Atrioventricular conduction disturbance in adults with secundum atrial septal defect

The atrioventricular (A V) conduction time in 7 adult patients with secundum atrial septal defect (ASD) was investigated at preoperative cardiac catheterization utilizing His bundle electrograms (HBE) were recorded from the right or left ventricle or both ventricles. In all patients, the diagnosis was confirmed at surgery. Analysis of the intracardiac electrograms was made for the evaluation of 6 component parts: P A interval, A H interval, H duration, H V interval, right bundle branch (RB) and left bundle branch (LB) durations, RB V and LB V intervals. The interatrial conduction time was determined by simultaneous recording of right and left atrial electrograms. The P R intervals ranged from 0.14 to 0.21 sec. The mean QRS frontal plane axis in all patients was to the right of +60°. Right bundle branch block (RBBB) was noted in 5 patients, 2 complete and the remainder incomplete. The A H interval was within the normal limits in all patients. Definite prolongation of the HV interval (over 60 msec) was noted in 3 out of 7 patients. This prolongation was attributable to prolonged H RB and H LB intervals in one, to prolonged H LB and LB V intervals in another, and to prolonged H RB interval in the remaining one. In one of these 3 patients, second degree A V block with a block distal to the H potential was recorded during HB electrography. The P A interval was prolonged (over 50 msec) in one of the 5 patients in whom HBE was recorded from the right ventricle and the onset of A wave could be clearly identified, The interatrial conduction time was prolonged (over 50 msec) in 2 out of 3 patients studied. Hypertrophy and dilatation of the basal portions of the free wall of the right ventricle and the higher portions of the interventricular septum due to a prolonged volume overloading may probably account for the prolongation of the His Purkinje system conduction time (H V interval). Increased size of the atria may likewise be responsible for the prolonged internodal (P A interval) and interatrial conduction times.