1.Introduction
Stroke is the second leading cause of death in the world and of disability in developed countries. In North America, 550 000 new strokes occur each year and there are approximately five million people who have had a stroke, 60% of whom have some residual disability. Stroke is also responsible for a substantial proportion of deaths and disability in developing countries.Strokes can be prevented by lowering blood pressure in people with hypertension and by the use of antiplatelet agents in people with vascular disease. Although a person’s risk of stroke increases with blood pressure, the population attributable risk of stroke is greatest at pressures that would not currently be treated with drugs.9 We therefore need additional strategies that lower the risk of stroke across a broad range of patients at high risk.
Angiotensin converting enzyme inhibitors have been shown to block the activation of the renin-angiotensin system in the plasma as well as in the vascular wall. Recent experimental and human data suggest that angiotensin converting enzyme inhibitors reduce proliferation of vascular smooth muscle; enhance endogenous fibrinolysis; have the potential to stabilise plaques; and decrease angiotensin II mediated atherosclerosis, plaque rupture, and vascular occlusion. Angiotensin converting enzyme inhibitors therefore have the potential to lower the risk of ischaemic vascular events, including strokes, through mechanisms that are independent of lowering blood pressure.
We provide a detailed analysis of the impact of ramipril, an angiotensin converting enzyme inhibitor, on stroke, its subtypes, and the related disability and report the effects in various subgroups of patients in the heart outcomes prevention evaluation (HOPE) study.
2. Design and methods
The HOPE study was a double blind randomised trial with a two by two factorial design, in which participants were randomised to receive up to 10 mg of ramipril, 400 IU of vitamin E, both, or matching placebos. We provide a brief outline here.
3.Participants
Participants were aged 55 or over and were at high risk of cardiovascular events because of previous coronary artery disease, cerebrovascular disease, or peripheral arterial disease or diabetes plus one additional risk factor. Patients were excluded if they were taking either an angiotensin converting enzyme inhibitor or vitamin E; had heart failure or a known left ventricular ejection fraction of less than 0.40, known proteinuria, or uncontrolled hypertension; or had had a previous stroke or a myocardial infarction less than one month before enrolment in the study. Informed consent was obtained from all participants before enrolment in the study, and the study was approved by the ethics committee at each centre.
4.Intervention
Eligible patients entered a run-in phase in which they received 2.5 mg ramipril daily for 7-10 days, after which serum creatinine and potassium levels were measured. Participants then started a 10-14 day course of placebo. Those who tolerated and adhered to this regimen were then randomised to receive either placebo or 2.5 mg ramipril daily for one week, followed by placebo or 5.0 mg ramipril for a further three weeks. One month after randomisation the patient’s serum creatinine and potassium were measured; if these were satisfactory the patient continued on either placebo or 10 mg ramipril for the remainder of the study. Participants were seen after six months and then every six months until the end of the study, with an average follow up of 4.5 years.
Of the 10 576 patients who entered the run-in phase, 1035 were not randomised because of non-adherence, side effects, or withdrawal of consent; 244 patients were entered into a substudy of 2.5 mg ramipril and are not included in this paper. Outcome results were available on 9539 (99.9%) of the 9541 patients randomised. The first participant was recruited in December 1993. The originally scheduled completion date was November 1999, but the ramipril arm of the study was terminated early (April 1999) because of clear benefit.
5.Outcome measures
The primary outcome was the composite end point of myocardial infarction, stroke, or cardiovascular death.12 The individual components of this composite end point were analysed separately. All outcomes were adjudicated by a central committee. This analysis focuses on stroke.
Investigators reported the occurrences of stroke or transient ischaemic attack at follow up visits. For every stroke reported, information on the stroke, including symptoms and functional impairment, was documented. The investigators used a simple six point scale to record if there was full recovery, persistent symptoms, some functional impairment, functional impairment necessitating the assistance of others to perform activities of daily living, or inability to perform activities of daily living even with help at seven days or at discharge if earlier. Discharge summaries, consultation notes, and results of computed tomography or magnetic resonance imaging were documented. A central committee adjudicated all strokes on the basis of predetermined definitions. Classification of a stroke as either ischaemic or haemorrhagic was confirmed by computed tomography or magnetic resonance imaging within 14 days of onset or by autopsy. All other strokes were classified as being of uncertain aetiology. Computed tomography, magnetic resonance imaging, or autopsy results were obtained for 84% of strokes.
Blood pressure was measured at entry to the study, after two years, and at the end of the study. Two measurements were taken on each arm after the patient had been supine for five minutes. The lowest measurements on each arm were averaged to obtain the systolic and diastolic values that were recorded.
6.Statistical analysis
The study had 90% power to detect a 13.5% reduction in relative risk for the primary outcome, with an annual event rate of 4% in 9000 patients studied for five years. Assuming a stroke rate of 1.2% per year in the control group for five years, the study had 80% power to detect a 22.0% reduction in the relative risk of stroke with a two sided Embedded Imagelevel of 0.05 in an intention to treat analysis. We estimated survival curves according to the Kaplan-Meier procedure and compared treatments by using the log rank test.13 Because of the factorial design, we stratified all analyses for the randomisation to vitamin E or placebo. We conducted subgroup analyses by using tests for interactions in the Cox regression model. We used this model to estimate the reduction in relative risk and the 95% confidence intervals associated with ramipril treatment in unadjusted analyses and after controlling for changes in blood pressure.
The data and safety monitoring board monitored the study. Monitoring boundaries for the study were four standard deviations between the two groups in terms of benefit of ramipril in the first half of the study and three standard deviations in the second half. For harm, the boundaries were three standard deviations in the first half of the study and two standard deviations in the second half. Because of clear benefit, the study was terminated on 22 March 1999.
7. Study organisation
The study was conducted in 267 hospital clinics in 19 countries. It was coordinated by the Canadian Cardiovascular Collaboration in Hamilton, Canada.
8.Results
Reduction in blood pressure was modest (3.8 mm Hg systolic and 2.8 mm Hg diastolic). The relative risk of any stroke was reduced by 32% (156 v 226) in the ramipril group compared with the placebo group, and the relative risk of fatal stroke was reduced by 61% (17 v 44). Benefits were consistent across baseline blood pressures, drugs used, and subgroups defined by the presence or absence of previous stroke, coronary artery disease, peripheral arterial disease, diabetes, or hypertension. Significantly fewer patients on ramipril had cognitive or functional impairment.
9.Conclusion
Ramipril reduces the incidence of stroke in patients at high risk, despite a modest reduction in blood pressure.
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