Prolonged QT interval linked to SIDS

by Ralph A. Franciosi, MD

Ralph Franciosi, MD, was medical adviser for the Infant Death Center of Wisconsin and pathologist at Children's Hospital of Wisconsin. He also was a professor of Pathology and Laboratory Medicine at the Medical College of Wisconsin.

An electrocardiogram, or EKG, is a test done on the heart that gives a graphic tracing of the electrical impulses generated by the heart muscle.

A person's heart beats in a cycle which begins with the contraction of the atria (the upper two chambers of the heart), the opening and closing of the ventricles (the lower two chambers of the heart) and a resting period before the next heart beat.

The blips shown on the diagram represent these different areas of the heart and are marked with letters. The P wave precedes the contraction of the atria, the QRS waves precede the contraction of the ventricles, the T wave represents the recovery or closing of the ventricles and precedes the resting period before the next cycle.

EKG tests usually are used to document a heart attack, but also are helpful in demonstrating an abnormal heart rhythm such as a heart block which impedes the normal electrical activity that occurs between the atria and ventricles.

A current medical article noted an association between a prolonged QT interval and Sudden Infant Death Syndrome. More than 33,000 infants were given an EKG at 3 to 4 days old and test results were stored. After 19 years, 34 infants had died, 24 from SIDS. When the EKGs of infants who had died of SIDS were compared with the others, a prolonged QT interval was found in 12 (or half) of the SIDS infants.

The researchers speculated a prolonged QT interval indicates a defect in the part or parts of the brainstem that control breathing and heart rate. This functional birth defect may cause a susceptibility to stressors/triggers in the first year of life.

What does this mean? Does this abnormality found in the first three to four days of life persist into the time period when most SIDS cases occur? Should we do EKGs on all newborns? These questions await studies that can confirm the validity of this finding. The authors of this study warned, "Even if our hypotheses were proved to be correct, such identification and treatment would not be a simple task."

My view is the prolonged QT interval finding is added proof that SIDS infants are physiologically abnormal and until we can prevent this defect, we need to avoid known risk factors, such as prone sleep position and maternal cigarette smoking, which increase the number of SIDS cases.

< Back