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.

Transthoracic cardioversion of atrial fibrillation: comparison of rectilinear biphasic versus damped sine wave monophasic shocks

BACKGROUND

Clinical studies have shown that biphasic shocks are more effective than monophasic shocks for ventricular defibrillation. The purpose of this study was to compare the efficacy of a rectilinear biphasic waveform with a standard damped sine wave monophasic waveform for the transthoracic cardioversion of atrial fibrillation.

METHODS AND RESULTS

In this prospective, randomized, multicenter trial, patients undergoing transthoracic cardioversion of atrial fibrillation were randomized to receive either damped sine wave monophasic or rectilinear biphasic shocks. Patients randomized to the monophasic protocol (n=77) received sequential shocks of 100, 200, 300, and 360 J. Patients randomized to the biphasic protocol (n=88) received sequential shocks of 70, 120, 150, and 170 J. First-shock efficacy with the 70-J biphasic waveform (60 of 88 patients, 68%) was significantly greater than that with the 100-J monophasic waveform (16 of 77 patients, 21%, P<0.0001), and it was achieved with 50% less delivered current (11+/-1 versus 22+/-4 A, P<0.0001). Similarly, the cumulative efficacy with the biphasic waveform (83 of 88 patients, 94%) was significantly greater than that with the monophasic waveform (61 of 77 patients, 79%; P=0.005). The following 3 variables were independently associated with successful cardioversion: use of a biphasic waveform (relative risk, 4.2; 95% confidence intervals, 1.3 to 13.9; P=0.02), transthoracic impedance (relative risk, 0.64 per 10-Omega increase in impedance; 95% confidence intervals, 0.46 to 0.90; P=0.005), and duration of atrial fibrillation (relative risk, 0.97 per 30 days of atrial fibrillation; 95% confidence intervals, 0.96 to 0.99; P=0.02).

CONCLUSIONS

For transthoracic cardioversion of atrial fibrillation, rectilinear biphasic shocks have greater efficacy (and require less energy) than damped sine wave monophasic shocks.

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.

Idiopathic right ventricular outflow tract tachycardia: narrowing the anatomic location for successful ablation

Pace mapping used to locate the site for ablation of idiopathic right ventricular outflow tract (RVOT) ventricular tachycardia remains difficult and time-consuming. A method to facilitate pace mapping and the most common site of ablation of this tachycardia are reported. In 18 consecutive patients with RVOT ventricular tachycardia, electrocardiographic criteria based on the QRS orientation in lead 1 and the R wave progression in the precordial leads were used to find pace maps matching the arrhythmia. Identical pace maps were obtained on the septum of the RVOT in 16 patients and resulted in successful ablations. These sites were concentrated in the anterior superior aspect of the RVOT determined by fluoroscopic imaging. In the remaining two cases identical pace maps could not be found in this area. The results of this study narrow the anatomic location for radiofrequency ablation of idiopathic RVOT ventricular tachycardia. This is the first description of an electrocardiography-guided approach to finding an identical pace map in the RVOT.

Autonomic nervous system activity and the spontaneous initiation of ventricular tachycardia. ESVEM Investigators. Electrophysiologic Study Versus Electrocardiographic Monitoring Trial

OBJECTIVES

We hypothesized that neurohormonal activity contributes to the initiation of sustained ventricular tachycardia (VT) as reflected in indices of heart rate variability (HRV).

BACKGROUND

Autonomic nervous system activity participates in experimental arrhythmias but clinical studies have been inconsistent.

METHODS

Holter electrocardiograms from 53 patients with VT were analyzed. Heart rate variability indices were determined over 5 and 15 min and 24 h and examined for changes before the onset of VT. Heart rate variability indices in the frequency domain included ultra low frequency power (FP) (ULFP): 0-0.0033 Hz; very low FP (VLFP): 0.0033-0.04 Hz; low FP (LFP): 0.04-0.15 Hz; high FP (HFP): 0.15-0.4 Hz; total power (TP); normalized LFP (LFPn); normalized HFP (HFPn), and the ratio: LFP/HFP.

