Cardiac rhythm in sudden infant death syndrome

As part of an ongoing effort to assess the possible role of cardiac dysrhythmia in the pathogenesis of sudden infant death syndrome, cardiac rate and rhythm were continuously monitored electrocardiographically for 24 h in 9 patients with 'near-miss' or aborted sudden infant death syndrome. Two of the 9 had had siblings who had been victims of sudden infant death syndrome but all were previously well and had normal postadmission physical and laboratory examination results, including electroencephalograms and 12-lead electrocardiograms [lead II mean QT(c) = 0.41 ± 0.03 (S.D.)s; lead V₁ mean QT(c) = 0.39 ± 0.01 s]. Sinus rhythm, ranging from 73 to 225 beats min^-1, was the prevailing rhythm in all patients. Six infants had frequent episodes of mild irregularity of sinus rhythm, 2 had infrequent moderate irregularity and 1 infant had one episode of marked irregularity. Atrial ectopics occurred infrequently in 2 patients. Monitoring lead QT(c) was normal in all (mean 0.39 ± 0.02 s) with the maximum individual variation during the monitoring period averaging 0.10 ± 0.03 s. Because of an episode of marked irregularity of sinus rhythm, 1 infant was given a demand-mode ventricular pacemaker at 4 weeks of age. Despite appropriate functioning of the pacemaker, this infant had another 'near-miss' episode at age 6 weeks and died suddenly of indeterminable cause at age 8 weeks. The other 8 infants have remained well after a mean follow-up interval of 36 months. These observations suggest that significant cardiac dysrhythmia (including QT prolongation) is not readily detectable in a population at high risk of sudden infant death syndrome and that bradyarrhythmia or bradycardiac arrest is not the primary cause of all cases of sudden infant death syndrome.