["Supernormal" A-V conduction during chaotic atrial rhythm. A case report].

We describe the electrocardiogram of a patient who had a chaotic atrial rhythm with partial A-V block. Only the late P waves (R-P greater than 1 sec.), and the early ones (with one R-P interval between 44 and 52 hundredths of a second) were conducted to the ventricle. On the contrary, no P waves with coupling intervals between 52 and 100 hundredths of a second reached the ventricles. Careful analysis of the tracing showed that the conduction of the early P waves could not depend upon the atrial pacemaker site, or upon concealed conduction of preceding atrial impulses. The existence of a "gap" phenomenon although unlikely, could not be excluded. Supernormal A-V conduction, or early diastolic decrease of the vagal tone due to hemodynamic mechanism could be responsible for the early ventricular captures observed in this patient.