Treatment of Arrhythmogenic Right Ventricular Cardiomyopathy/Dysplasia: An International Task Force Consensus Statement

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Ablation of ventricular tachycardia

Ablation is an important management tool for the treatment of ventricular arrhythmias. Even at experienced centers ventricular tachycardia ablation carries a minor but significant risk for potential complications, including vascular and thromboembolic complications, air embolism, volume overload and the precipitation of congestive heart failure, cardiac tamponade from catheter perforation or from steam pop with RF energy delivery, valve or subvalvular support structure disruption, conduction system disruption with development of heart block, coronary artery injury when ablating in the coronary cusps region or trying to gain access to the LV chamber, precipitation of cardiogenic shock from ablation of viable myocardium in patients with marginal reserve and failure to resuscitate or precipitation of cardiogenic shock from repeated VT induction, and with epicardial ablation the potential complications of epicardial access, coronary arteries and phrenic nerve damage. Recognition of these risks is paramount for their avoidance with careful pre-procedure planning and intraprocedural technique being essential to minimize the potential for complications.

Effects of linear, irrigated-tip radiofrequency ablation in porcine healed anterior infarction

INTRODUCTION

Radiofrequency (RF) catheter ablation for ventricular tachycardia (VT) in healed infarction is modestly successful. More extensive, anatomically based procedures and irrigated RF delivery may improve outcome. However, limited data exist regarding the characteristics of irrigated RF lesions in infarcted myocardium. This study addresses this shortcoming.

METHODS AND RESULTS

Linear lesions were created at the medial border of a healed anterior infarct in eight pigs using irrigated RF energy guided by sinus rhythm electroanatomic voltage mapping and intracardiac echocardiography (ICE). Lesion morphology and effects on ventricular function were assessed with ICE imaging and pathologic analysis (n = 5). The response to programmed stimulation also was determined before and after linear lesions (n = 6). A mean of 9.4 +/- 1.3 RF applications created linear lesions 37.0 +/- 10.6 mm long, 5 to 12 mm wide, and 4 to 8 mm deep. Thrombus formation was not observed. Lesion delivery resulted acutely in increased local wall thickness at the RF site (26.9% +/- 27.5%; P < 0.0001) and transient systolic dysfunction in adjacent normal myocardium (fractional shortening -38% +/- 34%; P < 0.01). Uniform sustained VT (cycle length 232 +/- 41 msec) was induced in 4 of 6 pigs before ablation, but sustained VT could not be induced afterward.

CONCLUSION

Irrigated RF energy produced relatively large lesions in infarcted myocardium without thrombus formation. Changes in tissue thickness and echo density observed with ICE verify irrigated RF lesion delivery. Temporary left ventricular dysfunction is consistently observed in the normal myocardium adjacent to the linear lesion.

Changes in local wall thickness correlate with pathologic lesion size following radiofrequency catheter ablation: an intracardiac echocardiographic imaging study

INTRODUCTION

High-resolution intracardiac echocardiographic (ICE) imaging can accurately assess wall thickness during radiofrequency (RF) catheter ablation procedures. This study investigated the correlation of changes in wall thickness at the ablation site with pathologic lesion size.

METHODS AND RESULTS

ICE image-guided 31 RF applications (30-50 W, up to 120 sec) were performed in five anesthetized closed chest swine (n = 5, body weight 35-60 kg). Twenty-four lesions were delivered in the right and left atria with standard RF; seven lesions were delivered in the left ventricle (LV) with irrigated (30-40 ml/min) RF. Wall thickness and tissue echo density measured by ICE imaging (pre- and 1-minute post-RF delivery) with increased focal echo density following RF deployment in the atria (4.5 +/- 1.5 vs 2.3 +/- 1.0 mm pre-RF) and the LV (9.8 +/- 2.3 vs 6.8 +/- 2.2 mm pre-RF; P < 0.01). The observed changes in wall thickness (DeltaWT) following ablation in the LV were greater than in the atria (3.0 +/- 1.4 vs 2.2 +/- 1.2 mm; P < 0.05). A significant correlation between DeltaWT and lesion depth (ventricular: r = 0.85, P < 0.05; atrial: r = 0.82, P < 0.01) was demonstrated at all ablation sites. Local wall thickness measured post-RF also significantly correlated with lesion depth (r = 0.89, P < 0.01), especially with that of transmural lesions (r = 0.95, n = 23, P < 0.001) at atrial and LV sites.

CONCLUSION

Therapeutic RF ablation results in mural swelling and increased echo density. These changes can be detected by ICE imaging and correlate with pathologic lesion size. ICE imaging may be useful in online quantification of lesion size, especially for transmural lesions during clinical catheter ablation procedures.

Echocardiographic lesion characteristics associated with successful ablation of inappropriate sinus tachycardia

INTRODUCTION

Catheter ablation of inappropriate sinus tachycardia has proven difficult. Despite the use of intracardiac echocardiography to help direct radiofrequency (RF) application to the anatomic target of the superolateral crista terminalis (CT), multiple RF lesions often are required. Furthermore, the characteristic echo-anatomic changes with RF application associated with a reduction in heart rate have not been defined. A characteristic echo signature, if present, may facilitate the ablation process. The purpose of this retrospective study was to define the echocardiographic characteristic changes associated with effective RF ablation for inappropriate sinus tachycardia.

METHODS AND RESULTS

Detailed intracardiac echocardiographic imaging characterization of the superolateral CT was performed before and at the time of successful heart rate reduction. Using on-line videotape intracardiac echocardiography (9 MHz, 9 French), changes in wall thickness and echodensity at the CT lesion site were assessed at baseline, after each RF lesion, and with the lesion that produced heart rate reduction in 17 patients (age 32 +/- 9 years; 15 women) with inappropriate sinus tachycardia. In all patients, RF ablation was anatomically based and targeted only the superolateral CT. RF lesions were created using 20 to 50 W for up to 2 minutes using an 8-mm tip electrode. Successful heart rate reduction (> or = 20 beats/min) was achieved in 15 of 17 patients and required 41 +/- 31 RF applications (range 5 to 110, median 40). Effective RF (reduced heart rate) was observed starting with the 34th +/- 24th lesion (range 3rd to 86th, median 25th). After effective RF, CT wall thickness was increased (11.4 +/- 3.1 mm vs 7.7 +/- 2.4 mm at baseline) and wall swelling expanded to adjacent superior vena cava, but the degree of thickening was not specific for effective RF associated with heart rate reduction. Importantly, we noted echodensity changes reaching directly to the epicardium with the development of a linear low echodensity or echo-free space at the time of effective RF resulting in heart rate reduction. In two patients without effective heart rate reduction, echodensity changes never reached the epicardium. No complications (superior vena cava-right atrial junction orifice narrowing >50% or pericardial effusion) of RF were identified.

