Tuesday, 19 October 2010

SIDS: Prolongation of the QT interval and the sudden infant death syndrome.

August 1998
 New Engl J Med. 1998;338:1760. Schwartz et al performed a remarkable feat by prospectively collecting the electrocardiograms of over thirty-four thousand Italian newborns between 1976 and 1994 and then performing a follow-up at one year. There were 34 deaths, with 24 due to sudden infant death syndrome (SIDS). The authors found a strong association between the prolongation of the heart rate-corrected QT interval and SIDS. The authors propose that a simple screening EKG could provide "early identification of a substantial percentage of infants at risk for SIDS." An accompanying editorial by Towbin and Friedman describes the existence of several chromosomal abnormalities associated with long QT syndromes, but points out that it is yet too early to recommend either genetic or EKG screening as routine tests.

How do these papers relate to the practice of anesthesiology? All of us who care for children are concerned about the possibility of postoperative apnea, bradycardia, and unexpected death. Many of us in practice have heard of cases where an infant had a completely uneventful anesthetic/surgical procedure and appeared well in recovery only to be discovered dead in bed later that day. The vast majority of these cases are never reported in the medical literature because they are the subject of litigation and as such the records are generally sealed. The EKG and genetic findings discussed above, I think, may offer some hope in terms of improving our ability to identify such patients who are at risk and also happen to have an anesthetic/surgical procedure. These tests may also offer the potential for determining the possible cause of such tragedies, so that the anesthesia/surgical team is not held responsible. Who knows? perhaps a rhythm strip collected at the beginning of each case and some blood sequestered in the lab for later genetic testing may be useful, both for counseling families and protecting anesthesiologists. I am not advocating, by any means, that such approaches be integrated into current practice‹our paranoia regarding litigation is already so high that I do not want to add to it. But if further studies confirm these observations, someday it may be common practice to perform such screening prior to discharge from the newborn nursery.


Background. The sudden infant death syndrome (SIDS) is multifactorial in origin, but its causes remain unknown. We previously proposed that prolongation of the QT interval on the electrocardiogram, possibly resulting from a developmental abnormality in cardiac sympathetic innervation, may increase the risk of life-threatening ventricular arrhythmias and contribute to this devastating disorder. We prospectively tested this hypothesis.

Methods. Between 1976 and 1994, we recorded electrocardiograms on the third or fourth day of life in 34,442 newborns and followed them prospectively for one year. The QT interval was analyzed with and without correction for the heart rate.

Results. One-year follow-up data were available for 33,034 of the infants. There were 34 deaths, of which 24 were due to SIDS. The infants who died of SIDS had a longer corrected QT interval (QTc) than did the survivors (mean [±SD], 435±45 vs. 400±20 msec, P<0.01) and the infants who died from causes other than SIDS (393±24 msec, P<0.05). Moreover, 12 of the 24 SIDS victims but none of the other infants had a prolonged QTc (defined as a QTc greater than 440 msec). When the absolute QT interval was determined for similar cardiac-cycle lengths, it was found that 12 of the 24 infants who died of SIDS had a QT value exceeding the 97.5th percentile for the study group as a whole. The odds ratio for SIDS in infants with a prolonged QTc was 41.3 (95 percent confidence interval, 17.3 to 98.4).

Conclusions. Prolongation of the QT interval in the first week of life is strongly associated with SIDS. Neonatal electrocardiographic screening may permit the early identification of a substantial percentage of infants at risk for SIDS, and the institution of preventive measures may therefore be possible. (N Engl J Med. 1998;338:1709-14.)


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