Coronary Reserve of High- and Low-Flow Regions in the Dog Heart Left Ventricle

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Abstract
Background —Left ventricular myocardial blood flow is spatially heterogeneous. The hypothesis we tested was whether myocardial areas with a steady-state 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 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 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.

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