CONCLUSION

An echocardiographically guided anatomic approach to RF ablation of inappropriate sinus tachycardia is safe and effective. A characteristic echocardiographic signature suggesting transmural/epicardium damage appears to be present at the time of successful heart rate reduction and may serve as an appropriate guide for directing additional RF when using this anatomic echocardiographically based approach.

Clinical characteristics and catheter ablation of left ventricular outflow tract tachycardia

Left ventricular outflow tract (LVOT) tachycardia is an uncommon form of idiopathic ventricular tachycardia (IVT). The underlying mechanism of this arrhythmia appears to be cyclic AMP-medicated triggered activity. The tachycardia occurs in the absence of structural heart disease and is generally benign, presenting commonly as palpitations and presyncope. It can manifest either a right or left bundle branch block morphology with an inferior axis. Subtle variations in the QRS morphology in leads I, V1, and V2 can help in localizing the anatomic site of origin (SOO). The arrhythmia is typically responsive to a variety of pharmacologic agents (beta-blockers, calcium channel blockers, Class I and II agents). Radiofrequency catheter ablation of LVOT tachycardia SOO as determined by pace mapping is quite efficacious (success rates of 90%). Magnetic electroanatomic mapping augments this by permitting three-dimensional catheter mapping and reproducible localization of the SOO. Catheter ablation should be considered relatively early in patients who experience severe symptoms with their arrhythmia and have failed, or are reluctant to take medications for the disorder.

Intracardiac echocardiographic evaluation of ventricular mural swelling from radiofrequency ablation in chronic myocardial infarction: irrigated-tip versus standard catheter

INTRODUCTION

The production of larger, particularly deeper lesions may improve the success rate for radiofrequency (RF) ablation of post infarction ventricular tachycardia (VT). Therapeutic RF ablation causes left ventricular (LV) mural swelling. This swelling can be detected as increased wall thickness at the ablation site by intracardiac echocardiography (ICE) and correlates with pathologic lesion size. This study compared the extent of mural swelling caused by linear ablation lesions created with irrigated tip and standard RF ablation in a porcine model of healed anterior infarction.

METHODS AND RESULTS

In anesthetized closed-chest swine ICE guided multiple RF applications to construct linear lesions at the border zone of the infarct region using an irrigated RF (n=6 swine) and a standard RF (n=6 swine) ablation catheter. 47 individual lesions were created with irrigated RF ablation; 57 lesions created with standard RF ablation. At all sites, wall thickness (measured at end-diastole Pre- and 1 min Post-RF delivery) increased following either irrigated (p<0.0001) or standard (p<0.004) RF deployment. Irrigated RF ablation produced more mural swelling at border zone sites than standard RF ablation (wall thickness increase of 21.2 versus 15.1 %, p<0.003). This difference was more pronounced at RF sites within the infarct (40.7 versus 12.0 %, p<0.0007). Thrombus formation or intramural explosion were not observed; surface crater formation was not more frequent with irrigated compared to standard RF ablation (14/47 versus 12/57 lesions, p=NS).

CONCLUSION

Irrigated RF ablation may produce larger lesions than standard RF ablation, particularly for ablation targets within infarcted tissue. ICE imaging provides on line data about the characteristics of the developing lesion which may prove useful in dosing irrigated-tip RF energy application.

Electroanatomic magnetic mapping during ablation of isthmus-dependent atrial flutter

INTRODUCTION

Although recent studies have demonstrated that the endpoint of isthmus conduction block is superior to that of termination and subsequent inability to induce atrial flutter (AFl), the optimal method for determining isthmus conduction block has not been determined. Electroanatomic magnetic mapping during coronary sinus (CS) pacing may provide a reliable endpoint for AFl ablation.

METHODS AND RESULTS

Catheter mapping and ablation was performed in 42 patients with isthmus-dependent AFl. The patients were divided into two groups, based on procedural endpoint: Group I (28 patients) - isthmus conduction block was determined based on multipolar catheter recordings and electroanatomic mapping, and Group II (14 patients) - isthmus conduction block was determined by electroanatomic mapping during CS pacing alone. In Group I, ablation procedures were acutely successful in 25 of 28 patients (89 %). A 100 % concordance between the data presented by multipolar catheter recordings and electroanatomic mapping was noted in determining the presence or absence of isthmus conduction block. In Group II, ablation procedures were acutely successful in 13 of 14 patients, 13 (93 %). After a mean of 16.3+/-3.7 months follow up, there was 1 atrial flutter recurrence in the 38 patients (2.6 %) with demonstrated isthmus block at the end of the procedure.

CONCLUSIONS

Electroanatomic magnetic mapping during CS pacing is comparable to the multipolar catheter mapping technique for assessing isthmus conduction block as an endpoint for AFl ablation procedures.

Localization of arrhythmogenic triggers of atrial fibrillation

INTRODUCTION

Mapping procedures to identify triggers of atrial fibrillation from pulmonary veins (PVs) are not well established. We sought to determine the value of multipolar recordings from the coronary sinus (CS) and crista terminalis (CT) for identifying the origin of paced and atrial premature depolarizations (APDs) initiating atrial fibrillation from left versus right PVs.

METHODS AND RESULTS

Fifteen patients with paroxysmal atrial fibrillation refractory to medications had decapolar catheters (5-mm electrode, 2-mm interelectrode spacing) placed in the CS and posterior medial to the CT. Bipolar electrograms were recorded at each site. Electroanatomic left atrial endocardial maps were created in sinus rhythm, and each PV was identified and paced. During spontaneous APDs initiating atrial fibrillation and PV pace maps, the atrial activation and the earliest electrogram at CS and CT were compared. PV sites were designated as sites of origin of APDs when (1) intracardiac electrograms in the CS and CT during arrhythmogenic APDs matched those of PV pace maps, (2) local activation preceded CS and CT recordings by at least 40 msec (all sites), and (3) atrial depolarizations were eliminated by application of radiofrequency energy (24/26 sites). Pacing from each of the 30 right PV sites resulted in proximal to distal CS activation and later recordings at the CS than the CT (earliest CS-CT activation range: -15 to -58 msec, mean -32 +/- 12). In contrast, pacing from the left PV sites typically (28/30 sites) activated the CS from the distal to proximal poles and demonstrated simultaneous or earlier (CS-CT range: -14 to +54 msec, mean 13 +/- 17) recordings of the CS than the CT (P < 0.0001). For 13 APDs mapped to the right PVs, CS minus CT activation was -17 to -49 msec (mean -31 +/- 8). For 13 APDs localized to the left PVs, the CS minus CT activation time ranged from -8 to +28 msec (mean 14 +/- 15).

CONCLUSION

Activation sequence mapping from multipolar catheters placed in the CS and along the posterior medial CT rapidly differentiates right and left PV sites of origin of atrial depolarization.

