Cardiovascular regulation and vascular structure in prehypertension and coronary heart disease

Abstract

The aim of this thesis was to characterize vascular structure and different aspects of cardiovascular regulation in otherwise healthy subjects with slightly elevated blood pressure and compare to healthy subjects with normotension and also investigate patients with established primary or secondary hypertension and coronary heart disease. Altered cardiac repolarization and arterial baroreflex function has been associated with adverse prognosis and increased risk for ventricular arrhythmias in patients with cardiovascular diseases.

We used the sequence method to measure the baroreflex sensitivity (BRS) and the baroreflex effectiveness index (BEI). The latter is an index of the numbers of times the arterial baroreflex is being active in controlling the heart rate. The myocardial repolarization was assessed using the QT variability index (QTVI), which is a non-invasive measurement of subtle beat to beat fluctuations of the QT interval. A novel very high frequency (55MHz) ultrasound technique was used to measure the vessel wall and separate the intima media (IMT) complex into measurements of intima and media thickness . Increased lability of myocardial repolarization and impaired baroreflex function were seen in subjects with prehypertension and in otherwise healthy subjects with an attenuated reduction in blood pressure during night (non-dippers) compared to healthy subjects. Patients with renovascular hypertension and patients with coronary heart disease, who underwent coronary artery by-pass grafting (CABG) showed strikingly increased lability of myocardial repolarization. The alterations of myocardial repolarization after CABG improved during rehabilitation. Subjects with prehypertension showed increased radial artery intimal wall thickness compared to healthy subjects. Subjects who report low physical activity had increased intima thickness. In conclusion, subjects with prehypertension show increased lability of myocardial repolarization, impaired baroreflex function and increased intimal wall thickness. Healthy individuals with a non-dipping blood pressure pattern had increased myocardial repolarization lability and impaired baroreflex function. The current findings may contribute to the increased risk for cardiovascular mortality and morbidity previously reported in the studied populations.