The emergence of personal monitoring devices
In recent years there has been an increasing array of direct-to-consumer
devices capable of detecting AF, predominantly utilizing smart phones
and smart watches. Survey data from the Pew Research Center
(www.pewresearch.org) suggests that
the proportion of US adults with a smart phone has roughly doubled since
2011 to over 80% and the proportion who use a smartwatch or fitness
tracker now exceeds 20%, with ongoing expansion each year as more
products enter the marketplace. The resulting growth in patient driven
heart rhythm monitoring without direct physician oversight has empowered
patients to investigate their own rhythm abnormalities either as a
screening tool or for disease management. Current methods available to
monitor for AF include smart phone finger pulse wave
photoplethysmography (PPG) using downloadable applications and hardware
already present in modern smartphones, external electrodes that
communicate with an app downloaded to a smart phone used to generate an
mobile single or six-lead electrocardiogram (iECG), or smart watch PPG
with or without single lead iECG confirmation (by touching the crown of
the watch with opposite hand to create a single lead ECG).
Personal monitoring devices have been shown to have a relatively high
accuracy in detecting AF. The SEARCH-AF study used iECGs to screen 1000
pharmacy customers for AF using 12 lead ECG confirmation, finding a
sensitivity of 98.5% and specificity of 91.4% for AF, diagnosing new
AF in 1.5% of customers, all of which had a CHADS-VASc score of 2 or
more and therefore would conceivably benefit from anticoagulation to
reduce stroke risk28,29. Chan and colleagues screened
1013 primary care patients with a smartphone camera-based PPG algorithm
against iECG tracings reviewed by two cardiologists and found a
sensitivity of 92.9% and specificity of 97.7%, though lower
sensitivities are reported outside the research
setting30. The WATCH AF trial31compared the accuracy of an automated wrist watch PPG algorithm in
diagnosing AF in 672 hospitalized patients as compared to a single lead
iECG interpreted by cardiologists as a reference. Although 21.8% of PPG
datasets were not interpretable, the remaining datasets had a
sensitivity of 93.7% and specificity of 98.2% for detecting AF.
Contact-free facial PPG using subtle beat-to-beat variations of skin
color has similarly shown promise in detecting AF with similar
sensitivity32. As a proof of concept on a larger
community scale, the Apple Heart Study recruited 419,297 participants
with smart watches using an irregular pulse notification algorithm and
mailed a 7-day continuous Holter monitor patch to those with an
irregular pulse. They found that 0.52% of participants received
notifications of an irregular pulse, of which 34% had AF diagnosed on
the monitoring patch that was placed on average 13 days
later33. Of the 86 participants that had an irregular
pulse notification subsequently while wearing a patch, the positive
predictive value of the irregular pulse notification was 0.84 in
detecting AF confirmed on the patch.
Advancements in wearable AF-sensors raises the possibility that
assessment of AF duration and burden over long time horizons will no
longer require implantable devices. In a study of 24 patients Wasserlauf
and colleagues compared the accuracy of a simultaneous deep
convolutional neural network PPG algorithm with single lead iECG
confirmation using KardiaBandTM (AliveCor, Mountain
View, CA) with simultaneous ICM recordings34. The
smart watch algorithm had a sensitivity of 97.5% in detecting AF
episodes > 1 hour and had a high correlation
(R2 0.996) with the duration of AF recorded on the
ICM. With studies suggesting that stroke risk is highest for the 30 days
following an episode of AF35 and that hours and not
minutes of AF is likely necessary to increase stroke risk in those with
few vascular risk factors, wearable AF-detection devices raise the
possibility that stroke risk and bleeding risk can be reduced by
targeted, time-delimited, “pill-in-pocket” anticoagulation in those
with infrequent episodes of paroxysmal AF, either spontaneously or as
the result of AF ablation or surgery.