Use of multisite electroanatomic mapping to facilitate ablation of intra-atrial reentry following the Mustard procedure

Ablation of intra-atrial reentrant tachycardia following Mustard or Senning procedures has low success rates. The Biosense Carto system was used to map intra-atrial reentry in a 22-year-old woman who had undergone a Mustard procedure. A line of block was created connecting a Mustard baffle suture line to the tricuspid valve annulus, which terminated the arrhythmia and prevented its reinitiation. Multisite electroanatomic mapping was invaluable in defining atrial anatomy and the intra-atrial reentrant pathway, and in creating a contiguous line of block. This mapping may improve ablation success rates in patients following the Mustard or Senning repair.

Sex-specific triggers for right ventricular outflow tract tachycardia

BACKGROUND

Right ventricular outflow tract tachycardia (RVOT-VT) is a common arrhythmia in young patients without heart disease. The arrhythmia is characterized by repetitive bursts and premature ventricular contractions with a left bundle branch block, inferior-axis QRS morphology, and symptoms of palpitations. Although more frequent in women, sex-specific triggers for symptomatic RVOT-VT have not been identified.

METHODS AND RESULTS

We interviewed 34 women and 13 men referred for ablation of RVOT-VT to determine if predictable but sex-specific exacerbations in symptomatic RVOT-VT exist. After a general query asking if there was predictability to what triggered palpitations, we then specifically queried all patients about symptomatic RVOT-VT initiation with exercise, stress, caffeine, fatigue, and, in women only, periods of recognized hormonal flux. The times identified as states of hormonal flux included premenstrual, gestational, perimenopausal, and coincident with the administration of birth control pills. In response to the completed interview, the most common recorded trigger for RVOT-VT in women was recognized states of hormonal flux with 20 (59%) of 34 women responding positively and 14 (41%) of the 34 indicating that states of hormonal flux were the only recognizable triggers. Men were more likely than women to report that their RVOT-VT was predictably triggered by exercise, stress, or caffeine: 12 (92%) of 13 men versus 14 (41%) of 34 women (P <.01).

CONCLUSIONS

Triggers for RVOT-VT initiation are sex specific. Women have RVOT-VT initiation with recognized states of hormonal flux. Men more commonly have RVOT-VT initiated by exercise or stress. These data have important implications related to patient education and counseling in the setting of RVOT-VT and may influence the timing of drug treatment and electrophysiologic evaluation in selected patients.

Accuracy of fluoroscopic localization of the Crista terminalis documented by intracardiac echocardiography

The crista terminalis is an important anatomic target for ablation of atrial arrhythmias. We determined the accuracy of catheter placement guided by fluoroscopy alone when directed to 24 sites along the crista terminalis in 6 patients. The sites selected included the most medial superior, most lateral superior, mid lateral, and most inferolateral sites along the crista terminalis in each patient. These sites were selected because of their recognized importance in sinus node and/or atrial tachycardia ablation and the importance of avoiding caval structures when targeting the most superior and/or inferior right atrium. The position of the catheter tip was documented using a catheter based ultrasound transducer in the right atrium or vena cava. The operator was blinded to the intracardiac echocardiographic (ICE) results until reviewing the images after the procedure in each patient. The catheter tip, guided by fluoroscopy alone, was identified by ICE to be within the right atrium and within 1cm of the crista terminalis at only 10 of the 24 sites (42%). Importantly, when targeting the most superior and inferior sites along the crista terminalis, the catheter tip, guided by fluoroscopy, was noted to be adjacent to the venous junction with the right atrium but actually located in the superior or inferior vena cava at 5 of the 18 such sites. The catheter was positioned appropriately (within 1 cm of the crista and within the right atrium) guided by fluoroscopy alone when targeting 1 of the 12 sites in the first 3 patients versus 9 of 12 sites in the last 3 patients, p<0.05. In conclusion, it appears that using fluoroscopic guidance alone: 1) localization of the crista terminalis is frequently inaccurate and 2) catheter positioning in the superior/inferior vena cava is commonly noted when targeting very superior and inferior sites along the crista terminalis. A learning curve, assisted by review of ICE recordings after each procedure, appears to improve the accuracy of catheter placement by fluoroscopy alone but still does not result in uniform success. ICE appears to facilitate and ensure accurate targeting of specific anatomic sites along the crista terminalis and thus may serve as an important adjunctive imaging technique in electrophysiology.

Hybrid therapy for ventricular arrhythmia management

Optimum arrhythmia management has evolved to couple ICD therapy with catheter ablative and drug therapy to attempt to eliminate or reduce arrhythmia risk. No longer should the clinician approach such therapy as a choice among single alternative strategies only. Optimum patient management includes not only recognition of the indications and benefits of such hybrid therapy but also a complete understanding of potential pitfalls of such therapy.

Using intracardiac catheter recordings from the His and proximal coronary sinus to distinguish isthmus conduction block during catheter ablation of type I atrial flutter

Isthmus conduction block, demonstrated with the use of multipolar catheter recordings, is considered the preferred endpoint for ablation of type I atrial flutter. This study investigated the feasibility of using recordings from the His and coronary sinus (CS) to document isthmus conduction block. Isthmus conduction block was produced with linear radiofrequency (RF) ablation in 27 patients with type I atrial flutter. In 13 patients (group I), RF was delivered until bidirectional isthmus conduction block was demonstrated with multipolar Halo catheter recordings. In 14 patients (group II), RF was delivered during pacing from the lateral isthmus at 600 ms until a reversal in activation of the proximal CS and His occurred. At this point, data from the Halo recordings were reviewed to see if reversal correlated with conduction block; if not, further ablation was performed until block was demonstrated. The initial reversal in His and CS activation during RF energy delivery correlated with isthmus block in only 4 (28.6%) of 14 patients in group II. Additional RF delivery produced isthmus block in the other ten patients resulting in a further increase in the St-CS interval of 35 +/- 20 ms. A His-CS interval of at least -40 ms signified isthmus block with a sensitivity and specificity of 48% and 100%, respectively. Reversal in His-CS activation during pacing from the lateral margin of the isthmus is not specific for the creation of isthmus block. While activation of the proximal CS bipole > 40 ms after activation of the His appears specific for isthmus block, the low sensitivity of this finding limits its clinical use.

Linear ablation lesions for control of unmappable ventricular tachycardia in patients with ischemic and nonischemic cardiomyopathy

BACKGROUND

Conventional activation mapping is difficult without inducible, stable ventricular tachycardia (VT).

