Background and Objectives. The purpose of this study was to compare the inotropic and chronotropic effects of ropivacaine, bupivacaine, and lidocaine in an isolated, spontaneously beating rabbit heart preparation. The ability to electrically pace the heart in the presence of local anesthetic also was examined.

Methods. Hearts were perfused with Krebs-Hense-leit solution, then exposed to ropivacaine or bupivacaine at 1, 6, or 13 μg/ml or lidocaine at 6, 20, or 40 μg/ml ( n = 6, each concentration). Left ventricular pressure, left ventricular dP/dt (rate of change derivation from analog waveform of the left ventricular pressure wave), pulmonary artery flow, oxygen consumption, and electrocardiogram were monitored through-out the studies. Drug exposure was for 30 minutes or until a 75% decrease in left ventricular pressure occurred.

Results. All preparations were exposed to 1 μg/ml bupivacaine or ropivacaine and 6 μg/ml lidocaine for the full 30 minutes. At the intermediate concentrations, only one of six bupivacaine preparations (6 μg/ml) survived the full 30-minute exposure period, compared to six of six preparations for both ropivacaine (6 μg/ml) and lidocaine (20 μg/ml; p < 0.05). Similar results were found with exposure to the highest concentrations of these local anesthetics. No electrocardiogram changes were observed with any of the three lidocaine concentrations or with the lowest ropivacaine and bupivacaine concentration. At the intermediate concentration, atrioventricular conduction changes were seen with bupivacaine in five of six preparations, compared to one of six ropivacaine preparations ( p < 0.05). With the high concentration, ventricular tachycardia occurred in four of six bupivacaine preparations, compared to zero of six with ropivacaine ( p < 0.05). In general, left ventricular systolic pressure, dP/dt, heart rate, and oxygen consumption were reduced during exposure to all concentrations of the three local anesthetics. The most profound effects (>75% reduction) were seen with 13 μg/ml bupivacaine. All local anesthetics caused an increase in the voltage required to pace the hearts via the atria. With 6 μg/ml bupivacaine and 13 μg/ml ropivacaine, 50% of the preparations could not be paced via the atria; and with 13 μg/ml bupivacaine, none of the preparations could be paced via the atria. The depressant effects of 6 μg/ml bupivacaine approximated those seen with 13 μg/ml ropivacaine. The reductions in oxygen consumption and pulmonary artery flow were not significantly different between treatment groups.

Conclusion. The results of this study indicate that bupivacaine is more cardiodepressant and arrhythmogenic than either ropivacaine or lidocaine.