The study provides what is believed to be the most accurate estimates of stroke after heart attack among elderly patients. This is because it includes the largest and most geographically diverse sample of older heart attack patients who have not been excluded from the study based on other illnesses or older age.
"The importance of stroke after myocardial infarction (MI) has been underappreciated, especially among older persons," said Judith Lichtman, assistant professor in the Department of Epidemiology and Public Health at Yale School of Medicine. "Our results demonstrate that stroke after MI is much more common than previously reported."
Lichtman, whose study is published in the March issue of the journal Circulation, said the rate of stroke following a heart attack has frequently been based on clinical studies that often exclude older patients and those with more significant medical problems. Yet, among patients hospitalized with a stroke, 77 percent are 65 years of age or older and half are older than 75 years of age.
"With improved survival after MI and an increasing number of elderly people in the population, stroke after MI will be increasingly common problem in the coming decades," she said.
Lichtman and her co-authors analyzed the data from more than 111,000 elderly patients included in the Cooperative Cardiovascular Project, which is a large, geographically diverse population-based group of patients hospitalized with acute myocardial infarction (AMI).
"Overall, 2.5 percent were admitted with an ischemic stroke within six months of discharge," Lichtman said.
She said older patients, African American patients, and patients with any frailty are at increased risk for a stroke after a heart attack. Conditions associated with higher stroke admission rates included prior stroke, hypertension, diabetes, atrial fibrillation, heart failure, and peripheral vascular disease.
History of hypertension, diabetes, and peripheral vascular disease, are generally accepted as risk factors for stroke, but have not been previously identified as predictors of stroke after a heart attack. Lichtman also noted that aspirin at discharge was associated with reduced stroke admission rates.
The risk of stroke among the 20 percent of patients who had at least four of the eight identified factors was four times higher than patients with none of these factors. Patients in this group had a one in 25 chance of being hospitalized for a stroke in the six months after discharge.
This data, Lichtman said, can be used to target high risk patients for more aggressive therapies and counseling, including information about the signs and symptoms of a stroke and the appropriate action if these signs are present. Studies have shown that most patients do not recognize the signs and symptoms of a stroke, which results in delays that limit the ability to use time-dependent acute therapies.
The senior author of the study was Lawrence Brass, M.D. Co-authors included Harlan Krumbolz, M.D., Yun Wang, and Martha Radford, M.D.
The study was supported in part by a grant from the Patrick and Catherine Weldon Donaghue Medical Research Foundation. Lichtman is a Goddess Fund Career Development Scholar.