METHODS AND RESULTS

We evaluated 16 patients with drug refractory, unimorphic, unmappable VT. Nine patients had ischemic and 7 had nonischemic cardiomyopathy. All patients had implantable defibrillators and had experienced 6 to 55 VT episodes during the month before treatment. Patients underwent bipolar catheter mapping during baseline rhythm. The amount of endocardium with an abnormal electrogram amplitude was estimated using fluoroscopy in 3 patients and a magnetic mapping system (CARTO) in 13 patients. For the magnetic mapping, normal endocardium was defined by an amplitude >1.5 mV; this measurement was based on sinus rhythm maps in 6 patients who did not have structural heart disease. Radiofrequency point lesions extended linearly from the "dense scar," which had a voltage amplitude <0.5 mV, to anatomic boundaries or normal endocardium. To limit radiofrequency applications, 12-lead ECG during VT and pacemapping guided placement of linear lesions. No new antiarrhythmic drug therapy was added. The amount of endocardium demonstrating an abnormal electrogram amplitude ranged from 25 to 127 cm(2). A total of 8 to 87 radiofrequency lesions (mean, 55) produced a median of 4 linear lesions that had an average length of 3.9 cm (range, 1.4 to 9. 4 cm). Twelve patients (75%) have been free of VT during 3 to 36 months of follow-up (median, 8 months); 4 patients had VT episodes at 1, 3, 9, and 13 months, respectively. Only one of these patient had frequent VT.

CONCLUSIONS

Radiofrequency linear endocardial lesions extending from the dense scar to the normal myocardium or anatomic boundary seem effective in controlling unmappable VT.

Efficacy and safety of catheter ablation in octogenarians

OBJECTIVES

To determine whether catheter ablation is safe and effective in patients over the age of 80.

BACKGROUND

There is a tendency to withhold invasive therapy in the elderly until it has been proven safe and effective.

METHODS

Over a two-year period from February 1, 1996 to February 1, 1998, 695 consecutive patients underwent 744 catheter ablation procedures of supraventricular and ventricular arrhythmias. These patients were divided into three groups based on age: > or =80 years, 60 to 79 years and <60 years. Acute ablation success, using standard criteria and complication rates for these three groups were determined.

RESULTS

There were 37 patients > or =80 years, 275 patients 60 to 79 years and 383 patients <60 years old. The overall acute ablation success rate for the entire group was 95% with no difference in rates among the three groups (97%, > or =80 years; 94%, 60-79 years; 95%, <60 years). The percentage of patients undergoing His bundle ablation was greatest in the > or =80-year-old group (43% vs. 19% vs. 2%, p < 0.01), and the percentage of patients undergoing accessory pathway ablation was greatest in the <60-year-old patients (0% vs. 4% vs. 25%, p < 0.01). The overall complication rate for the entire group was 2.6%, and there was only one major/life-threatening complication. There was no difference in complication rates among the groups (0%, > or =80 years; 2.2%, 60 to 79 years; 3.1%, <60 years). Based on the sample size, the 95% confidence interval is 0% to 7.8% for an adverse event in the octogenarian.

CONCLUSIONS

Catheter ablative therapy for the arrhythmias attempted in the very elderly appears to be effective with low risk. Ablation results appear to be comparable with those noted in younger patients.

Basket catheter localization of the origin of atrial tachycardia with atypical morphology after atrial flutter ablation

Atrial activation from a site in the low lateral right atrium will typically proceed in a superior direction. We present a case of a low lateral right atrial tachycardia with a surface electrocardiographic P wave morphology that appeared to have an inferiorly directed axis. The tachycardia occurred 2 years after successful atrial flutter ablation. The use of a multipolar basket catheter allowed confirmation of the focal origin of the tachycardia, permitted its rapid localization, facilitated catheter ablation, and provided clues to atrial activation that helped describe the appearance of the P wave.

Concomitant device and drug therapy: current trends, potential benefits, and adverse interactions

Antiarrhythmic drug therapy in patients with implantable cardioverter defibrillators (ICDs) has decreased over the last 10 years. This trend, primarily seen with class I agents, has occurred mainly in patients with a cardiac arrest. However, despite this overall decrease, antiarrhythmic drug therapy remains an important adjuvant to ICD therapy. In addition to primary prevention of ventricular tachycardia and supraventricular tachycardia, antiarrhythmic drug therapy may potentiate tachycardia rate slowing and make ventricular tachycardia more tolerated hemodynamically and possibly more amendable to pacing therapy. Some of the class III antiarrhythmic drugs may actually lower defibrillation threshold. Unfortunately, these drugs may have adverse interactions with ICDs. An increase in defibrillation threshold or rate-dependent increase in pacing threshold may interfere with the effectiveness of device therapy. Proarrhythmic effects of antiarrhythmic drugs may enhance the frequency of device use. The bradycardic effects of antiarrhythmic drug therapy may similarly enhance the requirements for persistent bradycardia pacing and lead to early battery depletion and other adverse consequences. An awareness of potential benefits and adverse effects of antiarrhythmic drug therapy along with careful electrophysiologic assessment are necessary for optimum combination drug and device therapy.

Electroanatomic left ventricular mapping in the porcine model of healed anterior myocardial infarction. Correlation with intracardiac echocardiography and pathological analysis

BACKGROUND

Catheter ablation for ventricular tachycardia in healed infarction is limited to patients with inducible, tolerated arrhythmias. Strategies that would allow mapping during sinus rhythm might obviate this limitation.

METHODS AND RESULTS

Two sets of experiments were performed in adult pigs to refine a new technique for left ventricular mapping. First, detailed endocardial maps were done in 5 normal pigs and 7 pigs 6 to 10 weeks after left anterior descending coronary artery infarction to characterize electrograms in normal and infarcted tissue by electroanatomic mapping (CARTO, Biosense). Electrogram recording sites were verified by intracardiac echo (ICE, 9 MHz) and grouped by location: infarct (area of akinesis by ICE), border (0.5-cm perimeter of akinetic area), and remote. Compared with remote sites, electrograms from infarct sites had smaller amplitudes (1.2+/-0.5 versus 5.1+/-2.1 mV, P<0.001), longer durations (74.2+/-26.3 versus 36.3+/-6.4 ms, P<0.001), and more frequent notched or late components. Border zone electrograms were intermediate in amplitude and duration. Second, infarct characterization by electroanatomic mapping was compared with pathological (exclusion of triphenyltetrazolium chloride staining) and ICE measurements. Infarct size by pathology correlated with the area defined by contiguous electrograms with amplitude </=1 mV (r=0.98, P=0.0001). Infarct size by ICE imaging correlated with the area defined by contiguous electrograms with amplitude </=2 mV (r=0.95, P=0.0016).

CONCLUSIONS

Electroanatomic mapping during sinus rhythm allows accurate 3D characterization of infarct architecture and defines the relationship of electrophysiological and anatomic abnormalities. This technique may prove useful in devising anatomically based strategies for ablation of ventricular tachycardia.

