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DALLAS -- Neurologists couldn't agree that stroke survivors with a small burden of atrial fibrillation (Afib) could get away with skipping anticoagulation during a debate here at the American Stroke Association's International Stroke Conference (ISC).

"The issue for me is that the drugs we use to anticoagulate patients are expensive and have some risk associated with them. So we have to be cautious in prescribing them in a reflexive manner just because a report comes back that 30-second Afib has been detected on an implanted device. These results have to be taken in context," said Karen Furie, MD, MPH, of Brown University and Rhode Island Hospital in Providence.

Yet it's well established that Afib is a high-risk condition for a second ischemic stroke. The guidelines are clear: patients with nonvalvular Afib and stroke or transient ischemic attack (TIA) are advised to take oral anticoagulation to reduce the risk of recurrent stroke, a class I recommendation in the from the American Heart Association/American Stroke Association.

Maintaining the position of the status quo was Roland Veltkamp, MD, of Imperial College London.

"Evidence from ongoing [randomized clinical trials] is needed to build an even stronger case for oral anticoagulation," Veltkamp acknowledged, though he "would stick with what we have in case of doubt."

On the other hand, Furie argued that there may be indications -- albeit very few, she acknowledged -- that should give a clinician pause and consider an alternative intervention or therapy. "There are patients who have some degree of Afib, by history or that we detect, and it doesn't make sense to anticoagulate them," she said. "We have to be a little nuanced to how we approach this and we certainly need more data on this topic."

She reasoned that the concept of Afib burden and risk of stroke is still evolving. There is still no agreement on how to classify Afib burden -- by number of Afib episodes during a monitoring period, say, or proportion of time in Afib -- and how that should be related to risk.

And what is the clinical significance of an Afib episode under 5 minutes? "We really don't understand the effects of very brief durations of Afib," Furie said. She cited the from 2012 that had established 6 minutes of Afib as the threshold for increased ischemic stroke risk.

Then there are reliability issues with implanted monitors exhibiting false positives or missed episodes, and -- as demonstrated by ASSERT and other studies -- the between subclinical Afib and subsequent stroke to preclude claims of causality, she said.

Veltkamp ceded that Furie "has rightly said there are some caveats" for universal secondary prevention anticoagulation in Afib.

Nevertheless, he pointed out that ASSERT was conducted in a primary prevention cohort -- whereas treatment of Afib can be expected to have more impact if episodes are detected after stroke. In , he recalled, apixaban (Eliquis) reduced the annualized incidence of stroke or systemic embolism by an absolute 6.4% per year in secondary prevention patients, compared with just 1.38% per year in primary prevention.

"The prognostic implications of even short runs of Afib greater than 30 seconds detected by long-term recorders are likely to be different for patients with recent stroke compared to candidates for primary prevention," Veltkamp said.

Furie concluded that she and her debate opponent likely agree more than disagree on secondary prevention anticoagulants in Afib.

"I hope moving forward, we get better at quantifying this concept of burden and identifying patients with brief spells who do deserve and require anticoagulation for secondary prevention," she said.

To that latter point, the 3-year results of the STROKE AF trial, also presented here at ISC, have confirmed that long-term monitoring after a large artery or small vessel stroke improves detection of Afib at a level that would trigger many clinicians to initiate anticoagulation for secondary prevention.

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