Atrial premature beats with variable return cycle lengths--a clue to sinus node re-entry?

ABSTRACT

A patient with atrial premature beats (APBs) with variable return cycle lengths is reported. Two rare responses of the sinus node were observed APBs in which the return and sinus cycle lengths were equal and APBs which were interpolated. Several possible mechanisms for these unusual effects of APBs on the sinus node are discussed. One mechanism which can explain both of these observations is sinus node re-entry. This possibility is indirectly supported by documentation of sinus node re-entry during electrophysiologic studies.