Screening for AF: More Questions Than Answers

In the early days of the pandemic, we were debating the merits of telemedicine to avoid bringing patients into the office. I was very much in favor of telemedicine, but some of my colleagues argued that seeing patients in person in the clinic gave you the opportunity to do ECGs and catch atrial fibrillation (AF).

I don't doubt that you will catch some AF that way and that some patients might have AF and not realize it if they don't regularly come into contact with the medical system. But screening for AF has always been a tricky proposition and the evidence for it has been scant.

Two recent trials from the European Society of Cardiology (ESC) have actually made the question less clear, at least in my mind. The findings from LOOP and STROKESTOP were, superficially at least, contradictory. LOOP showed no benefit to screening asymptomatic, at-risk patients for AF whereas STROKESTOP did.

However, the different approaches used to screen for AF likely explain some of these differences. The LOOP study used an implantable loop recorder and anticoagulated anyone with episodes of AF lasting 6 minutes or more, whereas STROKESTOP had patients in the intervention arm get twice-daily ECGs for 2 weeks.

Much ink has been spilled on these results already but, in brief, LOOP showed an increase in AF detection, and it would have been shocking if that had not been the case with implantable loop recorders in patients. But the increased AF detection and subsequent anticoagulation did not reduce the incidence of stroke and systemic embolism, nor the risk for death or even cardiovascular death. STROKESTOP by contrast did show a benefit for screening and anticoagulating, albeit a modest one in their primary endpoint that included stroke, embolism, bleeding, and hospitalizations.

When comparing trials, one must always remember that these are different studies with different protocols, done in different patient populations. While we are not quite comparing apples to oranges, we are at least comparing two different types of apples. Follow-up was longer in STROKESTOP, the primary endpoint was different, and the studies were conducted in different countries. But the biggest difference between the trials is clearly the approach to AF screening. LOOP used continuous monitoring whereas STROKESTOP used an intermittent screening strategy with regular ECGs. Continuous monitoring by definition is going to pick up shorter and probably less clinically significant AF episodes that don't require anticoagulation. Knowing where to draw that anticoagulation line is far from clear, though.

All this to say, there may be some benefit to regular AF screening in high-risk populations, but how to do it in the practical sense is far from certain. I've found that most patients are not willing to have implantable devices, and the negative findings from LOOP seem to be justifying their reluctance. But I suspect that many patients are going to be equally unwilling to come in to clinic twice a day for an ECG, which should remind us that what works in a clinical trial doesn't always work in day-to-day practice.

What is more likely is that patients are going to increasingly use home monitoring devices that can record a rhythm strip when synced to a smartphone, or perhaps record their heart rhythm on a smartwatch like the Apple Watch. I will confess to having gleaned useful information from a small number of patients who have managed to record and document specific arrhythmias using their Apple Watch, although I'm less certain of the benefit if these smartwatches start picking up short episodes of asymptomatic atrial fibrillation.

We are often reluctant to admit when we are uncertain about a specific course of action, but I think it is fair to say that some uncertainty about AF screening remains. The benefit of continuous monitoring seems to be somewhat in doubt, but the best way to implement intermittent screening remains very debatable. Given the ubiquity of ECG use when patients interact with the healthcare system, our current status quo of opportunistic screening may serve us well for the time being. We may have to wait and see.

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