Durations of Transmembrane Action Potentials and Functional Refractory Periods of Canine False Tendon and Ventricular Myocardium:

Abstract

The relationship between the functional refractory periods of the specialized cardiac conduction system and of the ventricular muscle is of major importance in the genesis of ventricular fibrillation by a single premature beat arising in the specialized conducting system. Wiggers and Wegria 1 demonstrated that premature ventricular excitation must occur in late systole during the inscription of the T wave in order for ventricular fibrillation to be initiated by a single premature stimulus, i.e., excitation must occur in the functional refractory period of ventricular fibers. If the functional refractory period of Purkinje tissue exceeds that of the ventricular muscle, an early premature discharge in the Purkinje system or an impulse transmitted from the A-V node could not excite the ventricles sufficiently early to cause ventricular fibrillation; excitation of ventricular muscle via the Purkinje system would by necessity occur after expiration of the ventricular vulnerable period. However, if the Purkinje tissue has a functional refractory period equal to or less than that of ventricular muscle, a premature systole conducted over

Cycle length dependence of human action potential duration in vivo. Effects of single extrastimuli, sudden sustained rate acceleration and deceleration, and different steady-state frequencies.

“…In the steady state, APD had a close linear correlation to cycle lengths ranging from 350 to 800 ms and at very long cycle lengths (above 800-1,000 Ms) deviated from the linear relationship to approach a maximum plateau value. A linear relationship between APD and cycle length with flattening above cycle lengths of 1 s has been demonstrated previously in vitro for frog (38), canine (10,11), sheep (30), cat (28) and guinea-pig ventricular muscle (12,39), and canine Purkinje fibers (40). Also consistent with these previous in vitro findings, changes in the steady-state APD of human myocardium in situ were due to a change in phase 2 duration without alteration ofphase 3 slope (Fig.…”

Glass Microelectrode Studies on Intramural Papillary Muscle Cells

“…Standard Preparations.-Transmembrane potentials recorded from ventricular muscle cells in standard endocardial and epicardial surface preparations were qualitatively and quantitatively similar to those reported by other investigators (32,43,44). That the measured electrophysiological values were in the low to the middle range of previously reported means (Table 1) Papillary Muscle Slices us.…”

The effects of stimulation rate on calcium‐dependent action potentials recorded from chick embryo heart cell aggregates.

“…Increases in action potential plateau height with moderate increases in frequency have been reported in adult ventricular tissue of dogs (Hoffman & Suckling, 1954;Moore, Preston & Moe, 1965;Greenspan, Edmands & Fisch, 1967), rabbits (Gibbs & Johnson, 1961) and cats (Bass, 1975).…”