Energy dose and other variables possibly affecting ventricular defibrillation during cardiac surgery

Previous studies have suggested that shocks of 5-10 J are required for direct ventricular defibrillation during open heart surgery. However, the efficacy of shocks of less than 5 J, the effects of thermal, biochemical, and temporal factors, and the influence of disease process on defibrillation have not been fully investigated, particularly with modern techniques of myocardial preservation. The purpose of this prospective study in 150 adult cardiac surgical patients was to evaluate the energy, current, and myocardial resistance with low energy DC shocks of 1, 2.5, and 5 J and to relate which biochemical, temporal, thermal, or other factors influence the outcome of a DC shock. Twenty-eight percent of shocks of 1 J and 55% of shocks of 2.5 J produced defibrillation. Above 2.5 J, the success rate reached a plateau at 55%. Other factors associated with the success of DC shocks were high normal serum potassium levels, high PaO2, high ionized calcium levels, and longer reperfusion times at mean arterial and coronary perfusion pressures above 50 mm Hg. Disease process may also play a role because patients with valvular heart disease were more difficult to defibrillate. Heart weight and thickness of ventricular myocardium, measured angiographically, appeared less important in direct defibrillation, except with 1 J shocks when thinner-walled ventricles defibrillated more easily.