Assessment of QT intervals and prevalence of short QT syndrome in Japan.

Background: Long QT syndrome causes ventricular tachyarrhythmias and sudden death. Recently, a short QT interval has also been shown to be associated with an increased risk of tachyarrhythmia and sudden death. However, the prevalence of short QT syndrome is not well-known.

Hypothesis: The aim of this study was to assess the distribution of corrected QT intervals (QTc) and prevalence of short QT syndrome.

Methods: This study comprised 12,149 consecutive subjects who received a consultation at Kanazawa University Hospital, Kanazawa, Japan, and had an electrocardiogram (ECG) between February 2003 and May 2004. Of these subjects, 1,165 subjects were excluded because of inappropriate ECGs, while the remaining 10,984 subjects had their last-recorded ECGs analyzed.

Results: The QTc values showed a nearly normal distribution (408 +/- 25 msec(1/2)), and were significantly longer in females (412 +/- 24 msec(1/2)) than in males (404 +/- 25 msec(1/2)) (p < 0.05). Among 5,511 males, 69 subjects (1.25%) exhibited QTc < 354 msec(1/2) (2 standard deviations [SDs] below the mean in males), and among 5,473 females, 89 subjects (1.63%) exhibited QTc < 364 msec(1/2) (2 SDs below the mean in females). Only 3 subjects (0.03% in all subjects and 0.05% in males) exhibited QTc < 300 msec(1/2), however, none had clinical symptoms of short QT syndrome.

Conclusions: Short QT syndrome may be very rare.