Babies who die of Sudden Infant Death Syndrome (SIDS) are more likely to have abnormal heartbeats a few days after birth, according to a study in tomorrow's New England Journal of Medicine. If the finding is confirmed by other studies, it may help doctors identify higher-risk babies and could lead to drug treatments that prevent some SIDS deaths.
When a child less than 1 year old dies suddenly of unexplained causes, doctors usually rule SIDS as the cause of death. Researchers suspect that several abnormalities contribute to SIDS deaths, including breathing trouble, gastrointestinal diseases, and metabolic disorders. More than 20 years ago, several cardiologists, including Peter Schwartz of the Policlinico San Matteo in Pavia, Italy, proposed that babies with a so-called long QT interval in an electrical recording of their heartbeat might be at higher risk for SIDS. The QT interval measures roughly the time it takes the heart muscle to recover after receiving an electrical signal to contract. If some patches of heart tissue take longer to recover than others, they can beat out of sync, and lead to sudden death. The long-QT syndrome, commonly caused by genetic abnormalities, is a leading cause of sudden death in children and young adults.
Schwartz and his colleagues began a long-term study in 1976, recording electrocardiograms of apparently healthy babies three or four days after birth. After 19 years, they had data on more than 34,000 infants. Of the 33,034 they were able to follow through their first birthday, 34 had died, with 24 deaths blamed on SIDS. Of those 24, half had unusually long QT intervals; none of the 10 who died of other causes had this problem. This suggests, the authors write, that heart abnormalities detectable in the first week of life may be responsible for a significant percentage of SIDS deaths.
Some experts aren't convinced. While Schwartz's team was collecting its data, other scientists published several studies reporting no evidence of long QT intervals in smaller groups of high-risk infants--the siblings of SIDS victims and babies who had survived close calls. And another study of more than 7000 randomly chosen babies found that the electrocardiograms of 15 who died of SIDS were not significantly different from those of healthy control babies.
But if Schwartz's findings are replicated, they could be put to good use: Older children with long-QT syndrome are commonly treated with drugs called beta-blockers, which help to smooth out uneven heart rhythms. If long QT intervals are a risk factor, says pediatric cardiologist Richard Friedman of the Baylor College of Medicine in Houston, some cases of SIDS "may be a preventable type of thing."