Quantifying myocardial repolarization instability using wearable radar-based non-skin-contact estimation of the JT...

Myocardial repolarization instability measured by electrocardiography (ECG) as the QT variability index (QTVI) predicts arrhythmic risk. This proof-of-concept study aims to validate a non-skin-contact wearable radar-based technique for monitoring myocardial repolarization instability.

QTVI by ECG (normalized QT variability to normalized heart rate variability) was compared to the analogous J-point-to-T-end variability index (JTVI) by ECG. Simultaneous 2-minute ECG and wearable radar recordings acquired under controlled, seated conditions were analysed using an intelligent algorithm to extract mechanical correlates of the J-point and T-end from radar-derived cardiac motion signals, and compared to JTVI by ECG.

Based on a selection of publicly available datasets of 9 patients with atrial fibrillation, 11 patients with sinus rhythm, and 20 healthy people (n=40, 23% with atrial fibrillation, mean ± SD heart rate 85 ± 12 beats/min, QTVI -0.36±0.75, JTVI -0.10±0.75), the SD of JT and QT intervals strongly agreed (R²>0.99, bias -0.4±1.5 ms, 1.1±3.9%), and JTVI and QTVI correlated closely (R²>0.98, QTVI =1.0× JTVI -0.26, bias -0.26±0.11 ms). Among a separate group of healthy volunteers (n=20, age 43±11 years, 25% female, heart rate 66±14 beats/min, JTVI -0.52±0.51), there was excellent agreement for ECG-derived and radar-estimated SD of JT (R²=0.88, bias 0.1±4.9 ms, 6.4±2.7%), SD of beat-to-beat interval (SDNN) (R²=0.93, bias 16.0±22.1 ms, 9.5±4.9%), and JTVI (R²>0.99, bias 0.00±0.05, 0.0±6.5%).

QTVI and JTVI demonstrate strong agreement with a small systematic bias in quantifying myocardial repolarization instability, and JTVI can be accurately and precisely estimated using radar sensors. This study provides an initial proof-of-concept demonstration of the feasibility of non-skin-contact wearable radar-based monitoring of arrhythmic risk, with particular applicability to culturally sensitive populations.