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The relative contributions of adherence and treatment intensity to blood pressure (BP) control are not well understood. The authors studied patients with uncontrolled hypertension (N=410) from 3 primary care clinics in the Veterans Affairs (VA) medical system. A questionnaire was used to assess patient adherence to therapy, and VA system pharmacy fills were used to assess the intensity of the antihypertensive regimen. At baseline, an inadequate antihypertensive regimen was implicated as the most probable reason for uncontrolled BP in a majority of patients (72%), while nonadherence could only be implicated in 13%. In multivariate longitudinal analyses, patients who had an increase in their medical treatment during the study had lower final diastolic BP levels compared with the patients who did not (−3.70 mm Hg; P<.05). While patient adherence to therapy plays a role, vigorous clinical management by the clinician is a more important contributor to BP control.
Despite concerted efforts to improve the treatment of hypertension, only 64% of the hypertensive patients in the United States who were treated in 2003 and 2004 had controlled blood pressure (BP) (<140/90 mm Hg).1 There are 3 main causes of failure to control BP despite therapy: patient nonadherence, insufficient titration of therapy, and resistant disease. A large body of research has documented the contribution of patient non-adherence to poor control in many chronic conditions, including hypertension.2–4 More recently, a growing body of literature has also documented clinician failures to escalate therapy to bring a chronic condition under control.5–7 Hypertension is only one of many chronic conditions to be affected by this failure to appropriately titrate therapy, which Phillips and colleagues8 have called “clinical inertia.” Finally, it has long been recognized that some patients have resistant hypertension, which is defined as a BP level that remains >139/89 mm Hg despite apparently adequate adherence and therapeutic intensity.9,10 Understanding the relative contributions of these factors to uncontrolled hypertension is important for designing effective interventions to improve hypertension control; however, no previous study has addressed this issue in a primary care population.
We undertook this prospective cohort study of a group of patients from the Veterans Affairs (VA) medical system with uncontrolled hypertension to address 2 questions. First, what proportion of patients with uncontrolled hypertension had poor adherence, inadequate management, or neither of these? Second, would patient adherence and treatment intensity predict BP control at the end of the study? By addressing these questions, we sought to address the relative impact of poor adherence and treatment intensity on BP control.
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There were 410 patients with baseline uncontrolled hypertension (group 1) in our study cohort (Table III). Of these 410 patients, 17% were on adequate regimens, while 67% were on <3 medications and 16% were on ≥3 medications but at inadequate doses or without the use of a diuretic. The 338 patients whose therapy was inadequate at baseline in light of their uncontrolled BP formed a second group for analysis (group 2). During the 2-year study period, 51% of the patients experienced a change in their medical regimens with an increase in medication.
Table III. Baseline Characteristics of the Cohorta
|Characteristic||Group 1 (n=410)||Group 2 (n=338)|
| 64 or younger||173 (42)||136 (40)|
| 65–74||131 (32)||109 (32)|
| 75 or older||106 (26)||93 (28)|
|Initial systolic BP, mean (SD), mm Hg||155.0 (13.9)||155.0 (13.8)|
|Initial diastolic BP, mean (SD), mm Hg||80.2 (11.9)||80.6 (11.9)|
|<0.5 BP measurements per month||131 (32)||117 (35)|
| Non-Hispanic black||236 (58)||191 (57)|
| Non-Hispanic white||174 (42)||147 (43)|
|Obesity (body mass index ≥30)||200 (50)||152 (46)|
|Diabetes mellitus||189 (46)||145 (43)|
|Coronary artery disease||192 (47)||151 (45)|
|Renal disease||105 (26)||78 (23)|
|Values are expressed as No. (%) unless otherwise indicated. aGroup 1 is all patients with uncontrolled blood pressure (BP) at baseline, while group 2 is the subset of group 1 who also had inadequate therapy at baseline considering their uncontrolled BP.|
The average patient was followed for 438 days, with 95% of the sample having at least 221 days of data. The median patient had 12 BP values during the study; 95% of the sample had at least 5 BP values. The average age was 66.5 years, and more than half of the patients (58%) were black. The prevalence of comorbid conditions was high; only 27% of the patient population did not have at least 1 of 3 comorbidities, namely diabetes, renal disease, and coronary artery disease. Also, 49% of the sample was obese.
