Regional Myocardial Function during Acute Coronary Artery Occlusion

Myocardial regional function during acute coronary artery occlusion was studied using ultrasonic dimension gauges in open-chest dogs. Three pairs of 2mm 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.