Intracardiac echocardiography (9 MHz) in humans: methods, imaging views and clinical utility

A new low-frequency (9 MHz, 9 Fr) catheter-based ultrasound (US) transducer has been designed that allows greater depth of cardiac imaging. To demonstrate the imaging capability and clinical utility, intracardiac echocardiography (ICE) using this lower frequency catheter was performed in 56 patients undergoing invasive electrophysiological procedures. Cardiac imaging and monitoring were performed with the catheter transducer placed in the superior vena cava (SVC), right atrium (RA) and/or right ventricle (RV). In all patients, ICE identified distinct endocardial structures with excellent resolution and detail, including the crista terminalis, RA appendage, caval and coronary sinus orifices, fossa ovalis, pulmonary vein orifices, ascending aorta and its root, pulmonary artery, RV and all cardiac valves. The left atrium and ventricle were imaged with the transducer at the limbus fossa ovalis of the interatrial septum and in the RV, respectively. ICE was important in identifying known or unanticipated aberrant anatomy in 11 patients (variant Eustachian valve, atrial septal aneurysm and defect, lipomatous hypertrophy, Ebstein's anomaly, ventricular septal defect, tetralogy of Fallot, transposition of the great arteries, disrupted chordae tendinae and pericardial effusion) or in detecting procedure-related abnormalities (narrowing of SVC-RA junction orifice or pulmonary venous lumen, atrial thrombus, interatrial communication). In patients with inappropriate sinus tachycardia, ICE was the primary ablation catheter-guidance technique for sinus node modification. With ICE monitoring, the evolution of lesion morphology with the three imaging features including swelling, dimpling and crater formation was observed. In all patients, ICE was contributory to the mapping and ablation process by guiding catheters to anatomically distinct sites and/or assessing stability of the electrode-endocardial contact. ICE was also used to successfully guide atrial septal puncture (n = 9) or RA basket catheter placement (n = 4). Thus, ICE with a new 9-MHz catheter-based transducer has better imaging capability with a greater depth. Normal and abnormal cardiac anatomy can be readily identified. ICE proved useful during electrophysiological mapping and ablation procedures for guiding interatrial septal puncture, assessing placement and contact of mapping and ablation catheters, monitoring ablation lesion morphological changes, and instantly diagnosing cardiac complications.

Implantable cardioverter-defibrillator follow-up: what everyone needs to know

Over the past few years, remarkable advances in the treatment of ventricular tachycardia, ventricular fibrillation, and sudden cardiac death have occurred. One of the most significant treatment modalities has been the addition of the implantable cardioverter-defibrillator (ICD). Because of the rapidly expanding indications for ICD therapy, it is common for internists, family practitioners, emergency room physicians, and general cardiologists to treat defibrillator patients. Basic skills related to ICD follow-up are therefore essential for many physicians. In this review, we will summarize routine device follow-up, provide instructions regarding emergency ICD deactivation, discuss common complications and how to detect them, and answer some frequently asked questions.

Narrowing of the superior vena cava-right atrium junction during radiofrequency catheter ablation for inappropriate sinus tachycardia: analysis with intracardiac echocardiography

OBJECTIVES

The study explored the potential for tissue swelling and venous occlusion during radiofrequency (RF) catheter ablation procedures using intracardiac echocardiography (ICE).

BACKGROUND

Transient superior vena cava occlusion has been reported following catheter ablation procedures for inappropriate sinus tachycardia (IST). Presumably, venous occlusion could occur owing to thrombus formation or tissue swelling with resultant narrowing of the superior vena cava-right atrial (SVC-RA) junction.

METHODS

Intracardiac echocardiography (9 MHz) was used to guide ablation catheter position and for continuous monitoring during RF application in 13 ablation procedures in 10 patients with IST. The SVC-RA junction was measured prior to and following ablation. Successful ablation was marked by abrupt reduction in the sinus rate and a change to a superiorly directed p-wave axis.

RESULTS

Eleven of 13 procedures were successful, requiring 29 +/- 20 RF lesions. Prior to the delivery of RF lesions, the SVC-RA junction measured 16.4 +/- 2.9 mm. With RF delivery, local and circumferential swelling was observed, causing progressive reduction in the diameter of the SVC-RA junction to 12.6 +/- 3.3 mm (24% reduction, p = 0.0001). A reduction in SVC-RA orifice diameter of > or = 30% compared to baseline was observed in five patients.

CONCLUSIONS

The delivery of multiple RF ablation lesions, often necessary for cure of IST, can cause considerable atrial swelling and resultant narrowing of the SVC-RA junction. Smaller venous structures, such as the coronary sinus and the pulmonary veins, would also be expected to be vulnerable to this complication. Thus, ICE imaging may be helpful in preventing excessive tissue swelling leading to venous occlusion during catheter ablation procedures.

Antidromic reciprocating tachycardia in patients with paraseptal accessory pathways: importance of critical delay in the reentry circuit

Previous studies in patients with antidromic reciprocating tachycardia (ART) have observed a critical anatomic requirement (> 4 cm) between an antegrade bypass tract limb and a retrograde AV nodal limb. We report two patients with ART utilizing a paraseptal accessory pathway. In both cases, a critical degree of slow conduction within the circuit provides unusual electrophysiologic substrate to overcome the expected anatomical constraints.

Imaging technique and clinical utility for electrophysiologic procedures of lower frequency (9 MHz) intracardiac echocardiography

Intracardiac echocardiography using a new 9-MHz ultrasound catheter was performed in 30 patients undergoing percutaneous catheter mapping and radiofrequency ablation of a tachyarrhythmia, because the imaging capabilities with this intracardiac echocardiographic catheter permit detailed identification of normal and abnormal cardiac anatomy with improved imaging depth. Intracardiac echocardiography is of significant clinical utility during ablation for guiding interatrial septal puncture, assessing placement and contact of mapping/ablation catheters, monitoring ablation lesion morphologic changes, and diagnosing procedure-related complications.

Interactions between implantable cardioverter-defibrillators and class III agents

Although implantable cardioverter-defibrillators (ICDs) can successfully terminate ventricular arrhythmias, antiarrhythmic drugs are often required to prevent recurrent events. Class III antiarrhythmic agents have emerged as the safest, most effective, and widely used agents in the 40-70% of ICD patients who require concomitant antiarrhythmic medication. Antiarrhythmic agents can influence the effectiveness of ICDs to terminate arrhythmias through their effect on defibrillation threshold. All class III agents share the ability to prolong ventricular refractoriness and those with "pure" class III activity consistently decrease defibrillation threshold in the normal canine heart model. Sotalol, amiodarone, and bretylium all have other Vaughan Williams class actions that influence their respective effects on defibrillation threshold. Sotalol has been associated with a decrease in defibrillation threshold in both animal and in clinical studies, whereas amiodarone has been associated with variable effects in animal models and an increase in defibrillation threshold in clinical studies. Additionally, antiarrhythmic agents may prolong ventricular tachycardia (VT) cycle length, which may affect the ability to pace terminate or cardiovert VT. Amiodarone has a moderate slowing effect on the VT cycle length. Finally, class III drugs also have proarrhythmic potential that may affect the defibrillator's function. Sotalol can be associated with dose-related torsade de pointes, whereas amiodarone may slow the VT cycle length below the tachycardia detection rate cutoff. In conclusion, class III pharmacotherapy can be safely administered in conjunction with ICD therapy as long as the interaction between these therapeutic modalities is appreciated.

