Deep Learning Approach to AF Detection Using
Photoplethysmography Data
Photoplethysmography (PPG) data is a pulse pressure waveform detected
using a light source and a photodetector.80 This
technology has been successfully used previously to detect oxygen
saturation, heart rate and respiratory rate. On PPG data, AF is
manifested as variable pulse-to-pulse intervals and
morphologies.80 Several studies have tested DL
algorithms on PPG data to detect AF, although many of these included
very few patients.81,82
There is also a trend towards the use of consumer-grade wristbands and
watches to detect AF. In Huawei heart study, of the 187,912 individuals
who used smart devices for PPG analysis, only 0.23% received ‘suspected
AF’ notification.83 Out of those undergoing an
effective follow up, 87% were confirmed as having AF. These results
show an impressive positive predictive value of
91.6%.83
In Apple Heart Study, Apple smartwatches were used to detect AF using a
proprietary PPG based algorithm.84 Of the 419,297
patients enrolled over an 8-month period, only 2161 (0.52%) received a
notification for irregular pulse. After a telemedicine visit, ECG
patches were mailed to the patients to be worn for up to 7 days. Among
450 patients who returned patches with analyzable data, only 34% were
diagnosed with AF, even though the algorithm was designed to maximize
specificity. Furthermore, sensitivity and thus usefulness as a screening
tool could not be assessed from this study.84
The Fitbit Heart Study- another large prospective study applying a
similar methodology is currently underway.85 These
studies highlight the barriers to mass screening for AF in healthy
populations particularly given the low benefit to cost ratio.
Some key limitations of using PPG data include high false positive rate
due to detection of other arrythmias mimicking AF, low signal to noise
ratio and motion artifacts.80 One study showed that
almost 40% of the signal was unusable.86 Due to these
limitations, the 12-SL ECG remains the gold standard to detect
arrythmias including AF.