Use-dependent effects of lidocaine in neonatal and adult ventricular myocardium.

Tissues from different areas of the heart and from animals of different ages are not uniform in regard to their action potential characteristics. Thus, they would not be expected to respond homogeneously to pathological processes or cardioactive drugs. Our objectives were to determine the age-related changes in canine epicardial and guinea pig papillary muscle transmembrane potentials and to determine the age-related effects of lidocaine on these tissues. Standard microelectrode techniques were used. We found the neonatal canine epicardial action potential plateau to be more positive and rounded and the action potential duration to be longer than that of the adult epicardium. In contrast, guinea pig papillary muscles did not show any differences in neonatal and adult transmembrane potentials. Significant age-related differences in the use-dependent effects of lidocaine were found in the canine epicardial tissue. The neonatal epicardium reached a steady-state level of block more rapidly and recovered from this block more slowly when compared to the adult epicardium. The guinea pig papillary muscles showed no age-related differences in the kinetics of use-dependent lidocaine block. These data suggest that age-related differences in the voltage-time course of the action potential plateau and repolarization may be largely responsible for the age-related differences seen in lidocaine's effects on canine epicardium.