The influence of guideline revisions on the process and outcome of hypertension management in general practice: A descriptive study

Abstract

Background: Blood pressure does not reach guideline targets in the majority of hypertensive patients. Longitudinal data from general practice records on trends in hypertension management and the influence of guideline changes are lacking. Objective: To describe the longitudinal impact of guideline revisions on the process and outcome of hypertension management in a primary care based database. Methods: We extracted data from the Nijmegen Monitoring Project (NMP), an academic practice-based research network with 50 000 patients listed. Based on the years of publication of the first Dutch guideline on hypertension (1991) and two revisions (1997 and 2003), we formed three cohorts of patients newly diagnosed with hypertension. We compared data such as patient characteristics, 2-year blood pressure course, type of first-choice antihypertensive drugs, and number of medications after 2 years of treatment. Results: Both the mean age at time of diagnosis of hypertension and pulse pressure rose between cohorts. In agreement with revisions in the guidelines, the use of diuretics as first-choice drugs increased significantly from the first to the last cohort. The percentage of patients with three or more antihypertensive drugs remained equal. The relative 2-year systolic blood pressure decline did not differ with clinical relevance between the cohorts.

Conclusion: Our study has demonstrated that general practitioners achieve substantial and prolonged blood pressure reduction. However, guideline revisions do not seem to influence the amount of reduction, despite clear formulation of stricter treatment goals. In addition to qualitative research to identify the causes of this phenomenon, research to evaluate the effect of expert support systems on risk awareness and risk gain by additional treatment is necessary.

• Hypertension
• management
• guidelines
• general practice
• quality of care

Introduction

International guidelines on hypertension and cardiovascular risk management stress the importance of strict blood pressure regulation, defining targets that have become increasingly demanding over the last few decades [1–5]. Despite these guidelines, blood pressure decrease–often expressed as control rates–appears to be insufficient. In addition, these rates have improved little in recent decades [6]. Control rates can easily be misinterpreted or misused, because they depend highly on the population and hypertension guideline under study [7], [8]. Therefore, research data on quality of care solely based on control rates need to be scrutinized with caution. The current approach to hypertension in the context of cardiovascular risk management demonstrates a lack of cost effectiveness in “controlling” all hypertensive (≥140/90 mmHg) patients in primary care or the open population [3], [4].

Of course, hypertension management in general practice could be improved. Both patient-related factors (e.g., comorbidity, poor treatment adherence) and doctor-related factors (e.g., lack of knowledge of guideline content, disagreement with guidelines) contribute to substandard treatment of population-based blood pressure [7]. However, it is hard to accept that all the efforts of both researchers and guideline developers to improve blood pressure outcomes seem to have been of little value.

We hypothesized that interpretation of the progress (or lack thereof) of blood pressure management over the last few decades is biased by comparing data of different populations in different settings using different types of guidelines (or using current guideline definitions retrospectively). Therefore, we studied the impact of guideline revisions on the process and outcome of hypertension management in one primary care based database that has continuously and structurally monitored hypertension management since 1986: the Nijmegen Monitoring Project, the Netherlands.

Methods

Database

We extracted data from the Nijmegen Monitoring Project (NMP), a research database involving nine practices. The practices were fully computerized and had approximately 50 000 patients listed in total, with a sex and age distribution representative for the general Dutch population. The historical background of the NMP has been described in further detail in the editorial of this issue.

The database was founded in 1986 to monitor the management of three common chronic conditions: hypertension, diabetes mellitus, and chronic obstructive pulmonary disease. A specific data extraction form was filled in for each condition-related consultation. In the case of hypertension, several aspects were recorded: the diagnostic process; cardiovascular risk factors; type of treatment (with or without medication); initiation of drug treatment; type of medication; changes in medication or dosage; and control/evaluation moments. The quality of the data was ascertained by monthly meetings of representatives of all nine practices on quality control, knowledge, and protocol development, and annual feedback on process and outcome.

Blood pressure management

Practice protocols for blood pressure measurement and management (including diagnosis) of hypertension are based on the guidelines of the Dutch College of General Practitioners (most recent guideline: “Cardiovascular Risk Management”, 2006) [9]. Over the last few decades, protocols have been adjusted when guideline updates contained relevant changes. Since the start of the NMP, the first hypertension guideline and two guideline updates have been published [1–3].

