Myocardial regional function during acute coronary artery occlusion was studied using ultrasonic dimension gauges in open-chest dogs. Three pairs of 2-mm ultrasonic crystals were implanted 1 cm apart near the endocardium in an ischemic segment, a control segment, and a segment at the margin of the ischemic zone. In the ischemic segment, coronary artery occlusion resulted in prompt dyskinesis which progressed to holosystolic expansion; length at enddiastole (diastolic length) increased by 11%, segment stroke work decreased by 91%, and the diastolic pressure-length relationship was displaced and steepened. In the marginal segment, active shortening and stroke work decreased by 37% and diastolic length increased by 4%. In the control segment, an initial increase in active shortening was observed, followed by compensatory operation of the Frank-Starling mechanism. Nitroglycerin administered during coronary artery occlusion decreased diastolic length and increased shortening in all three segments. An early beneficial effect of isoproterenol on all segments was later replaced by deterioration in marginal and ischemic segments. After propranolol administration, the decrease in shortening of the marginal segment was reduced to half of that observed during a control coronary artery occlusion, suggesting a protective effect of this drug. These results indicate the power of this approach, which provides continuous quantification of regional wall function in myocardial ischemia and during therapeutic interventions. Parts of this investigation were presented before the Annual Scientific Sessions, American Heart Association, November, 1973, Atlantic City, New Jersey.Please address reprint requests to John Ross, Jr., M.D., Director, Cardiovascular Division, P.O. Box 109, La Jolla, California 92037.Received May 28, 1974. Accepted for publication September 3, 1974. 896 chemia (4-6). The goal of the present study was to apply a newly developed ultrasonic technique for the simultaneous characterization of the motion of small segments of the myocardium in ischemic, marginally ischemic, and normal zones and thus to study the effects of a brief coronary artery occlusion together with the modifications caused by nitroglycerin, isoproterenol, and propranolol. MethodsSeventeen mongrel dogs weighing 24-32 kg (average 28 kg) were anesthetized with sodium pentobarbital (25 mg/kg, iv), and small supplemental doses were administered as required. Respiration was controlled by a Harvard pump delivering room air via an endotracheal tube. A thoracotomy was performed in the fifth left intercostal space, and the pericardium was opened. A high-fidelity Konigsberg P-22 pressure micromanometer was inserted into the left ventricular chamber through the cardiac apex. The left anterior descending coronary artery was dissected free distal to its site of origin, and epicardial electrocardiographic (ECG) mapping was carried out using previously described techniques (4). After a con-

We examined in conscious dogs the effects of reductions in myocardial blood flow (MBF) in three different layers across the wall on regional myocardial contractile function in the ischemic zone, measured as systolic wall thickening (%WT). In 16 dogs, %WT was measured with sonomicrometry and MBF was determined with microspheres (10- to 12-microns diam) during coronary stenosis of the left circumflex coronary artery. The stenoses were categorized into six groups by the effect on %WT (each group representing progressive 20% decrements in %WT from control), and individual and pooled regression analyses were performed on data from six of the dogs having multiple data points to evaluate the shape (linear or curvilinear) of the relationships between MBF and changes in %WT. Transmural contractile function was highly sensitive to acute reductions in MBF, especially reductions in the subendocardium. The shape of the normalized subendocardial MBF-%WT relation was mildly curvilinear by regression analysis (quadratic equation, gamma = -0.75x2 + 2.15x -0.39, r2 = 0.92). Likewise, mean transmural and midmyocardial MBF correlated well and closely with changes in %WT. Subepicardial MBF, however, correlated poorly with changes in %WT, there being no change in subepicardial MBF until %WT had been reduced more than 50%.

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