The Relationship between Myocardial Blood Flow and Contraction by Myocardial Layer in the Canine Left Ventricle during Ischemia

We investigated the relationship between regional myocardial blood flow (MBF) and segmental shortening in 17 open-chest dogs. The left anterior descending coronary artery was cannulated and perfused from the left carotid while measuring perfusion pressure. Graded occlusion was produced by a screw clamp. Extent of occlusion was monitored by perfusion pressure. Percent systolic shortening (%ΔL) was measured using ultrasonic crystals implanted in normal and ischemic endocardium and ischemic epicardium. MBF was measured in ischemic and normal endocardium and epicardium with tracer microspheres. Dogs underwent 1 to 4 grades of coronary stenosis. Myocardial blood flow both to endocardium and epicardium was found to be linearly related to diastolic perfusion pressure below 50 mmHg (r = 0.803 and 0.748, respectively). Normalized %ΔL (N%ΔL) was best related to fraction normal zone MBF in the endocardium by the sigmoidal equation, N%ΔL = e9.01 MBF - 4.03/l + e9.01 MBF - 4.03. %ΔL was only weekly related to myocardial blood flow in the epicardium (r = 0.584), and, in four dogs, %δL was zero in the epicardium despite normal regional blood flow. However, %ΔL in the epicardium was linearly related to %ΔL in the endocardium (r = 0.78). Thus, endocardial wall motion is related to MBF by a sigmoidal relationship while epicardial wall motion is tethered to endocardial wall motion. Circ Res 48: 430-438, 1981