Observations on the Ventricular Dysrhythmia Associated with Atrial Fibrillation in the Dog Heart

The distribution of ventricular cycle lengths and the incidence of “long” cycles were studied during episodes of atrial fibrillation induced by electrical stimulation of the right atrium in exposed dog hearts. It was concluded that the ventricular dysrhythmia can be interpreted in terms of concealed conduction. Long cycles (bracketing one or more responses concealed in the A-V node) tend to favor the occurrence of subsequent long cycles. The probability of occurrence of long cycles is shown to be a function of the duration of the “concealment zone” and of the atrial input frequency.