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So-called silent infarcts were not uncommon for older atrial fibrillation (Afib) patients, even when on oral anticoagulation, in a prospective Swiss study.

Over a 2-year period, 5.5% of well-treated Afib patients had a new brain infarct, with 85.3% of these being clinically silent and 75% being silent while on an anticoagulant, David Conen, MD, MPH, of McMaster University of Hamilton, Ontario, reported at the .

Silent infarcts were more frequent than clinical strokes and transient ischemic attacks, which occurred in 2.3% of patients during the 2-year period between scans.

The findings offered insight into the hidden impact of silent strokes, Conen said at an HRS press conference.

"These infarcts were associated with cognitive decline," he said. "They may be an iceberg under the water compared to the clinical strokes above the water, and anticoagulation may not be sufficient to prevent brain damage in patients with atrial fibrillation."

In the new study, researchers prospectively followed a Swiss cohort of 1,737 Afib patients ages 65 and older (mean 71, female 26%) for 2 years. Researchers performed follow-up brain MRIs at 2 years for 1,227 participants (71%).

Those who suffered from silent infarcts had a slightly lower yet still statistically significant decline in cognitive function, Conen said.

While the decline was very small, he said, researchers were surprised because "this is only a 2-year follow up, and cognitive decline and dementia takes years to develop."

In 2016, the American Heart Association noted in a scientific statement that silent infarcts are "associated with on standardized testing, cognitive decline, gait impairment, psychiatric disorders, impairments in activities of living, and other adverse health outcomes."

Conen added that "the rate of new brain infarcts in patients who are well-treated is pretty high." In the study, 87% of those who had infarcts were taking anticoagulation drugs, as were 88% of those who suffered silent infarcts specifically. Information about medication adherence wasn't available.

Silent infarcts are believed to be much more common than clinical strokes, and research suggests about 25% people over the age of 80 in the U.S. have had them. Researchers have linked Afib to a .

"Epidemiologic studies suggest that the annual incidence of silent stroke in older adults is approximately 2-4%. As such, an incidence of 5.5% over 2 years aligns with previous population estimates," commented Phillip Vlisides, MD, of Michigan Medicine in Ann Arbor. "What's interesting in this study, however, is that silent strokes occurred despite anticoagulation. This suggests that stroke may be occurring from causes other than blood clot formation."

The study reinforces the fact that "the risk of stroke is not 0%, even in some patients prescribed anticoagulation in the setting of AF," said HRS President Andrea Russo, MD, of Cooper Medical School of Rowan University in Camden, New Jersey. "We should confirm adherence to oral anticoagulant medications in patients with AF and continue to address all issues, including hypertension, that may contribute to stroke risk."

The study left open questions about anticoagulation, such as adherence levels and the role of risk factors other than Afib, she noted. Low enrollment of women in the study was also a concern, she said. "Women may be at higher risk for stroke in the setting of AF than men, and this makes me think it could be possible that the incidence for silent strokes could be even higher in women."

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