Objective To evaluate the effects of bupivacaine and ropivacaine on guinea pig papillary muscle
action potential Methods
The guinea pig papillary muscle preparation was exposed to ropivacaine (1, 3 or 5μg·ml -1 ) or bupivacaine ( 1, 3 and 5μg·ml -1 ) respectively, to measure maximum rate of depolarization (Vmax ),
action potential amplitude (APA),action potential duration at 50% of repolarization(APD 50 ), and action potential duration at 90% of repolarization(APD 90 ) Results Vmax significantly decreased after exposure to both agents at all concentrations, Vmax decreased by 27 4% with ropivacaine at 5μg·ml -1 , and the degree was similar to that with bupivacaine at 3 μg·ml -1 (28 4%) ,but was significantly lower than that with bupivacaine at 5 μg·ml -1 (42 6%) (P<0 05) At ropivacaine of 5 μg·ml -1 APA decreased by 2 56%, APD 50 by 1 86% and APD 90 by 1 60%, the degrees were significantly less than those at the equal concentration of bupivacaine (5 98% , 7 23% and 4 96%) (P<0 05) Conclusions Ropivacaine is less potent than bupivacaine on cardiac action potential,either
cardiotoxicity is related to the inhibition on sodium channel to depress cardiac excitability and conduction.