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

Background and Aims 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. Methods 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. Results 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 . 3 6 ± 0 . 7 5 , JTVI − 0 . 1 0 ± 0 . 7 5 ), the SD of JT and QT intervals strongly agreed ( 𝑅 2 > 0 . 9 9 , bias − 0 . 4 ± 1 . 5 ms, 1 . 1 ± 3 . 9 %), and JTVI and QTVI correlated closely ( 𝑅 2 > 0 . 9 8 , QTVI = 1 . 0 × JTVI − 0 . 2 6 , bias − 0 . 2 6 ± 0 . 1 1 ms). Among a separate group of healthy volunteers (n=20, age 4 3 ± 1 1 years, 25% female, heart rate 6 6 ± 1 4 beats/min, JTVI − 0 . 5 2 ± 0 . 5 1 ), there was excellent agreement for ECG-derived and radar-estimated SD of JT ( 𝑅 2 = 0 . 8 8 , bias 0 . 1 ± 4 . 9 ms, 6 . 4 ± 2 . 7 %), SD of beat-to-beat interval (SDNN) ( 𝑅 2 = 0 . 9 3 , bias 1 6 . 0 ± 2 2 . 1 ms, 9 . 5 ± 4 . 9 %), and JTVI ( 𝑅 2 > 0 . 9 9 , bias 0 . 0 0 ± 0 . 0 5 , 0 . 0 ± 6 . 5 %). Conclusion 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.