Exploring the Impact of Sensor Location on Seismocardiography-Derived Cardiac Time Intervals

Cardiac time intervals (CTIs) are important parameters for evaluating cardiac function and can be measured noninvasively through electrocardiography (ECG) and seismocardiography (SCG). SCG signals exhibit distinct spectrotemporal characteristics when acquired from various locations on the chest. Thus, this study aimed to explore how SCG measurement location affects the estimation of SCG-based CTIs. ECG and SCG signals were acquired from 14 healthy adults, with three accelerometers placed on the top, middle, and bottom of the sternum. A custom-built algorithm was developed to estimate heart rates (HRs) from ECG (HRECG) and SCG (HRSCG) signals. Moreover, SCG fiducial points and CTIs, including aortic valve opening and closure, R-R interval, pre-ejection period, left ventricular ejection time, and electromechanical systole, were estimated from the SCG signals at different sternal locations. The average and correlation coefficient (R2) of the CTIs and HRs derived from all three locations were compared, along with the analysis of mean differences for the CTIs and their corresponding sensor locations. The results indicated strong correlations between HRECG and HRSCG, with average R2 values of 0.9930, 0.9968, and 0.9790 for the top, middle, and bottom sternal locations, respectively. Additionally, the study demonstrated that SCG-based CTIs varied depending on the SCG measurement locations. In conclusion, these findings underscore the importance of establishing consistent protocols for reporting CTIs based on SCG. Furthermore, they call for further investigation to compare estimated CTIs with gold-standard methods like echocardiography to identify the best SCG measurement location for accurate CTI estimations.