Fifty-two (13%) patients endorsed ≥2 of the adherence questions and were thus labeled as poorly adherent with their therapy. Of the adherent patients, 297 (72%) were on an inadequate regimen of antihypertensive medications considering their BP . Sixty-one patients (15%) with uncontrolled hypertension did not report poor adherence and were on an adequate regimen of medications. These patients were considered to have resistant hypertension, presumably due to physiologic factors.
The mean final BP level in the entire sample was 142/75 mm Hg, a marked improvement from the initial mean level of 155/80 mm Hg. When we examined the subset of patients with inadequate therapy at baseline despite their uncontrolled hypertension (n=338), none of our independent variables significantly predicted the final systolic BP. Higher treatment intensity, however, significantly predicted a lower diastolic BP level in adjusted analyses (Table IV).
Table IV. Predictors of Follow-Up Systolic and Diastolic BP Levels in Patients With Uncontrolled BP and Inadequate Therapy at Baselinea
| ||SBP (95% CI)||DBP (95% CI)|
|Poor adherence to medication||0.19 (−6.18 to 6.56)||0.18 (−3.49 to 3.85)|
|Any change in therapy vs none||−2.83 (−7.05 to 1.38)||−3.70 (−6.13 to −1.28)b|
|Baseline SBP or DBP (per mm Hg)||0.43 (0.27 to 0.58)b||0.35 (0.24 to 0.46)b|
|<0.5 BP measurements per mo||1.78 (−2.86 to 6.42)||−0.15 (−2.75 to 2.46)|
|Age (oldest vs youngest)||3.61 (−4.11 to 11.33)||−5.48 (−10.07 to −0.89)b|
|Age (moderate vs youngest)||−0.95 (−8.06 to 6.17)||−5.49 (−9.66 to −1.33)b|
|Body mass index ≥30||0.68 (−3.59 to 4.95)||0.78 (−1.68 to 3.24)|
|Diabetes mellitus||2.89 (−1.53 to 7.30)||−1.12 (−3.67 to 1.42)|
|Coronary artery disease||−0.93 (−5.17 to 3.32)||0.26 (−2.20 to 2.72)|
|Renal disease||1.50 (−3.75 to 6.75)||−1.41 (−4.42 to 1.60)|
|Black race||0.03 (−4.57 to 4.63)||0.50 (−2.09 to 3.09)|
|aResults from multivariate linear regression models, accounting for site of care as a random effect. bResults are significant at the .05 level (n=338). β-Coefficients are expressed in units of mm Hg; a β-coefficient of +1.0 indicates a 1.0-mm Hg increase in final blood pressure (BP). Abbreviations: CI, confidence interval; DBP, diastolic BP; SBP, systolic BP.|
Controlled BP (<140/90 mm Hg) was achieved in a substantial proportion of the cohort (46%) by the end of the study. In bivariate analyses, BP control was achieved in patients with poor adherence 33% of the time by the end of the study, compared with 47% for the other patients (P=.04). In patients with inadequate therapy at baseline, after adjustment for covariates (Table V), this result was no longer statistically significant (odds ratio, 0.52; 95% confidence interval, 0.25–1.09; P=.08).
Table V. Predictors of Follow-Up BP Control in Patients With Uncontrolled BP and Inadequate Therapy at Baselinea
| ||OR||95% CI|
|Poor adherence to medication||0.52||0.25–1.09|
|Any change in therapy vs none||1.23||0.77–1.96|
|Initial systolic BP (per mm Hg)||0.965||0.947–0.983b|
|Fewer than 0.5 BP measurements per mo||0.99||0.60–1.64|
|Age (oldest vs youngest)||0.65||0.27–1.53|
|Age (moderate vs youngest)||1.23||0.56–2.67|
|Body mass index ≥30||0.82||0.52–1.32|
|Coronary artery disease||1.08||0.68–1.73|
|aResults of a multivariate logistic regression analysis accounting for site of care as a random effect. bResults are significant at the .05 level (n=338). Odds ratios (OR) >1.0 indicate a higher likelihood of controlled blood pressure (BP) at the end of the study. Abbreviation: CI, confidence interval.|
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We compared the effects of patient adherence and clinician management of hypertension on the initial and follow-up BP of a group of patients in the VA medical system. Our baseline analysis suggests that inadequate treatment intensity, or clinical inertia, is the most common reason for uncontrolled hypertension (72%). In addition, in longitudinal analyses, increased treatment intensity was associated with a lower final diastolic BP level, while the effects of adherence were not statistically significant.
