Regional myocardial dysfunction and hemodynamic abnormalities during strenuous exercise in dogs with limited coronary flow.

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Abstract
Regional myocardial dynamics were studied during brief, strenuous bouts of running in 12 conscious dogs by telemetry before and after partial circumflex coronary artery (CCA) constriction. Regional myocardial dimensions were measured by an ultrasonic method in a control segment (CS) and segment to be made ischemic (IS). In control runs heart rate (HR), left ventricular (LV) systolic pressure, and dP/dt [change of pressure with time] increased markedly, and segment end-diastolic lengths (EDL) increased along with augmentation of regional myocardial performance. Following CCA constriction, resting hemodynamics and segment dynamics remained within the control range; during running, HR was elevated similarly to the control (approximately 280/min), but LV systolic pressure and dP/dt changes were significantly reduced. Shortening of CS did not change significantly, but IS shortening, velocity and indices of segment power and stroke work were rapidly and markedly depressed. In 2 dogs, ventricular fibrillation occurred during and immediately after running. After exercise, IS shortening usually required from 5 to 10 min to recover to near pre-exercise levels. When regional and total cardiac function are within the normal range at rest, strenuous exercise in the presence of coronary stenosis induces rapid, severe regional myocardial dysfunction accompanied by significant hemodynamic abnormalities and, occasionally, by sudden death. Abnormal regional wall motion during and following exercise appears to provide a specific indicator of limited coronary reserve.

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