From the Journals

Is AFib a stroke cause or innocent bystander? The debate continues


Implications for noncontinuous OAC

“The hope is that there are people who have very little AFib: They may have several hours, and then they have nothing for 6 months. Do they have to be anticoagulated or not?” Dr. Singer asked.

“If you believe the risk-marker story, you might say they have to be anticoagulated. But if you believe our results, you would certainly think there’s a good chance they don’t have to be anticoagulated,” he said.

“So it is logical to think, if you have the right people and continuous monitoring, that you could have time-delimited anticoagulation.” That is, patients might start right away on a direct OAC once reaching the AFib threshold in a day, Dr. Singer said, “going on and off anticoagulants in parallel with their episodes of AFib.”

The strategy wouldn’t be feasible in patients who often experience AFib, Dr. Singer noted, “but it might work for people who have infrequent paroxysmal AFib.” It certainly would first have to be tested in prospective trials, he said. Such trials would be more practical than ever to carry out given the growing availability of continuous AFib monitoring by wearables.

“We need a trial to make the case whether it’s safe or not,” Dr. Turakhia said of such a rhythm-guided approach to OAC for AFib. The population to start with, he said, would be patients with paroxysmal AFib and low CHA2DS2-VASc scores. “If you think CHA2DS2-VASc as an integrated score of vascular risk, such patients would have a lot fewer reasons to have strokes. And if they do have a stroke, it’s more reasonable to assume that it’s likely caused by atrial fib and not just a marker.”

Importantly, such a strategy could well be safer than continuous OAC for some patients – those at the lowest vascular risk and with the most occasional AFib and lowest AFib burden “who are otherwise doing fine,” Dr. Turakhia said. In such patients on continuous OAC, he proposed, the risks of bleeding and intracranial hemorrhage could potentially exceed the expected degree of protection from ischemic events.

Discordant periods of AFib burden

Dr. Singer and his colleagues linked a national electronic health record database with Medtronic CareLink records covering 10 years to identify 891 patients who experienced an ischemic stroke preceded by at least 120 days of continuous heart-rhythm monitoring.

The patients were then categorized by their pattern of AFib, if any, within each of two prestroke periods: the most recent 30 days, which was the test period, and the preceding 91-120 days, the control period.

The analysis then excluded any patients who reached an AFib-burden threshold of at least 5.5 hours on any day during both the test and control periods, and those who did not attain that threshold in either period.

“The ones who had AFib in both periods mostly had permanent AFib, and ones that didn’t have AFib in either period mostly were in sinus rhythm,” Dr. Singer said. It was “close to 100%” in both cases.

Those exclusions left 66 patients, 7.4% of the total, who reached the AFib-burden threshold on at least 1 day during either the test or control periods, but not both. They included 52 and 14 patients, respectively, with “discordant” periods, that is, at least that burden of AFib in a day during either the test or control period, but not both.

Comparing AFib burden at test versus control periods among patients for whom the two periods were discordant yielded an OR for stroke of 3.71 (95% confidence interval, 2.06-6.70).

Stroke risk levels were not evenly spread throughout the 24-hour periods that met the AFib-burden threshold or the 30 days preceding the patients’ strokes. The OR for stroke was 5.00 (95% CI, 2.62-9.55) during days 1-5 following the day in which the AFib-burden threshold was met. And it was 5.00 (95% CI, 2.08-12.01) over 30 days if the AFib burden exceeded 23 hours on any day of the test period.

The study’s case-crossover design, in which each patient served as their own control, is one of its advantages, Dr. Singer observed. Most patient features, including CHA2DS2-VASc score and comorbidities, did not change appreciably from earliest to the latest 30-day period, which strengthens the comparison of the two because “you don’t have to worry about long-term confounding.”

Dr. Singer was supported by the Eliot B. and Edith C. Shoolman fund of the Massachusetts General Hospital. He discloses receiving grants from Boehringer Ingelheim and Bristol-Myers Squibb; personal fees from Boehringer Ingelheim, Bristol-Myers Squibb, Fitbit, Johnson & Johnson, Merck, and Pfizer; and royalties from UpToDate.

Dr. Turakhia discloses personal fees from Medtronic, Abbott, Sanofi, Pfizer, Myokardia, Johnson & Johnson, Milestone Pharmaceuticals, InCarda Therapeutics, 100Plus, Forward Pharma, and AliveCor; and grants from Bristol-Myers Squibb, the American Heart Association, Apple, and Bayer.

A version of this article first appeared on


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