Significance of regional wall thickening abnormalities relative to transmural myocardial perfusion in anesthetized dogs

Abstract

In 15 open-chest, anesthetized dogs, regional systolic wall thickening (%ΔWT) was measured with sonomicrometry and regional blood flow was determined with tracer microspheres (7-10 μm) before and after various degrees of coronary artery narrowing were created with a hydraulic occluder. The stenoses were categorized into four groups by the effect on %ΔWT, and the corresponding myocardial blood flow (MBF) was determined in four layers across the ventricular wall (layer 1: subendocardium; layer 4: subepicardium). In group 1, %ΔWT decreased 44 ± 10% and only layer 1 MBF was significantly reduced (-28%); in group 2, %ΔWT decreased 77 ± 8% and MBF was reduced in both layers 1 and 2 (-52% and 36%, respectively); in group 3, %ΔWT decreased 104 ± 3% and MBF was reduced in the three inner layers (layer 1: -65%; layer 2: -58%; layer 3: -34%); in group 4, %ΔWT decreased 145 ± 9% (systolic wall thinning) and transmural reduction of MBF was found (layer 1: -74%; layer 2: -68%; layer 3: -55%; layer 4: -29%). We conclude that (1) up to 75% reduction in systolic wall thickening may occur when perfusion to only the inner one-half of the myocardium is decreased; (2) akinetic wall motion may be observed when perfusion remains normal in the subepicardial one-fourth of the wall; and (3) dyskinesia (wall thinning) occurs when blood flow is reduced transmurally.