Continuous Monitoring Finds AF Up to 3 Years After Noncryptogenic Stroke

Roughly one out of every five patients with a stroke attributed to large-artery atherosclerosis or a small-vessel occlusion and no prior diagnosis of atrial fibrillation (AF) will have the arrhythmia detected on an insertable cardiac monitor (ICM) when followed for up to 3 years, extended follow-up from the STROKE-AF trial shows.

That’s a much greater proportion compared with patients who are followed in a standard way without prolonged monitoring (21.7% vs 2.4%; HR 10.0; 95% CI 4.0-25.2), Lee Schwamm, MD (Massachusetts General Hospital, Boston), reported today at the International Stroke Conference in Dallas, TX.

It’s not surprising that more AF will be found if you look harder for it, but these results show that new subclinical AF continues to accrue even beyond 1 year in this population, which is not typically targeted for prolonged rhythm monitoring. Guidelines reserve that type of strategy for investigation of patients who have ischemic strokes without a clear underlying cause, based on data from trials like CRYSTAL-AF and EMBRACE, with the idea that finding occult AF will lead to appropriate treatment with oral anticoagulation to prevent recurrent strokes.

Whether treating AF episodes detected through continuous monitoring will improve clinical outcomes remains to be proven in randomized trials, but “if you think finding fibrillation is important, this population is enriched with fibrillation, and if you’re going to go after it aggressively in patients with cryptogenic embolism, you should be going after it equally aggressively” in this group, Schwamm told TCTMD.

STROKE-AF After 3 Years

The STROKE-AF trial, conducted at 33 US centers, included patients with strokes attributed to cervical or intracranial large-artery atherosclerosis or a small-vessel occlusion and no prior history of AF. Investigators randomized 492 patients (mean age 67 years; 38% women) to continuous rhythm monitoring with the Reveal LINQ ICM system (Medtronic) or to usual care that included external cardiac monitoring. Median CHA₂DS₂-VASc score was 5.

As previously reported, the 1-year results showed that continuous monitoring with an ICM picked up more cases of subclinical AF than did standard care (12.5% vs 1.8%), regardless of the cause of the initial stroke.

Extending the results out to 3 years showed that these AF episodes were not just a transient occurrence after the initial stroke but, in fact, continued to accrue, similar to what was seen in the CRYSTAL-AF trial. Most of the ICM-detected episodes (88%) were asymptomatic. Moreover, roughly two-thirds of these patients had at least one episode of AF lasting more than 1 hour, which speaks to the clinical relevance of the finding.

Of note, many AF episodes were detected over the long term and thus would not have been identified using short-term monitoring—the median time to the first adjudicated AF episode was 99 days at 1 year of follow-up and 284 days at 3 years.

The longer follow-up allowed researchers to identify predictors of AF, which included congestive heart failure, left atrial enlargement, a body mass index over 30 kg/m², and a QRS greater than 120 ms. The rate of ICM-detected AF rose to 30.0% in patients with at least one of these factors, which compares with a detection rate of 8.6% in the control arm.

Subclinical AF and Recurrent Stroke Risk

A big question that remains, Schwamm said, is whether these largely subclinical, device-detected AF episodes convey the same risk of recurrent stroke as AF that takes patients to the doctor’s office. “That needs to be studied further, but I just think the answer is: you can’t look the other way,” he said. “If you really care about finding fibrillation, it’s common in this population and you need to start thinking about fibrillation as a biomarker of patients at risk for stroke.”

Similar to what was observed at the 1-year time point in STROKE-AF, there was no significant difference in the rate of recurrent stroke between the ICM and control arms at 3 years (17.0% vs 14.1%; P = 0.71), although the trial was not powered for clinical outcomes.

Schwamm reported, however, that only three of the 34 patients who had a recurrent stroke in the ICM arm had AF detected before the event, and only one of those three was on oral anticoagulation at the time. That means most of the recurrent events are related to the small-vessel disease or large-artery atherosclerosis that caused these patients’ strokes in the first place, he said, noting that the challenge will be determining whether larger, more-devasting strokes are being prevented by finding subclinical AF and getting patients on oral anticoagulation.

Additional trials will be needed to answer that question, and although such a study would be difficult to conduct due to the needed size and length of follow-up, it could be done, Schwamm said.

“It’s hard because people are worried that this might be an inappropriate overtreatment of these patients, but I think we fundamentally have equipoise,” he said. “I do think people would randomize patients in the trial, but it [would] have to be very large trial.”

Philip Gorelick, MD (Northwestern University Feinberg School of Medicine, Chicago, IL), chair of the American Heart Association’s stroke brain health science subcommittee, agreed that such a trial could be done in a group of patients with a high enough rate of AF.

But, Gorelick commented to TCTMD, “the real main question is: what are the characteristics of atrial fibrillation that are going to put you at high risk for having a stroke?” Research into that question is ongoing, but one thought is that individuals with sustained amounts of AF should be the focus on treatment with oral anticoagulation, he said.

Schwamm said it’s premature to change guidelines to recommend prolonged monitoring in patients like those enrolled in STROKE-AF or to provide advice on treatment. However, he added, “if I was going to make a change in the guidelines, it would be to say that for the detection of fibrillation, intermittent or short-term external monitoring is insufficient to detect fibrillation.”

He noted that it’s unclear where consumer wearable devices like smartwatches might fit in, pointing to uncertainties about accuracy and how the data will be managed by the healthcare system. “If finding fibrillation is important, then the data clearly shows that continuous insertable cardiac monitors are the preferred method of detection for occult atrial fibrillation,” said Schwamm.