Infants with apparent life threatening events. Cardiac rhythm and conduction.

The role of cardiac dysrhythmias in the pathogenesis of Sudden Infant Death Syndrome (SIDS) is uncertain, but there have been several reports of infants with Apparent Life Threatening Events (ALTE) due to significant dysrhythmias. To further characterize the cardiac rhythm and conduction of these "at-risk for SIDS" infants, we performed 24-hour continuous (Holter) electrocardiograms on 100 full term, healthy infants with ALTE. Sixty-two patients (62%) had one or more dysrhythmias on Holter monitor. Twenty-five patients (25%) had premature ventricular depolarizations (PVD), including five with couplets. Thirty (30%) had QTc greater than 2 SD above the mean, and, of these, 40 percent had PVD's. Fifteen (15%) had premature atrial depolarizations and 39 (39%) had evidence of moderate or marked sinus node irregularity. There was no prexcitation, supraventricular tachycardia, ventricular tachycardia, or atrioventricular block. Two patients with marked sinus node dysfunction were treated with propantheline and did well. All patients were monitored at home, with no deaths or clinically significant dysrhythmias on follow-up (1-32 months (mean = 18]. In summary, when Holter monitoring was performed, a high incidence of dysrhythmia was found in infants with ALTE. Most dysrhythmias were clinically insignificant. The incidence of ventricular dysrhythmias and long QTc are consistent with previously advanced theories of cardiac electrical instability in some of these patients, but no patient with ventricular dysrhythmias required therapy. The incidence of sinus node dysfunction requiring therapy was 2 percent. Although Holter monitoring of infants with ALTE only infrequently determines therapy, it may provide data linking theories of cardiac etiology of SIDS with actual clinical events.