Complementary Rather Than Competitive Methods

Clinic (office) blood pressure (BP) measurement has a well-established role in medical practice and is the standard on which most of the literature is based. However, clinic BP has several important limitations, including the potential for inadequate or misleading estimates of a patient’s true BP status and suboptimal prediction of cardiovascular risk. Particularly relevant is the concern that clinic BP measured with standard techniques may not provide a representative estimate of an individual’s usual BP outside the medical setting. Out-of-office BP assessment takes 2 forms at the present time, self (or home) BP measurement (SBPM) and ambulatory BP monitoring (ABPM). These 2 techniques have attracted considerable attention in recent years because of the potential for better classification of hypertensive status compared with office BP. SBPM devices allow for repeated measurements outside the medical environment, and their use has been recommended by several international guidelines.1,2 ABPM is currently considered the gold standard for the correct diagnosis of hypertension on the grounds that the ambulatory BP provides extensive information on several BP parameters other than the average BP, including BP variability, the morning BP surge, BP load, and the nocturnal fall in BP.3 However, it should be noted that all of the clinical guidelines still focus on the importance of the mean ambulatory BP for clinical practice, and all of the other parameters are still considered experimental. ABPM is not widely available in primary care practice and is considered most helpful when self-measured BP is within borderline values. According to most authorities, self-BP measurement should be used as an initial step to evaluate the out-of-office BP1–3 and, thus, used as a screening procedure that should lead to an ABPM for confirmation. However, it is not well known whether this strategy is appropriate because ambulatory BP and self-measured BP may provide different and complementary clinic information. Indeed, several studies have shown that these 2 measures do not have a high correlation4 and that disagreement in the diagnosis of hypertension between the 2 methods is not uncommon.5 Only 2 studies have compared the prognostic value of ABPM with that of SBPM within the same population, the Pressioni Arteriose Monitorate E Loro Associazioni (PAMELA) Study6 and the Ohasama Study.7 In this issue of Hypertension, Hara et al7 investigated the usefulness of ambulatory, home, and clinic BP measurements to predict subclinical cerebrovascular diseases in the general population from Ohasama. They found that 24-hour, daytime, and nighttime ambulatory BPs and home BP were closely associated with the risk of silent cerebrovascular lesions and carotid atherosclerosis, whereas clinic BP was not. However, when home and one of the ambulatory BPs were simultaneously included in the same regression model, each of the ambulatory BP values remained a significant predictor of silent cerebrovascular lesions, whereas home BP lost its predictive value. In agreement with most published reports, mean nighttime ambulatory BP had a better prognostic accuracy than 24-hour or daytime BP. In contrast, home BP was more closely associated with the risk of carotid atherosclerosis than any of the ambulatory BPs. These results led the authors to conclude that the clinical significance of ABPM and SBPM for predicting target organ damage may differ for different target organs. Although the reasons for the differential association of ambulatory BP and home BP with the 2 measures of target organ damage are not readily apparent, these data indicate that both pressures may be equally important for stratification of the cardiovascular risk. Previous studies showed some differences in the relationship of ambulatory BP and self-measured BP with organ damage but no evidence of any systematic difference in favor of one or the other out-of-office pressure.8 Inconsistencies in the literature may depend on the number of readings used to compute self-measured BP, which, in some studies, was only measured twice, thereby favoring a better relationship of target organ damage with ambulatory BP. A strength of the study of Hara et al7 is the large number of BP readings (mean: 49) used to calculate home BP, which was comparable to that collected during the 24-hour recordings (mean: 44). This ensures that the different associations with measures of organ damage were not attributed to a different number of readings used to calculate the 2 pressures and suggests that the 2 methods have a supplementary, rather than a competitive, role in the assessment of hypertensive patients. The above data are in keeping with those obtained in the PAMELA Study.6 In that prospective study, the risk of cardiovascular death showed a progressive increase in the patients with a selective clinic BP elevation, a selective out-ofoffice BP elevation, and elevation in both clinic and out-ofoffice BP. The progressive increase in mortality from the entirely normotensive to the entirely hypertensive group occurred regardless of whether the above conditions were identified based on clinic versus ambulatory or clinic versus home BP. In addition, selective elevation in home versus ambulatory BP or vice versa also carried an increased risk. Indeed, in the The opinions expressed in this editorial are not necessarily those of the editors or of the American Heart Association. From the Department of Clinical and Experimental Medicine, University of Padova, Padua, Italy. Correspondence to Paolo Palatini, Clinica Medica 4, University of Padova, via Giustiniani, 2-35128 Padova, Italy. E-mail [email protected] (Hypertension. 2012;59:2-4.) © 2011 American Heart Association, Inc.