Aims: The study concerns the relationship of the corrected QT (QTc) interval to 6.4 years of survival and to measures of cardiac function, such as echocardiographic variables and plasma levels of brain natriuretic peptide (BNP), in 75-year-old people.
Methods and results: QTc was measured in a 12-lead electrocardiogram (ECG) in 210 men and 223 women, comprising a randomly selected sample from the general population (70% participation rate). The Sicard 440/740 computer-analysis program, with Hodges' formula for heart rate-based QT correction, was used. The optimal cut-off point for predicting survival according to the receiver operating characteristic curve was found between 429 and 430 ms. Individuals with a QTc interval of > or =430 ms (n = 115) had decreased survival when compared with those with shorter QTc interval (n = 318); the relative risk was 2.4 (95% confidence interval 1.5-3.7). The predictive ability of QTc reflects an association between QTc and the following variables: BNP, left ventricular mass, and left ventricular ejection fraction (but not diastolic filling patterns). Both Hodges' and Bazett's formulae for heart rate correction of the QT interval were useful for predicting survival. The median QTc was 415 ms using Hodges' formula and 430 ms with Bazett's formula. The QRS component of QTc predicted survival better than the rest of the QTc interval and was approximately as useful as the QTc interval itself.
Conclusion: The computer-derived QTc obtained from the ordinary 12-lead ECG identifies high-risk individuals among elderly people from the general population.