Efficacy of radiofrequency catheter ablation for ventricular tachycardia in healed myocardial infarction

Radiofrequency catheter ablation has been useful in the treatment of ventricular tachycardia (VT) in selected patients with healed myocardial infarction. Previous studies have demonstrated success rates of 60% to 96% for targeted VT morphologies; however, these studies included patients only after they have had successful mapping procedures and have received radiofrequency lesions. All patients referred for VT ablation from July 1992 to November 1996 were included in this analysis on an intention-to-treat basis. Ninety-five procedures were performed in 66 patients for 77 distinct presentations with tolerated, sustained VT. Fifty-five procedures were successful (58%) and 40 procedures failed. Reasons for procedural failure included failed radiofrequency application despite adequate VT mapping (21 procedures), no tolerated VT induced (12), and aborted procedures due to complications or technical difficulties (7). Fifty-five patients (71%) eventually had a successful VT ablation, although 10 required > 1 procedure. This analysis revealed factors that contribute to failure of VT ablation procedures in addition to inadequate mapping and lesion formation. Procedural difficulties, particularly the inability to induce tolerated VT, frequently prevent successful catheter ablation in patients who present with tolerated, sustained VT.

Type I atrial flutter ablation guided by a basket catheter

Bidirectional isthmus conduction block has been associated with a low recurrence rate after atrial flutter ablation. We present the case of a type I, typical or "counterclockwise" atrial flutter ablation guided by stimulation and recordings obtained from a basket catheter, which allowed for constant electrogram recording from splines positioned along the right lateral free wall and septum. After atrial flutter termination with radiofrequency application, the ability to record and stimulate from multiple sites in the atrium using the basket catheter was useful to detect residual bidirectional slow conduction through the isthmus. Complete isthmus block could be documented after additional radiofrequency energy applications.

Rapid ventricular pacing in a pacemaker patient undergoing magnetic resonance imaging

Magnetic resonance imaging (MRI) generates potent electromagnetic forces in the form of a static, gradient, or pulsed radiofrequency magnetic field that can result in pacemaker malfunction. This report documents a case of rapid cardiac pacing during MRI in a patient with a dual chamber pacemaker. Although the mechanism of rapid cardiac pacing is unclear, it was directly related to radiofrequency pulsing. We postulated that the lead acts as an antenna for radiofrequency energy that interacts with the pacemaker's output circuit, thus, causing cardiac pacing at a cycle length representing a multiple of the repetition time; or perhaps rapid pacing is related to induced currents generated between the MRI unit and the pacing lead.

Implantable defibrillator diagnostic storage capabilities: evolution, current status, and future utilization

There has been a rapid and significant evolution in the stored diagnostic information available from implantable cardioverter defibrillators (ICDs). The diagnostic information available in current generation ICDs has greatly enhanced the clinicians' ability to determine the rhythm triggering device therapy as well as to identify potential problems with the ICD system. Furthermore, this information may be useful in identifying triggers of ventricular arrhythmias in patients at high risk for sudden death. The history, evolution, value, and limitations of the stored diagnostic capabilities of implantable defibrillators are discussed.

Clinical presentation and analysis of risk factors for infectious complications of implantable cardioverter-defibrillator implantations at a university medical center

The objective of this report is to describe the characteristics of patients who develop infections associated with implantable cardioverter-defibrillators (ICDs) implanted with sternotomy and thoracotomy approaches. A retrospective chart review identified all patients who underwent ICD implantation at a university medical center from November 1982 through February 1990. Several patient and procedural variables were compared between infected patients and noninfected patients. One hundred fifty-seven patients underwent 202 ICD generator implantations (45 generator changes), and nine of these patients developed infection (4.5% per implantation and 5.7% per patient). Of the patient variables analyzed, a significant correlation (P < .0001) was made only with a diagnosis of diabetes mellitus: 36% of diabetics versus 3.9% of nondiabetics were infected. The only patient- or procedure-specific variable that was found to correlate with the development of infection was the presence of diabetes mellitus.

Characterization of the excitable gap in human type I atrial flutter

OBJECTIVES

We sought to characterize the excitable gap of the reentrant circuit in atrial flutter.

BACKGROUND

The electrophysiologic substrate of typical atrial flutter has not been well characterized. Specifically, it is not known whether the properties of the tricuspid valve isthmus differ from those of the remainder of the circuit.

METHODS

Resetting was performed from two sites within the circuit: proximal (site A) and distal (site B) to the isthmus in 14 patients with type I atrial flutter. Resetting response patterns and the location where interval-dependent conduction slowing occurred were assessed.

RESULTS

Some duration of a flat resetting response (mean +/- SD 40.1 +/- 20.9 ms, 16 +/- 8% of the cycle length) was observed in 13 of 14 patients; 1 patient had a purely increasing response. During the increasing portion of the resetting curve, interval-dependent conduction delay most commonly occurred in the isthmus. In most cases, the resetting response was similar at both sites. In three patients, the resetting response differed significantly between the two sites; this finding suggests that paced beats may transiently change conduction within the circuit or the circuit path, or both.

CONCLUSIONS

Some duration of a flat resetting response was observed in most cases of type I atrial flutter, signifying a fully excitable gap in all portions of the circuit. The isthmus represents the portion of the circuit most vulnerable to interval-dependent conduction delay at short coupling intervals.

Transcatheter radiofrequency ablation for congenital junctional ectopic tachycardia in infancy

Congenital junctional ectopic tachycardia (JET) is a difficult to treat arrhythmia with a variably poor response to pharmacologic intervention. We report on the successful treatment of a 17-day-old infant with JET via transcatheter radiofrequency ablation of the arrhythmogenic focus resulting in resolution of the tachycardia and maintenance of normal atrioventricular nodal function. Transcatheter radiofrequency ablation techniques should be considered in infants with life-threatening arrhythmia recalcitrant to standard forms of drug therapy.