RESULTS

Heart rate variability indices were severely diminished: TP: 12,009+/-11,076 ms2; ULFP: 10,087+/-9,565 ms2; VLFP: 1,416+/-1,571 ms2; LFP: 544+/-620 ms2; HFP: 161+/-176 ms2, and LFP/HFP: 3.68+/-2.83. Heart rate increased before VT (80.4+/-17.3 to 85.3+/-17.4 bpm, p < 0.001). Several HRV variables declined 30 min before VT compared to 24-h values (VLFP: -5.89+/-17.81%, p = 0.031; LFP: -5.23+/-14.3%, p = 0.003; HFP: -4.35+/-13.7%, p = 0.04). LFPn and the LFP/HFP ratio decreased significantly before the onset of VT (-17.7+/-46.9%, p = 0.035 and -8.24+/-38.8%, p = 0.037, respectively), whereas HFPn increased slightly (4.29+/-29.9%, p = 0.097).

CONCLUSIONS

Heart rate rose, whereas LFP, LFPn and LFP/HFP fell before the onset of VT. This pattern of changes could be explained by a rise in sympathetic activity and saturation of the HRV signal resulting in dissociation of the average and rhythmical effects of sympathetic activity. These findings suggest that alterations in autonomic activity contributed to arrhythmogenesis in this group of patients.

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.

Comparison of a novel rectilinear biphasic waveform with a damped sine wave monophasic waveform for transthoracic ventricular defibrillation. ZOLL Investigators

OBJECTIVES

We compared the efficacy of a novel rectilinear biphasic waveform, consisting of a constant current first phase, with a damped sine wave monophasic waveform during transthoracic defibrillation.

BACKGROUND

Multiple studies have shown that for endocardial defibrillation, biphasic waveforms have a greater efficacy than monophasic waveforms. More recently, a 130-J truncated exponential biphasic waveform was shown to have equivalent efficacy to a 200-J damped sine wave monophasic waveform for transthoracic ventricular defibrillation. However, the optimal type of biphasic waveform is unknown.

METHODS

In this prospective, randomized, multicenter trial, 184 patients who underwent ventricular defibrillation were randomized to receive a 200-J damped sine wave monophasic or 120-J rectilinear biphasic shock.

RESULTS

First-shock efficacy of the biphasic waveform was significantly greater than that of the monophasic waveform (99% vs. 93%, p = 0.05) and was achieved with nearly 60% less delivered current (14 +/- 1 vs. 33 +/- 7 A, p < 0.0001). Although the efficacy of the biphasic and monophasic waveforms was comparable in patients with an impedance < 70 ohms (100% [biphasic] vs. 95% [monophasic], p = NS), the biphasic waveform was significantly more effective in patients with an impedance > or = 70 ohms (99% [biphasic] vs. 86% [monophasic], p = 0.02).

CONCLUSIONS

This study demonstrates a superior efficacy of rectilinear biphasic shocks as compared with monophasic shocks for transthoracic ventricular defibrillation, particularly in patients with a high transthoracic impedance. More important, biphasic shocks defibrillated with nearly 60% less current. The combination of increased efficacy and decreased current requirements suggests that biphasic shocks as compared with monophasic shocks are advantageous for transthoracic ventricular defibrillation.

Postoperative lead-related complications in patients with nonthoracotomy defibrillation lead systems

OBJECTIVES

This study sought to document postoperative complications attributable to nonthoracotomy defibrillation lead systems in a large cohort.

BACKGROUND

The incidence of postoperative complications specifically associated with nonthoracotomy defibrillation lead systems is unknown.

