Effect of sympathetic nerve stimulation and cardiac denervation on MBF during LAD occlusion

Augmentation of cardiac sympathetic tone during myocardial ischemia has been shown to increase myocardial oxygen demand, arrhythmias, and infarct size in the canine model. The purpose of the present study was to compare the levels of myocardial blood flow (MBF) in normal and infarcted tissue during 6 h of left anterior descending (LAD) coronary artery occlusion in dogs with 1) a constant, known level of sympathetic input (3 Hz, 5 ms, 1-3 mA) to the heart, 2) acutely denervated hearts, 3) chronically denervated hearts, or 4) chronically sympathectomized hearts. MBF was measured with 15-μm spheres periodically after LAD occlusion. The highest blood flow in the infarcted region (IMBF) at 2 min was used as an estimate of the amount of blood flow necessary to maintain viability. All dogs, groups 1-4, underwent 6 h of LAD occlusion, after which animals were killed and left ventricular infarct sizes were determined using nitroblue tetrazolium. Group 1 developed extensive transmural infarcts (28 ± 1.7% LV wt) with an IMBF of 42.1 ± 2.1 ml x min^-1.100 g^-1. Infarct size in group 2 was significantly smaller (P<0.05), averaging 21.5 ± 2.3%, but transmural in only half the dogs. IMBF was 30.6 ± 1.6 ml x min^-1.100 g^-1, which was less (P<0.05) than in group 1. Infarcts in chronically denervated (group 3) or sympathectomized (group 4) hearts (13.1 ± 2.7 and 15.1 ± 1.8%, respectively) were significantly smaller than those in groups 1 and 2. IMBF was 22.8 ± 1.8 ml.min^-1.100 g^-1 in group 3 and 25.0 ± 2.1 ml x min^-1.100 g^-1 in group 4; both of these were significantly lower than those of groups 1 and 2. These data demonstrate that the amount of ischemic damage as determined by nitroblue tetrazolium after LAD occlusion is significantly less in acutely denervated dog hearts. However, damage was even less severe in chronically denervated and sympathectomized hearts. These smaller infarcts were associated with an increase in the amount of partially infarcted tissue and a lower IMBF, presumably secondary to a decrease in oxygen requirements of the denervated heart.