[Study of ventricular repolarization in an experimental model of arterial hypertension associated with obesity]

High fat diet (HFD) in dogs is associated with obesity and hypertension (HTN) but also with a significant and early decrease in heart rate variability (HRV). Decreased HRV has been shown to be a good predictor of sudden cardiac death due mainly to arrhythmic event. The aim of this work was to investigate the changes in ventricular repolarization through 24 hours EKG recordings in dogs with hypertension and rendered obese by 20 weeks of HFD. This was achieved through 24 hour EKG recording analysis of QT parameters. The aims of this work was i) feasibility of this method in dogs and ii) identification of potential arrhythmic risk factors that could explain overmortality during obesity.

Six dogs received a high fat diet (HFD) ad libitum during 20 weeks. A 24 hour EKG recording was realized just before and after 20 weeks of HFD. The following parameters studying QT interval were collected: QT interval lasting from the beginning of the Q wave to the apex (QTa) and to the end of the T wave (QTe), QT intervals plotted against RR intervals and two regression lines were calculated characterized by their slope and intersection with the Y axis, QT dispersion (longest minus shortest QT interval for each RR value) as well as the difference of QT interval between night and day at a fixed RR value considered as a marker of the sympathovagal balance. Our results show that HFD significantly increased body weight, blood pressure, heart rate, left ventricular mass and insulinemia. QT dispersion was increased in a non-significant manner both during day (+35%) and night (16%) for QTa and only during day for QTe (+27%). This increased dispersion of QT was not associated to any increase of QT interval. There was no effect of HFD on QT dynamicity parameter nor on the night-day difference at any RR interval from 300 to 1,300 ms.

HFD tend increase QT dispersion without any effect on QT interval. These results are compatible with a heterogeneous repolarization probably related to abnormal autonomic nervous system tone. This study could partly explain occurrence of lethal arrhythmias during obesity which might lead to overmortality of obese patients. These results are different for QTa and QTe, but these two parameters are characterizing different type of ventricular cells. This study confirms the feasibility of this method in an experimental model, but results need to be validated in larger groups and in human.