Distribution and prognostic significance of QT intervals in the lowest half centile in 12,012 apparently healthy persons.

The presence of an abnormally short QT interval has been noted among survivors of idiopathic ventricular fibrillation and among close relatives of victims of unexplained sudden death. Most reported cases have had rate-corrected QT (QTc) intervals of <300 ms. The prevalence of such values in the community has not been documented. We reviewed the electrocardiograms (ECGs) of 12,012 subjects who underwent routine medical examinations for occupational reasons. The QT interval was measured by 2 physicians in all cases, and QTc interval was calculated. All ECGs with QTc values in the lowest 5% were reviewed by 2 cardiologists expert in QT analysis, and the QT measurement was corrected if necessary. Information about subsequent survival was obtained from the case file or from public records. In the lowest 1/2 centile, the distribution of QTc values continued to follow a normal pattern without evidence of a distinct subpopulation of low values. The shortest QTc encountered was 335 ms. Information about subsequent survival was available for 36 of the 60 subjects with the lowest 1/2 centile of QTc values. None of these subjects died during the 7.9 +/- 4.5 years subsequent to the ECG that demonstrated the short QT interval. In conclusion, a QTc interval of <or=330 ms is extremely rare in healthy subjects, and the presence of a QT interval in the lowest 1/2 centile of the normal range does not imply a significant risk of sudden death.