Randomized, prospective comparison of four burst pacing algorithms for spontaneous ventricular tachycardia

Incidence and Characteristics of Type-2 Breaks in Response to Antitachycardia Pacing Therapy in Implantable Cardioverter Defibrillator Patients

INTRODUCTION

Antitachycardia pacing (ATP) effectively treats monomorphic ventricular tachycardia (VT). The VT may cease immediately upon ATP completion (type-1 break), or it may persist or change to another tachyarrhythmia for one or more beats before termination (type-2 break). We investigated the prevalence and characteristics of type-2 breaks in ICD patients.

METHODS AND RESULTS

We analyzed VT episodes with stored electrograms that had at least one ATP therapy delivered in PainFREE Rx trial, a multicenter trial with 220 coronary artery disease patients. Further subanalysis was performed by classifying the VT as slow or fast based on the cycle length (CL); slow VT: CL >320 ms, fast VT: 240 < or =CL < or =320 ms. To assess the effect of ATP on VT, comparison was performed of pre-ATP and post-ATP CL variability, average CL, and morphology. A total of 514 episodes (264 slow VT and 250 fast VT) were analyzed. The burst ATP terminated 457 (89%; 239 slow VT and 218 fast VT) of 514 episodes. Forty five (10%) episodes in 18 (32%) patients had type-2 breaks. The mean number of beats during type-2 breaks was 5.4 +/- 3.1 (median 4). The mean time for episode termination measured from the end of ATP to return of first sinus/paced beat was 2.9 +/- 1.2 seconds (median 2.6). The VT CL variability increased by 150% after ATP delivery. The ATP affected either VT CL or morphology, or both of 36 (80%) type-2 breaks (9% accelerated, 47% decelerated, 22% changed in morphology only). Among the 9 (20%) episodes that remained unchanged in morphology and CL, four episodes (9%) were unaffected by ATP.

CONCLUSION

Approximately 10% of VT episodes that were successfully terminated with burst ATP therapy had type-2 breaks. Type-2 breaks are associated with an increase in CL variability. Approximately 9% of all type-2 episodes may be spontaneously terminating nonsustained VT given that ATP did not affect these episodes in any way.

Effect of elevated heart rate preceding the onset of ventricular tachycardia on antitachycardia pacing effectiveness in patients with implantable cardioverter defibrillators

The incorporation of antitachycardia pacing (ATP) into implantable cardioverter defibrillators (ICDs) has provided a better tolerated alternative to shocks. ATP has been shown to be effective in terminating approximately 80% to 90% of spontaneous ventricular tachycardia (VT) episodes. Although ATP is routinely used, little is known about predictors of ATP failure. Based on the evaluation of stored electrograms, we aimed to prospectively follow patients with ICDs, and to analyze parameters affecting ATP effectiveness. One hundred eighteen consecutive patients received ICDs for standard indications. Before discharge, empirical, standardized ATP therapy was programmed in all patients within VT zones. A total of 1,218 spontaneous tachycardia episodes occurred in 51 patients during a mean follow-up of 24.5 +/- 12 months. Among these, 888 VTs were diagnosed. One hundred four fast VTs were detected in the ventricular fibrillation zone and treated with primary shock delivery. ATP was attempted 881 times in the remaining 784 VT episodes. ATP terminated 640 VTs successfully, ATP failed in 55 VTs finally reverted by shocks, and 89 VTs converted to a slower VT outside the VT zone. Fifty-one of these slower VTs reverted spontaneously, and 38 were redetected and treated. Finally, in primary intention-to-treat basis, ATP was successful in 691 VTs (88%) and unsuccessful in 93 VTs (12%). There was no influence of VT cycle length on ATP success rate. Furthermore, ATP efficacy was similar between patients with left ventricular ejection fraction < or =35% or >35%, between daytime and nighttime, as well as between patients with ischemic or nonischemic cardiomyopathy. A faster heart rate immediately preceding the onset of VT (103 +/- 19 vs 78 +/- 14 beats/min, respectively, hazard ratio 4.08, 95% confidence interval 2.11 to 7.89, p <0.001), and absence of beta-blocker therapy (82% vs 93%, respectively, hazard ratio 2.71, 95% confidence interval 1.72 to 4.29, p = 0.02) were found, by Cox proportional-hazard analysis, to be the sole independent predictors of ATP ineffectiveness in ICD recipients. Thus, the present study identified both preceding sinus tachycardia (reflecting an increased sympathetic tone) and lack of beta-blocker use as independent risk factors for reduced success of ATP therapy in terminating VT. Therefore, modification of sympathetic tone may be beneficial for patients with ICDs.

Shock reduction using antitachycardia pacing for spontaneous rapid ventricular tachycardia in patients with coronary artery disease

BACKGROUND

Implantable cardioverter-defibrillators (ICDs) can terminate some ventricular tachycardias (VTs) painlessly with antitachycardia pacing (ATP). ATP has not routinely been applied for VT >188 bpm because of concerns about efficacy, risk of acceleration, and delay of definitive shock therapy. This prospective, multicenter study evaluated the efficacy of empirical ATP to terminate fast VT (FVT; >188 bpm).

METHODS AND RESULTS

Two hundred twenty coronary artery disease patients received ICDs for standard indications. Empirical, standardized therapy was programmed so that all FVT episodes (average cycle length [CL] 240 to 320 ms, 250 to 188 bpm) were treated with 2 ATP sequences (8-pulse burst pacing train at 88% of the FVT CL) before shock delivery. A total of 1100 episodes of spontaneous ventricular tachyarrhythmias occurred during a mean of 6.9+/-3.6 months of follow-up. Fifty-seven percent were classified as slow VT (CL>/=320 ms), 40% as FVT (240 ms</=CL<320 ms), and 3% as ventricular fibrillation (CL<240 ms). A total of 446 FVT episodes, mean CL=301+/-24 ms, occurred in 52 patients (median 2 episodes per patient). ATP terminated 396 FVT episodes (89%), with an adjusted efficacy of 77% (95% CI 68% to 83%). VT acceleration caused by ATP occurred in 10 FVT episodes (4%). FVT arrhythmic syncope occurred on 9 occasions (2%) in 4 patients.

CONCLUSIONS

FVT (CL<320 ms) is common in ICD patients. ATP can terminate 3 of 4 of these episodes with a low incidence of acceleration and syncope. ATP for FVT may safely reduce the morbidity of painful shocks.