Approximately 20 percent of strokes are secondary to atrial fibrillation, and these strokes are often associated with a poor outcome. An additional 30 percent of strokes are cryptogenic and potentially caused by undetected atrial fibrillation. The aim of the newly published LOOP trial was to investigate whether continuous screening for atrial fibrillation — with a subsequent anticoagulant treatment when atrial fibrillation was detected — might prevent stroke in elderly persons at high risk.
The trial evaluated 6,004 elderly patients (aged 70-90) in Denmark without atrial fibrillation and with at least one risk factor for stroke. These risk factors included hypertension in 91 percent, diabetes in 28 percent, a prior stroke in 18 percent, and heart failure in four percent. Medication use included renin-angiotensin inhibitors (66%), statins (58%), and platelet inhibitors (48%). Patients were randomized to continuous electrocardiogram (ECG) monitoring using an implantable loop recorder or to a control group. Patients implanted with the loop recorder were monitored remotely via automated transmissions that were reviewed daily by a physician. If a patient had an episode of atrial fibrillation lasting at least six minutes, the physician recommended initiation of oral anticoagulation therapy. In the control group, patients received usual care involving an annual interview with a study nurse and an appointment with a general practitioner. The primary outcome of the trial was the risk of stroke or systemic arterial embolism.
All the patients completed the follow-up at a median duration of 64.5 months. Compared with the control group, the patients who had been continuously monitored exhibited higher rates of diagnosed atrial fibrillation (31.8% vs. 12.2%, p < 0.0001) and of anticoagulation therapy initiation (29.7% vs. 13.1%, p < 0.0001). However, there was no statistically significant difference in the risk of stroke or systemic arterial embolism (4.5% vs. 5.6%, hazard ratio 0.8, 95% CI 0.61-1.05). The risk of death or major bleeding was also similar between the two groups. Complications leading to the surgical removal of the monitoring device were rare, occurring in nine patients (0.6%).
The trial had several limitations. The effect of the anticoagulation therapy on stroke prevention may not be similar for short-lasting and long-lasting atrial fibrillation episodes. Moreover, the study may have been underpowered because the risk of stroke associated with short duration asymptomatic atrial fibrillation detected by continuous monitoring may be lower than that diagnosed through usual methods (which presumably includes a higher percentage of people with symptoms or sustained atrial fibrillation). An additional factor may have been the high percentage of patients on antiplatelet agents.
Patients who have a smart watch or other readily available monitoring devices are coming into medical offices wondering what to do with transient bursts of tachycardia. Those devices may someday make implantable monitors obsolete (or alternatively, we may see a Choosing Wisely recommendation to stop paying attention to the devices). Studies like this one will be helpful in developing guidance for patients who are concerned about transient asymptomatic tachycardia. To close the LOOP, this trial indicates that screening for atrial fibrillation within these parameters is probably not ready for prime time.
For more information, see the topic Atrial Fibrillation in DynaMed®.