METHODS

Postoperative lead-related complications were evaluated in 170 patients with a nonthoracotomy defibrillation lead system who were followed up for a mean (+/- SD) of 17 +/- 12 months. Each system incorporated one or more intravascular leads. In 117 patients (69%), the system incorporated a subcutaneous defibrillation patch. All implantations were performed in an operating room by cardiothoracic surgeons. Defibrillation thresholds were measured at implantation, before hospital discharge (mean 3 +/- 2 days) and at 4 to 18 weeks after implantation. Patients were evaluated every 2 to 3 months after implantation or as indicated by clinical exigency.

RESULTS

Twenty-seven patients (15.9%) were diagnosed with a lead-related complication that either extended the initial hospital period or led to a second hospital admission. Complications included endocardial lead or subcutaneous defibrillation patch dislodgment in eight patients (4.7%), which was diagnosed between 2 and 345 days after implantation; endocardial or subcutaneous patch lead fracture in six (3.5%), which was diagnosed between 53 and 600 days after implantation; subcutaneous patch mesh fracture in one, which was diagnosed at 150 days after implantation; subclavian vein thrombosis in three (1.8%), which was diagnosed at 2 to 50 days after implantation; and unacceptably elevated defibrillation threshold (within 5 J of maximal device output) in nine (5.3%), which was documented at one of the two postimplantation evaluations in eight patients or at the time of failure to terminate a spontaneous ventricular tachycardia in one. Seventeen of the 27 patients required reoperation for correction of their complication. In addition, system infection requiring complete explantation occurred in seven other patients (4.1%) at an interval from implantation ranging from 14 to 120 days.

CONCLUSIONS

Postoperative complications related to a nonthoracotomy defibrillation lead system were common and frequently required reoperation for correction. The rate of system explantation due to infection was also significant. Postoperative defibrillation testing and vigilant outpatient follow-up evaluation are necessary to ensure normal lead function.

Electrical impedance properties of normal and chronically infarcted left ventricular myocardium

BACKGROUND

Previous reports have disclosed that a significant difference exists between the electrical impedance properties of healthy and chronically infarcted ventricular myocardium.

PURPOSE

To assess the potential utility of electrical impedance as the basis for mapping in chronically infarcted left ventricular myocardium. Specifically: (1) to delineate electrical impedance properties of healthy and chronically infarcted ventricular myocardium, with special emphasis on the infarction border zone; (2) to correlate impedance properties with tissue histology; (3) to correlate impedance properties with electrogram amplitude and duration; (4) To demonstrate that endocardial impedance can be measured effectively in vivo using an electrode mounted on a catheter inserted percutaneously.

METHODS

An ovine model of chronic left ventricular infarction was utilized. Sites of healthy myocardium, densely infarcted myocardium and the infarction border zone were investigated. Bulk impedance was measured in vitro using capacitor cell, four-electrode and unipolar techniques. Epicardial and endocardial impedances were measured in vivo using four-electrode and unipolar techniques. Impedance was measured at multiple frequencies. Electrographic amplitude, duration and amplitude/duration ratio were measured using bipolar electrograms during sinus rhythm. Quantitation of tissue content of myocytes, collagen, elastin and neurovascular elements was performed.

RESULTS

Densely infarcted myocardial impedance was significantly lower than healthy myocardium. Impedance gradually decreased in the border zone transitioning between healthy myocardium and dense infarction. Decreasing impedance correlated with a decrease in tissue myocyte content. The magnitude of the difference in impedance between densely infarcted and healthy myocardium increased as the measurement frequency decreased. Healthy myocardium exhibited a marked frequency dependence in its impedance properties; this phenomenon was not observed in densely infarcted myocardium. There was a direct association between impedance and both electrogram amplitude and amplitude/duration ratio. There was an inverse association between impedance and electrogram duration. Endocardial impedance, measured in vivo using a electrode catheter inserted percutaneously, was demonstrated to distinguish between healthy and infarcted myocardium.