Only limited research has compared the relative contributions of patient adherence, clinical inertia, and resistant hypertension with the failure to control the BP in hypertensive patients receiving pharmacotherapy. Two case series document the experience of a single hypertension referral center.17,21 These studies found that an inadequate medical regimen was the most common cause of uncontrolled hypertension on referral to their clinic (58%), followed by poor adherence as the second most common cause (16%); these proportions are similar to what we found. In a smaller but intriguing study, Javors and Bramble22 reviewed the care of 30 patients with various chronic conditions to investigate the relative effects of guideline-based management and patient adherence on long-term control. In their study, BP in the majority of patients was not well controlled, and clinician failure to adhere to guideline-based management was strongly predictive of uncontrolled disease. Patient adherence was generally high in their sample and did not predict control of the chronic conditions. Like their study, ours suggests that vigorous clinical management may contribute more to the control of chronic conditions than patient adherence to therapy.
It is of interest to note that in a recent Harris Survey, >90% of hypertensive patients reported that they were receiving antihypertensive therapy but, consistent with other reports, >30% did not have their medication increased despite continued elevated BP levels.23
In part, our study examined clinician adherence to JNC 6 guidelines, which were current at the time of this study, regarding BP goals and what constitutes a reasonable regimen for resistant hypertension.12 JNC guidelines have been widely disseminated for many years, but there is some evidence that clinicians may not be aware of them or may not agree with all of their recommendations. In a physician questionnaire study published in 2000, Hyman and Pavlik24 showed that in contrast to the JNC 6 recommendation to intensify therapy when the BP level exceeds 139/89 mm Hg, 25% of physicians would not intensify therapy for a diastolic BP level of 94 mm Hg and 33% would not intensify for a systolic BP level of 158 mm Hg. In their study, 41% of physicians were not familiar with the JNC guidelines, and such nonfamiliarity was associated with higher treatment thresholds.24 Recent improvements in meeting BP targets in the VA system25 may attest to increasing clinician acceptance of the 140/90 mm Hg threshold to intensify therapy.
Some strengths of our study should be noted. Ours was a multisite study including many practitioners, extending the generalizability of the results. In addition, unlike previous studies on this issue, our patients were seen in a primary care environment, the setting in which most hypertension is managed.
Our study also had several limitations, however. First, we analyzed only male patients due to the predominantly male patient population in the VA system and a high percentage of patients were black. Similarly, the VA population tends to be older and have more comorbidities than the US population, and our study is no exception.
Second, our adherence data were collected by patient report, which is a limitation although this has been shown to be a reliable measure of adherence.4,15 There are other ways to measure patient adherence to medication, including medication possession ratios, which are derived from the frequency of pharmacy fills. Recent reports have cast doubt on the continued validity of such measures in the VA system, however, especially because many prescriptions are refilled automatically by mail and thus are not a reflection of patient adherence.26
Third, we used clinical BP values, rather than obtaining BP through a standardized research protocol. Since we were studying clinician behavior, however, it makes sense that we should analyze the same BP values that guided the actual decisions about whether to escalate therapy. Fourth, sample size limited our ability to detect some effects, especially with regard to systolic BP.
Fifth, regression to the mean, as well as secular trends of improving BP control at the VA, probably accounted for some of the impressive reduction in mean BP level during the study (ie, from 155/80 mm Hg to 142/75 mm Hg). The VA has incorporated BP control to <140/90 mm Hg as a performance measure during the past 5 years, and the attainment of this goal in the VA has increased during this period.25 Since all patients would be equally affected by secular trends and regression artifact, however, this does not lessen the validity of our results.
Sixth, many of our patients had only moderately uncontrolled BP; the mean BP level was 155/80 mm Hg at study inception and 142/75 mm Hg at the end of the study. We might have found a different relationship between the effects of adherence and treatment intensity on BP control in a population with more severely uncontrolled hypertension, and our results may not apply to such patients.
Finally, our methods of analysis might have muted the effects of some predictors. For example, many studies have found that patients on more vigorous regimens actually have higher BP due to confounding by indication.27 One way around this limitation is to compare observed with expected treatment intensity, as was done by Berlowitz and colleagues6 We did not have the data to pursue such a strategy. Although we found that any increase in the therapy was associated with a lower final diastolic BP, we might have found a more robust effect had we used methods to limit confounding by indication.