Biochemical indicators of myocardial ischaemia during coronary artery bypass grafting

Cardiopulmonary support mitigates the effects of experimental myocardial ischemia

The effectiveness of cardiopulmonary support (CPS) as a rescue method following failed angioplasty is unknown. The proximal left anterior descending (LAD) was occluded for 20 min in 21 dogs. Group 1 animals (n=15) were given CPS and group 2 animals (n=6) served as controls. During coronary occlusion, animals receiving CPS had increased mean arterial pressure (71+/- 12 vs 58+/-7 mm Hg), decreased left atrial pressure (3+/-3 vs 12+/-3 mm Hg), increased ischemic area blood flow (0.20+/-0.16 vs 0.02+/-0.04 mL/min/g) and myocardial oxygen consumption (0.014+/- 0.008 vs 0.003+/-0.006 mL O2/min/g), decreased remote area myocardial oxygen consumption (0.026+/-0.010 vs 0.091+/-0.047 mL O2/min/g), and an improved myocardial oxygen consumption index (0.60+/-0.33 vs 0.02+/-0.03) when compared with controls (p<0.05). During reperfusion (no CPS), group 1 animals had increased cardiac index (210+/-95 vs 117+/-46 mL/min/kg), renal blood flow (110+/-38% vs 53+/-45%), ischemic area blood flow (1.13+/-0.40 vs 0.58+/-0.27), and myocardial oxygen consumption (0.066+/-0.015 vs 0.032+/-0.018) when compared with controls (p<0.05). CPS improves oxidative metabolism in selective myocardial segments during coronary occlusion, promotes recovery of the postischemic myocardium, and results in improved peripheral circulation.

Myocardial ischemia after cardiopulmonary bypass

Intraoperatively, myocardial ischemia is more common after cardiopulmonary bypass (CPB) than before CPB. Ischemia associated with coronary vasospasm and thrombosis may be much more common toward the end of surgery and early in the postoperative period than previously appreciated. This may be because the coagulation system is altered during CPB, and the coronary endothelium is damaged significantly as a result of cardioplegic arrest followed by reperfusion. In this milieu, vasospasm and thrombosis may be caused by the administration of protamine. Some of the ischemia observed in this period actually is not reversible and is associated with myocardial injury and infarction. It may be ameliorated by the administration of calcium channel blockers, aspirin, and anticoagulants. Electrocardiography may be the most suitable modality for the detection of ischemia after CPB and postoperatively. During this period, many episodes of ST deviation are of a nonischemic etiology, and the ECG needs careful interpretation. Transesophageal echocardiography is suitable for use intraoperatively and early on in the intensive care unit.