CONCLUSIONS

The electrical impedance properties of healthy and infarcted left ventricular myocardium differ markedly. The properties of the infarction border zone are intermediate between healthy and infarcted myocardium. Impedance may be a useful assay of cardiac tissue content and adaptable for cardiac mapping in vivo. Condensed Abstract. To delineate the electrical impedance properties of healthy and chronically infarcted left ventricular myocardium emphasizing the infarction border zone, impedance was measured in chronically infarcted ovine hearts. Densely infarcted myocardial impedance was significantly lower than healthy myocardium. Impedance gradually decreased in the infarction border zone in transition between healthy myocardium and dense infarction. This correlated with a decreasing myocyte content. The magnitude of the difference in impedance between densely infarcted and healthy myocardium increased as measurement frequency decreased. There was a direct association between impedance and electrogram characteristics. Endocardial impedance, measured in vivo using an electrode catheter inserted percutaneously, distinguished between healthy and infarcted myocardium

ICD data storage: value in arrhythmia management

Sophisticated diagnostic information is provided by the latest generation of implantable defibrillators. The success of therapy and the type of therapy successful in terminating ventricular arrhythmias is provided by interrogating the ICD device. In addition, R to R interval information can be retrieved. In selected devices, either local bipolar electrograms from the rate sensing leads or wide bipolar electrograms from the energy delivering leads provide visual confirmation of the presence of ventricular tachyarrthythmic events leading to therapy. The value and limitations of this sophisticated diagnostic information in providing insight into the electrical events triggering therapy and the events triggering ventricular arrhythmias are discussed.

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.

Cardiac swelling associated with linear radiofrequency ablation in the atrium

OBJECTIVES

To characterize myocardial swelling in response to application of endocardial radio-frequency ablation lesions.

BACKGROUND

In individual patients, we have observed that ablation in the posterior right atrium was associated with echocardiographic evidence of atrial and contiguous right pulmonary vein wall swelling.

METHODS

1. Human Subjects: "linear" ablation was performed in the posterior right atrium in 10 subjects; a portion of the ablation lesion was contiguous to the right pulmonary vein; this area was defined as the "contiguity zone". In the contiguity zone, right atrial wall thickness and pulmonary vein lumen diameter were measured utilizing intracardiac echocardiography. Measurements were made just prior to (baseline) and immediately after ablation.2. Porcine Subjects: linear ablation was performed in the posterior right atrium of 14 pigs. In the contiguity zone, atrial wall thickness, interstitial space thickness, right pulmonary vein wall thickness and lumen diameter were measured using intracardiac echocardiography. Measurements were made at baseline, immediately after ablation, and at 1, 4, 8 or 12 weeks after ablation (followup). Post-mortem pathologic evaluation of the contiguity zone was performed.

RESULTS

1. Human Subjects: Immediately after ablation, relative to baseline right atrial wall thickness was significantly increased (9.4+/-3.1mm versus 5.4+/-1.5 mm) and right pulmonary vein lumen diameter was significantly decreased (6.2+/-2.9 mm versus 8.1+/-2.9 mm).2. Porcine Subjects: Immediately after ablation, right atrial wall thickness (4.1+/-1.2 mm), interstitial space thickness (1.9+/-1.1mm), and right pulmonary vein wall thickness (1.2+/-0.4 mm) were each significantly increased relative to baseline (1.0+/-0.3 mm, 0+/-0 mm, and 0.7+/-0.2 mm, respectively) and pulmonary vein lumen diameter was significantly decreased (5.0+/-1.4 mm versus 6.9+/-2.2 mm). Similar findings were made at the 1 week followup interval. At 4, 8 and 12 week followup intervals, thicknesses and lumen diameter were not significantly different from baseline. At post-mortem examination, direct measurements of wall thickness were significantly correlated with echocardiographic measurements. Histologic analysis demonstrated edema to be the cause of the early wall thickness and lumen diameter changes. Ablation lesions were transmural in the right atria of all animals; in some animals, lesion formation was also observed in the pulmonary vein wall.

CONCLUSIONS

Cardiac edema resulting from right atrial linear ablation results in swelling of atrial and contiguous right pulmonary vein walls, as well as the interposed extracardiac interstitial space. These changes are associated with a decrease in pulmonary vein lumen diameter. Swelling evolves rapidly and resolves within 4 weeks.

