Abstract 2136: Influence of Variations in the Duration of RR Intervals on Antitachycardia Pacing Effectiveness in Terminating Spontaneous and Monomorphic Ventricular Tachychardias
Despite the high efficacy of antitachycardia pacing (ATP) in terminating monomorphic ventricular tachycardias (MVT) in ICD patients, 5–25 % of such episodes, depending on the cycle length (CL), are not finished by ATP. We speculated that variations in the duration of RR intervals (RRv) of MVT could predict the result of the subsequent ATP because they may be related to the circuit refractory period. Our aim is to determine prospectively the relationship between RRv of the 12 RR intervals previous to ATP and the efficacy of this latter. The variables analyzed were: 1-the mean of the difference between each RR interval duration and the next one (Mn-RRv); 2-the percentage of variation (P-RRv): [Mn-RRv / mean CL of MVT] * 100.
Methods: A total of 200 ICD patients (LVEF: 31±10) were included in this study. We analyzed the result of the first ATP (f-ATP). Detection and first therapy for VT were programmed as follows: Fast-VT zone (CL: 250 –320 ms; burst of 5 pulses at 84% of CL); slow-VT zone (CL: >320 ms; burst of 15 pulses at 91%). RR intervals were measured from the marker channel.
Results: During a follow-up of 602±368 days, 546 MVT (CL: 329±35 ms; 41% fast-VT; 22 %) were recorded in 64 patients. Success rate of f-APT was 82%. RRv was higher in successful f-ATP (S-fATP): Mn-RRv: 8.7±5.6 vs. 4.4±3.8 ms; P-RRv: 2.7±1.7 vs. 1.3±1.2, (p<0.001 for both). These variables correlated with the probability of S-fATP: C-coefficient=0.76 (Mn-RRv) and 0.78 (P-RRv), p<0.001 for both. Classifying the events into three groups according to the tertiles of P-RRv (≤1.75%, 1.76%–2.99%, ≥3%), the frequency of S-fATP increased with the P-RRv: 69% vs. 82% vs. 98% (all MVTs; p<0.001), and 68% vs. 83% vs. 97% (fast-MVTs; p<0.001). In a multivariate analysis which included LVEF, aetiology, indication, functional class and CL, P-RRv remained as an independent predictor of S-fATP: OR: 2.1 (95% Confidence Interval: 1.7–2.7); p<0.001. MVT with lower values of P-RRv presented higher frequencies of acceleration (5.8% vs. 2.5% vs. 0.6%; p=0.01) and appropriate discharges (18.7% vs. 10.8% vs. 1.7%; p<0.001).
Conclusions: Among ICD patients, small fluctuations in the duration of RR intervals significantly increase the likelihood of first ATP terminating MVT.