Trigeminy transformed into allorhythmic triplets

Abstract

The patient was a 79-year-old woman with chronic coronary artery disease who was seen in the cardiology clinic for increasing angina pectoris. She was asymptomatic at the time. Her routine 12-lead electrocardiogram is shown in Fig 1. The first impression of the electrocardiogram is that there is an overall tachycardia, approximately 108 beats/min. Regular sinus P waves can be mapped throughout, at the rate of 79 beats/min to 82 beats/min, but every third sinus cycle sandwiches an additional beat, producing an allorhythmic triplet. Allorhythmia is a regularly recurring irregularity, named and defined by Sommerbrodt in 1877. 1 This patient’s allorhythmia consists of triplets separated by 2 normal sinus cycles. The extra beat, flanked by sinus beats in each triplet, is only minimally different from its neighbors: They all have the same basic left bundle branch block morphology. The difference may be because of the variation in the intraventricular conduction imposed by different cycle lengths; even the flanking sinus beats are not exactly identical. The complex in the middle, however, may also be different because of its junctional origin, what Schamroth called nonphasic aberrant ventricular conduction. 2 Although the phasic variety involves long– short cycle sequences, this allorhythmia is predicated on the different wave-front when spreading from a junctional focus. It can be seen in both junctional escape and premature beats as a slight but constant variation of the basic supraventricular morphology.