Evidence has been provided that all these blood pressures play a prognostic role in the clinical course of the disease and participate at determining the cardiovascular risk profile of a given hypertensive patient. The question, however, is whether and to what extent one of the above mentioned blood pressures may be superior to the others in predicting cardiovascular risk. The answer to this question would have obvious important practical implications for current clinical practice.
Limited relationship between ambulatory and office blood pressure
Several investigators have documented that office blood pressure values (i.e. the blood pressure values obtained through the sphygmomanometer in the doctor’s office) are usually greater than ambulatory blood pressure values with which they show a limited relationship. This is exemplified by the untreated hypertensive subjects of the European Lacidipine Study on Atherosclerosis (ELSA), in which an office diastolic blood pressure of about 95 mmHg was associated with a wide range of 24-hour average diastolic values (1). It is further exemplified by the treated hypertensive patients of the Hypertension Optimal Treatment (HOT) Study in which office and ambulatory systolic and diastolic blood pressure values showed a very limited relationship to each other (2). It is finally exemplified in an analysis of the large data base our group has collected throughout the years showing that the degree of blood pressure reduction induced by treatment was very different, not only quantitatively but also qualitatively, when assessed by office or ambulatory blood pressure (3).
Blood pressure and target organ damage
The limited relationship between different blood pressure measurements poses with strength the question of which blood pressure is prognostically more important, an issue that has been addressed by cross-sectional as well as longitudinal studies.
Cross-sectional data have almost invariably shown that the end-organ damage associated with, and determined by, hypertension is more closely related to 24-hour average than to office blood pressure, no matter where and how the cardiovascular functional and structural alterations are assessed (3).
Longitudinal studies have been less conclusive, however, because in several instances their design was uncontrolled (4). In one study with a controlled design, however, more than 200 hypertensive patients with echocardiographic evidence of left ventricular hypertrophy were followed for one year to assess whether the regression of cardiac structural alterations was more closely related to the treatment-induced reduction of 24 hour or office blood pressure (4). The results of the study show that the reduction in left ventricular mass was significantly related to the fall in 24 hour average systolic and diastolic blood pressure but much less or not so to the concomitant fall in other blood pressure values.
This allows to conclude that daily life blood pressure control by treatment reflects much more accurately than office blood pressure control the improvement of the organ damage, and thus of vital organ protection, accompanying hypertension.
A final consideration on the superiority of ambulatory blood pressure measurements in reflecting target organ damage refers to the evidence that this technique has allowed to show that “white coat hypertension” and “masked hypertension” (Table 1) are associated with structural cardiac alterations (i.e. left ventricular hypertrophy) (5).
Table 1- Main defining features of white coat and masked hypertension.
|Office blood pressure
|Ambulatory blood pressure
|White coat hypertension
Ambulatory blood pressure and prognosis
Stratifying patients into different risk categories on the basis of ambulatory blood pressure values require studies that
- establish in populations or in large groups of hypertensive patients the relation of cardiovascular morbidity and mortality with the different 24-hour ambulatory blood pressure values selected and
- evaluate how prognosis of patients is modified when ambulatory blood pressure is reduced by treatment, leading to a change in ambulatory blood pressure-based staging. This information is only partly available, however, because the association between the incidence of cardiovascular disease and 24-hour blood pressure has been examined in only a few studies of suitable size.
Longitudinal studies of patients with treated or untreated hypertension or diabetes, however, have shown that blood pressure values averaged over the whole or part of the 24 hours predict progression of organ damage or risk of cardiovascular disease better than or in addition to blood pressure values obtained in the office environment (6-8).
This is the case for the Office versus Ambulatory Pressure (OVA) study, that in almost 2000 treated hypertensives has shown the superiority of 24-hour blood pressure values in predicting cardiovascular events (9).
This is also the case for the already mentioned Pressioni Arteriose Monitorate E Loro Associazioni (PAMELA) study, showing the adverse prognostic effects of ambulatory blood pressure elevation (9). This study, however, also showed that each of the available blood pressures (office, home and 24 hour ), when elevated, carries an increase in risk mortality, thereby implying the importance that antihypertensive treatment effectively reduces all these pressures.
A final comment refers to the evidence, again provided by the PAMELA Study, that even in the general population the risk of cardiovascular events increases more with a given increase in home or ambulatory than office blood pressure (10). This finding once again documents the value of ambulatory (and home) blood pressure in predicting the risk of cardiovascular and all cause death.
The content of this article reflects the personal opinion of the author/s and is not necessarily the official position of the European Society of Cardiology.