Concealed conduction in the reentrant pathway as a mechanism of stable ventricular quadrigeminy

Variability in repeated pattern ventricular arrhythmia: application of a reentry model

Repeated pattern ventricular arrhythmia (RPVA) is often observed in electrocardiogram recordings as a repeated sequence of a fixed number of normal sinus QRS complexes interposed between ventricular ectopic beats. The number of interposed sinus complexes is defined as the order of the repeated pattern ventricular arrhythmia. Regions of orders as a function of sinus RR and coupling intervals and duration of refractory periods of normal conduction and reentry pathways were derived from a computer model that simulates a reentry mechanism. Refractory periods of both the normal and reentry conduction pathways could be estimated from electrocardiogram measured time intervals. A variable relationship of RR intervals for different orders was found among patients. According to the reentry model, these order changes were more likely to occur with changes in the reentry refractory period than with heart rate changes. The longer RR intervals of interpolated beats in some patients were also explained by the model.

Apparent bradycardia-dependent right bundle branch block associated with atrial fibrillation: concealed electrotonic conduction as a possible mechanism

A 79-year-old woman with atrial fibrillation was reported in whom apparent bradycardia-dependent right bundle branch block was suggested. When a conducted supraventricular impulse occurred within a critical period after the preceding conducted impulse, the impulse was blocked in the right bundle branch except when it fell in the supernormal period of the right bundle branch. When the conducted impulse occurred between the critical period and another longer period, it was conducted without bundle branch block. When the impulse occurred beyond that longer period, it was usually blocked in the bundle branch again. However, when the impulse occurred beyond a still longer period, it was conducted without bundle branch block again. These findings suggest that when impulses fell in the right bundle branch shortly after the preceding conducted impulses, they were blocked in both bundle branches; however, it seemed that concealed electrotonic conduction of the blocked impulses affected conduction of the subsequent impulses.