173 Study of the circadien variation of the QT dynamics in myocardial infarction

IntroductionThe relation between the QT interval and heart rate is linear. The QT interval/RR interval relationship is generally described as QT dynamics. the linear QT/RR slope is influenced by the autonomic nervous system. In healthy individuals, the slope exhibits circadian variations: it is steeper during the day than during the night.AimThe aim of this study is to evaluate the circadian variation of the QT interval and the QT/RR slope in patients experiencing myocardial infarction.MethodsThis prospective study included 90 patients having myocardial infarction. They underwent 21 days after the acute phase, 24 hours ambulatory ECG (Holter) recording. The following parameters were studied : the QT end interval (QTe), the QT apex interval (QTa) and the slopes of QTe/RR and QTa/RR during diurnal and nocturnal periods.ResultsThere was no significant difference regarding the QTe and the QTa intervals during the day and night. The mean diurnal slope and nocturnal slopes of QTe/RR were similar (0,147±0,073 vs 0,131±0,062, p=NS). The mean diurnal slope and nocturnal slopes of QTa/RR were also comparable (0,123±0,067 vs 0,119±0,065, p=NS).ConclusionThe lack of circadian variation of the QT interval and the linear QT/RR slope in myocardial infarction patients reflects an imbalance in the autonomic nervous system. These results suggest an increase in the nocturnal sympathic tone and may be associated with a higher risk of arrhythmia in this population. Further studies are needed to evaluate the role of the QT/RR slope in risk stratification after myocardial infarction