Flutter and fibrillation-like phenomenon of His bundle observed in a patient with persistent atrial standstill

A diagnosis of persistent atrial standstill was made in a patient with syncopal attacks, based on: (1) the lack of P waves both in the routine 12-lead electrocardiogram (ECG) and in the right atrial cavity lead; (2) the absence of "a waves in the right atrial pressure curve; and (3) the failure of the atria to respond to electrical stimulation. Compared with previously reported cases of persistent atrial standstill with a slow, regular escape rhythm of supraventricular origin, the present case was characterized by alternate periods of bradycardia and tachycardia, the latter being suggested as AV junctional tachycardia with exit block. Furthermore, the His bundle electrogram (HBE) showed either regular, high frequency deflictions or irregular, deformed potentials, suggesting flutter and fibrillation-like phenomena in the His bundle.