ATLANTA – Acute myocardial infarction is associated with a risk of stroke that extends beyond the 1-month time window currently considered the at-risk period, according to an analysis of Medicare data.
“The results of our study may allow clinicians to more accurately counsel patients regarding their stroke etiology and may allow refinement of stroke etiology classification systems and clinical trial selection criteria,” lead study author, said in an interview in advance of the annual meeting of the American Neurological Association.
In an effort to better understand the duration of heightened stroke risk after acute myocardial infarction, Dr. Merkler, a neurologist at New York–based Weill Cornell Medicine, and his colleagues conducted a retrospective cohort study using inpatient and outpatient claims during 2008-2015 from a nationally representative 5% sample of Medicare beneficiaries who were at least 66 years old. They used previously validated ICD-9-CM diagnosis codes to ascertain the exposure variable of acute MI and the outcome of ischemic stroke but excluded strokes that occurred during an acute MI hospitalization.
Patients were censored at the time of ischemic stroke, death, end of Medicare coverage, or by Sept. 30, 2015. The researchers fit Cox regression models separately for the groups with and without acute MI to examine its association with ischemic stroke after adjusting for demographics, stroke risk factors, and Charlson comorbidities. Next, they used the corresponding survival probabilities to compute the hazard ratio (HR) in each 4-week interval after discharge, up to week 12. They also conducted a subgroup analysis to evaluate the duration of heightened ischemic stroke risk by MI type: ST-segment elevation MI (STEMI) versus non-STEMI (NSTEMI).
Dr. Merkler and his colleagues drew from data on 1.7 million eligible beneficiaries. Of these, 46,182 were hospitalized for acute MI and 80,466 for ischemic stroke. After they adjusted for demographics, stroke risk factors, and Charlson comorbidities, the researchers found that the risk of ischemic stroke was highest in the first 4 weeks after discharge from the MI hospitalization (HR, 2.7), yet remained elevated during weeks 5-8 (HR, 2.0) and weeks 9-12 (HR, 1.6). It was no longer significantly elevated afterward. The prolonged period of heightened ischemic stroke risk was evident in patients with both STEMI and NSTEMI.
“We were surprised by how long the risk of stroke lasts after MI,” Dr. Merkler said. He acknowledged certain limitations of the analysis, including the fact that patients were all over the age of 65 years. “In addition, we lack granular detail such as severity of MI [and] the extent of stroke work-up,” he said.
Dr. Merkler disclosed that he is supported by a grant from the National Institutes of Health and by the Leon Levy Foundation in Neuroscience. Most of his coauthors are also supported by NIH grants.
Source: Ann Neurol. 2018;84[S22]:S146-7,.
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