Effects of defibrillation shocks delivered directly over a major coronary artery

This study investigated the influence of defibrillator shocks delivered directly over a coronary artery, independent of ventricular fibrillation, on cardiac hemodynamics. Thirty-six open chest, halothane anesthetized pigs were randomized to receive six shocks at one of 5.0, 7.5, or 10.0 joules (J). Shocks were delivered between two mesh electrodes (Medtronic TX-7) sutured onto the epicardium, one over the left anterior descending coronary artery and the second directly opposite on the posterobasal ventricular surface. Shock delivery was synchronized to the R wave of the cardiac cycle, to reduce the risk of inducing fibrillation, with a 5-minute stabilization period between successive shocks. Pressure from the left ventricle, the left anterior descending coronary artery, distal to the mesh electrode and the left circumflex (control) artery and contractility in the regions perfused by both arteries were measured. The shocks invariably produced an immediate (2-second postshock), but transient, depression in systolic pressure of the same magnitude for the left anterior descending coronary artery, circumflex artery and the left ventricle that recovered by 5-minute postshock. There was no dose dependent relationship to energy. Also there was no clear difference in myocardial wall motion between the area perfused by the left anterior descending coronary artery and that perfused by the circumflex artery. These results suggest that shocks up to 10 J delivered over an epicardial artery do not cause arterial spasm and do not compromise coronary artery blood flow.