Optimal intraoperative protection of myocardium distal to coronary stenoses

Metabolic evidence of improved delivery of cardioplegic solutions by adjuvant use of nitroglycerin (NTG) and reinfusing these solutions distal to an obstructed coronary artery was sought in 40 dogs subjected to cold cardioplegic arrest. The left anterior descending coronary artery was occluded prior to initiating arrest by intra-aortic root infusion. Cardioplegic solution was reinfused with the left anterior descending occluded throughout ischemia (Group I), or with this artery reopened, to simulate a completed distal anastomosis (Group II). Serial biopsy specimens of the left ventricular apex were assayed for adenosine triphosphate and creatine phosphate, while specimens from the posterior left ventricular wall served as controls. Regional myocardial temperatures were recorded throughout ischemia. Half of the hearts in each group received 300 micrograms of nitroglycerin in the cardioplegic solution. Adenosine triphosphate was preserved in myocardium distal to a patent coronary artery whether nitroglycerin was added to the cardioplegic solution or not (control, control + NTG). Moreover, nitroglycerin did not prevent the 26% to 34% (p less than 0.05) decline in adenosine triphosphate levels when the left anterior descending remained obstructed throughout ischemia (Group I, I + NTG). However, opening the left anterior descending for reinfusion of cardioplegic solution allowed adenosine triphosphate to be preserved at end-ischemia (Group II, II + NTG). In addition, the metabolic reperfusion injury manifested by a 37% (p less than 0.01) decline in adenosine triphosphate levels after aortic unclamping (Group II) was obviated when nitroglycerin was added to the cardioplegic solution delivered in this manner (II + NTG). The depletion of cardioplegic solution stores during ischemia was more severe in the experimental groups than in controls (p less than 0.05). These metabolic changes did not correlate with regional myocardial temperature gradients. The data indicate that myocardium jeopardized by coronary stenoses can be preserved as well as myocardium supplied by a patent coronary artery by adjuvant use of nitroglycerin and varying the mode of delivery of the cardioplegic solution.