Morphological and Temporal Variations of Seismocardiograms Across the Chest: A Guide for Single Channel Sensor Placement

Context: Accuracy of single channel Seismocardiogram (SCG) for cardiac monitoring relies on sensor placement, owing to the signal attenuation and delay caused by propagation effects on the chest. Aims: This work comprehensively evaluates the morphological and time delay variation in SCG data across the chest in comparison with the conventionally used xiphoid channel SCG (xSCG). Methods: Multichannel SCG (mSCG) on the chest were recorded with a high-fidelity air-borne ultrasound based Surface Motion Camera from 15 healthy volunteers. Cross-correlation and Dynamic Time Warping (DTW) based distance analysis were performed between the mSCG and xSCG to quantify the similarity, delay and morphological dissimilarity as well. Results: Although the correlation similarity is preserved (>0.7) over all channels localized over the heart, the morphological dissimilarity increases while moving away from the xiphoid with the DTW distance increasing to 50% near the aortic and pulmonary auscultation points. Channels near the apex of the heart shows a time advancement of
$8\quad \pm\quad 7\quad ms$
compared to xSCG. Conclusions: These findings can aid in the sensor placement problem to ensure better accuracy and robustness for single channel SCG based cardiac monitoring applications.