Energy Level and Success of Internal Defibrillation for Shockable Rhythm during Cardiopulmonary Bypass in Cardiac Surgery: A Retrospective Study

Internal defibrillation is commonly indicated for shockable rhythm following cross-clamp removal in cardiac surgery. Low energy decreases the success rate of defibrillation but high energy can cause myocardial damage. This study aimed to determine the success rate of internal defibrillation for shockable arrhythmias after cardiac surgery.Retrospective data of 1,424 patients who developed shockable rhythms (ventricular fibrillation or ventricular tachycardia), and required internal defibrillation after aortic cross-clamp removal during cardiac surgery, without deep hypothermic circulatory arrest technique, from August 2015 to July 2017, were reviewed.The overall success rate of internal defibrillation in the first attempt of defibrillation was 61.5%. The success rate of the energy levels at 30, 10, and 7 Jules were 66.7, 64.9, and 61.5%, respectively. The success rate was higher in patients who had a better ejection fraction than those who failed after defibrillation. This was significantly associated with higher pH, higher bicarbonate, lower serum calcium, and lower total cardioplegic volume during cardiopulmonary bypass (CPB). Redo-valve surgery, valvular surgery, and combined coronary artery bypass graft with valvular surgery had a non-significantly lower success rate (p-value = 0.989). Incidence of failure for defibrillate patients in redo-valvular surgery, combined coronary artery bypass graft with valve surgery, adult congenital heart defect, and valvular surgery; requiring four or five shocks was non-significantly increased. Recurrent rate of ventricular fibrillation/ventricular tachycardia was 13.5%.The success rate of internal defibrillation was not related to the dose of energy used after being weaned off CPB.

Abstract 9386: Ramp Biphasic Waveforms Have a Lower External Defibrillation Threshold

Introduction: We have previously shown that waveforms with an ascending ramp in both phases have a lower internal defibrillation threshold (DFT). The purpose of this study was to test whether waveforms with rectilinear, ascending and descending ramps in the second phase would reduce the DFT compared with a standard exponential biphasic waveform with external defibrillation shocks. Methods: In 6 pigs, DFTs were determined for 10 waveforms: a standard truncated exponential biphasic waveform with 60% tilt (Fig 1, #1) and 9 biphasic waveforms with an 8 ms ascending ramp 1st phase and one of 3 rectilinear, ascending ramp or descending ramp 2nd phases. The 3 rectilinear 2nd phases were: 1 ms, 200% of peak voltage of phase 1 (#2); 2 ms, same voltage as phase (#3); 3 ms, half the voltage of phase 1 (#4). The 3 ascending ramp 2nd phases were: 2 ms, 200% of voltage of phase 1(#5); 3 ms, same voltage as phase 1(#6); 4.5 ms, half the voltage of phase 1(#7). The 3 descending ramp 2nd phases were: 2 ms, 200% of voltage of phase 1(#8); 3 ms, same voltage as phase 1(#9); 4.5 ms, half the voltage of phase 1(#10). Results: Phase 2 ascending ramp (#7) and descending ramp (#8, #9) waveforms had the lowest DFTs, which were significantly smaller than for the truncated exponential waveform. (Fig 1, *indicates p<0.05). Conclusions: Waveforms with a ramp in phase 2 (#7, #8, #9) have a lower DFT.