Effect of measurement location on cardiac time intervals estimated by seismocardiography

Cardiac time intervals (CTIs) are important parameters for assessing cardiac function and can be measured using noninvasive methods such as electrocardiography (ECG) and seismocardiography (SCG). It is widely accepted that SCG signals, when measured from various locations on the chest surface, exhibit distinct temporal and spectral characteristics. In that regard, the goal of this study was to determine the effect of the SCG measurement location on estimating SCG-based CTIs. For this purpose, ECG, SCG, and phonocardiography (PCG) signalswere acquired from fourteen healthy adult subjects, both male and female (Age: 23.5 5.16 years old). Subjects laid still in a supine position and were instructed to breathe normally. Data was recorded for 2 minutes and external noise, if any, was noted and removed. For ECG measurement, Einthoven s triangle was used by placing three ECG electrodes under the left and right clavicle, and the right lower abdomen. For SCG, three tri-Axial accelerometers were attached on the top, middle, and bottom of the sternum with double-sided tape. In this study, only the dorsoventral components of the SCG signals were analyzed. Using Pan-Tompkin s algorithm, ECG R peaks and their temporal indices were found. Then, a custom-built algorithm in MATLAB was developed to estimate heart rate (HR) from ECG (HRECG) and SCG (HRSCG) signals. Furthermore, SCG fiducial points and CTIs were defined based on the literature and estimated from the SCG signals recorded from different sternal locations. These fiducial points and CTIs include the temporal indices of aortic valve opening, aortic valve closure, and R-R interval, as well as pre-ejection period, left ventricular ejection time, and electromechanical systole. The average and correlation coefficient (R2) of the CTIs and HRs derived from all three locations were compared. Mean difference and standard deviation were analyzed for the CTIs and their respective sensor location. Results showed that the average R2 values between HRECG and HRSCG were 0.9930, 0.9968, and 0.9790 for the top, middle, and bottom sternal locations, respectively. In addition, results demonstrated that SCG-based CTIs varied with the SCG measurement locations. In conclusion, these results highlighted the importance of establishing consistent research and clinical protocols for reporting CTIs based on SCG. Thiswork also calls for further investigation into comparing estimated CTIs with gold-standard methods such as echocardiography and 4D cardiac computed tomography. This will help determine the SCG measurement location that provides the most accurate CTI estimations which in turn can improve the accuracy of SCG-based cardiovascular disease diagnosis algorithms.