The contribution of ventricular apicobasal and transmural repolarization patterns to the development of the T wave body surface potentials in frogs (Rana temporaria) and pike (Esox lucius)

The study aimed at the simultaneous determination of the transmural and apicobasal differences in the repolarization timing and the comparison of the contributions of these two repolarization gradients to the development of the body surface T wave potentials in animals with the single heart ventricle (fishes and amphibians). Unipolar potentials were measured on the body surface, epicardium and in the intramural (subepicardial, Epi; midmyocardial; and subendocardial, Endo) ventricular layers of 9 pike and 8 frogs. Activation times, repolarization times and activation–recovery intervals were determined. A transmural gradient in repolarization durations in frogs (Endo > Epi, P < 0.024) corresponds to the gradient in repolarization times. No significant transmural difference in repolarization duration is observed in pike that produces a repolarization sequence from Endo to Epi (Endo < Epi, P < 0.02) according to the activation sequence. On the apicobasal axis in both species, the repolarization sequence proceeds from apex to base (P < 0.024) which is expressed in similar body surface potential distributions during the T wave in spite of the opposite transmural repolarization patterns. The present study suggests that the apicobasal repolarization gradient provides the major contribution to the development of the T wave potentials on the body surface in pike and frogs.