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Home Monitoring of Blood Pressure
Despite the fact that conventional measurement of blood pressure (BP) in the office (OBP) has been the cornerstone for hypertension diagnosis and management for decades, it is recognized that this method might often be misleading, mainly because of the white-coat and masked hypertension phenomena, which are common among both untreated and treated subjects. Furthermore, the small number of BP readings, the usually unstandardized setting and conditions, and the observer bias and error, further weaken the reliability of OBP in the diagnosis and management of hypertension.
In the last decades, self-monitoring of BP by patients at home (HBPM) and 24-hour ambulatory BP monitoring (ABPM) have both gained ground compared with OBP for hypertension management, aiming to overcome the abovementioned drawbacks. These methods have major similarities, because they both provide multiple measurements taken in the individual’s usual environment. However, they have also important differences, as HBPM is performed only at home and in the sitting posture, whereas ABPM is performed in ambulatory conditions, at work, at home and during sleep. Therefore, it is still debated whether their role in the clinical management of hypertension is interchangeable or complementary.
The clinical value of ABPM is strongly supported by evidence from short-term and longitudinal trials, whereas HBPM has been less well investigated. However, evidence has recently accumulated from studies investigating the diagnostic value of HBPM and its association with target organ damage and cardiovascular risk, aiming to support the utility of this method as an indispensable tool for the initial evaluation of elevated BP, for treatment initiation and adjustment, as well as for long-term follow-up of treated hypertension.
Advantages and Limitations
Table 10.1 presents the main advantages and limitations of HBPM. HBPM is widely available and well accepted by patients for long-term use, it has superior reproducibility to OBP and similar to ABPM, identifies the white-coat and the masked hypertension phenomena allowing accurate diagnosis of hypertension, and improves long-term compliance with treatment and thereby hypertension control rates. On the other hand, HBPM requires patient education and training, as well as the use of validated devices. In addition, patients often misreport their self-taken BP readings, which is the “Achilles’ heel” of HBPM and might lead in overtreatment or undertreatment, especially in high risk hypertensives or those with high BP variability. It should be mentioned that even if HBPM is performed under ideal circumstances, it only provides BP readings at home and in the sitting posture under fully standardized conditions and thus not representing the dynamic behavior of BP during usual daily activities.
TABLE 10.1
Advantages and Limitations of Home Blood Pressure Monitoring
| Advantages | Limitations |
|---|---|
|
|
BP, Blood pressure, PC, personal computer.
Clinical Indications
The main clinical indications for HBPM include the detection of white-coat and masked hypertension, identification of white-coat reaction and masked hypertension effect in treated hypertensives, overcoming considerable variability of OBP over the same or different visit(s), identification of true and false resistant hypertension.
Several previous cross-sectional studies have investigated the diagnostic performance of HBPM by taking ABPM as reference. Most of these studies have looked at selected diagnostic phenotypes of hypertension (sustained, white-coat, masked, or resistant) and included populations with different characteristics (untreated subjects, treated hypertensives, patients with type 2 diabetes, chronic kidney disease). Overall, these data suggest considerable diagnostic agreement between the two methods ranging from about 70% to 90%, with consistently high specificity and negative predictive value (>80%) and lower sensitivity and positive predictive value (60% to 70%). One of these studies examined the diagnostic accuracy of HBPM separately in 613 untreated and treated subjects and reported that the sensitivity for hypertension diagnosis varied between 48% and 100% in untreated subjects and 52% and 97% in treated subjects and specificity between 44% and 93% and 63% and 84% respectively. Another study in resistant hypertension also showed that HBPM was a reliable alternative diagnostic method to ABPM. These findings should be interpreted with caution because they are based on the assumption that ABPM, which was used as reference method, is perfectly reproducible and reliable, which certainly is not the case. Moreover, the diagnostic disagreement between the two methods is mostly present in subjects whose BP levels are very close to the diagnostic thresholds, and is probably attributed, to a great extent, to the imperfect reproducibility of all BP measurement methods.
