The relationship of transmural myocardial blood flow to midwall function

Abstract

The relationship of transmural myocardial blood flow to midwall function was evaluated in seven adult mongrel dogs anesthetized with morphine SO 4 (3 mg/kg) and a-chloralose (80 mg/kg) and instrumented with catheters for measuring aortic and left ventricular end-diastolic pressures and dp/dt. Three pairs of miniature ultrasonic transducers (3 mm diameter) were positioned at midwall level of the left ventricle along the minor axis within each of the three regions: anterior, lateral, and posterior segments. Transmural blood flow in the epicardium and endocardium was measured utilizing 8- to 10-μm tracer microspheres before and after a 60-sec circumflex occlusion. Functional data for extent (ΔL) and rate ( dl/dt) of systolic shortening were determined and systolic excursion was normalized to an initial end-diastolic length of 10 mm. Total circumflex occlusion for 1 min was associated with a severe flow imbalance to the posterior endocardium (endocardium/epicardium 0.2 ± 0.1) resulting in marked functional impairment ( ΔL = -0.5 ± 0.2 mm, dl/dt = -1.6 ± 1.1 mm/sec) and holosystolic bulging. Flow within the lateral region was not as severely impaired (endocardium/epicardium 0.5 ± 0.1, P < 0.05), and was associated with less dysfunction ( P < 0.01) without regional bulging. Function and flow in the anterior region were augmented. These data suggest that midwall regional function is dependent on flow, especially endocardium. Holosystolic bulging represents marked flow reduction (97%) while flow may be decreased by 79% without holosystolic bulging.