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.