High oxygen requirements of dyskinetic cardiac muscle

This study assesses the regional oxygen requirements of muscle segments that are beating and working, beating and empty, arrested and decompressed, and nonischemic that move dyskinetically. Regional oxygen demands were evaluated by producing a dyskinetic segment by infusing regional cardioplegic solution through a left anterior descending coronary artery catheter with and without extracorporeal circulation. The results show that the O2 demands of the perfused dyskinetic cardiac muscle segment (4 to 8 ml/100 gm/min) are approximately 55% of the contracting (beating, working) segment (7 to 12 ml/100 gm/min) and are fivefold more than when the same muscle segment is arrested and decompressed by total vented bypass (0.8 to 1.2 ml/100 gm/min). Additional studies showed that ischemia for 2 hours (left anterior descending coronary artery ligation) produced severe dyskinesia (-24% control systolic shortening), which failed to recover after reperfusion with the heart in the beating, working state. In contrast, lowering O2 demands by reperfusion during bypass restored occasional contractile function as a consequence of left ventricular decompression. Dyskinetic muscle segments have a high oxygen requirement that may affect their capacity to be salvaged if reperfusion is conducted without left ventricular decompression. These observations suggest that the value of revascularization in the working heart (i.e., streptokinase with or without angioplasty) may be limited unless the left ventricle is decompressed during reperfusion and provide an explanation for the delayed recovery of mechanical function in hearts reperfused surgically with normal blood during cardiopulmonary bypass.