Time delay between RR and RT heart beat intervals in exercise test of normal subjects and elderly ischemic patients

The RR and RT time intervals extracted from the electrocardiogram measure respectively the duration of cardiac cycle and repolarization. The series of these intervals recorded during the exercise test are characterized by a global minimum. We model these series as a sum of a deterministic trend and random fluctuations, and estimate the trend using a multi scale wavelet decomposition. Data analysis performed on a group of 20 healthy subjects and 30 elderly ischemic patients provides evidence that the minimum of the RT series follows the minimum of the RR series, with a mean delay respectively of 67 and 28 beats.