The Stroke Council of the American Heart Association (AHA) has issued a scientific statement on the primary prevention of ischemic stroke. The statement is based on the findings of an ad hoc writing group formed by the AHA council to review pertinent literature, published guidelines and expert opinions regarding risk factors for ischemic stroke. The scientific statement includes an overview of established and potential risk factors and recommendations.
The AHA scientific statement appears in the January 2/9, 2001, issue of Circulation and can be accessed at the AHA Web site:http://www.circ.ahajournals.org/cgi/content/full/103/163.
According to the AHA council, each recommendation is based on five different levels of evidence:
Level I: data from randomized trials with low false-positive and false-negative errors (grade A strength of evidence).
Level II: data from randomized trials with high false-positive or false-negative errors (grade B strength of evidence).
Level III: data from nonrandomized concurrent cohort studies (grade C strength of evidence).
Level IV: data from nonrandomized cohort studies using historical controls (grade C strength of evidence).
Level V: data from anecdotal case series (grade C strength of evidence).
Further classification within the AHA scientific statement includes the potential for modification (nonmodifiable, modifiable or potentially modifiable) of the identified risk factor and the strength of evidence (well documented, less well documented).
Nonmodifiable risk factors include age, sex, race/ethnicity and family history. Well-documented modifiable risk factors (all level I, grade A) include hypertension, smoking, diabetes/hyperinsulinemia/insulin resistance, asymptomatic carotid stenosis, atrial fibrillation, other cardiac disease (e.g., valvular heart disease, intracardiac congenital defects), sickle cell disease and hyperlipidemia.
From this category, hypertension, considered a major risk factor for stroke, remains underdiagnosed and inadequately treated. The relationship between stroke and systolic and diastolic blood pressures is “direct, continuous and apparently independent.” More than 30 years of evidence reveals that adequately controlled hypertension is a factor in preventing stroke, as are beta-blocker and highdose diuretic therapy. Particularly in elderly persons, isolated systolic hypertension is considered an important risk factor for stroke (systolic blood pressure of more than 160 mm Hg and diastolic blood pressure of less than 90 mm Hg). One trial involving 4,695 elderly patients with isolated systolic hypertension was terminated when a stroke reduction rate of 42 percent was reached in the patients who were actively treated compared with those taking placebo. The AHA recommends that adult patients undergo routine screening for hypertension at least every two years.
Risk factors in the less well-documented, potentially modifiable category include obesity, physical inactivity, poor diet/nutrition, alcohol abuse, hyperhomocysteinemia, drug abuse, hypercoagulability, hormone replacement therapy, oral contraceptive use and inflammatory processes.
The role of obesity in stroke is based on its predisposition to cardiovascular disease and its association with increased blood pressure, blood sugar and blood lipid levels. Although evidence from prospective randomized studies does not support a decreased risk of stroke directly related to weight loss, data from large level IV studies suggest that abdominal obesity, rather than body mass index (BMI) or general obesity, is more closely related to the risk of stroke in men. In women, obesity is associated with an increased risk of ischemic stroke with increasing BMI. The AHA endorses this data as strong enough to recommend that abdominal obesity in men and obesity and weight gain in women should be considered independent risk factors for stroke.
The management strategies for the above risk factors are outlined in the accompanying table on page 514 and are based on published guidelines and/or consensus statements. Not included in the table are risk factors for which specific guidelines have not been previously adopted.
The AHA council notes that many gaps exist in the curent knowledge about risk factors for stroke. In addition, the effect of treatment of the less well-documented, potentially modifiable factors is uncertain, while further research is necessary to understand the differences between gender-specific risk factors.