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The Prognostic Significance of Ambulatory Blood Pressure Monitoring in a General Population

Tine Willum Hansen 

Summary

A high office blood pressure is a well-known risk factor for cardiovascular morbidity and mortality. However, blood pressure is influenced by physical and emotional factors. Therefore, ambulatory blood pressure monitoring would be expected to provide a better estimate of the risk related to blood pressure. This idea has been shown to hold true in patients with hypertension, but until now only two large studies have examined this in a general population. Knowledge about the prognostic value of ambulatory blood pressure in the general population is therefore spare.

The present thesis describes results from a prospective study conducted in a random sample of 1700 men and women, age 41-72 years, without major cardiovascular diseases. At baseline, ambulatory blood pressure, office blood pressure, and other risk factors were recorded. The endpoints were all cause mortality, cardiovascular mortality, and a combined endpoint consisting of cardiovascular mortality, ischemic heart disease and stroke. The mean study duration was 9.5 years. In the follow up period 174 participants died; 63 of the deaths were classified as cardiovascular. A total of 156 combined endpoints were recorded.

According to all endpoints, ambulatory blood pressure provided prognostic information above and beyond that of office blood pressure. Thus, compared to normotension (office blood pressure < 140/90; daytime blood pressure < 135/85) isolated office hypertension (office blood pressure ≥ 140/90; daytime blood pressure <135/85) was not a risk factor, and isolated ambulatory hypertension (office blood pressure < 140/90; daytime blood pressure ≥ 135/85) tended to be a risk factor. The risk of mortality declined as ambulatory blood pressure decreased with no indication of a threshold. Risk of mortality depended on blood pressure, age and smoking status and therefore it was not meaningful to talk about a general upper “acceptable” ambulatory blood pressure limit without considering the presence of other risk factors. This study also demonstrated that monitoring of the entire 24-hours period was especially valuable in subjects with daytime ambulatory hypertension; a blunted blood pressure fall at night in these subjects was an indicator of an increased risk. In addition, it was shown that by increasing the number of measurements a more precise estimate of risk was obtained, and it was demonstrated 33 that no particular period during the 24-hours was especially valuable for the prediction of risk.

In conclusion, 1) ambulatory blood pressure was superior to office blood pressure in identifying subjects who probably needed treatment or who probably did not need treatment. 2) The risk of mortality declined as ambulatory blood pressure decreased with no indication of a threshold. 3) Risk of mortality depended on blood pressure, age and smoking status and therefore a general upper “acceptable” ambulatory blood pressure limit needed to be considered in relation with other risk factors. 4) A blunted blood pressure fall at night was a risk factor in subjects with daytime ambulatory hypertension. 5) By increasing the number of blood pressure measurements a more precise estimate of risk could be obtained.