Population and data collection

Based on the year of publication of the original 1991 and revised (1997 and 2003) hypertension guidelines, we formed three cohorts of patients newly diagnosed with hypertension. Patients for cohort 1 were selected in the period 1992–1996; for cohort 2 in the period 1998–2002; and for cohort 3 in the period 2004–2006. Not all hypertensive patients of the NMP practices were included in the study cohorts. Only patients treated with medication, with follow-up data covering a minimum of 2 years, and at least one blood pressure related consultation per year were included.

In Table I, we have summarized the key points of the guidelines used in this study according to four domains. Based on these domains, we have formulated several hypotheses about the expected change in actual diagnosis and management of hypertension in daily practice during the periods under study.

Table I.  Summary points of hypertension guidelines in studied period.

	Guideline 1 (1991) [1]	Guideline 2 (1997) [2]	Guideline 3 (2003) [3]
1. Diagnosis	DBP ≥ 95 mmHg	DBP ≥ 95 mmHg or SBP ≥ 160 mmHg	SBP ≥ 140 mmHg and/or DBP ≥ 90 mmHg
2. Indications medical treatment	DBP criterion for diagnosis and treatment	Both DBP and SBP criteria for diagnosis and treatment	Both DBP and SBP criteria for diagnosis and SBP criterion for treatment
	DBP < 100 mmHg: no medication DBP 100–104 mmHg: medication if two more risk factors present DBP ≥ 105 mmHg: always start medication	DBP < 100 and/or SBP < 160 mmHg: no medication DBP 100–104 and/or SBP 160–180 mmHg: medication if one or more other risk factors present DBP ≥ 105 and/or SBP ≥ 180 mmHg: always start medication	Based on risk function; medication indicated when 10-year absolute risk on cardiovascular morbidity or mortality ≥ 20% Patients with CVD, DM, familial dyslipidaemia, and patients with SBP ≥ 180 or DBP ≥ 100 mmHg: always start medication
3. Target of treatment	DBP < 90 mmHg	DBP < 90 or SBP < 160 mmHg	SBP < 140 (160 in healthy patient of 60 years and older without other risk factors) and DBP < 90 mmHg
4. Medical treatment	No protocol, choice doctor–patient; decision based on comorbidity, costs, and adverse drug events Patients with DM: 1) ACE-inhibitor	Protocols for patients with and without comorbidity Patients without comorbidity: 1) diuretic; 2) beta-blocker; 3) calcium channel blocker	Protocol for patients with and without comorbidity Without comorbidity: 1) diuretic; 2) beta-blocker; 3) ACE-inhibitor Patients with DM: protocol as without comorbidity

DBP: diastolic blood pressure; SBP: systolic blood pressure; CVD: cardiovascular disease; DM: diabetes mellitus; ACE: angiotensin-converting enzyme.

For domain 1, we hypothesized an increase in the prevalence of hypertension and a decrease in the mean age of the cohorts. For domain 2, we expected an increase in the number of people treated with medication (increase in cohort size) and no change in the mean blood pressure at time of diagnosis. For domain 3, we expected an increase in the achieved systolic blood pressure reduction. For domain 4, we hypothesized an increase in the use of diuretics and beta-blockers as first-choice drugs; in addition, we hypothesized an increase in the percentage of patients on two or more types of antihypertensive drugs.

Analysis

Descriptive statistics were used where applicable. We used Mantel-Haenszel chi-square tests to determine significance in trends for variables expressed in percentages. Analysis of variance (ANOVA) testing was used to compare cohorts for differences in continuous variables such as age and blood pressure. All statistical analyses were performed with SAS software, version 9.1.

Results

In the studied period of 1992–2006, 2251 patients were registered with newly diagnosed hypertension by general practitioners (GPs) working in the NMP practices. Of these patients, 2021 (90%) started on medication at the time of diagnosis or the first blood pressure control thereafter. The mean blood pressure was 176/102 mmHg compared to 165/99 mmHg in the 10% of patients without medication.

Two or more years of follow-up data were lacking for 945 patients. In 56% of these patients, the diagnosis of hypertension was made in the last 2 years of cohort period 3, so that it was not possible to obtain 2 years of follow-up data; in 30% of patients, control frequency was irregular and therefore did not meet the inclusion criteria. Other reasons were: patient died (4.1%), patient moved (4.8%), and miscellaneous (5.2%).

An overview of the patient characteristics for each of the three studied cohorts is given in Table II. The mean age rose significantly (p<0.0001); the mean diastolic blood pressure at time of diagnosis decreased significantly (p<0.0001).

Table II.  Characteristics of study population (at time of diagnosis of hypertension).

