- ECG =
- electrocardiogram •
- SIDS =
- sudden infant death syndrome
The article by Schwartz et al1 published in the New England Journal of Medicine reports on electrocardiographic (ECG) measurements made over a period of 18 years on infants on the 3rd day of life. It identifies those infants previously studied who died suddenly and unexpectedly and were diagnosed as having died of sudden infant death syndrome (SIDS), and compares their ECGs with those of the survivors.
The idea that SIDS may be related to dysrhythmic events, the predisposing factor being an abnormally long QT interval, is one that at least merits attention. However, there are problems with any investigation whose basis relies on measurement of the QT interval as the authors admit. These problems include the possibility of including U waves in the measurement, the validity of using standard formula to calculate the QTc, and how one should deal with the variation of the QT interval with variation in heart rate.
Schwartz reports that half of the SIDS infants had prolonged QT intervals on their ECGs and concludes that a prolonged QT interval in the newborn period is predictive of future tragedy—although only 2 infants had impressively long QT intervals ie, >345 msec2. That is 2 infants out of 34 442 infants studied. The study was conducted over 18 years, and from recordings made in 10 institutions.
There are even more obvious reservations as to its relevance to the problem of SIDS today.
The incidence of SIDS in Italy is given as 0.7/1000 live births and the rate in the sample is said to be the same. But was that the rate in Italy—or the sample—over the whole period of the study? The rest of the world has reduced the rate very substantially over the last 5 years.3 ,4
A credible hypothesis of causation of death or sickness must be compatible with the proven epidemiologic parameters.5 ,6 In the last 18 years epidemiologic studies of SIDS have elucidated risk factors of the victim and of concomitant infant care practices. In fact the very definition of the condition7 is tightening. To make a diagnosis will soon require the investigator to examine the clinical history of the infant, the circumstances of the death, and a death scene report as well as the results of a careful and full autopsy. Schwartz et al give no details of this nature so we cannot judge the validity of those diagnoses.
The most compelling parameter for SIDS is the age of occurrence. It is rare in the first month of life, occurs most frequently between 2 and 4 months, and is again rare after 6 months. It would seem impossible for such a condition to be caused solely by a cardiac defect although a cardiac condition might exacerbate other noxious influences such as airway occlusion or “rebreathing” imposed by prone sleeping. Schwartz et al do not give any information of the circumstances of either their own series' deaths or of the controls. Were the infants who died sleeping prone when their chance of dying would have been high no matter what their pathology? Had any rolled from side to prone as many SIDS victims are known to do?8 Had any been the victims of “wedging” eg, their heads becoming stuck between a deep mattress and the side of a cot? How many mothers in either group—deaths or survivors—were smokers? How many had been in another sleeping person's bed when they were found dead?
Prolongation of the QT interval may well be a factor in some instances of SIDS, but it is doubtful that it is relevant in all cases. This would explain the relatively weak or absent correlation found by different workers.1 Many of the complexities related to this issue have been explored.9
The prevention of SIDS would seem to be most logically addressed by educating the population to avoid the known epidemiologic risk factors as has been so successful in many parts of the world,3 ,10rather than by subjecting vast numbers of infants to ECG investigations and perhaps to potentially harmful medication.
The presently proven preventive measures that parents can take are:
Put the infant to sleep on his/her back, feet to the foot of the cot, so that bedding cannot cover the face.
No smoking during pregnancy or around the infant.
For smokers particularly make sure the infant is in a safe sleeping place when the parent is asleep.
- Received August 8, 1998.
- Accepted November 5, 1998.
Reprint requests to (S.L.T.) New Zealand Cot Death Association, 5 Clonbern Rd, PO Box 28-177, Auckland 5, New Zealand.
- ↵Davignon A. Percentile charts, ECG standards for children. Pediatr Cardiol. 1979/80;1:133–152
- Mitchell EA,
- Brunt JM,
- Everard C
- Daalvert AK,
- Yen N,
- Skyrven R,
- Lorentz MI
- ↵Beckwith JB. In: Bergman B, Beckwith JB, Ray CG, eds. Sudden Infant Death Syndrome. Seattle, WA and London, England: University of Washington Press; 1970:18
- ↵Mitchell EA, Tuohy PG, Brunt JM, et al. Risk factors for sudden infant death syndrome following the prevention campaign in New Zealand: a prospective study. Pediatrics. 1997;100:5:835–839
- Maron BJ,
- Clark CE,
- Goldstein RE,
- Epstein SE
- ↵Wigfield RE, Fleming PJ, Berry J, Rudd PT, Golding J. Can the fall in Avon's sudden infant death rate be explained by changes in sleeping position? Br Med J. 304:282–283
- Copyright © 1999 American Academy of Pediatrics