Multi-Tier Validation of a Single-Lead Wearable ECG Signal-Processing Pipeline: Clinical Comparison and Algorithmic Benchmarking on Public Expert-Annotated Databases

Wearable single-lead electrocardiogram (ECG) devices are increasingly used for out-of-clinic rhythm monitoring, but the rigour with which their signal-processing pipelines are validated varies widely across the literature, with most published reports relying on either a single clinical comparison or a single algorithmic benchmark. We propose and apply a multi-tier validation methodology—combining clinical reference comparison, expert-annotated database benchmarking, and a deliberate morphological stress-test—and demonstrate it on the SmartGuard single-lead wearable ECG device and its signal-processing pipeline. The three tiers comprise (i) a within-subject clinical comparison in 31 healthy adult volunteers against a Bionet Cardio 7 limb-lead Lead I reference with cardiologist-confirmed measurements (a two-electrode limb configuration approximating Lead I, not a full diagnostic 12-lead ECG), (ii) algorithmic benchmarking on the Lobachevsky University ECG Database (LUDB, 200 records, expert annotations), and (iii) a robustness stress-test on the QT Database (QTDB, 103 records, hybrid expert annotations). The pipeline integrates discrete wavelet transform-based PQRST delineation with a derivative-based QRS-width refinement, a tangent-method T-wave end estimator, and median-absolute-deviation robust averaging. In the clinical tier, mean within-subject biases were negligible for heart rate, QT, QTc and RR (all p > 0.6) and borderline for QRS duration (+7.3 ms, p = 0.066), with a systematic R-wave amplitude underestimation (−0.15 mV, p < 0.0001). On LUDB, heart-rate and RR-interval agreement were excellent (Pearson r > 0.95) and QRS duration good (r = 0.73, MAE 13.8 ms). On QTDB, performance degraded in line with the increased morphological heterogeneity of the dataset, particularly for QT-related metrics. Despite this minimal mean bias at the population level, individual-record QT and QTc errors showed high dispersion, precluding accurate clinical QT interpretation from single wearable traces in individual patients. Moreover, the resting, healthy-adult design of the clinical tier means its findings cannot be extrapolated to arrhythmic conditions or exercising states. The protocol is described in sufficient detail to serve as a template for evaluating other wearable single-lead ECG devices.