DOAC or don’t. Asymptomatic AF.

When I was younger, the main thing my watch reminded me of, was that it was considerably shitter than anything the rich kids at school were wearing. Unfortunately, things have got worse. Not happy with creating status anxiety, watches have now started creating health anxiety. If you have eight espressos following a night of sleep training, and then watch the Merseyside Derby, you best be ready for your watch to tell you have AF.

But what do we do with these essentially asymptomatic pick-ups? Guidelines focus on CHA₂DS₂-VASc, but they were created in more simpler times, when AF was generally picked up when people had symptoms (hence why they had the ECG in the first place).

Circulation meta-analysis

A recent Circulation meta-analysis combined data from two randomised controlled trials (NOAH-AFNET 6 and ARTESiA). NOAH-AFNET 6 looked at over 2,500 older patients with short episodes of AF detected by implanted devices. Participants were randomly assigned either Edoxaban or placebo. ARTESiA studied a slightly higher-risk population of more than 4,000 patients with device-detected AF. This time, researchers compared Apixaban with Aspirin.

Results

The results showed that direct oral anticoagulants (DOACs) modestly reduced stroke risk in asymptomatic, device-detected AF, yet increased bleeding rates. In these trials, AF was detected via pacemakers, implanted cardioverter defibrillators, or implantable cardiac monitors, and the patients were otherwise asymptomatic. The median CHA₂DS₂-VASc score in NOAH-AFNET 6 was 4 (IQR 3–5), while ARTESiA reported a mean of 3.9 (±1.1 SD).

When the results of NOAH-AFNET 6 and ARTESiA were combined, anticoagulation reduced the relative risk of ischaemic stroke by 32%. However, it also increased the relative risk of major bleeding by 62%.

The relative numbers sound impressive, but the absolute effects were much smaller because the overall event rates were low. Across these studies, anticoagulation reduced stroke by roughly 3 to 4 events per 1,000 patients treated each year, while causing approximately 6 to 11 additional major bleeds per 1,000 patients treated each year.

In other words, anticoagulation appears to prevent some strokes in patients with device-detected AF, but the absolute benefit is modest and is accompanied by a similar, if not greater, increase in serious bleeding.

The striking finding from both trials is just how low the baseline stroke risk was in patients with device-detected AF.

Clinical implications

Now this cohort of patients is different to our smart watch wearers. Most people who wear this type of device are often health conscious. They are more likely to have a lower CHA₂DS₂-VASc score and thus have an even lower risk of stroke.

Unfortunately there isn’t a well conducted study that answers that particular question for this (it sounds like a wonderful PhD idea). This seems like a perfect time for shared decision making, and this study provides some general ball park figures to help.

Some patients may accept the risk of bleeding to prevent a stroke, particularly if they are active etc. Would anti-coagulation prevent a debilitating stroke? As ever, there are more questions than answers.