Pragmatic Method Using Blood Pressure Diaries to Assess Blood Pressure Control

The purpose of this study was to provide physicians with a pragmatic method to quickly and accurately assess blood pressure control from patient home blood pressure (HBP) diaries. The superior prognostic utility of HBP and ambulatory blood pressure (ABP, the reference standard) monitoring over clinical blood pressure (CBP) has been well documented. However, these methods are limited by physician time constraints in the standard consultation, notably the requirement for manual calculation of the average of multiple values from patient diaries. The authors sought to determine the optimal percentage of home systolic blood pressure readings above threshold (>135 mm Hg) for the last 10 recorded to denote blood pressure control (confirmed by ABP). The best predictor of uncontrolled blood pressure was >3 elevations of the last 10 home systolic blood pressure readings (>30%), and patients meeting this criterion also demonstrated statistically significant differences in markers of target organ disease associated with hypertension. The authors propose that physicians utilize this method to assess data from HBP diaries and tailor management accordingly.

In the introduction, the authors acknowledge that CBP is widely used for patient management despite its potential limitations in accurately reflecting true underlying blood pressure. The student discussion group unanimously supported this statement. One student shared that his own blood pressure is consistently elevated when taken in a clinical setting, while another student expressed discomfort with altering management based on one reading. Also in the introduction, the authors reference alternative methods of blood pressure assessment (i.e. 7-day HMP and 24-hour ABP) with superior prognostic utility with respect to target organ disease. Interestingly, many of the students were not familiar with these alternative methods, despite the claim that "HMP has an advantage of already being in wide use." The group, aware that this study was conducted in Australia, discussed the possibility that variations in clinical practice between our country (U.S.) and other countries could factor into our limited breadth of knowledge of the subject matter. This notion is supported by the fact that HBP is ignored as a clinical tool in U.S. guidelines for the management of high blood pressure in adults, as alluded to by the authors in their discussion. However, at least two students were able to empathize with the study: both presented with a HBP diary the past week, and neither with a pragmatic method to interpret the data.

This is a cross-sectional study; measurements of mean ABP, HMP values, and markers of target organ disease were consecutively acquired in the shortest time frame possible (approximately 10 days). A total of 286 patients being treated for hypertension by their primary care physicians were recruited in 3 Australian centers as part of a randomized clinical trial. Patients were recruited through general practice clinics and community advertisements. The authors did not specify how general practice clinics were targeted, which increases the difficulty to reproduce the study. Additionally, the group would have liked to see what percentage of patients recruited agreed to participate as a means to assess motivation to commit to undertaking HBP (duplicate readings 3 times per day for 7 days per protocol). Sample size was rather small, although the group recognized the potential burden in evaluating markers of target organ disease. Patients were eligible for inclusion if they were non-pregnant adults receiving antihypertensive therapy for noncomplicated essential hypertension and taking no more than 3 antihypertensive drugs. These inclusion criteria may induce some selection bias (e.g. elderly patients are more likely to be seen by a physician for all causes, in turn increasing the likelihood that hypertension is identified, diagnosed, and treated), and this bias may be supported by the fact that 80% of study participants were >60 years old. The group felt the exclusion criteria were appropriate.

In defining uncontrolled blood pressure, the authors considered two definitions: 24-hour ABP systolic blood pressure >130 mm Hg or 24-hour ABP daytime systolic blood pressure >135 mm Hg. While the student discussion group was able to recognize the value of this approach in determining the optimal cut point, it was unclear as to how these thresholds were chosen; the group would have benefited from an explanation of this (and the validity of these values). Similarly, the group assumed that diastolic blood pressure was not included in the analysis because it is less associated with markers of target organ disease, although this was never explained. The rationale for restriction to the last 10 (rather than 14) home systolic blood pressure readings was thorough. Students were in agreement that this adjustment would make interpretation of HBP diaries more feasible and implementation more practical.

While beyond the scope of most students, the use of multiple indices to compare accuracy of predictions at different binary classifications (Table 2) increased group consensus that the results obtained are reliable and reproducible. The student discussion group also agreed with the authors' reconciliation of the optimal cut point (validation analysis) using markers of target organ disease associated with hypertension. However, many students did not fully understand the clinical utility of these markers. One student mentioned that the inclusion of normal values in Table 1 or Table 3 would have helped him interpret the meaning of these markers of target organ disease in addition to their relationship to the cut points.

Students also probed the validity of the cardiovascular measures selected by the authors to assess target organ disease, cardiovascular events, and cardiovascular and all-cause mortality. Heart failure may be due to either systolic or diastolic dysfunction of the left ventricle. While both are characterized by elevated left ventricular filling pressure, ejection fraction can be reduced (HFrEF) or preserved (HFpEF) depending on the underlying etiology. HFpEF is characterized by diastolic dysfunction and mild systolic dysfunction, and is an increasingly common form of cardiac disease associated with aging (64 + 8 years in present study), obesity (BMI 29.4 + 4.8 in present study), and hypertension. Although ejection fraction is preserved at rest, enhancement in ejection fraction with stress is markedly limited in HFpEF.[1] In the present study, all cardiovascular measures of target organ damage were obtained at rest; consequently, the data may be inadequate in identifying significant pathologies that exist. If this study were to be repeated, the prognostic yield could be greatly increased by including measurements of ejection fraction during locomotion. Furthermore, population-based studies over the past decade have shown that many patients with HFpEF have either concentric remodeling in the absence of hypertrophy, or even normal LV geometry.[2,3,4] These findings may limit the prognostic utility of certain cardiovascular measures (e.g. relative wall thickness, left ventricular ejection fraction, etc.) with respect to cardiovascular and all-cause mortality. Such limitations warrant discussion by the authors, and may even support the recommendation of >4 elevations of the last 10 home systolic blood pressure readings (>40%) as the best predictor based on the fact that this cut point produced the greatest difference of means for left ventricular filling pressure (an acceptable marker of HFpEF).

1. Borlaug, B. A. Pathophysiology of HFpEF. Nat. Rev. Cardiol. 11, 507-515 (2014).
2. Lam, C. S. et al. Cardiac structure and ventricular-vascular function in persons with heart failure and preserved ejection fraction from Olmsted County, Minnesota. Circulation 115, 1982-1990 (2007).
3. Borlaug, B. A., Lam, C. S., Roger, V. L., Rodeheffer, R. J. & Redfield, M. M. Contractility and ventricular systolic stiffening in hypertensive heart disease insights into the pathogenesisof heart failure with preserved ejection fraction. J. Am. Coll. Cardiol. 54, 410-418 (2009).
4. Zile, M. R. et al. Prevalence and significance of alterations in cardiac structure and function in patients with heart failure and a preserved ejection fraction. Circulation 124, 2491-2501 (2011).

Competing interests: None declared