Effect of bupivacaine on the isolated rabbit heart: developmental aspect on ventricular conduction and contractility.

BACKGROUND Newborns and infants seem to be at greater risk of bupivacaine cardiotoxicity than adults do. Few experiments have studied the effects of local anesthetics on myocardium associated with developmental changes, and their conclusions are conflicting. The authors compared the effects of bupivacaine on an isolated heart preparation in newborn and adult rabbits. METHODS The authors used a constant-flow, nonrecirculating Langendorff preparation paced atrially. Adult and newborn rabbit hearts were exposed to step-increasing concentrations of bupivacaine. For each concentration, heart rate was modified with pacing from 180 to 360 beats/min by increments of 30 beats/min. QRS complex duration (index of ventricular conduction) and the first derivative of left ventricular pressure (index of contractility) were measured. The two groups were compared using an Emax model. RESULTS In newborn and adult rabbits, QRS complex duration increased with increasing bupivacaine concentration. No difference was observed between neonatal and adult hearts. Contractility decreased with increasing bupivacaine concentration. Newborn rabbits were approximately three times more sensitive than adult rabbits to the effects of bupivacaine. However, the concentration leading to 50% decrease in the first derivative of left ventricular pressure was much higher than the concentration leading to half maximum increase in QRS complex duration. CONCLUSIONS In conclusion, using a whole organ preparation, the authors demonstrated that bupivacaine induces similar impairment in ventricular conduction in newborn and adult rabbits. In particular, the tonic and the phasic blocks were of similar intensity in both groups. Conversely, the effect of bupivacaine on contractility was markedly higher in newborn rabbits than in adult rabbits. Also, contractility was less impaired than ventricular conduction in both groups.