Conference Coverage

Subclinical AF found in 1/3 of asymptomatic elderly

Publish date: January 22, 2017
Author(s):
Mitchel L. Zoler, PhD

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Findings weaken stroke, subclinical AF link

The results reported by Dr. Healey provide robust data that bridges a major gap we have had in our understanding of atrial fibrillation. The new finding of a high prevalence of subclinical atrial fibrillation in elderly people with cardiovascular risk factors, regardless of whether they had a prior stroke, substantially weakens the case that subclinical atrial fibrillation detected following a stroke has a causal relationship to the stroke. This implication is quite important.

Dr. N.A. Mark Estes III Mitchel L. Zoler/Frontline Medical News

Dr. N.A. Mark Estes III

The finding that 34% of the studied patients have subclinical atrial fibrillation is consistent with results from several prior studies, which have documented subclinical atrial fibrillation prevalence rates of 12%-55%. Many of the prior studies used implanted pacemakers or defibrillation devices to monitor atrial fibrillation; the current study used an implanted loop recorder. For example, a prior study by Dr. Healey involving 2,580 patients with either a pacemaker or implanted defibrillator found that about a third of these patients developed subclinical AF during an average 2.5 years of follow-up (New Engl J Med. 2012 Jan 12;366[2]:120-9). It’s unknown whether there is a difference in the nature of atrial fibrillation detected by a pacemaker or defibrillator and detected by a loop recorder.

Many questions remain about the meaning of subclinical atrial fibrillation. What relationship does it have with stroke, and what thresholds exist for atrial fibrillation to raise stroke risk? Also, what are the risks and benefits of anticoagulation in people with subclinical AF and is intermittent anticoagulation helpful?

N.A. Mark Estes III, MD , is professor of medicine and director of the New England Cardiac Arrhythmia Center at Tufts Medical Center in Boston. He has been a consultant to Boston Scientific, Medtronic and St. Jude. He made these comments as designated discussant for ASSERT-II.


 

AT THE AHA SCIENTIFIC SESSIONS

NEW ORLEANS – 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.

Jeff S. Healey

Jeff S. Healey

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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