ICD-antiarrhythmic drug and ICD-pacemaker interactions

Antiarrhythmic drugs and separate bradycardia pacing systems are prescribed commonly in patients with implantable cardioverter defibrillators (ICDs). Adverse effects of antiarrhythmic drugs on ICD function and adverse interactions between ICDs and pacemakers have been documented. The effect of antiarrhythmic drugs on the defibrillation threshold (DFT) in patients has not been well assessed. Most studies have been performed in animal models in which cardiac function was normal and drug doses were supraphysiologic. In addition, most studies have utilized monophasic defibrillation shock waveforms and epicardial lead systems. Despite the lack of clinical data applicable to current defibrillation systems, it appears that chronic amiodarone administration causes a significant DFT increase. In addition, antiarrhythmic drugs can influence antitachycardia pacing and tachycardia sensing. Defibrillation shocks can cause transient failure of pacemaker sensing and pacing, and cause spurious pacemaker reprogramming. Pacemaker function can result in ICD oversensing, leading to inappropriate therapy, or cause ICD undersensing, potentially resulting in failure to deliver therapy during ventricular fibrillation. The susceptibility of an ICD to undersensing appears related to the amplitude of the pacing stimulus artifact recorded by the ICD rate-sensing circuit and to the characteristics of the fibrillation electrogram. Preliminary data suggest that undersensing of ventricular fibrillation by current ICDs is an unlikely event.

Implantable cardioverter defibrillator oversensing during periods of rate-related bundle branch block

A patient with an implantable cardioverter defibrillator (ICD) and a dual chamber pacemaker experienced inappropriate ICD therapies only during periods of rate-dependent right bundle branch block. Analysis of both stored and real-time ICD electrograms was critical to correctly diagnosing the problem and offering a solution.

Adenosine as an antiarrhythmic agent

Adenosine produces acute inhibition of sinus node and atrioventricular (AV) nodal function. This profound but short lived electrophysiologic effect makes adenosine a suitable agent for treating supraventricular tachycardias (SVT) that incorporate the sinus node or AV node as part of the arrhythmia circuit, or for unmasking atrial tachyarrhythmias or ventricular pre-excitation. Its antiadrenergic properties also make it an effective agent for use with some unique atrial and ventricular tachycardias. Appropriate dosing and rapid bolusing with intravenous administration is required. Recognition of infrequent proarrhythmic risks and potential drug interactions with xanthine derivatives and dipyridamole should maximize its safe and effective use. This review will highlight adenosine's mechanism of action, administration, clinical indications, efficacy, and risks when used in tachyarrhythmic management.

Right ventricular radiofrequency ablation of ventricular tachycardia after myocardial infarction

Radiofrequency transcatheter ablation of ventricular tachycardia in the setting of a prior myocardial infarction is typically performed with application of energy to the left ventricular endocardium. In this article, two cases are described in which successful radiofrequency transcatheter ablation of ventricular tachycardia occurred with energy delivery to the right ventricular septum after failed ablation attempts from the left ventricle. Both patients had tachycardias with a left bundle branch block morphology and markedly presystolic activity recorded from the right ventricular septum. Right ventricular septal activation mapping during ventricular tachycardia should be performed in patients with left bundle branch block tachycardia morphology and coronary artery disease to maximize efficacy of the catheter ablation procedure.

Repetitive monomorphic tachycardia from the left ventricular outflow tract: electrocardiographic patterns consistent with a left ventricular site of origin

OBJECTIVES

This study sought to characterize the electrocardiographic patterns predictive of left ventricular sites of origin of repetitive monomorphic ventricular tachycardia (RMVT).

BACKGROUND

RMVT typically arises from the right ventricular outflow tract (RVOT) in patients without structural heart disease. The incidence of left ventricular sites of origin in this syndrome is unknown.

METHODS

Detailed endocardial mapping of the RVOT was performed in 33 consecutive patients with RMVT during attempted radiofrequency ablation. Left ventricular mapping was also performed if pace maps obtained from the RVOT did not reproduce the configuration of the induced tachycardia.

RESULTS

Pace maps identical in configuration to the induced tachycardia were obtained from the RVOT in 29 of 33 patients. Application of radiofrequency energy at sites guided by pace mapping resulted in elimination of RMVT in 24 (83%) of 29 patients. In four patients (12%), pace maps obtained from the RVOT did not match the induced tachycardia. All four patients had a QRS configuration during RMVT with precordial R wave transitions at or before lead V2. In two patients, RMVT was mapped to the mediosuperior aspect of the mitral valve annulus, near the left fibrous trigone; catheter ablation at that site was successful in both. In two patients, RMVT was mapped to the basal aspect of the superior left ventricular septum. Catheter ablation was not attempted because His bundle deflections were recorded from this site during sinus rhythm.

CONCLUSIONS

RMVT can arise from the outflow tract of both the right and left ventricles. RMVTs with a precordial R wave transition at or before lead V2 are consistent with a left ventricular origin.

Prediction of outcome of patients with life-threatening ventricular arrhythmias treated with automatic implantable cardioverter-defibrillators using SPECT perfusion imaging

BACKGROUND

In the present study, we examined the predictors of outcome of 103 patients with coronary artery disease and left ventricular dysfunction who had life-threatening ventricular arrhythmias and were treated with implantable cardioverter-defibrillators with the use of single-photon emission computed tomography (SPECT).

METHODS AND RESULTS

During a mean follow-up of 29 months, there were 29 cardiac deaths. In comparison with patients who died, survivors had less diabetes mellitus (45% versus 19%, P < .007), higher left ventricular ejection fraction (23 +/- 9% versus 27 +/- 11%, P = .04), and fewer perfusion defects as determined with stress SPECT (15 +/- 5 versus 12 +/- 5, P < .004). Most of the perfusion defects were fixed, indicative of scarring; the extent of reversible defects did not differ (2 +/- 3 in survivors and 3 +/- 4 in nonsurvivors). Multivariate Cox survival analysis identified the number of fixed defects as the only independent predictor of death (chi 2 = 10, P = .002). There were six deaths among 42 patients (14%) with < 8 fixed defects compared with 23 deaths among 61 patients (38%) with > or = 8 defects (P = .005). The 4-year survival was better in patients with < 8 segmental fixed defects than in those with > or = 8 fixed defects (80% versus 36%) (chi 2 = 8, P = .005).

CONCLUSIONS

The myocardial perfusion pattern is an important determinant of outcome in patients with life-threatening ventricular arrhythmias who are treated with a implantable cardioverter-defibrillator. The extent of scarring separates patients into high- and low-risk groups with a 2.7-fold difference in death rate.

Does the initial presentation of patients with implantable defibrillator influence the outcome?