As mentioned previously, the usefulness of HBPM is manifested through the identification of white-coat and masked hypertension phenomena, which remain undiagnosed and inadequately treated when considering exclusively OBP measurements. White-coat hypertension is defined by normal HBPM (<135/85 mm Hg) but elevated OBP values (≥140/90 mm Hg), thus not truly reflecting the “true” BP of an individual. These individuals should not be considered as normotensives because they present an intermediate cardiovascular risk between normotensives and hypertensives and are more likely to develop sustained hypertension within the next years. On the other hand, masked hypertensives have elevated HBPM (≥135/85 mm Hg) but normal OBP levels (<140/90 mm Hg), and present higher prevalence of preclinical target organ damage and increased cardiovascular risk, similar to that of the sustained hypertensives. The masked hypertension phenomenon is also frequent in treated hypertensives (masked uncontrolled hypertension). In these patients OBP measurements often reflect the peak effect of morning antihypertensive drug treatment on BP, whereas morning and evening HBPM readings can reveal trough or plateau effect respectively. When the diagnosis of these phenomena is confirmed by repeat OBP and HBPM or ABPM, treatment adjustment should be considered, particularly in subjects with high cardiovascular risk.
Prognostic Value
Association With Target-Organ Damage
Preclinical organ damage is recognized as an intermediate stage in the continuum of the cardiovascular disease and its presence indicates increased cardiovascular risk while assessing asymptomatic hypertensive subjects. Several cross-sectional studies have evaluated the association of HBPM with indices of preclinical target-organ damage including the heart, large arteries, and kidneys. Two recent metaanalyses included studies that evaluated the association of HBPM with preclinical target-organ damage. The first one examined the association of HBPM versus OBP and ABPM with indices of organ damage. Most of the available data regarded echocardiographic left ventricular mass index and analysis of 10 studies revealed stronger correlation coefficients for HBPM versus OBP (systolic/diastolic, pooled r = 0.46/0.28 versus 0.23/0.19 respectively). Data from nine studies indicated similar coefficients for HBPM and ABPM. Less evidence was available for carotid intima-media thickness, pulse wave velocity and urine protein excretion, with a consistent trend towards stronger coefficients for HBPM than OBP, with the latter not reaching statistical significance. The second metaanalysis included more data and demonstrated that HBPM is a stronger determinant of proteinuria than OBP.
Prediction of Cardiovascular Events
The superiority of HBPM over OBP in determining target-organ damage confirms the hypothesis that HBPM better reflects the true BP status; yet this superiority refers to intermediate (surrogate) endpoints and, by itself, does not imply superiority in terms of cardiovascular risk stratification or prediction of outcome (cardiovascular events or deaths). Indeed, the ultimate criterion to identify a useful method for the assessment of a cardiovascular risk factor in clinical practice is its actual ability to predict future cardiovascular events. Two metaanalyses have investigated the evidence sourced from outcome trials in the general population, in primary care and in hypertensive patients and assessed the prognostic ability of HBPM compared with OBP measurements. Both were based on data from eight prospective studies and 17,688 patients followed for 3.2 to 10.9 years, which resulted in the availability of information based on almost 100,000 person/years of follow-up, and showed HPBM to be superior to OBP measurements, with this difference being beyond chance for systolic BP. Moreover, in the metaanalysis by Ward et al, HBPM remained a significant predictor of cardiovascular mortality and cardiovascular events even after adjusting for OBP, suggesting its independent prognostic value over and beyond that of OBP. However, one major limitation of the abovementioned metaanalyses was that these were based on aggregate data.
In 2012, the International Database of HOme blood pressure in relation to Cardiovascular Outcome (IDHOCO) was constructed using individual participants’ data of published population studies (n = 6753, mean follow-up 9.2 years) that evaluated the prognostic value of HBPM. One of the major findings of this analysis was that HBPM substantially refined risk stratification at OBP levels assumed to carry no or only mildly increased risk, in particular in the presence of masked hypertension. More specifically, in participants with optimal or normal OBP, hazard ratios for a composite cardiovascular endpoint associated with a 10-mm Hg higher systolic home BP were 1.28 (95% CI 1.01 to 1.62) and 1.22 (1.00 to 1.49), respectively. At high-normal OBP and in mild hypertension, the hazard ratios were at about 1.20 for all cardiovascular events and 1.30 for stroke. A further analysis of the same dataset was performed separately in untreated and treated subjects. Among untreated subjects, cardiovascular risk was higher in those with white-coat hypertension (adjusted hazard ratio 1.42), masked hypertension (1.55) and sustained hypertension (2.13) compared with normotensive subjects. Among treated patients, the cardiovascular risk did not differ between those with high office and low home BP (white-coat) and treated controlled subjects (low office and home BP). However, treated subjects with masked hypertension (low office and high home BP) and uncontrolled hypertension (high office and home BP) had higher cardiovascular risk than treated controlled patients.
