The shortage of short QT intervals.

BACKGROUND

Syncope or sudden death has been associated with a short QT interval (QTc, < 300 ms), the so-called short QT syndrome. The current prevalence of this syndrome is unknown. The aim of this study was to evaluate the prevalence of short QT intervals (ie, QTc, < 300 ms) in a general hospital population.

METHODS

We retrospectively queried 479,120 consecutive ECGs that had been archived (Marquette MAC 5000 Resting ECG System; GE Healthcare; Boston, MA) over a 16-year period. We examined the distribution of QT intervals in our population from 150 randomly selected ECGs with normal findings, excluding patients who had been receiving medications known to prolong the QT interval.

RESULTS

From 1988 to 2004, 479,120 ECGs from 106,432 patients were analyzed, which reported 215 tracings with a QTc of < 300 ms. Each ECG was then measured manually, and no QTc of < 300 ms was validated (67% were found to be in error because of a pacemaker artifact, 17% showed supraventricular tachycardia with inaccurate detection of the T-wave offset, and 16% were found to have an error in the cycle length calculation). Therefore, not one of the 106,432 patients was found to have a QTc of < 300 ms. The mean QTc (+/- SD) was 430 +/- 19 ms (95% confidence interval, 392 to 468 ms). The QTc of < 300 ms would then reflect > 5 SDs shorter than the mean QTc.

CONCLUSIONS

The short QTc reported by an ECG computer was inaccurate and required manual correction. Short QT syndrome, defined as a QTc of < or = 300 ms, is rare. We were unable to find one patient among a population > 100,000 patients with a true QTc of < 300 ms.