Determinants of reperfusion cardiac electrical activity after cold cardioplegic arrest during coronary bypass surgery.

In a prospective study of 99 patients with coronary artery disease, reperfusion of the heart after a period of ischemia (protected by contemporary techniques of myocardial preservation) resulted in spontaneous resumption of cardiac electrical activity in 53%, spontaneous defibrillation in 10%, reperfusion ventricular fibrillation (VF) in 32% and indeterminate rhythm in 5%. In hearts spontaneously developing rhythms excluding VF (as opposed to hearts requiring direct-current shock), factors significantly associated were a higher plasma potassium concentration (5.2 vs 4.8 mEq/liter), shorter reperfusion time (1 vs 4 minutes), higher plasma magnesium concentration (1.36 vs 1.25 mg/dl) and a lower myocardial temperature (27 vs 32 degrees C). The duration of ischemia, arterial blood gas levels, plasma catecholamine levels, plasma ionized calcium levels, volume of cardioplegia and mean arterial pressure did not relate to occurrence of spontaneous episodes. However, VF developed in 39 of 52 patients (75%) with spontaneous resumption of electrical activity. This event was associated with lower myocardial temperature. Thus, direct-current shocks were ultimately required in 77 of the 99 patients (78%). Although certain thermal, biochemical and hemodynamic variables facilitate spontaneous resumption of cardiac rhythm, the development of VF may negate the potential benefit of this event in the prevention of myocardial damage from direct-current defibrillation.