His-Purkinje responses and refractory periods during atrial extrastimulation in children with heart defects.

Abstract

SUMMARY During atrial extrastimulation, split His potentials, prolonged His-to-ventricular (H,V,) intervals and block distal to the His bundle deflection were observed in both preoperative and postoperative children with heart defects. His-Purkinje responses and refractoriness were identified in 31 of 78 (40%) pediatric patients (20 of 51 preoperative and 11 of 27 postoperative) during atrial extrastimulation coupled to sinus and/or paced cycle lengths. Split His potentials were found in 14 patients (eight preoperative and six postoperative) and His bundle relative refractory periods ranged from 250-490 msec. Prolonged H2V2 intervals were found in these and in an additional 16 patients (11 preoperative and five postoperative) and the relative refractory period of the His-Purkinje system ranged from 230-500 msec. Block distal to the His deflection occurred in seven patients (five preoperative and two postoperative) and the effective refractory period ranged from 230-510 msec.Split His potentials, long H2V2 intervals and block distal to the His bundle deflection produced by atrial extrastimulation were found in preoperative as well as postoperative children. These responses probably represent functional electrophysiologic characteristics of the pediatric cardiac conduction system. CONDUCTION DISTURBANCES after surgical repair of congenital cardiac defects have been identified by studies of the scalar ECGs and vectorcardiograms.'8 Electrophysiologic studies have delineated more precisely the location of these abnormalities.9-16 The prognostic implications of surface electrocardiographic studies are controversial,4 8 and the significance of electrophysiologic studies is speculative. Few data are available on the functional characteristics of the conduction system in the normal child and in the preoperative child with a cardiac defect.'7-21 Most electrophysiologic studies in children have concentrated on the conduction characteristics of the sinus node, atrium and atrioventricular (AV) node, for the longer refractory periods of the proximal conducting system often preclude elucidation of the conduction properties of the distal system. Nevertheless, His-Purkinje responses and refractoriness have been described in animals22 and in a limited number of human adults17 23-25 and children',`a s representing normal characteristics and in pathologic settings. 26' 27 Clearly, the limits of "normal" refractoriness must be determined before meaningful judgments may be made concerning management. In this paper, we report the His-Purkinje responses and refractory periods in 31 of 78 pediatric cardiac patients and discuss the clinical implications of these findings in both the preoperative and postoperative patient.