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.