Age- and sex-based normal reference ranges of the cardiac time intervals: the Copenhagen City Heart Study

Background Color tissue Doppler imaging (TDI) M-mode can be used to measure the cardiac time intervals including the isovolumic contraction time (IVCT), the left ventricular ejection time (LVET), the isovolumic relaxation time (IVRT), and the combination of all the cardiac time intervals in the myocardial performance index (MPI) defined as [(IVCT + IVRT)/ LVET]. The aim of this study was to establish normal age- and sex-based reference ranges for the cardiac time intervals. Methods and results A total of 1969 participants free of cardiovascular diseases and risk factors from the general population with limited age range underwent an echocardiographic examination including TDI. The median age was 46 years (25th- 75th percentile: 33-58 years), and 61.5% were females. In the entire study population, the IVCT was observed to be 40 +/- 10 ms [95% prediction interval (PI) 20-59 ms], the LVET 292 +/- 23 ms (95% PI 248- 336 ms), the IVRT 96 +/- 19 ms (95% PI 59-134 ms) and MPI 0.47 +/- 0.09 (95% PI 0.29-0.65). All the cardiac time intervals differed significantly between females and males. With increasing age, the IVCT increased in females, but not in males. The LVET did not change with age in both sexes, while the IVRT increased in both sexes with increasing age. Furthermore, we developed regression equations relating the heart rate to the cardiac time intervals and age- and sex- based normal reference ranges corrected for heart rate. Conclusion In this study, we established normal age- and sex-based reference ranges for the cardiac time intervals. These normal reference ranges differed significantly with sex.