Stroke remains a leading cause of morbidity and mortality in the United States, despite the fact that it is a preventable condition. Known risk factors include hypertension, myocardial infarction (MI), atrial fibrillation, diabetes mellitus, hyperlipidemia, carotid artery disease and lifestyle choices. Early recognition of these risk factors plays an important role in reducing the incidence of first stroke. Gorelick and colleagues, writing for the Advisory Board of the National Stroke Association (NSA), reviewed the literature from 1990 to mid-1998 to produce a consensus statement outlining their recommendations for prevention of first stroke. The MED-LINE database was searched for relevant guidelines, meta-analyses and statements. The listed risk factors were also reviewed.
Hypertension is the most common, yet the most preventable, risk factor for stroke, and its treatment reduces the risk of stroke significantly. Decreasing diastolic blood pressure by only 5 to 6 mm Hg reduces the risk of stroke by 42 percent. Treatment of isolated systolic hypertension in the elderly reduces the risk by 36 percent. The NSA recommends three strategies for lowering blood pressure: (1) controlling blood pressure in at-risk patients with hypertension; (2) encouraging at-home monitoring of blood pressure in patients with hypertension; and (3) checking blood pressure of all patients at every physician visit. Treatment with antihypertensive agents is useful in decreasing the morbidity associated with stroke. Diuretics offer a 39 percent odds reduction, and beta blockers a 25 percent odds reduction in older patients with hypertension.
The risk of stroke is only 1 to 2 percent a year following an MI but is much greater (31 percent) in the first month after an MI. The NSA recommends warfarin therapy in patients with an MI and either persistent atrial fibrillation, decreased left ventricular function or left ventricular thrombi within several months after the MI. Unless at least one of these risk factors is present with an MI, warfarin therapy should not be used, as the absolute risk reduction is only about 1 percent a year. Antiplatelet agents reduce the odds of nonfatal stroke by 39 percent in patients with a history of an MI, but the absolute stroke risk reduction is too small to be useful in preventing a first stroke after an MI. The NSA recommends statin therapy in patients with normal to high lipid levels following an MI, as these agents offer a 31 percent risk reduction for stroke, compared with a placebo.
Nonvalvular atrial fibrillation (NVAF) is another common risk factor for stroke. Warfarin reduces the incidence of stroke by 68 percent in patients with NVAF and risk factors for stroke. Aspirin reduces the risk by 21 percent. The NSA recommends that patients younger than 65 years of age with NVAF and no risk factors for stroke should take 325 mg of aspirin daily, while patients with risk factors should be given warfarin (with an INR goal of 2.0 to 3.0). Older patients, between 65 and 75 years of age, with NVAF and risk factors should receive warfarin, but those without risk factors can be given either warfarin or aspirin. All patients with NVAF who are older than 75 years should be given warfarin. The risk of stroke should be weighed against the risk of hemorrhage in all cases. For more information, see the accompanying table listing complete NSA recommendations for prevention of a first stroke.