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The QT interval throughout the first 6 months of life: a prospective study
Insights
This study establishes normal QT interval values in infants, finding it temporarily lengthens in early months. This lengthening may transiently impair cardiac electrical stability, potentially linking to sudden infant death syndrome (SIDS).
Area of Science:
- Pediatrics
- Cardiology
- Neonatology
Background:
- The QT interval, a measure of cardiac repolarization, is crucial for assessing cardiac electrical stability.
- The "QT hypothesis" suggests a link between prolonged QT intervals and sudden infant death syndrome (SIDS).
- Establishing normative QT interval data in infants is essential for identifying potential risks.
Purpose of the Study:
- To determine baseline electrocardiographic (ECG) measurements, specifically the QT interval, in infants.
- To investigate the "QT hypothesis" concerning its potential role in SIDS.
- To provide definitive normal QT interval values during infancy.
Main Methods:
- A prospective electrocardiographic study enrolled 4205 newborns.
- ECGs were recorded on the fourth day of life and at 2, 4, and 6 months.
- Infant health at 1 year was assessed via phone call.
Main Results:
- Mean QTc (QT interval corrected for heart rate) values were established at different infant ages.
- A physiological, temporary lengthening of the QTc was observed during the first few months of life.
- Three SIDS cases were identified among 2000 infants; one had a QTc exceeding the mean by over 9 standard deviations.
Conclusions:
- The study provides definitive normal QTc values for infants.
- Findings support the "QT hypothesis" by showing a correlation between extremely prolonged QTc and SIDS, though more data is needed.
- Transient lengthening of the QT interval in infancy may temporarily affect cardiac electrical stability.
Abstract:
A prospective electrocardiographic study was designed to establish baseline values for electrocardiographic measurements, with specific reference to the QT interval during infancy, and to test the "QT hypothesis" for the sudden infant death syndrome (SIDS). In this ongoing study, ECGs are recorded on the fourth day of life and in the second, fourth and sixth months. The state of health at 1 year is ascertained by a phone call. So far, 4205 newborns have been enrolled. The mean QTc (QT interval corrected for heart rate) was 397 +/- 18 msec (+/- SD) at the fourth day, 409 +/- 15 msec (p less than 0.0001) at the second month, and 406 +/- 15 msec at the fourth month; by the sixth month, it returned to 400 +/- 14 msec. In 88 newborns, the QTc increased by over 40 msec at the second month. Among the 2000 infants checked at 1 year, there have been three sudden and unexpected deaths. The QTc of one of the victims at the fourth day was 563 msec, which exceeded the mean by more than 9 standard deviations, while the QTc of the other SIDS victims exceeded the mean by more than 2 and 3 standard deviations. These results are consistent with the "QT hypothesis," but more data are necessary before any conclusion on the potential relationship between QT interval prolongation and SIDS can be drawn. This study provides definitive waking normal values for QT interval in infancy and indicates that the QT interval lengthens physiologically and temporarily during the first months of life. In some infants, this lengthening may transiently impair cardiac electrical stability.