Correction for heart rate is not necessary for QT dispersion in individuals without structural heart disease and patients with ventricular tachycardia.

BACKGROUND: It remains controversial whether QT dispersion should be corrected for heart rate, especially when the limitations of rate correction formulae are considered. We investigated whether incremental atrial pacing affects QT dispersion and the rate-corrected values according to Bazett's formula in individuals without structural heart disease and in patients with history of sustained ventricular tachycardia.

METHODS: We studied 32 individuals without structural heart disease (group A), and 16 patients with a history of sustained ventricular tachycardia (group B). QT dispersion and corrected for heart rate QT dispersion using Bazett's formula (QTc dispersion) were calculated in sinus rhythm, and during continuous right atrial pacing for one minute at 100 and 120 beats/min.

RESULTS: Interobserver variability was not significant (P > or = 0.10). QT dispersion did not differ at rest between groups A and B and did not change significantly from baseline at any heart rate in both groups. However, QTc dispersion increased significantly with atrial pacing in a similar manner in group A and group B (42 +/- 19 ms at rest vs 53 +/- 23 ms at 120 beats/min, P < 0.001 for group A, 39 +/- 16 ms at rest vs 60 +/- 19 ms at 120 beats/min, P < 0.001 for group B).

CONCLUSIONS: We conclude that QT dispersion remains unchanged during atrial pacing at heart rates up to 120 beats/min in both individuals without structural heart disease and in patients with a history of sustained ventricular tachycardia. Correction by Bazett's formula results in prolongation of QTc dispersion, yielding values which may be misleading.