Cardiac rhythm and symptomatic arrhythmia in right atrial isomerism.

Background: The conduction system in right atrial isomerism may be complicated by the presence of paired sinus nodes and twin atrioventricular nodes. With a large cohort of infants and children with right atrial isomerism, we sought to investigate the nature of atrial rhythm, its prevalence, factors predisposing patients to symptomatic cardiac arrhythmia, and the relation of arrhythmia to long-term morbidity and mortality.

Methods: Standard 12-lead baseline electrocardiograms were performed in 110 infants and children with right atrial isomerism at a median age of 1 day, and their clinical records were reviewed. The type, timing, and precipitating factors of symptomatic cardiac arrhythmia that occurred in 15 patients, among a cohort of 85 patients who had or were awaiting surgical interventions, were noted.

Results: All patients except 1 had a sinus rhythm with intact atrioventricular conduction. Of these, 87% (95/109) had single P-wave morphology, whereas 13% (14/109) had multiple P-wave morphologies. For patients with a single P-wave morphology, the frontal P-wave axis was between 0 degrees and 90 degrees in 62% (59/95), 90 degrees and 180 degrees in 23% (22/95), and superior in 15% (14/95). There was no relation between either P-wave axis or morphology and cardiac anatomy. Symptomatic cardiac arrhythmia occurred in 15 of 85 patients (18%); 11 of the 15 patients had supraventricular tachycardia, and 1 patient each had atrial tachycardia, atrial flutter, ventricular tachycardia, and congenital complete heart block. The arrhythmias occurred before surgery in 4 patients, early after surgery in 5 patients, and late after surgery in 6 patients. Although 3 of the 7 patients who died suddenly had a history of symptomatic arrhythmia, arrhythmia was the documented cause of mortality in only 1 of the 32 fatalities (3.1%). Freedom from arrhythmia at 1, 5, 10, 15, and 20 years was 93% +/- 3%, 86% +/- 4%, 80% +/- 6%, 73% +/- 9%, and 48% +/- 15% (mean +/- SE), respectively. No risk factors for symptomatic arrhythmia were identified by means of logistic regression.

Conclusions: The atrial pacemaker varies in location within and between patients with right atrial isomerism. Although symptomatic cardiac arrhythmias are not uncommon, they do not seem to relate to the overall high mortality rate and occurrence of sudden death in this patient group. Nonetheless, detailed assessment and aggressive management of cardiac arrhythmias once they occur are warranted because of the precarious single ventricular hemodynamics.