES

This study examined the performance of the 62-lead body surface electrocardiogram (ECG) in identifying the site of origin of ventricular tachycardia in patients with a previous myocardial infarction.

BACKGROUND

Because the accuracy of ECG localization of ventricular tachycardia using standard 12-lead recordings is restricted to the identification of rather large ventricular areas, application of multiple torso lead recordings may augment the resolving power of the surface ECG and result in more discrete localization of arrhythmogenic foci.

METHODS

Thirty-two patients were selected for electrophysiologically guided ablative therapy for drug-resistant postinfarction ventricular tachycardia. In these patients, QRS integral maps of distinct monomorphic ventricular tachycardia configurations were correlated with a previously generated infarct-specific reference data base of paced QRS integral maps. Each paced pattern in the data base corresponded with ectopic endocardial impulse formation at 1 of 18 or 22 discrete segments of the left ventricle with a previous anterior or inferior myocardial infarction, respectively. Electrocardiographic localization was compared with the results obtained during intraoperative or catheter endocardial activation sequence mapping.

RESULTS

Body surface mapping was performed during 101 distinct ventricular tachycardia configurations. Compared with the activation mapping data that were acquired in 64 of 101 ventricular tachycardias, body surface mapping identified the correct segment of origin in 40 (62%) of 64 tachycardias, a segment adjacent to the segment where the arrhythmia actually originated in 19 (30%) of 64 tachycardias and a segment disparate from the actual segment of origin in 5 (8%) of 64 tachycardias. With respect to infarct location, the segment of origin was correctly identified in 28 (60%) of 47 ventricular tachycardias in patients with anterior, 7 (70%) of 10 tachycardias in patients with inferior and 5 (71%) of 7 tachycardias in patients with combined anterior and inferior myocardial infarction.

CONCLUSIONS

This study shows that body surface mapping enables precise localization of the origin of postinfarction ventricular tachycardia in 62% and regional approximation in 30% of tachycardias. The multiple-lead ECG may be used to guide and shorten catheter-based mapping procedures during ventricular tachycardia and to provide relevant information on the origin of tachycardias that cannot be mapped with conventional single-site mapping techniques because of unfavorable characteristics.

Effects of heptanol, class Ic, and class III drugs on reentrant ventricular tachycardia. Importance of the excitable gap for the inducibility of double-wave reentry

BACKGROUND

Double-wave reentry (DWR) can be a mechanism for acceleration of ventricular tachycardia (VT) with a large excitable gap (EG). The purpose of this study was to determine the effects of heptanol, class Ic, and class III drugs on the inducibility of DWR.

METHODS AND RESULTS

In 11 Langendorff-perfused rabbit hearts, a thin ring of anisotropic left ventricular epicardium was created by a cryoprocedure. VT with a revolution time of 180 +/- 26 milliseconds and an EG of 106 +/- 8 milliseconds was induced by incremental pacing. During control, entrainment with 10 stimuli at a 99 +/- 15-millisecond interval terminated VT in seven hearts. In four hearts VT was accelerated from 205 +/- 24 to 115 +/- 14 milliseconds by introduction of a second circulating wave in the ring. In the seven VTs that could not be accelerated, 0.5 mumol/L Org7797 (class Ic) and 1.0 mmol/L heptanol (uncoupling agent) prolonged the cycle length of VT by 32% and 37%, respectively. Because the refractory period (RP) only increased by 11%, the EG prolonged by 71% and the ratio between EG and RP was increased from 0.66 to 1.00. Under these conditions, DWR could be induced in all seven hearts. In the four VTs that could be accelerated during control, administration of the class III drug D-sotalol (35 mumol/L) only slightly slowed VT by 6%. Because the RP was prolonged by 15%, the ratio between the EG and the RP decreased from 0.76 to 0.63. Entrainment now failed to accelerate VT in two of four hearts, whereas in the two other hearts, double-wave reentry self-terminated within eight cycles.

CONCLUSIONS

Drugs that increase the ratio of EG and RP enhance the susceptibility to acceleration of VT, whereas drugs that decrease this ratio prevent induction of sustained double-wave reentry.