[Study of the heart conduction system in atrioventricular disorders]

A His electrogram was registered with a Castillo tripolar catheter in seven patients with atrio-ventricular discordance and transposition of the great arteries (corrected transposition). They all had ventricular septal defect, six had pulmonary stenosis. two had atrial septal defect, and only one patient presented first degree AV block. The QRS was of normal duration, 4 had RBBB morphology in the left precordials. Two with ASD and VSD had a prolonged P/A interval. In one, the His recording was polyphasic with a prolonged H-V (55 msec) and two others showed a wide polyphasic His potential (25 and 26msec), with a prolonged H-V. These 3 cases with prolonged His had a minor degree of RBBB. The remaining 3 showed normal AV conduction. In all, the Purkinje electrogram was registered. The duration of the Pu potential and the Pu-V were normal. Corrected transposition shows a high incidence of slow AV conduction, frequently not detectable in the usual electrocardiogram in agreement with previous anatomo-pathological studies. The distal block would explain the frequency of complete AV block with low cardiac output and frequent sudden death in this type of heart disease. The distal block would compel us to take e more agressive steps in its treatment. Atrial septal defect with slowing of the intra-arial conduction is not detected in the electrocardiogram.