Quantitative evaluation of left ventricular bypass in reducing myocardial ischemia

A controlled study was undertaken to evaluate the relationship between myocardial oxygen consumption (MVO2) and epicardial S-T segment improvement in an ischemic heart preparation during left ventricular (LV) bypass. Twelve mongrel dogs were prepared with left ventricular-aortic bypass, coronary sinus cannulation, and a multiple point epicardial electrocardiographic technique. The left anterior descending coronary artery was ligated low (Group I) or high (Group II) after baseline studies. After ischemic baseline studies, increasing degrees of LV bypass were performed at a constant mean aortic pressure and heart rate. The final infarct size was determined by the nitroblue tetrazolium staining technique. Group I--a significant reduction in the average (S-T) segment elevation occurred during 50 to 59 percent of LV bypass during which MVO2 was reduced 10.9 percent from controls. A maximum S-T reduction of 75 percent occurred during LV decompression during which MVO2 was reduced 52.8 percent from controls. The final infarct size for Group I was 9.8 +/- 0.9 Gm. per 100 Gm. of LV. Group II--a significant reduction in S-T segment elevation occurred only after 90 to 99 percent LV bypass was achieved during which MVO2 was reduced 28.1 percent from controls. LV decompression produced a maximum S-T reduction of 63 percent during which MVO2 was reduced 50.2 percent from controls. The final infarct size for Group II was 21.1 +/- 0.4 Gm. per 100 Gm of LV. This study indicates that larger degrees of bypass are required to decrease the ischemic areas encountered in larger infarctions. LV decompression is most beneficial in reducing ischemic myocardium surrounding large infarctions.