Signal processing
AFib Detection via RR Irregularity Analysis
PPG-based atrial fibrillation detection exploits the hallmark irregularly irregular ventricular rhythm of AF by analyzing statistical properties of consecutive interbeat intervals — coefficient of variation, RMSSD, sample entropy, and Poincaré plot dispersion — to distinguish AF from normal sinus rhythm.
How it works
Schematic summary of this guide. Waveforms are illustrative, not measured data.
AF produces chaotic atrial electrical activity that conducts irregularly through the AV node, creating unpredictable ventricular intervals. This translates to highly variable pulse-to-pulse intervals in PPG with characteristic statistical signatures: elevated coefficient of variation, high RMSSD relative to mean IBI, increased sample entropy (loss of regular periodicity), and dispersed Poincaré plots with SD1 >> SD2 (cloud pattern vs. ellipse).
The key challenge is distinguishing paroxysmal AF (intermittent episodes) from frequent ectopic beats, which produce similar IBI irregularity.
Two large studies tested consumer PPG irregular-rhythm algorithms. In the Apple Heart Study (Perez et al. 2019, doi:10.1056/NEJMoa1901183), the positive predictive value of an irregular pulse notification for simultaneous AF on an ECG patch was 0.84. In the Fitbit Heart Study (Lubitz et al. 2022, doi:10.1161/CIRCULATIONAHA.122.060291), the positive predictive value for concurrent AF was 98.2%. The studies used different definitions, so the figures should not be compared directly.
Frequently Asked Questions
What is the minimum AF episode duration detectable by PPG?
Detection depends on how often the algorithm samples the pulse and how long a window it analyses, so brief paroxysmal episodes can be missed. Continuous monitoring increases the chance of capturing an episode.
Can PPG differentiate AF from frequent premature beats?
Frequency of premature beats (PACs/PVCs) confounds simple irregularity metrics.
What is the false positive rate for PPG AF screening?
False positives are higher in younger populations with physiological sinus arrhythmia.