960-90 Ventricular Fibrillation Induction Efficacy of Low Energy T-Wave Synchronized Shocks in Patients with Nonthoracotomy ICDs

Abstract

Incremental ventricular pacing or alternating current have been traditionally used to induce ventricular fibrillation (VF) while testing defibrillating function of the ICD. The available data are limited on ventricular fibrillation induction efficacy of the low energy T-wave shocks. To determine this, we analyzed data in 14 patients with Medtronic ICDs (7219C 9 pts, 7219D 2 pts, PCD 3 pts) who had undergone a total of 110 VF induction attempts either at time of ICD implant or during follow-up noninvasive EPS. The underlying heart disease was coronary in all patients with prior myocardial infarction in 10 patients. The LV ejection fraction was 30 ± 12% (range 15–64%). QT interval 440 ± 57 ms (range 360–560 ms) and QTc interval 449 ± 49 ms (range 336–520 ms) The low energy synchronized shocks (0.2–2 J) were delivered to the T wave of last of the 8 beat paced train at 400 ms with S l -T delays ranging between 290–340 ms. Of 110 attempts with T wave shocks, the inducible arrhythmia was VF in 69%. nonsustained polymorphic ventricular tachycardia (VT) in 15%, monomorphic VT in 2% and none in 14%. The VF induction efficacy was 75% (69 of 92 attempts) for T-wave shock energy of >0.6 J compared with 50% (9 of 18 attempts) for T-wave shock energy of ≤ 0.6 J (P < 0.05). In contrast, the VF induction efficacy was unaffected by S 1 -T delays ranging from 290–330 ms. It was 80% 14/5) at S 1 -T delay of 290 ms, 80% (4/5) at S 1 -T delay of 300 ms, 70% (44/66) at S 1 -T delay of 310 ms, 78% (7/9) at S 1 -Tdelay of 320 ms, 74% (17/23) at S 1 -T delay of 330 ms and 0% (0/2) at S 1 -T delay of 340 ms. In no patients incremental ventricular pacing or alternating current had to be used to induce VF. We conclude that a low energy (1–2 J) shock, when synchronized to the paced-T wave withS 1 -T delays of 290–330 ms, induces VF in over 70–80% of the attempts. This precludes the need for prolonged ventricular bursts or the use of alternating current and should, thus, be the preferred modality of choice while inducing VF to check ICD function.