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.

Benefits and lessons learned from stored electrogram information in implantable defibrillators

Implantable defibrillators have evolved from simple event counters to sophisticated diagnostic monitoring units capable of storing electrocardiographic information surrounding arrhythmia events and device therapy. In this review, the nature and characteristics of these stored electrocardiographic recordings are discussed and examples displayed. Potential benefits and limitation of stored electrogram analysis are described with respect to both clinical utility and the ability to enhance our understanding of ventricular arrhythmogenesis. Finally, future developments to improve data storage, retrieval, and analysis are identified.

Anatomy-guided linear atrial lesions for radiofrequency catheter ablation of atrial fibrillation

The surgical atrial maze procedure has provided proof that atrial fibrillation can be cured by performing atrial incisions based on anatomical and electrophysiological principles. Preliminary reports of attempts at radiofrequency catheter ablation of atrial fibrillation utilizing an anatomy-based "linear incision" method have shown the feasibility of the method. However, postprocedural atrial fibrillation recurrence has been common and in addition new, uniform tachycardias have developed in some patients. Both of these outcomes may be in part due to incomplete or inconsistent lesion deployment. This article details the use of the CARTO system for deploying anatomy guided linear atrial lesions for the purpose of curing atrial fibrillation. The procedure is comprised of three phases, which are discussed in detail: (1) baseline map; (2) lesion deployment and; (3) lesion assessment. Using a single standard ablation electrode, lesions can be deployed safely, and complete lesions can be confirmed. Paradigms for right and left atrial incisions are proposed.

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.

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.

ICD waveform optimization: a randomized, prospective, pair-sampled multicenter study

The theoretical tissue model-based estimates of phase 1 and phase 2 duration of biphasic waveforms are considerably shorter than the pulse widths currently used in ICDs with standard tilt. This study used a tissue resistance/capacitance (RC) model to identify optimal biphasic pulse widths. By paired step-down defibrillation threshold (DFT) testing, the efficacy of standard versus "tuned" biphasic waveforms was evaluated in 91 patients. Standard waveforms consisted of a phase 1 set to 65% tilt and phase 2 = phase 1. The tuned waveform was based on an RC model of membrane characteristics with a time constant of 3.5 ms. The optimal phase 1 truncation point is at the peak of membrane response. The optimal phase 2 duration ends with a membrane response near or just below 0. In paired analysis, no significant differences were found in DFT or impedance between standard and tuned waveforms. In patients with DFTs > 400 V, the tuned waveform lowered the DFT by an average of 38 V (P < 0.05). Multivariate analyses showed a significant inverse relationship between DFT and impedance (P < 0.001). As impedance increased, the tuned waveform was associated with DFTs comparable to the standard waveform with shorter pulse duration and lower delivered energy. No single tilt value allowing an easy calculation of delivered energy was related to ICD waveform efficacy. The use of ICDs with tuned optimal pulse durations offer a greater flexibility of choice for patients with high DFTs.

Abnormalities of the corrected QT interval in familial dysautonomia: an indicator of autonomic dysfunction

We report abnormalities in corrected QT intervals with changes in position and after exercise in patients with familial dysautonomia and confirm the previously reported finding of abnormal heart rate and blood pressure responses. Prolonged corrected QT intervals (> 440 msec) with lack of appropriate shortening with exercise is a noninvasive means of demonstrating an aberration in autonomic regulation of cardiac conduction.

The results of atrial flutter ablation in patients with and without a history of atrial fibrillation

To determine the impact of atrial flutter radiofrequency catheter ablation on recurrence of atrial flutter and atrial fibrillation, 32 patients with atrial flutter (18 with a history of atrial fibrillation) were followed for a mean of 8.6 months; atrial flutter has not recurred after 1 (26 patients) or 2 (5 patients) successful ablation procedures. Atrial flutter did not appear proarrhythmic for atrial fibrillation, with only 1 of 15 patients without a history of atrial fibrillation developing the arrythmia in the absence of an alcohol binge or cocaine use.

