THE EXCITATORY PROCESS IN THE MAMMALIAN VENTRICLE

Abstract

Times of initial negativity have been plotted on the hearts of 9 dogs and 9 Macacus rhesus monkeys, using 3 string-galvanometers focussed simultaneously on a single camera. Arrival times increase in an orderly fashion from apex to base along the fibers of the superficial bulbo- and sino-spiral muscles. There is no hiatus in the passage of excitation across the interventricular groove. Conduction rates calculated from point to point along a muscle strand give a mean value of 2375 [plus or minus] 128 mm/sec. This velocity is of the same order in both dogs and monkeys. Bisection of a muscle bundle does not affect an apical electrode but does delay or prevent the arrival of excitation at points basal to the lesion. (Delay is proportional to the completeness of the transection, and the blood supply to either point is intact.) These observations are not in accord with a general application of the hypothesis that excitation passes radially outwards from the endocardium of the ventricles. It is suggested that on the surface of the heart the excitatory process appears first at the apex and thence spreads axially along the muscle fibres towards the base.