Effects of Intracoronary Fentanyl on Left Ventricular Mechanoenergetics in the Excised Cross-circulated Canine Heart

BACKGROUND: It is still unclear whether fentanyl directly alters left ventricular (LV) contractility and oxygen consumption. This is because of the difficulty in defining and evaluating contractility and energy use independently of ventricular loading conditions and heart rate in beating whole hearts. METHODS: This study was conducted to clarify the mechanoenergetic effects of intracoronary fentanyl in six excised cross-circulated canine hearts. The authors used the framework of the E(max) (a contractility index)-PVA (systolic pressure-volume area, a measure of total mechanical energy)-VO2 (myocardial oxygen consumption per beat) relationship practically independent of ventricular loading conditions. The authors measured LV pressure, volume, coronary flow, and arteriovenous oxygen content difference to calculate E(max), PVA, and VO2. They first obtained the VO2-PVA relationship for varied LV volumes at control E(max). The authors then obtained the VO2-PVA relationship at a constant LV volume, whereas coronary blood fentanyl concentration was increased in steps up to 240 ng/ml. Finally, they obtained the VO2-PVA relationship for varied LV volumes at the final dose of fentanyl. RESULTS: Fentanyl at any concentrations did not significantly change E(max), PVA, and VO2 from the control. The linear end-systolic pressure-volume relations and their slopes were virtually the same between the control and fentanyl volume loading in each heart. Further, either the slope (oxygen cost of PVA) or the VO2 intercept (unloaded VO2) of the linear VO2-PVA relationship remained unchanged by fentanyl. CONCLUSIONS: These results indicate that intracoronary fentanyl produces virtually no effects on LV mechanoenergetics for a wide range of its blood concentration.