Collateral blood flow after coronary occlusion: influence of barbiturate anaesthesia and thoracotomy

A study was undertaken to determine whether barbiturate anaesthesia, with or without thoracotomy, adversely affects collateral blood flow during acute coronary artery occlusion. Twelve dogs were instrumented with an electromagnetic flow probe and pneumatic occluder on the left circumflex artery; seven days later, in the conscious state, complete coronary artery occlusion was induced for 8 min. Heart rate, mean aortic pressure, and subendocardial and subepicardial blood flow in the ischaemic zone were measured by radioactive microspheres before and 5 min into coronary artery occlusion. Measurements were repeated after pentobarbital 30 mg.kg-1 (n = 7) and after pentobarbital plus thoracotomy (n = 12). Compared with the conscious state, pentobarbital and thoracotomy produced a decrease in endocardial blood flow in the ischaemic zone (0.21(0.04) to 0.15(0.03) ml.min-1.g-1) and a modest redistribution from endocardium to epicardium (ratio of endocardial to epicardial flow 0.55(0.06) to 0.49(0.07) ml.min-1.g-1), coincident with an increase in heart rate from 127 to 178 beats.min-1 but no change in mean arterial pressure. Directionally similar, but smaller, changes occurred during anaesthesia without thoracotomy. To determine the role of tachycardia five of the animals were studied in the conscious state during a 50% increase in heart rate induced by atrial pacing. A similar decrease occurred in coronary blood flows as with anaesthesia. The results indicate that barbiturate anaesthesia and thoracotomy produce a diminution in collateral flow to ischaemic myocardium, together with an accentuation of its transmural maldistribution, and suggest that anaesthetic induced tachycardia is primarily responsible for these flow alterations.