Abstract

The direct chronotropic and inotropic effects of procaine, chloroprocaine, cocaine, lidocaine, mepivacaine, prilocaine, tetracaine, and bupivacaine were studied in an isolated guinea pig atrial preparation. All of the agents tended to produce a negative chronotropic and inotropic effect at high concentrations. Bupivacaine and tetracaine were most potent in terms of their negative chronotropic and inotropic effects, whereas procaine was least potent in terms of depression of atrial rate and contractility. The potency of the various agents with regard to their depressive cardiac effects is related to their potency as local anesthetic agents. No stimulatory effect on atrial rate was observed with any of the agents. With regard to atrial contractility, chloroprocaine did show a biphasic effect, i.e. initial positive inotropic action followed subsequently by a negative inotropic effect. The concentration of the various local anesthetics required to produce depression of cardiac rate and contractility which might be considered clinically significant occurred at concentrations which were higher than are usually seen during the normal use of these agents for regional anesthesia.