Current guideline statements for primary and secondary prevention of cardiovascular disease rely on estimates of absolute risk of coronary events. For example, the American Heart Association guidelines on primary prevention state that persons with ≥10% risk over ten years of myocardial infarction (MI) or coronary death should be considered for antiplatelet therapy with aspirin.1 Similarly, the National Cholesterol Education Program Adult Treatment Panel III (ATP III) guidelines2 state that target low-density lipoprotein (LDL) level should be based on projected absolute risk of future coronary events rather than on presence or absence of specific risk factors. These guidelines state that patients at high risk of MI and coronary death, defined as an absolute 10-year risk of 20% or more, should have a target LDL level <100 mg/dL and should receive statin therapy if needed to achieve this goal. Stroke, however, is not included as one of the outcomes contributing to these absolute risk levels.
Included in the group of patients with elevated risk, moreover, are those who already have ischemic heart disease, as well as patients deemed to be "coronary heart disease (CHD) risk equivalents," indicating those at the same elevated risk as patients with ischemic heart disease. CHD risk equivalents include patients with diabetes mellitus, those with multiple risk factors that put them at elevated risk based on calculation of their Framingham Score, and patients with "other forms of symptomatic atherosclerotic disease." The latter group is further defined to include those with peripheral arterial disease (PAD), abdominal aortic aneurysm (AAA), and carotid artery disease. The category of "risk equivalents" in the ATP III guidelines, however, does not include the vast majority (~80%3) of ischemic stroke patients without carotid artery disease as cause of their stroke.
Ischemic stroke is therefore notably excluded from the list of outcomes contributing to the absolute risk estimates used in these statements, and stroke patients are also excluded from the category of CHD risk equivalents. Evolving evidence suggests that ischemic stroke should be included in estimation of vascular risk and as a CHD risk equivalent. This inclusion could have implications for primary and secondary prevention.
The goal of this review is to summarize the evidence related to the following two questions: 1) Among stroke patients, is the risk of MI/coronary death high enough to justify calling stroke itself a risk equivalent?; and 2) Should stroke be included along with coronary heart disease in the vascular disease outcome cluster for purposes of absolute estimation of risk in primary and secondary prevention? In other words, should we speak of “coronary and stroke risk equivalents” rather than just “CHD risk equivalents”?
The answers to these questions have important clinical implications, as current guidelines may underestimate risk, leaving untreated patients who might be eligible for primary and secondary preventive therapies. These issues may be especially important for race-ethnic groups for whom stroke risk is as great as or exceeds coronary risk.4, 5