NEW ORLEANS (FRONTLINE MEDICAL NEWS) – About a third of elderly people at high cardiovascular risk but otherwise healthy and asymptomatic had subclinical atrial fibrillation in a multicenter study of 273 people.

This finding that subclinical atrial fibrillation (AF) is “extremely common” in elderly people with cardiovascular risk factors “weakens the case that detecting subclinical AF in patients following a stroke implies causality” of the stroke “because subclinical AF is so prevalent,” Jeff S. Healey, MD , said at the American Heart Association Scientific Sessions.

He advised against taking any new steps to screen for or treat subclinical AF. Possible benefit from treating patients with subclinical AF with an anticoagulant is “unproven,” noted Dr. Healey. He also called it “premature” to routinely screen people aged 65 or older with an enlarged left atrium by implanting a loop recorder.

“I think that subclinical AF is a distinct subgroup of AF, with a risk for stroke that is quite low, about 1.5%-2% per year,” said Dr. Healey, a cardiologist at McMaster University in Hamilton, Canada. “Given that this was an elderly population [study participants averaged 74 years old] with bleeding risk, it’s reasonable to question” whether many people with subclinical AF need anticoagulation. The question of whether “45 seconds of AF seen 6 months after a stroke is worthy of treatment with an anticoagulant should give people pause,” he said.

The Prevalence of Sub-Clinical Atrial Fibrillation Using an Implantable Cardiac Monitor ( ASSERT-II ) study initially enrolled 273 people at 26 sites in Canada and The Netherlands. Researchers actually placed a loop recorder in 256, and complete follow-up of at least 9 months occurred for 252. Enrolled patients had to be at 65 years old, and have at least one of these risk factors for AF or stroke: a CHA2DS2-VASc score of 2 or greater; documented obstructive sleep apnea; or a body mass index greater than 30 kg/m2. In addition, enrollees also had to have one of these risk factors for AF: a left atrial volume of at least 58 ml; a left atrial diameter of at least 4.4 cm; or a serum NT-proBNP level of at least 290 pg/mL.

Dr. Healey and his associates prespecified subclinical AF as at least 5 minutes of AF seen in the loop recording during follow-up, which occurred in 34% of the participants during an average 16 months of follow-up, he reported . At least 30 minutes of AF occurred in 22% during follow-up, at least 6 hours in 7%, and at least 24 hours in 3%.

In a prespecified set of subgroup analyses, people with a large left atrium formed the only subgroup with a statistically significant association with outcome. People with a left atrial size at or above the study median of 73.5 ml had an 85% increased rate of subclinical AF compared with those with smaller left atria in the multivariate analysis. But increased left atrial size alone did not fully explain subclinical atrial fibrillation. Even among participants in the lowest quartile for left atrial diameter, less than 4.3 cm, the prevalence of subclinical AF was 27%, Dr. Healey noted.

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