The SCG signal is measured by placing an accelerometer on the torso which captures the induced vibration of the heart propagated to the surface of the chest. The feasibility of using seismocardiogram (SCG), in conjunction with ECG, for finding cardiac time intervals was first investigated in 1990’s and has also been recently verified. Specific peaks of the SCG signal correspond to different events of the cardiac cycle (Fig. 1).
Systolic time intervals (STI) are important parameters that have been used for quantification of the performance of the heart and include the electro-mechanical systole, left ventricular ejection time (LVET), pre-ejection period (PEP) and isovolumetric-contraction. These parameters can be extracted from SCG as can be seen in the modified Wiggers diagram (Fig 1).
Detection of AO and AC points however is not a trivial task and there has been an extensive effort to properly annotate them with and without ECG signal.
Figure 1. Wiggers diagram amended by SCG. Pre-ejection period (PEP), Left ventricular ejection time (LVET) and Isovolumic contraction period (IVCP) are shown. The SCG annotation are MC (Mitral valve closure), AO (aortic valve opening) and AC (aortic valve closure)