Recently, Apple launched new heart-related features for their Apple Watch, including an app cleared by the US Food and Drug Administration that notifies wearers if atrial fibrillation has occurred. Apple admits, however, that the watch cannot detect all episodes; inconclusive results are possible; and it is not intended for people with known atrial fibrillation.1 Notably, this comes shortly after the US Preventive Services Task Force published an advisory stating: “the current evidence is insufficient to assess the balance of benefits and harms of screening for atrial fibrillation with electrocardiograms (ECG).”2 So, what is the public to do about atrial fibrillation screening? The answer depends on whether screening is needed (Table 1).
In patients with unexplained but atrial fibrillation-compatible symptoms, determining if atrial fibrillation is causative is important for diagnosis and therapy. However, this is quite different than mass screening of the public to seek atrial fibrillation when no hint of it exists, risk from atrial fibrillation is low, and treatment implications are uncertain. In contrast, understanding the relationship among atrial fibrillation, thromboembolism, and utility of prophylactic anticoagulation3 has prompted pre-event identification efforts using progressively advanced monitoring technologies in subjects with demographic, genetic, or laboratory risk markers4 that identify an increased likelihood of having atrial fibrillation with thromboembolic risk and in whom cost-effective oral anticoagulation reduces thromboembolic events. Monitoring such patients seems appropriate because atrial fibrillation is often asymptomatic and unrecognized until thromboembolism; symptomatic and asymptomatic atrial fibrillation patients have similar adverse outcome rates5; device-detected atrial fibrillation has been linked to increased stroke and death risk6; and, most of these atrial fibrillation-linked demographics are also high-risk markers for thromboembolism in patients with atrial fibrillation. This contrasts with the uncertain and likely low cost-benefit of mass population screening, especially with smartwatches most often worn by younger individuals,7 such as millennials in whom high-risk markers for thromboembolism in atrial fibrillation are infrequent.
If one believes detecting atrial fibrillation in subjects with high-risk markers for thromboembolism is an important public health goal and its treatment is warranted, then we should monitor such individuals. Detection may occur fortuitously during an electrocardiogram (ECG), but it is more likely via systematic ECG screening at specific time points, such as yearly medical visits; opportunistic ECG screening, such as during vaccinations or pharmacy visits; scheduled ambulatory ECG monitoring with varying devices for variable durations; semi-continuous monitoring with a smartwatch; or continuous monitoring with an inserted or implanted device. With external monitoring in differing populations using various devices but not smartwatches, atrial fibrillation detection has been 0.2%–5.3%.8, 9, 10, 11, 12, 13, 14 Importantly, detection of atrial fibrillation increases with longer durations of monitoring.8, 9, 10, 11, 12, 13, 14, 15 One could assume that general population screening with smartwatches (which are not worn continuously) would also yield single digits per year incidences. Of note, not all atrial fibrillation detected by devices is new. In an AFinder Program in Hong Kong,13 2.3% had atrial fibrillation detected, but detection of new cases of atrial fibrillation occurred in only 0.69%. That is contrasted with significantly higher newly detected cases of atrial fibrillation that ranged from 20% to 40% during 12-30 months of follow-up in single-arm trials using continuously recording implanted or inserted cardiac monitors in patients without known atrial fibrillation but with demographic or laboratory markers common to atrial fibrillation.15 Recognizing that atrial fibrillation is often intermittent or transient, one can understand why intermittent monitoring will miss many atrial fibrillation events that can be identified with inserted monitors (Figure 1).
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-James A. Reiffel, MD
This article originally appeared in the June 2019 issue of The American Journal of Medicine.
