Single Capacitive Discharge Utilizing an Auxiliary Shock in the Coronary Venous System Reduces the Defibrillation Threshold

Auxiliary shocks (AS) from electrodes sutured to the left ventricle (LV) prior to primary biphasic shocks (PS) have been shown to reduce defibrillation thresholds (DFT). Two capacitors are required to generate these waveforms. We investigate delivery of AS from one capacitor using a novel waveform. The epicardial surface of the LV is accessed transvenously via the middle cardiac vein (MCV) avoiding a thoracotomy. Methods: A defibrillation electrode was placed in the right ventricle (RV) and superior vena cava (SVC) in 12 pigs (37±2kg). A 50×1.8mm electrode was inserted in the MCV through a guide catheter. A can was placed in the left pectoral region. A monophasic AS (100F, 1.5J) was delivered along one pathway before switching to deliver a biphasic waveform (40% tilt, 2ms phase 2) along another. DFTs (PS+AS) were assessed using a binary search. Two configurations not incorporating AS acted as controls. DFTs were compared using repeated measures analysis of variance. Results: DFTs of the four novel configurations (AS/PS) were: RVCan/MCVCan=14.9±3.7J, MCVCan/RVCan=17.2±5.7J, RVSVC+Can/MCVSVC+Can=13.4±4.6J, MCVSVC+Can/RVSVC+Can=17.1±5.9J. Delivering AS in the RV followed by PS in the MCV reduced the DFT (RVCan (19.9±7.3 J, P<0.01) and RVSVC+Can (19.2±6.0 J, P<0.05)). Conclusions: Delivering AS prior to PS in the MCV reduces the DFT by up to a third compared to conventional configurations of RVCan and RVSVC+Can. This is possible using only a single capacitor and an entirely transvenous approach to the LV.