The rhythm of the heart beat. III—Disturbances of rhythm produced by early premature beats

Abstract In the preceding paper it was shown that the disturbance of rhythm produced by a premature beat introduced in the latter part of a normal cycle or of a premature beat cycle is a comparatively simple and regular one: the cycle following the premature beat so introduced is lengthened by an amount that varies with the degree of curtailment of the preceding cycle. The subsequent cycle is normal, or, when the shortening of the curtailed normal cycle is more marked, it may be slightly lengthened. This paper will deal with the disturbances of rhythm produced by a premature beat introduced earlier in a normal cycle or a premature beat cycle; they are more complex and less regular. Responses of this type have previously been observed by Drury and Brow (1926), who called them re-entrant beats, and by Miki and Rothberger (1922), but no attempt has been made to elucidate the mechanism of their production. The method used was that described in the previous paper, p. 308.