Cardiac rhythm in atrial isomerism.

Standard electrocardiograms from 126 consecutive patients with atrial isomerism were reviewed. Of 67 patients with left isomerism, 49 had sinus rhythm, 8 nodal rhythm and 10 atrioventricular (AV) block. Fifty-eight of 59 patients with right isomerism had sinus rhythm. Complete AV block was significantly more frequent in association with AV septal defect in left isomerism (5 of 45 patients) than in right isomerism (0 of 47 patients, p = 0.049). The P-wave axis was superior in 49% of patients with left isomerism but did not correlate with abnormalities of systemic or pulmonary venous connection. A significant shift of P-wave axis (more than 90 degrees) was seen on a subsequent electrocardiogram in 14 of 44 patients (32%) with left isomerism and 2 of 16 (13%) with right isomerism. Ambulatory electrocardiographic monitoring in 17 patients (14 with left isomerism) showed that only 4 had sinus rhythm throughout 24 hours. Only 1 patient with complete AV block received a permanent pacemaker. Despite the high incidence of electrocardiographic abnormalities, significant arrhythmias appear to be rare. The arrhythmias apparently do not influence the natural history of this condition or affect the outcome of palliative or corrective surgery. The prognosis is determined mainly or solely by the associated anatomic abnormalities.