Electrogram-guided radiofrequency catheter ablation of atrial tissue comparison with thermometry-guide ablation: comparison with thermometry-guide ablation

OBJECTIVES

To characterize a new method for radiofrequency energy titration during ablation of atrial tissue based on reduction in electrogram amplitude. To compare this method with energy titration using electrode thermometry.

BACKGROUND

Complications associated with "anatomy-based" atrial endocardial radiofrequency ablation for suppression of atrial fibrillation may be due to flawed methods of energy titration.

METHODS

The effect of radiofrequency ablation on electrogram amplitude was characterized in a porcine model. A method for energy titration guided by electrogram amplitude reduction ("electrogram-guided") was developed and validated prospectively. Focal (smooth and trabeculated endocardial areas) and linear (smooth endocardial areas) ablation was performed comparing energy titration guided by amplitude reduction with electrode thermometry.

RESULTS

Amplitude reduction during radiofrequency application was not necessarily equal among unipolar and bipolar electrograms in the ablation region; specific patterns of reduction could be discerned, based on factors such as catheter-endocardial orientation. A criterion of >90 % reduction of unipolar and/or bipolar amplitude best predicted pathologic lesion success. Electrogram-guided focal and linear lesions in smooth areas were free of lesion complications such as endocardial charring, barotrauma, or damage to contiguous extraatrial structures. However, there was a significant incidence of insufficient lesion size, principally non-transmurality, probably due to undertitration of energy. Thermometry-guided focal and linear lesions in smooth areas were uniformly transmural but frequently evidenced complications, due to overtitration of energy. Electrogram-guided focal lesions in trabeculated areas could usually not be achieved, probably due to insufficient contact of the ablation electrode with adjacent pectinate muscles. Thermometry-guided focal lesions in trabeculated areas were smaller than electrogram-guided lesions and did not evidence complications.

CONCLUSIONS

Electrogram-guided lesions in smooth endocardial areas were uncomplicated but had a significant incidence of non-transmurality. Thermometry-guided lesions were uniformly transmural but were frequently complicated.

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.

Circadian variation of ventricular arrhythmia recurrences after cardioverter-defibrillator implantation in patients with healed myocardial infarcts

Past studies using Holter monitoring and retrospective reviews of death certificates have documented peak occurrence of sudden death and nonsustained ventricular tachycardia (VT) in the morning hours. We used the Ventritex Cadence device (Ventritex, Sunnyvale, California) which documents the date and time of all stored arrhythmias leading to device therapy to evaluate the circadian pattern of sustained ventricular arrhythmia recurrence. Mean follow-up after defibrillator implantation was 628 +/- 285 days. All 390 patients had at least 1 episode (range 1 to 43) of sustained VT documented from analysis of the stored electrograms associated with an arrhythmia event. Stored electrograms were available for review and analysis in 3,041 device detections; 349 stored events were excluded because they did not fulfill the diagnostic criteria for VT or failed to document the onset of the ventricular arrhythmia at the beginning of the recorded event of the arrhythmia episode. Criteria for the diagnosis of VT or ventricular fibrillation were met in 2,692 arrhythmia episodes occurring in 390 patients. There was circadian variation for ventricular arrhythmia recurrence for the whole patient group with the data fit to the sinusoidal density function: f(t) = 126 - 51 x cos (-57 + 2 pi t/24) - 25 x sin (63 + 2 pi t/12) (p < 0.0001). Ventricular arrhythmia occurrence rate was lowest between 2:00 and 3:00 A.M., and highest between 10:00 and 11:00 A.M. In addition, the same circadian pattern was demonstrated regardless of patient age, gender, left ventricular ejection fraction (< 35% or > or = 35%), and VT cycle length (< 300 or > or = 300 ms).(ABSTRACT TRUNCATED AT 250 WORDS)