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.
Bourdillon
Peter J
PJ
ECG Department, Hammersmith Hospital, Imperial College Healthcare NHS Trust, London, U.K. pbourdillon@msn.com
D000328:Adult; D000367:Age Factors; D000368:Aged; D015331:Cohort Studies; D004562:Electrocardiography; D015716:Electrocardiography, Ambulatory / Q000379:methods; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D016014:Linear Models; D008133:Long QT Syndrome / Q000175:diagnosis / Q000208:ethnology / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D012016:Reference Values; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012737:Sex Factors; D006113:United Kingdom; D055815:Young Adult