BACKGROUND:

The original study "Calcium-Channel Blockers and Primary Prevention of Coronary Heart Disease" was conducted from 1991 to 1995 and was designed to determine whether the calcium-channel blockers reduced the incidence of myocardial infarction (MI) in patients with hypertension.

Secondary aims included the evaluation of the relative efficacy and safety of other major drug classes, including ACE inhibitors, beta-blockers, and alpha blockers. The study originated to answer questions concerning the 1988 recommendations from the Joint National Committee on Detection, Evaluation, and Treatment of High Blood Pressure (JNC V). The 1988 recommendations from the Joint National Committee revolutionized the step-care approach to the treatment of hypertension: the calcium- channel blockers, a then new class of agents, were included as first-line agents. That they lowered blood pressure was clear. But no randomized trial had yet evaluated their safety and efficacy in terms of the clinical endpoints of stroke and coronary heart disease. Because the results of previous randomized trials suggested that the treatment of hypertension did not reduce the incidence of coronary heart disease, the study was designed to answer that question.

In 1995, the study was renewed as "Antihypertensive Medications, MI and Stroke" and was designed to to determine whether calcium-channel blockers increased the risk of stroke among hypertensive patients and whether individual calcium-channel blockers representing the three major subclasses increased the risks of MI and of the combined endpoint of MI and stroke in patients with hypertension.

DESIGN NARRATIVE:

The study has a case-control design. Data collected from the Group Health Cooperative (GHC) computerized files were used to identify potential cases: all treated hypertensive patients, aged 30 to 79 years, were eligible as cases if, according to WHO criteria, they presented with an incident, fatal or non-fatal MI. A random sample of members listed in the GHC enrollment files served as the source of potential controls. Review of the outpatient medical records ensured that all study subjects met the same entrance criteria. The effort also secured information about blood pressures, duration of hypertension, and past medical history. A telephone interview provided information about other potential confounders, including smoking, diet, and physical activity. The GHC computerized pharmacy records, a database of all prescriptions filled by enrollees, served as the primary source of information about the use of calcium-channel blockers. Frequency matching controlled for the potential confounding effects of age and year of presentation, and data analysis involved logistic regression.

The study has been renewed twice. The first renewal was for an additional five years through May, 2000 in order to identify an estimated additional 1,007 stroke cases, an additional 1,020 MI cases, and an additional 2,500 controls. The second renewal was through August, 2005 to determine antihypertensive drug/gene interactions and cardiovascular events. The ongoing second renewal focuses on drug-gene interactions on the incidence of non-fatal myocardial infarction and stroke for hypertensive patients, emphasizing (1) the alpha adducin polymorphism and diuretic use; (2) the beta-2 adrenergic receptor-27 (B2AR27) polymorphism and beta-blockers; and (3) the ACE insertion/deletion polymorphism and the ACE inhibitor use. The study also assesses other potential gene-drug interactions with the G-protein beta-3 subunit (GB3) polymorphism, B2AR-16 polymorphism, the amiloride-sensitive epithelial sodium channel, and the angiotensinogen Met235Thr polymorphism. In addition, for fatal cases DNA extracted from surgical or pathological specimens will be used to assess genotypes.