Tetralogy of Fallot: postoperative electrophysiologic studies.

Electrophysiologic studies performed during postoperative cardiac catheterization in 51 patients following repair of tetralogy of Fallot (TF) were compared with studies performed in a control group of 30 patients. These studies include His bundle electrograms, measurement of atrioventricular (A-V) conduction at progressively increasing atrial pacing rates, and evaluation of sinus node recovery time. More postoperative TF patients (20%) had prolonged H-V intervals compared to the controls (7%). With atrial pacing, no patient in the control group developed second degree A-V block below 160 beats/min, while 23% of the postoperative TF patients developed block below this level. Half of these patients had normal His bundle studies. Stress of the A-V conduction system by atrial pacing may unmask conduction abnormalities not present on the surface electrocardiogram or on His bundle electrogram. Two-thirds of the patients had some form of conduction abnormality on the basis of evaluation of one or more parameters but about half of the patients with a given abnormality had normal findings in other areas. The high incidence of electrophysiologic abnormalities following TF repair may have future prognostic significance. Systematic evaluation of atrioventricular conduction during preoperative and postoperative cardiac catheterization may be of value.