Evidence for the supernormal phase and a recovery curve of conduction in the human heart.

Abstract

Recent work by Ashman 1 and by Ashman and Woolley 2 has demonstrated that the compressed or injured cardiac muscle of the turtle may, after excitation, recover its conductivity along a curve which passes through a supernormal phase. Thus an impulse traversing the compressed muscle will travel most rapidly during the supernormal period. If the degree of compression is sufficient only impulses arriving at the compressed region during the supernormal phase are transmitted; earlier or later ones are blocked. These experimental observations add much weight to the argument for a supernormal phase in the recovery of conductivity in the human hearts discussed below.

Lewis and Master 3 reported two cases of block in the human heart which they interpreted as evidencing a supernormal phase. In their first case typical complete heart block was interrupted at times by a ventricular systole in response to an auricular impulse and only when the latter arose during late systole or early diastole. Auricular impulses arising later in diastole were blocked.

We have obtained electrocardiograms of two clinical cases of heart Mock which show phenomena attributable to a supernorind phase. Our first case is similar to Lewis and Master's excepting that, (a) a series of auricular impulses are transmitted if the auricles are rapid; (b) ventricular standstill supervenes when, as a result of auricular slowing, conduction fails, and (c) the period of ventricular quiescence is interrupted at irregular intervals by idioveiitricular contractions which do or do not permit conduction depending upon their time relations with the auricular systoles. As in Lewis and Master's case, Conduction time increases slightly as the interval between the K-wave and the subsequent P-wave widens.