In conclusion, HBPM has independent prognostic value and allows more accurate risk stratification than OBP, particularly in cases with masked hypertension.
Home Blood Pressure Monitoring and Management of Hypertension
Treatment Adjustment
As mentioned earlier, the diagnostic accuracy of HBPM in identifying the hypertension phenotypes, as well as the prognostic significance of these phenotypes detected by HBPM in untreated and treated subjects, have rendered this method very important for treatment initiation and titration.
The association between treatment-induced changes in home, ambulatory, and office BP and treatment-induced changes in indices of preclinical organ damage has been investigated in two studies. In the Study on Ambulatory Monitoring of Blood Pressure and Lisinopril Evaluation (SAMPLE) in 206 hypertensives followed for 12 months, the treatment-induced regression in left ventricular hypertrophy was more closely associated with treatment-induced changes in ambulatory than in office or home BP. However, only two HBPM readings were obtained in this study, in contrast to the recommended minimum 3-day schedule and therefore the potential of HBPM was not exhausted. Another study in 116 hypertensives with 13.4 months follow-up, showed that treatment-induced changes in both 24-hour ABPM and 7-day HBPM were more closely related than OBP measurements with treatment-induced changes in organ damage (left ventricular mass index, pulse wave velocity, albuminuria). Interestingly, there were differences between HBPM and ABPM in their associations with the changes in different indices of organ damage, which implies that these methods are complementary rather than interchangeable in monitoring the effects of antihypertensive treatment on target-organ damage.
Nine randomized studies assessed treatment adjustment based on HBPM compared with OBP (seven studies) or ABPM (two studies). It should be noted that there are important differences among these studies regarding the inclusion criteria, population characteristics, BP measurement methodology, BP goals, and duration of follow-up. Three of the studies used the same threshold for OBP and HBPM, which is not in line with current guidelines and led to inferior BP control with HBPM. Four other studies showed larger BP decline with treatment adjustment based on HBPM rather than OBP measurements. Two studies compared HBPM versus ABPM for treatment adjustment. The first in 98 subjects followed for 6 months found no difference in BP control when using HBPM or ABPM. The second one randomized 116 subjects to treatment initiation and titration based either on HBPM alone or on combined use of OBP and ABPM. After an average follow-up of 13.4 months there was no difference between the two arms in BP decline and hypertension control assessed by HBPM or ABPM and, more important, there was no difference in treatment induced changes in several indices of preclinical target-organ damage.
Long-Term Follow-Up
HBPM has the unique advantage to enable patients to take multiple measurements not only through a period of days, but weeks, months and even years, and at minimal cost. Moreover, this method motivates the patients by increasing their awareness and rendering them active in their follow-up. The long-term use of HBPM by patients treated for hypertension is recommended by current guidelines, as it enhances their compliance to therapy, and prevents them from adhering to therapy only before an office visit, a phenomenon known as “white-coat adherence,” which is associated with increased cardiovascular risk. However, comparative data regarding the effects of long-term monitoring of treated hypertensives based on HBPM or ABPM are lacking.
Improvement of Patients’ Adherence and Blood Pressure Control
Several randomized controlled trials have shown that treated hypertensives who perform HBPM have improved long-term adherence to drug therapy, and thereby higher hypertension control rates. A systematic review of 72 randomized controlled trials that evaluated the effectiveness of several interventions aiming to improve BP control (HBPM, educational interventions, pharmacist- or nurse-led care, organizational interventions, appointment reminder systems) showed HBPM to be the most efficient method. The MONITOR study in treated uncontrolled hypertensives showed that a two-month HBPM protocol without medication titration led to superior ABPM control than the usual care control group. Another study in 1350 hypertensive patients attending a BP clinic showed that those using HBPM had higher BP control rates.
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