	Cohort 1 (1992–1996) n=285	Cohort 2 (1998–2002) n=508	Cohort 3 (2004–2006) n=112
Mean (SD) age, years	54.8 (12.3)	59.2 (12.1)	60.3 (12.9) ^φ
Sex,%
Female	58.6	55.5	56.2
Male	41.4	44.5	43.8
Mean (SD) BMI, kg/m^2	27.6 (4.1)	28.5 (4.9)	28.1 (5.2)
Diabetes,%	3.2	15.9	11.6
Mean (SD) SBP, mmHg	175.1 (19.8)	179.0 (19)	175.1 (15.7)
Mean (SD) DBP, mmHg	105.7 (7.4)	101.7 (9.7)	98.7 (8.8)^φ

SBP: systolic blood pressure; DBP: diastolic blood pressure.

^φp<0.0001 for difference between cohorts.

The age-adjusted prevalence of registered hypertension in the NMP practices increased in the last decade, from 5.5% in 1995 and 6.1% in 2000 to 7.0% in 2005.

Table III depicts the 2-year course of blood pressure for all three cohorts. In addition to the absolute decline, the table denotes the relative decline, correcting for the influence of an initial higher blood pressure on the potential of blood pressure decrease. The relative 2-year decline in systolic blood pressure was significantly lower in the first cohort compared to the other two cohorts. In contrast, the diastolic blood pressure decline was significantly lower in the last cohort as opposed to the other two.

Table III.  Two-year course of blood pressure per cohort.

	Cohort 1 (1992–1996) n=285	Cohort 2 (1998–2002) n=508	Cohort 3 (2004–2006) n=112
Mean SBP, mmHg	175.1	179.0	175.1
Mean 2-year SBP, mmHg	150.8	149.9	148.2
▵ SBP, diagnosis – 2 yr, mmHg	24.3	29.1	26.8
%▵ SBP, diagnosis – 2 yr	13.3^φ	15.7	14.9
Mean DBP, mmHg	105.7	101.7	98.7
Mean 2-year DBP, mmHg	88.8	85.6	85.3
▵ DBP, diagnosis – 2 yr, mmHg	16.8	16.1	13.4
%▵ DBP, diagnosis −2 yr	15.6	15.4	13.3*

SBP: systolic blood pressure; DBP: diastolic blood pressure.

^φp=0.002 compared to cohort 2, p=0.190 compared to cohort 3; *p=0.02 compared to cohort 1, p=0.027 compared to cohort 2.

The effect of guidelines on the prescription of types of antihypertensive medication at initiation of treatment can be derived from Table IV. While in cohort 1, beta-blockers were the first choice of treatment, in cohort 3 this had changed in favour of diuretics.

Table IV.  Type of initial drug choice in patients who started on mono therapy.

	Cohort 1 (1992–1996) n=241	Cohort 2 (1998–2002) n=392	Cohort 3 (2004–2006) n=85
Type of drug
ACE-inhibitor	17.0	19.9	10.6
ARB	0	0.3	5.9
Beta-blocker	43.6	37.0	36.5*
CCB	12.9	3.8	3.5
Diuretic	26.6	37.8	43.5^φ
Other	0	1.3	0

ACE: angiotensin-converting enzyme; ARB: angiotensin receptor blocker; CCB: calcium channel blocker.

^φp=0.001 for difference between cohorts; *p=0.121 for difference between cohorts.

In all three cohorts, approximately one-third of all patients were using one hypertensive medication after 2 years of treatment (Table V), and the number of patients on three or more medications was constant (p=0.743).

Table V.  Mono-duo-triple therapy per cohort at time of diagnosis and after 2 years of treatment (in% of patients).

	Cohort 1 (1992–1996) n = 285		Cohort 2 (1998–2002) n=508		Cohort 3 (2004–2006) n=112
	td	2 years	td	2 years	td	2 years
Number of antiHTs
0	0	7	0.2	4.3	1.8	0.9
1	84.6	32.6	77.2	31.1	75.9	44.6
2	15.1	36.8	19.9	42.1	19.6	32.1
≥3	0.4	23.4	2.8	22.4	2.7	22.3^φ

AntiHT: antihypertensive drug; td: time of diagnosis.

^φp=0.743 for difference between cohorts.

