Hypertension treatment and control rates

Site and study subjects

This was a cross-sectional chart review of patients attending a multiphysician family medicine clinic. The clinic is a teaching site for family medicine residents and students in the allied health professions at the University of Alberta. The University of Alberta Research Ethics Board approved the study. Subjects were eligible for inclusion if they had 1 or more visits coded for hypertension (International Classification of Diseases, Ninth Revision, code 401) within the past 3 years. Subjects were excluded if they only had 1 recorded visit to the clinic, were younger than 18 years of age, were cognitively impaired, resided in an institution, were a student or employee of our health region or the University of Alberta, or did not communicate in English. The list of eligible subjects was then stratified based on the treating physician, and 35 subjects were randomly selected from each group to ensure a balanced representation from each physician (Figure 1).

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Figure 1

Flow chart of subject selection

Data collection

A standardized case report form was used to abstract information from subjects’ clinic records regarding date of birth, sex, most recent blood pressure measurements, antihypertensive medication therapies, compelling medical conditions as indicated in the 2006 CHEP recommendations, as well as smoking status and alcohol use.12

The most recent blood pressure measurement was defined as the last clinic visit with a recorded blood pressure. Medication lists recorded in the chart were reviewed to identify antihypertensive medications and medications known to induce hypertension according to the 2006 CHEP recommendations.12 Each medication was recorded by its generic name and total daily dose in milligrams. Antihypertensive medications were categorized as previous, current, or new to characterize their potential effect on the most recent blood pressure measurement. Previous antihypertensive medications had been discontinued 3 months before the date of the most recent blood pressure measurement. In these cases, the date of discontinuation was also recorded. Current antihypertensive medications were considered ongoing therapy or medications that had been discontinued within 3 months of the most recent blood pressure measurement. New anti-hypertensive medications indicated a change in dose or addition of a new antihypertensive medication on or after the date of the most recent blood pressure measurement.

According to the 2006 CHEP recommendations, the approach to hypertension management might be influenced by specific compelling indications, including diabetes, chronic renal disease (CRD), ischemic heart disease, myocardial infarction, angina, dyslipidemia, heart failure, cerebrovascular accident, and left ventricular dysfunction.12 For this study, such compelling indications were considered present if they were documented in the charts. Diabetes and angina were also considered present if antidiabetic medications or nitro-glycerin products, respectively, were listed in subjects’ medication lists.13

Sample size and analyses

During the design stage of this study, the most recent information from NHANES was based on the 2001 to 2002 cycle, in which 1038 of the 1696 participants (61%) with hypertension were treated with antihypertensive medications.14 Using this published treatment rate as our external benchmark and assuming an α error of .05 and β error of .20, we determined that 187 subjects would be required to detect a 10% absolute difference in treatment rate. The sample size was increased to 210 subjects by selecting 35 hypertensive subjects from each of the 6 physicians in our clinic.

Patients were considered to be receiving treatment for hypertension if their medication history included at least 1 new or current antihypertensive medication. Controlled hypertension was defined as a blood pressure below 140/90 mm Hg or, if the subject had diabetes or CRD, below 130/80 mm Hg.12

All analyses of the extracted data were descriptive, using frequencies and means where appropriate. Differences in the characteristics of subjects with controlled versus uncontrolled hypertension were tested using χ² tests or 2-tailed t tests where appropriate. A P value less than .05 was considered statistically significant.