Observations on 100 patients with continuous intraoperative monitoring of intramyocardial pH. The adverse effects of ventricular fibrillation and reperfusion.

Intramyocardial pH and temperature data recorded in 100 patients undergoing cardiac operations were analyzed to elucidate the effects of ventricular fibrillation and reflow. All patients underwent a single period of aortic clamping. Systemic hypothermia (25 degrees C) and intermittent cold crystalloid K+ cardioplegia were employed for myocardial protection. Baseline myocardial pH was 6.88 +/- 0.03 at a temperature of 36.5 degrees +/- 0.2 degree C. During the period of hypothermic ventricular fibrillation prior to aortic clamping, ventricular fibrillation did not affect myocardial pH in 45 patients (Group 1). In 21 patients (Group 2), it caused a significant drop in intramyocardial pH despite cooling. Group 2 patients had a higher incidence of valvular heart disease and left ventricular hypertrophy. They also exhibited low intramyocardial pH values during the subsequent periods of aortic clamping and reflow, indicating inadequate myocardial protection. During the period of reflow, reperfusion acidosis (pH less than 6.8 at 32 degrees C) was encountered in 39 patients (Group B) as opposed to 37 patients (Group A) whose pH remained well above 6.8 during that period. Group B patients had a higher incidence of valvular heart disease and left ventricular hypertrophy, tended to have more ischemic anterior walls prior to cardiopulmonary bypass, sustained longer periods of aortic clamping, had intramyocardial pH evidence of suboptimal protection during aortic clamping, were affected more adversely by ventricular fibrillation during reflow, and tended to have a higher operative mortality. Thus: Depending on the underlying myocardial disease, the adequacy of protection during aortic clamping, and the conditions of reflow, intramyocardial pH in man can fall significantly during ventricular fibrillation and reflow. The metabolic correlate of injury with reflow is a reperfusion acidosis that can reach as low as pH 5.98. When encountered, reperfusion acidosis can be minimized by prompt defibrillation.