Influence of cycle length variations on antitachycardia pacing effectiveness among ICD patients.

Background: Antitachycardia pacing (ATP) fails to terminate 5% to 25% of ventricular tachycardias (VTs) occurring in implantable cardioverter-defibrillator patients. We speculated that small fluctuations in VT cycle length (CL) may be related to the efficacy of subsequent ATP.
Objective: The purpose of this study was to determine the relationship between the R-R variations of the last 12 R-R intervals before ATP and the efficacy of the first ATP attempt.
Methods: We studied 551 VTs (CL 329±35 ms) occurring in 67 patients. We also analyzed the percentage of variation (P-RR), which was calculated by dividing the mean difference between each R-R interval and the next one by the CL (×100), and the acceleration index (AI), which was calculated by dividing the CL of the first 6 R-R intervals by the CL of the next 6.
Results: The effectiveness of the first ATP therapy was 81%, being higher in VTs with AI<1 (85% vs 64%; P<.001). After classifying the events according to the tertiles of P-RR, ATP efficiency was better in higher values of P-RR (VTs with AI<1): 99% (third tertile) vs 85% (second tertile) vs 76% (first tertile), P<.001; and for VTs with AI≥1: 94% vs 68% vs 42% (P<.001). By logistic regression, P-RR (%; odds ratio 2.37; P<.001), and AI<1 (odds ratio 4.17; P<.001) were found to be independent predictors of successful first ATP attempts.
Conclusion: Small changes in CL increase the effectiveness of ATP significantly. VTs with lower degrees of R-R fluctuations, especially when the pattern is a progressive CL shortening, are infrequently terminated by ATP.
(Copyright © 2013 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.)