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

Rapid atrial pacing-induced infra-His conduction block in children

High right atrial pacing (abrupt initiation and random coupling to the spontaneous rhythm) was performed in 285 pediatric cardiac patients for diagnostic purposes. Nine patients (3%) were found to have pacing-induced infra-His conduction block. In two patients this occurred following a preceding long cycle as well as a preceding short-to-long sequence cycle length change. In five patients block occurred with an abrupt shortening of the coupling H-H interval (in three patients the infra-His block initiated a series of 2:1 infra-His block). In two patients with type II second-degree atrioventricular block the initiating events were not recorded. In one of them, when the rapid atrial pacing was incremented to the same cycle length with infra-His block, the atrioventricular response became 1:1 with normal conduction. These findings of pacing-induced infra-His conduction block can be explained by the normal response of the His-Purkinje system to changes in the preceding cycle lengths, and to the abrupt shortening of the coupling interval.

Site of conduction delay and electrophysiologic significance of first-degree atrioventricular block in children with heart disease

Associated electrophysiologic abnormalities and site of delay were studied in 20 patients, aged 1.5 to 16.5 years, with congenital heart disease and first-degree atrioventricular (AV) block (PR interval above the 98th percentile for age and heart rate). Eight of the 20 patients with first-degree AV block were studied after 1 or more cardiovascular operations. Refractory periods of the atrium, AV node, His-Purkinje system and ventricle were determined. As a further test for AV nodal integrity, rapid atrial pacing was performed and the cycle at which Wenckebach periodicity occurred was noted. Four groups were identified. Group I included 4 patients (20%) with intraatrial conduction delay (long PA interval). Three patients had depressed sinus nodal function and 1 had depressed AV nodal function. Group II included 7 patients (35%) with AV nodal delay (long AH interval). One patient had sinus nodal depression and 2 had AV nodal depression (prolonged AV nodal refractory period or Wenckebach at a long paced cycle length). Group III included 3 patients (15%) with His-Purkinje delay (long HV interval). Measured functions were normal in all patients. Group IV included 6 patients (30%) with normal or high normal intracardiac intervals with long PR. One patient had sinus nodal dysfunction, 2 patients had long atrial refractory periods, 1 had AV nodal depression; 2 had long refractory period of the His-Purkinje system, and 1 had long ventricular refractory period. Atrial flutter was induced in 1 patient.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction of nonsustained atrial flutter by programmed atrial stimulation in children: incidence, mechanisms, and clinical implications

Nonsustained atrial flutter was induced by programmed atrial extrastimulation in 6 (4%) of 137 children with preoperative congenital heart defects, who underwent electrophysiologic evaluation as part of cardiac catheterization. None of these patients had ECG or clinical evidence of arrhythmias. Atrial reentry was induced by programmed atrial extrastimulation in these six patients at coupling intervals slightly longer than the coupling interval at which flutter was induced. The flutter cycle length was similar to the atrial refractory periods. The duration ranged between 0.4 second and 60 seconds. The PA interval and the duration of the P wave were normal in all of the patients. Five of the six had normal PR intervals. It is concluded that nonsustained atrial flutter may be induced by programmed atrial extrastimulation in dysrhythmia-free children. The cycle length is determined by atrial refractoriness and, contrary to adults with clinical atrial flutter, prolonged PA and P wave duration are not predisposing factors.