Adaptive Autocorrelation Based Heart Rate Estimation from Single-Axis Seismocardiogram: A Comprehensive Benchmark...

We introduce AACFD (Adaptive Autocorrelation Function Detector), a lightweight, fully automatic pipeline for estimating window-averaged heart rate (HR) from a single-axis seismocardiogram (SCG) without ECG calibration or machine learning. AACFD combines two periodicity detectors-(i) a YIN-style difference-function analysis of an adaptive SCG envelope and (ii) a short-window autocorrelation branch-operating on 3 s segments. The two branches are fused by feature-aware weighting based on signal-quality indices and multi-scale features; and a Hampel filter plus temporal consistency checks remove outlier windows. The algorithm is efficient enough for real time implementation on commodity hardware. AACFD was validated on 535 subjects spanning six heterogeneous datasets (sampling rates 200 Hz-5 kHz): lab oratory mechanocardiograms (MCG), controlled-breathing SCG (CEBS), motion-rich multichannel SCG (MC-SCG), valvular heart-disease clinics (VHD), invasive right-heart catheterization (RHC), and smartphone recordingsfrom300 atrial-fibrillation/sinus-rhythm subjects. For each recording we analyzed non-overlapping windows of 10, 20, 30, and 60 s and compared the SCG-derived mean HR with ECG derived (or telemetry) reference values. After ECG- and SCG-based quality control and temporal refinement, the mean per-subject mean absolute error (MAE) on 30-s windows was 0.99 bpm in MCG, 0.72 bpm in CEBS, 4.38 bpm in VHD, 1.34 bpm in MC-SCG after removal of recordings with corrupted ECG, 3.58 bpm in RHC, and 7.67 bpm in the smartphone cohort. Across all datasets, more than 90% of non-overlapping 10-60 s windows passed ECG- and SCG based quality control, so the reported errors reflect nearly the full usable recording duration rather than a few selected clean segments. This cross-dataset benchmark indicates that a short window hybrid YIN and autocorrelation routine, guarded by simple robustness checks, attains sub-bpm accuracy on resting datasets and clinically acceptable accuracy on several pathological cohorts using only a single accelerom eter axis. Importantly, AACFD is deliberately designed and evaluated for reliable window-averaged HR estimation on 10-60 s time scales rather than instantaneous beat-to-beat HR; deriving robust heart-rate-variability indices from SCG remains an important direction for future work.