[Atrioventricular conduction disorders following total correction of tetralogy of Fallot. Analysis of the electrogram of the bundle of His].

A study was made of the electric activity of the atrioventricular (AV) conduction system in basal conditions and with atrial stimulation in order to discover the type, severity and prognosis of the AV disturbance in cases of total correction of tetralogy of Fallot. The authors studied thirteen patients from the Paediatric Department of the National Institute of Cardiology who had undergone such surgery, 7 males, 6 females from 3 to 22 years old. All presented advanced RBBB and sinus rhythm; in the immediate postoperative period, one presented complete transitory A-V block which required a stand by pacemaker; in 2 cases there was a first degree AV block; in two other, LAH and LPH. In 5 cases atrial stimulation was made with single charges and progressive frequency. Measurements were taken at the customary intervals. In basal conditions, prolongation of the AH interval was only found in 2 patients, both with first degree AV block in the peripheral EKG; both patients were taking digitalis. The HV interval was longer than normal in 3 cases, with one of these showing also a lengthened AH interval. The atrial stimulation showed prolonged ventricular activation in 2 cases, one of them with normal basal HV interval. The authors conclude that this procedure permits: 1) The discovery of alterations in the AV conduction system which could not be found in a peripheral EKG. 2) Localization of the site of the lesion. 3) The finding of disturbances of the ventricular conduction by atrial stimulation. 4) Identification of those patients who, after a complete correction of tetralogy of Fallot, show a potential high risk of developing complete complete AV block or of sudden death. 5) The establishment of a real prognosis in these patients.