Not another formula for heart rate correction of QT interval.

BACKGROUND

Normal limits for QT and heart rate were developed in a Japanese population undergoing 24 hour recordings of the electrocardiogram (ECG). The purpose of this study is to validate these normal limits in a West London population having 12-lead ECGs.

METHODS

A retrospective observational cohort of 10,099 patients aged 20-79 attending a hospital ECG department was studied. From the Japanese data z-scores were calculated for men under 50, for men over 50, for women under 50 and for women over 50. z-scores were used to compare the West London and Japanese populations.

RESULTS

Cardiac infarction injury scores (CIIS) for all four groups were less than zero indicating a population at low risk of cardiovascular disease. From the Japanese data a z-score of 1 is roughly 20 ms. West London mean (SD) z-scores for men under 50, for men over 50, for women under 50 and for women over 50 were 0.20 (0.85), -0.02 (0.86), 0.14 (0.93), and -0.45 (0.88), respectively.

CONCLUSIONS

The distributions of the QT and heart rate data of a West London population at low risk of cardiovascular disease are comparable to the Japanese data. The Japanese QT normal limits for women over the age of 50 are about 9 ms higher regardless of heart rate. The QT normal limits for Afro-Caribbeans are about 5 ms lower than other ethnic groups. The Japanese normal limits are applicable elsewhere, albeit adjusting for women over the age of 50 and for Afro-Caribbeans.