How to Use BP Monitor?
Several studies showed that 24-h ABPM better correlates with cardiovascular outcome than clinic BP levels (, ). In a substudy of the Systolic Hypertension in Europe (Syst-Eur) Trial, Staessen et al. showed that in elderly subjects with untreated isolated systolic HTN, ambulatory systolic BP was a significant predictor of cardiovascular risk over and above clinical BP values. In a prospective cohort study that included 1, 464 subjects who were followed for 6.4 years, Ohkubo et al. showed that ambulatory BPs were significantly better related to stroke risk than were screening office BP levels. Recently, Hara et al. showed in 1, 007 subjects that 24-h daytime and nighttime ambulatory BP values were closely associated with the risk of silent cerebrovascular lesions detected by brain magnetic resonance imaging, whereas the clinic B values were not associated with subclinical cerebrovascular events. Of the ambulatory BP values, nighttime BP was the strongest predictor of silent cerebrovascular events.
Comparison of ambulatory BP measurements with home measurements.
Home BP monitoring (HBPM) offers an attractive alternative to 24-h ABPM. Several studies have reported that target organ damage and cardiovascular outcomes are more strongly correlated with HBPM than with clinic BP measurements (–). HBPM provides measurements over a much longer period, is cheaper, more widely available, more convenient for patients (particularly for repeated measurements), and has been shown to improve patients’ compliance with treatment and HTN control. However, unlike ABPM it does not allow the assessment of BP during sleep or at work or the quantification of short-term BP variability. In addition, the recommendation to measure BP at home may induce anxiety that leads to excessive measurements and treatment changes made on the basis of erroneous measurements. A recent meta-analysis showed that HBPM and clinic BP measurements have insufficient sensitivity and specificity compared with 24-h ABPM to be used as a single test for diagnosing HTN in adults. It seems that HBPM should be used in conjunction with ABPM as a complementary method of BP assessment. When there is a concordance between the methods, HBPM may be appropriate for long-term follow-up of treated HTN patients.
Identification of white coat HTN.
The term white coat HTN (WCH) was originally used to describe subjects who are not receiving antihypertension treatment and have elevated office BP but normal 24-h ABPM. More recently, the term WCH is erroneously used with regard to patients who receive antihypertension treatment. The cardiovascular risk of patients with WCH is relatively low, and many studies have shown that the risk of these patients is very similar to the risk of normotensive subjects. It has been shown that in patients with WCH, antihypertensive treatment does not lower ambulatory BP levels and has no effect on cardiovascular morbidity and mortality. Many studies showed that WCH carries a more benign prognosis than sustained HTN, even in diabetic patients (, ). However, in some studies the risk of diabetic patients with WCH was significantly higher than the risk in normotensive subjects. This may be related to the high risk of developing true HTN in patients with WCH. Therefore, repeated 24-h ABPM should be done in subjects with WCH. A recent study suggests confirmation of a white coat effect with repeated 24-h ABPM within 3 months. In those with confirmed white coat effect, a 24-h ABPM follow-up should be done every 6–12 months depending on the BP values recorded during the ABPM. When office BP levels are elevated, 24-h ABPM should be done to confirm the diagnosis of HTN. When the subject is not medicated and the ABPM is normal, a diagnosis of WCH can be made. When the patient is medically treated and the ABPM is normal, the best definition is “treated normalized HTN”. When office BP is elevated and ABPM levels are less elevated than office levels, the best term is white coat effect. When office and ABPM are elevated to the same extent, a diagnosis of true HTN should be made. WCH is also associated with a long-term greater progression of blood glucose abnormalities and an increased risk of developing diabetes and may represent increased susceptibility to future weight gain and dyslipidemia (, ). This is largely accounted for by the metabolic abnormalities that are frequent components of this condition. WCH may be present in as many as 20% of subjects who appear to have HTN according to office measurements. WCH seems to be less frequent in the context of type 2 diabetes, and its impact on cardiovascular complications remains controversial. However, in a recent large study WCH was present in 33% of the diabetic patients. These subjects may receive long-term unnecessary and expensive drug treatment. Thus, the only way to prevent overdiagnosis of HTN is to confirm it by 24-h ABPM.Figure 1
Possible diagnosis of patients with elevated office BP levels according to ABPM. SBP, systolic BP; DBP, diastolic BP.
Identification of masked HTN.
Masked HTN is defined when office BP levels are normal in an untreated subject and ABPM levels are elevated. This condition is present in ~10–20% of subjects who are considered to be normotensive according to office BP measurements. Masked HTN is more common in diabetic patients, and it may be present in one of two subjects with type 2 diabetes and apparently normal office BP. Several studies have shown that the cardiovascular risk in patients with masked HTN is elevated and similar to the risk in patients with sustained HTN (, ). This condition should be identified and treated adequately to control BP. Yet, it is not practical to perform ABPM in all normotensive subjects to reveal masked HTN. Therefore, ABPM should be done only in normotensive subjects who are likely to have masked HTN, such as those with evidence of target organ damage (left ventricular hypertrophy, renal failure, and microalbuminuria), those with occasional elevated BP readings, and those with exaggerated BP response to exercise (, ).
Physiologically, BP falls by >10% during nighttime (asleep). When BP falls by 20% in BP during sleep time is known as extreme dipping. This pattern is not necessarily benign, since it may be associated with mild cognitive impairment in the elderly.
ABPM guiding management of HTN.
ABPM may guide management of HTN. Progressive decrease in sleep BP in nondipping patients reduces cardiovascular morbidity and mortality and therefore should be a therapeutic target. Achieving this target requires proper patient evaluation by 24-h ABPM. Bedtime treatment will be clearly indicated in patients with a nondipping pattern, whereas in extreme dippers evening dosing should be avoided.