Coronary reserve of high- and low-flow regions in the dog heart left ventricle

Abstract

Background - Left ventricular myocardial blood flow is spatially heterogeneous. The hypothesis we tested was whether myocardial areas with a steady-state flow <0.5 times mean flow are underperfused and areas with flow >1.5 times mean flow are overperfused. Methods and Results - In anesthetized beagle dogs (n=10), the relationship between local blood flow versus S- adenosylhomocysteine (SAH) concentration, a measure of the free intracellular adenosine concentration, and lactate, a measure of the myocardial NADH/NAD+ ratio, were determined under control conditions and after coronary constriction. Control local myocardial blood flow was 0.99±0.46 mL·min-1·g-1, with a coefficient of variation of 0.36±0.12 (n=256 per heart; sample wet mass, 125±30 mg). Tissue concentrations of SAH (3.4±2.5 nmol/g) and lactate (1.88±0.80 μmol/g) were not elevated in low-flow samples. However, after coronary artery constriction, poststenotic blood flow decreased from 1.00±0.27 to 0.49±0.22 mL·min-1·g-1 (P<0.04), with significant correlation between local SAH and flow (r=-0.59) and lactate and flow (r=-0.50). Although nearly all samples from control high-flow regions showed increased SAH concentrations if relative flow after stenosis was <1.0, control low-flow samples frequently displayed low SAH concentrations. The percent reduction in flow determined the changes in the local SAH and lactate concentration, independent of the local control blood flow. Conclusions - When the coronary inflow is unrestricted, the oxygen supply to control low- flow regions meets metabolic demand. Flow to control high-flow regions reflects a higher local demand rather than overperfusion. Thus, blood flow heterogeneity most likely reflects differences in aerobic metabolism.