Discussion

Summary of main results

Patients in cohort 3 were significantly older and had a significant higher pulse pressure than patients in cohort 1. In accordance with guideline revisions, diuretics became the first-choice drugs. Despite stricter and more clearly formulated treatment goals, the percentage of patients on three or more medications remained constant in all three cohorts. No clinically relevant changes were noted in blood pressure outcome, with 2-year systolic blood pressure reduction ranging from 13.3 to 15.7% (24 to 29 mmHg) between cohorts.

Interpretation of results

To our knowledge, no previous study has longitudinally evaluated hypertension management in general practice based on 15 years of data from the same general practice research network.

The changed perspective from focus on diastolic (1991 guideline) to systolic blood pressure in the context of 10-year absolute cardiovascular risk (2003 guideline) may explain the significant rise in mean age from cohort 1 to cohort 3 [1], [3]. In hindsight, applying current knowledge and guidelines of cardiovascular risk management, it could be that part of the (younger) population of cohort 1 was overtreated.

The rise in the age-adjusted prevalence of hypertension in our study has also been demonstrated in population-based surveys [10], [11]. Part of this rise may be explained by the lower cut-off levels used to define hypertension over the last 15 years. In theory, every lower cut-off level to define hypertension should result in a substantial rise in prevalence. However, general practitioners will often not register a patient to be hypertensive before he or she wants to initiate medical treatment. Therefore, our reported prevalence is substantially lower than those derived from the open population by screening and does not rise steeply [10], [11]. Stricter hypertension definitions do not automatically imply that treatment is initiated sooner. With the introduction in recent years of cardiovascular risk functions, the use of cardiovascular risk factors other than hypertension in the assessment whether antihypertensive medication is indicated has become more refined. However, in essence, this approach was already applied in the 1991 guideline (see Table I).

The outcome of blood pressure management, expressed in terms of relative 2-year systolic blood pressure reduction, did not differ substantially between cohorts. We would like to highlight two possible interpretations of this result. First, although changes in cut-off levels to define hypertension have caused more patients to be labelled as hypertensive, indications for medical treatment have only changed moderately throughout the years, and, for younger patients in particular, seem to even have become less strict. Second, treatment goals have been defined more clearly and have become stricter in the course of guideline revisions. Therefore, although medical treatment should in subgroups of patients be initiated at a later stage than in previous years, if treatment is indicated, it should reach stricter targets. In this respect, the unchanged blood pressure reduction as reported in our study is disappointing. Our results, as shown in Table V, are in agreement with previous studies and show that somehow doctors are reluctant to prescribe three or more antihypertensive medications, even when treatment goals are not reached [12], [13]. However, it is important to stress that the reported blood pressure reduction that was achieved in all three cohorts matches or exceeds that of results in the severely controlled environment of selected patients in randomized controlled trials (RCTs) [14–16].

Limitations

It is essential for optimal interpretation of our presented results to realize that data were derived from a well-described part of the hypertensive population of the NMP practices. We have not described patients registered with hypertension but not using medication, or the group of patients known to have high blood pressure but not yet registered by their GP as being hypertensive.

The NMP practices form an academic research network. The mere fact that these practices monitor chronic diseases will have enhanced the quality of care. As a consequence, our results may not fully represent average general practice in the Netherlands and may overestimate the quality of the process and outcome of hypertension management.

The last study cohort was relatively small compared to cohorts 1 and 2. In addition, compared to the first two cohorts, the number of patients in cohort 3 for whom the new guideline could be best applied were lacking. We assume it takes 1–2 years after the introduction of a new guideline before any kind of homeostasis is reached with regard to the application of new guideline recommendations in daily practice. In this respect, the results of cohort 3 could change for the better with two additional follow-up years (equal to cohorts 1 and 2).

Conclusion

Our study demonstrates the relevance of longitudinal data recording in understanding the management of chronic conditions. This type of data recording in one research network forms the basis of truly comprehending and interpreting medical outcomes in the context of the inevitable revisions in guidelines and protocols.

Guidelines and guideline revisions do result in changes in the process of hypertension management, but the resultant blood pressure outcome has not changed with any clinical relevance over the last 15 years. General practitioners achieve substantial and prolonged blood pressure reduction, which equals or exceeds reductions achieved in RCTs. However, despite the clear formulation of stricter treatment goals in the revised guidelines, general practitioners appear to be reluctant to subscribe three or more antihypertensive medications.

In addition to qualitative research to identify the causes of this phenomenon, research to evaluate the effect of expert support systems on risk awareness and risk gain by additional treatment is necessary.

Acknowledgements

We would like to thank all collaborators of the NMP practices for their contribution to monitoring hypertension management.