[Auricular fibrillation and flutter with slow ventricular frequency. Clinical and electrophysiological study]

We have studied atrio-ventricular conduction in 9 patients with atrial fibrillation and flutter and ventricular response below 90 per minute, by means of His bundle electrograms. Despite the finding of intraventricular conduction defects in 6 cases, the block of the atrial impulses occurred at the high atrio-ventricular junction in every case. In four patients the arrhythmia was an incidental finding and there were no other signs of cardiac disease. Several patients tolerated low ventricular rates for years without symptoms, but in two cases it was necessary to insert a pacemaker to treat cerebral ischemic symptoms. The problems of interpretation of the His bundle electrogram, in the presence of atrial fibrillation, are discussed in detail.