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

Abstract

SUMMARY We studied regional myocardial dynamics 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 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 two dogs, ventricular fibrillation occurred during and immediately after running. After exercise, IS shortening usually required from 5 to 10 minutes to recover to near pre-exercise levels. We conclude that 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.IN NORMAL experimental animals, exercise increases the cardiac output, systemic arterial pressure, heart rate, and myocardial contractility, and thereby markedly augments myocardial oxygen consumption and coronary blood flow.1 "" When the coronary blood supply is limited by experimental coronary artery stenosis or by obstructive coronary artery disease in man, exercise is known to evoke electrocardiographic S-T segment abnormalities 7 " and to cause redistribution of coronary blood flow. -9Such changes in the electrocardiogram, suggestive of subendocardial ischemia, have led to the widespread use of exercise stress testing in patients with coronary heart disease. 8Regional myocardial function measured by implanted ultrasonic crystals'" recently has been found to be a sensitive indicator of myocardial ischemia in conscious dogs,"~':l and we have now combined this approach with telemetry to make direct measurements of regional left ventricular dynamics and corresponding hemodynamic measurements in conscious exercising dogs before and during partial coronary artery stenosis. It was hypothesized that if coronary blood flow were limited by coronary stenosis during the resting state, regional myocardial function would remain within the normal range at rest. However, if the myocardial oxygen demands then rose to exceed the limited coronary reserve, regional myocardial performance in the ischemic area would promptly become depressed, and if the physiological stress were severe,...

Comparative effects of nitroglycerin, nifedipine and metoprolol on regional left ventricular function in patients with one-vessel coronary disease.

“…Investigations in conscious experimental animals with chronic coronary arterial stenosis indicated that exercise causes severe regional myocardial dysfunction and hemodynamic abnormalities. 22 Drug-induced changes in regional left ventricular function have also been studied in experimental formation is available on comparative effects of these agents on regional left ventricular function in man. With the introduction of noninvasive radionuclide ventriculography and quantitative analysis of regional left ventricular function, differences of drug effects on normal, ischemic and scar myocardial segments can be studied in man.…”

Exercise-induced regional dysfunction with subcritical coronary stenosis.

“…The change in subendocardial flow in St-Ex I was also not The modest abnormalities in regional contractile function observed in this study during exercise would undoubtedly be difficult to detect by conventional echocardiographic or nuclear angiographic analysis of regional wall motion. 6 However, recent studies using two-dimensional echocardiography with hyperemia at rest produced by dipyridamole readily demonstrated induced regional contraction abnormalities in patients with coronary stenoses of 70% or greater. 37 Newer techniques such as tomographic gated blood pool radionuclide ventriculography,38 nuclear magnetic resonance imaging,39 or digital processing of intravenous ventricular fluorographic images40 during exercise or hyperemia eventually may allow reliable detection of such minor contraction abnormalities in patients with subcritical coronary stenosis.…”

“…3, 596-605, 1986. EXERCISE-INDUCED ischemia has been studied in detail experimentally with analyses of regional myocardial blood flow (MBF),'-s regional contraction, [4][5][6][7] and overall left ventricular function.5 [8][9] These data and other studies in resting conscious dogs'0-2 have established that regional contractile function is responsive to reductions in MBF, especially to the subendocardium. For example, in the presence of critical coronary stenosis (normal resting flow but lack of vasodilator reserve), subendocardial coronary flow drops 50% below the resting value during exercise, with an assoicated 70% decrease of systolic wall thickening below the resting value.…”

The effects of nitroglycerin on exercise‐induced regional myocardial contractile dysfunction are not diminished by pretreatment with dihydroergotamine

“…Since a functional antagonism to coronary vasodilatation by intravenous administration of DHE was shown in a previous study (Raberger et al, 1976) (Battler et al, 1980;Brugge-Asperheim et al, 1969;Gallagher et al, 1982;Tomoike et al, 1978). The segment length was normalized according to Theroux et al (1976).…”