CHICAGO (AP) - A new study casts doubt on the value of home electronic monitors in preventing sudden infant death syndrome.

Many infants at risk for SIDS, such as those born prematurely, are sent home with so-called apnea monitors, even though the devices' effectiveness at reducing deaths has not been proved. The monitors are based on the theory that breathing interruptions and slow heart rates immediately precede a SIDS death.

But a study of 1,079 babies found that these episodes commonly occur in both premature babies and healthy, normal-term infants, and in most cases are not immediately followed by death.

Dr. George Lister, a Yale University professor of pediatrics and co-author of the study, said it is possible that the heart and breathing episodes detected by home monitors indicate that a child may be vulnerable to SIDS at some point. But the theory that these episodes immediately precede SIDS does not hold up, he said.

``These results should be important for designing future monitors,'' the researchers wrote in Wednesday's Journal of the American Medical Association. An accompanying editorial, however, argued that the study ``justifies a severe curtailing of home monitoring to prevent SIDS.''

More than 6,000 episodes of slow heart rate and breathing interruptions called apnea were detected during the nearly four-year study, funded by the National Institutes of Health.

``Based on more than 700,000 hours of monitor use, we determined that events previously described as `pathologic' are actually quite common, even in healthy term infants,'' the researchers wrote.

``Extreme events'' such as prolonged breathing lapses or those requiring resuscitation were rare, happening in just 116 infants, most of them premature. But these episodes suggest a respiratory problem that is too subtle to be detected by the kind of monitors usually given to parents, the researchers said.

Six infants died in the study, including four possible SIDS cases. None was being monitored at the time, so it is unknown if breathing or heart-rate lapses immediately preceded the deaths, Lister said.

Doctors do not know what causes SIDS, although a leading theory suggests it involves subtle brain-stem abnormalities that block normal reflexes. Babies who sleep on their stomachs are most vulnerable. A nationwide campaign promoting back-sleeping has greatly reduced the incidence, but nearly 3,000 U.S. infants still die of SIDS yearly.

A theory dating to the 1980s suggesting that breathing and heart-rate lapses immediately precede SIDS prompted a home-monitoring industry.

While the new study was not designed to determine how useful home monitors are in preventing SIDS, ``the physiological basis for such practice is more in doubt than ever,'' Dr. Alan Jobe of Children's Hospital Medical Center in Cincinnati wrote in an accompanying editorial.

Home monitors typically are about the size of a toaster, with electronic leads that measure heart rate and elastic bands that measure breathing. They cost about $300 a month to rent and are sent home with about 20,000 premature infants yearly, Jobe said.

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