Background: The volatile anesthetics may reduce cardiac contractility by limiting both membrane Ca2+ entry and altering intracellular Ca2+ release. Additional pharmacological effects of calcium channel blockers could potentially enhance anesthetic-induced depression. The aim of this study was to compare the direct cardiac effects of enflurane and a new volatile anesthetic, desflurane, in combination with diltiazem on the isolated Sprague-Dawley rat heart.
Methods: After stabilization period isolated rat hearts (n = 40) were perfused with an oxygenated modified Krebs' solution at 55 mmHg equilibrated with 1, 2 and 3 MAC of enflurane (1.7, 3.4 and 5.1 vol% respectively) or desflurane (6, 12 and 18 vol% respectively) in combination with 100 ng/mL diltiazem at 36 degrees C. Isovolumetric left ventricular pressure (LVP), rate of change of ventricular pressure (dp/dt), spontaneous heart rate and coronary flow were measured. To examine the indirect metabolic effect due to autoregulation of coronary flow, O2 delivery (DO2), myocardial O2 consumption (MVO2) and percent O2 extraction (POE) were also monitored.
Results: Diltiazem plus enflurane or desflurane depressed LVP and dp/dt dose-dependently. Enflurane plus diltiazem significantly decreased heart rate more than desflurane plus diltiazem in a dose-dependent manner. Desflurane plus diltiazem significantly increased coronary flow more than enflurane plus diltiazem and oxygen delivery increased proportionally with coronary flow. But there were statistically insignificant dose-dependent increases in both groups. Myocardial oxygen consumption and percentage of oxygen extraction were also decreased dose-dependently in both groups. Bradydysrhythmia that accompanied atrioventricular dissociation occurred with diltiazem plus high enflurane or desflurane concentration at an incidence of 46% and 40% respectively.
Conclusions: These in vitro results demonstrate that diltiazem plus enflurane or desflurane depresses left ventricular contractile function and diltiazem plus enflurane causes higher incidence of bradydysrhythmia more than equivalent levels of diltiazem plus desflurane.