The influence of the clinical presentation on the long-term outcome in 213 consecutive patients with ICDs, ECG storage capability, and nonthoracotomy leads, was analyzed. Sixty-six patients presented with cardiac arrest (CA), 81 patients with hemodynamically stable VT, and 66 patients with syncope (SY). Patient characteristics were: mean age CA 62, VT 61, SY 61 years; mean ejection fraction CA 31%, VT 29%, SY 30%; coronary artery disease CA 71%, VT 71%, SY 64% (all P > 0.05 Fisher's exact test); female gender CA 40%, VT 14%, SY 19% (CA vs VT and SY, P < 0.005); inducibility by programmed stimulation CA 50%, VT 84%, SY 61% (VT vs CA and SY, P < 0.001, CA vs SY, P > 0.05). During a mean follow-up of 14.5 months, 29 patients died: CA 12%, VT 14%, SY 9% (P > 0.05). Comparing Kaplan-Meier curves, no difference in the time course of overall mortality was found (log-rank P > 0.05). In the CA, VT, and SY groups, 543, 1,630, and 189 ICD therapies (including antitachycardia pacing, low energy cardioversion, and defibrillation) were observed, respectively. Actuarial analysis showed a shorter interval between implantation and first ICD therapy for VT versus CA and SY (log-rank P < 0.005). Patients presenting with VT experienced earlier and more frequent ICD therapies than patients with CA or SY independent of age, ejection fraction, and heart disease. No difference in overall mortality and time course of fatal events was observed among the three groups.

Conduction block in the inferior vena caval-tricuspid valve isthmus: association with outcome of radiofrequency ablation of type I atrial flutter

OBJECTIVES

We sought to 1) correlate conduction block in the isthmus of the right atrium between the inferior vena cava and the tricuspid annulus with the efficacy of catheter ablation of type I atrial flutter, and 2) characterize the effects of ablative lesions on the properties of isthmus conduction.

BACKGROUND

There are few data on the mechanism of persistent suppression of recurrence of atrial flutter by catheter ablation.

METHODS

Thirty-five patients with type I atrial flutter underwent catheter mapping and ablation. Radiofrequency lesions were applied in the isthmus. Transisthmus conduction before and after the lesions was assessed during atrial pacing in sinus rhythm from the medial and lateral margins of the isthmus at cycle lengths of 600, 400 and 300 ms and the native flutter cycle length. Isthmus conduction block was defined using multipolar recording techniques. There were three treatment groups: group 1 = radiofrequency energy applied during flutter, until termination (n = 14); group 2 = radiofrequency energy applied during atrial pacing in sinus rhythm from the proximal coronary sinus at a cycle length of 600 ms, until isthmus conduction block was observed (n = 14); and group 3 = radiofrequency energy applied until an initial flutter termination, after which further energy was applied during atrial pacing in sinus rhythm until isthmus conduction block was observed (n = 7).

RESULTS

In group 1, after the initial flutter termination, isthmus conduction block was observed in 9 of the 14 patients. In each of these nine patients, flutter could not be reinitiated. In each of the remaining five patients, after the initial flutter termination, isthmus conduction was intact and atrial flutter could be reinitiated. Ultimately, successful ablation in each of these patients was also associated with isthmus conduction block. In groups 2 and 3, isthmus conduction block was achieved during radiofrequency energy application, and flutter could not subsequently be reinitiated. Before achieving conduction block, marked conduction slowing or intermittent block, or both, was observed in some patients. In some patients, isthmus conduction block was pacing rate dependent. In addition, recovery from conduction block was common in the laboratory and had a variable time course. At a mean follow-up interval of 10 months (range 1 to 21), the actuarial incidence of freedom from type I flutter was 80% (recurrence in three patients at 7 to 15 months).

CONCLUSIONS

Isthmus conduction block is associated with flutter ablation success. Conduction slowing or intermittent block, or both, in the isthmus can occur before achieving persistent block. Recovery of conduction after achieving block is common. Follow-up has revealed a low rate of flutter recurrence after achieving isthmus conduction block, whether the block was achieved in conjunction with termination of flutter.

Multicenter comparison of truncated biphasic shocks and standard damped sine wave monophasic shocks for transthoracic ventricular defibrillation. Transthoracic Investigators

BACKGROUND

The most important factor for improving out-of-hospital ventricular fibrillation survival rates is early defibrillation. This can be achieved if small, lightweight, inexpensive automatic external defibrillators are widely disseminated. Because automatic external defibrillator size and cost are directly affected by defibrillation waveform shape and because of the favorable experience with truncated biphasic waveforms in implantable cardioverter-defibrillators, we compared the efficacy of a truncated biphasic waveform with that of a standard damped sine monophasic waveform for transthoracic defibrillation.

METHODS AND RESULTS

The principal goal of this multicenter, prospective, randomized, blinded study was to compare the first-shock transthoracic defibrillation efficacy of a 130-J truncated biphasic waveform with that of a standard 200-J monophasic damped sine wave pulse using anterior thoracic pads in the course of implantable cardioverter-defibrillator testing. Pad-pad ECGs were also examined after transthoracic defibrillation. After the elimination of data for 24 patients who did not meet all protocol criteria, the results from 294 patients were analyzed. The 130-J truncated biphasic pulse and the 200-J damped sine wave monophasic pulse resulted in first-shock efficacy rates of 86% and 86%, respectively (P = .97). ST-segment levels measured 10 seconds after the shock in 151 patients in sinus rhythm were -0.26 +/- 1.58 and -1.86 +/- 1.93 mm for the 130- and 200-J shocks, respectively (P < .0001).

CONCLUSIONS

We found that 130-J biphasic truncated transthoracic shocks defibrillate as well as the 200-J monophasic damped sine wave shocks that are traditionally used in standard transthoracic defibrillators and result in fewer ECG abnormalities after the shock.

Bundle branch reentry ventricular tachycardia: an investigation of the circuit with resetting

We describe a patient with bundle branch reentry ventricular tachycardia with 1:1 VA conduction in whom resetting was performed while obtaining simultaneous recordings from the right ventricular apex (V) and His-bundle electrogram. Both the tachycardia return cycle and the V-His interval demonstrated an increasing reset response, while the His-V interval demonstrated a flat reset response. These reset responses are consistent with a partially excitable gap localizing to the V-His portion of the bundle branch reentry circuit.

Insights into the electrophysiology of accessory pathway-mediated arrhythmias provided by the catheter ablation experience: "learning while burning, part III"

The success of catheter ablation has greatly improved the care of patients with paroxysmal tachycardias and has caused a revolution in the practice of electrophysiology. Some investigators have expressed that concern over procedural success in an increasingly interventional specialty threatens to eclipse attempts to understand the physiology of arrhythmia syndromes. Alternatively, due to the precise and directed nature of the lesions created with radiofrequency energy, catheter ablation procedures have allowed investigation to continue at a more focused level. In this article, the insights provided by the catheter ablation experience into the physiology of arrhythmias mediated by accessory AV pathways will be reviewed. Although the learning process was sometimes delayed by the nearly immediate success of radiofrequency catheter ablation, difficult situations have continued to renew efforts for understanding at a deeper level. Conscious attempts at "learning while burning" will provide the opportunity to investigate aspects of bypass tract physiology that remain incompletely characterized, such as partial response to therapy and late recurrence.