Assessing myocardial viability using the coronary flow response to intravenous dobutamine infusion in recent myocardial infarction.

Coronary flow response to low-dose (5 and 10 micrograms/kg/min) dobutamine infusion was used to assess myocardial viability at the time of cardiac catheterization in 13 patients (age, 60 +/- 11 years) with recent myocardial infarction. Echocardiographic improvement in regional wall motion performed 4 to 6 weeks after discharge was used as the marker for viability. Viable patients demonstrated a 2-fold increase in flow from baseline (p < 0.001) during intravenous infusion. In contrast, patients without viability demonstrated no increase in flow. The coronary flow response to dobutamine measured at the time of catheterization shows promise in identifying viable myocardium in postinfarction patients.

Intracoronary versus intravenous effects of cocaine on coronary flow and ventricular function.

BACKGROUND: Cocaine use has been associated with cardiomyopathy and ischemic coronary syndromes. However, the pathophysiological mechanisms responsible for these syndromes are not clear and have been suggested to involve direct effects of cocaine on myocyte contractility and coronary resistance as well as indirect effects via altered autonomic tone, secondary mediators, and myocardial metabolism. We sought to distinguish direct from indirect effects of cocaine on ventricular function and coronary resistance by comparison of the administration of intracoronary cocaine (0.12 to 0.36 mg/min constant infusion) with intravenous cocaine (5 mg/kg bolus infusion) in an in vivo anesthetized pig preparation. METHODS AND RESULTS: To control for changes in coronary resistance secondary to autoregulation and myocardial metabolism, the left anterior descending coronary artery was perfused at constant coronary pressure and the interventricular vein was cannulated for coronary venous oxygen saturation measurement. Coronary blood flow, regional percent segment shortening, myocardial oxygen consumption, and serum cocaine concentrations were measured. Intracoronary cocaine produced a dose-dependent decrease in percent segment shortening in the absence of significant changes in coronary flow or systemic hemodynamics. In contrast, intravenous cocaine had mild biphasic effects on coronary resistance with an initial brief vasodilation (30.0 +/- 5% increase in flow from control) followed by more prolonged vasoconstriction (17.0 +/- 3.3% decrease in flow from control), which were independent of autoregulation or myocardial metabolism. In addition, intravenous cocaine caused an early 48% decrease in percent segment shortening, at which time the measured cocaine concentration was 20.1 micrograms/mL blood. This was comparable to the intracoronary cocaine concentration of 17.1 micrograms/mL blood, which produced a similar 48% decrease in percent segment shortening. CONCLUSIONS: We conclude that the effects of acute cocaine exposure on ventricular function are predominantly direct but of brief duration and therefore probably not clinically relevant. The effects of cocaine on coronary tone are predominantly indirect and biphasic, with early vasodilation followed by mild and more prolonged vasoconstriction. In the absence of coronary stenosis or ventricular hypertrophy, this small amount of vasoconstriction is unlikely to cause ischemia.