Microcirculation and Alternating Transmural Flow Patterns in the Ischemic Left Ventricular Vascular Bed
A three-layer electrical analog model of the myocardium and four compartments of the coronary bed (large arteries > 200 μ, small arteries < 200 μ, small venules < 150μ, large veins > 150μ) was used to explore microcirculation and alternating transmural flow patterns in the ischemic left ventricular vascular bed. The myocardial compartments are represented by capacitances and resistances, accounting for the relationship between the vessels’ cross-sectional area and the transmural pressure. Collaterals and autoregulation are allowed for. The intramyocardial pressure is assumed, for simplicity, to decrease linearly from the cavity pressure at the endocardium to zero pressure at the epicardium. Calculations show that the phasic diastolic flow evident in the coronary arteries converts to systolic venular flow. Calculated inlet flows to the three layers in an ischemic bed are shown in the Figure indicating that retrograde flow at the subendocardium coexists with positive subepicardial flow at the beginning of systole, while the flow in diastole is redirected from the subepicardium to the subendocardium. Tracer washouts indicate an unexplained “hidden” component of perfusion in the ischemic bed. The alternating flow during coronary ischemia may explain the suspected “hidden” perfusion that enhances metabolic washout in the ischemic bed beyond the average perfusion level.