'Silent' Heart Attack Tied To Risk Of Future Stroke In Older Adults

Older adults who experience "silent" myocardial infarction (MI) without any clinical symptoms are at increased risk for suffering ischemic stroke, according to new research.

Silent MI refers to EKG or cardiac imaging evidence of MI without clinical recognition of the event, Dr. Alexander Merkler of Weill Cornell Medicine, in New York City, explained in a presentation at the American Stroke Association International Stroke Conference (ISC) 2021.

"Similar to silent stroke, silent MI is common, if not more common than clinically apparent chest-crushing MI. Prior studies have shown that silent MI is not benign. Silent MI increases the risk of clinically apparent MI, heart failure and death, but does silent MI increase the risk of stroke? That is the question that we sought to answer," Dr. Merkler said.

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He and his colleagues analyzed data on 4,224 adults in the Cardiovascular Health Study who were 65 or older at enrollment in 1989 to 1990.

During median follow-up of 9.8 years, 362 participants (8.6%) had evidence of silent MI, 421 (10.0%) had overt MI and 377 (8.9%) suffered ischemic stroke. There were 139 (36.8%) non-lacunar strokes, 57 (15.1%) lacunar strokes and 181 (48.0%) of other determined/unknown.

After adjusting for demographics and comorbidities, silent MI was independently associated with increased risk of subsequent ischemic stroke (hazard ratio, 1.47; 95% confidence interval, 1.01 to 2.16).

"This hazard ratio is similar to the association between overt MI and risk of ischemic stroke," with a hazard ratio of 1.60 (95% CI, 1.04 to 2.44), Dr. Merkler noted.

In the secondary analysis of specific stroke subtypes, silent MI was significantly associated with non-lacunar ischemic stroke, with a hazard ratio of 2.18, but not with lacunar or other/unknown stroke subtypes.

"The association between silent MI and non-lacunar ischemic stroke subtype was very similar or identical to the association between overt MI and non-lacunar stroke," Dr. Merkler reported.

These findings suggest that silent MI may be a new risk factor for stroke, he said.

He noted that while the mechanism is unclear, "silent MI may increase the risk of stroke through cardiac embolism similar to how clinically apparent MI or overt MI may increase the risk of stroke. Silent MI causes damage to the left ventricle. It causes both myocardial scar and left ventricular dysfunction. These pathophysiological changes may lead to left ventricular thrombus formation and increase the propensity for cardiac embolism and ischemic stroke."

A limitation of the study is that most participants were white. The results might not be applicable to younger adults or adults of other races or ethnic groups.

Dr. Merkler said more research is needed to understand how best to treat patients with silent MI to prevent stroke. "It may also be worthwhile to conduct studies aimed at evaluating whether routine cardiac evaluation for silent heart attacks is warranted in order to help stratify the risk of stroke," he said in a conference statement.

The study was funded by the National Institutes of Health. The authors have no relevant disclosures.

—Megan Brooks

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