Abstract
Delivery of low energy T-wave shocks may induce ventricular fibrillation (VF). Clinical use of this induction method is hindered due to the need for T-wave scanning with multiple shocks to identify the window of vulnerability (WV) to VF. The purpose of this study was to test the hypothesis that WV duration is directly related to shock strength. We studied the effect of shock strength on WV in 27 consecutive patients undergoing nonthoracotomy Medtronic 7219C/D PCD implantation ortesting. WVduration was tested after a 3 pulse 400 ms drive by T-wave scanning between coupling intervals (CI) of 220–420 ms in 20 ms steps using randomized 0.6 J and 2.0J truncated monophasic shocks. The results were (mean ± std): 0.6 J 2.0J P Min CI (ms) 270 ± 23 275 ± 28 N.S. Max CI (ms) 312 ± 31 333 ± 30 <0.05 WV Duration (ms) 39 ± 25 56 ± 33 <0.05 The mean increase in WV duration with 2.0 J shocks was 166 ± 134%, P < 0.05. Increased WV duration was due solely to persistence of VF inducibility further into diastole. Maximal VF induction efficacy was 20/27 (74%) patients using 2.0 J at 300 ms CI. Optimal induction with 0.6 J was 17/27 (63%) patients at a 280 ms CI. 1) Window of vulnerability duration is energy dependent, 2) Increasing shock strength extends the vulnerable period, 3) Greatest induction efficacy for a single shock strength and CI is 74%, and 4) Need for T-wave scanning may be minimized by increasing shock energy.
Published Version
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