Definition of Fiducial Points in the Normal Seismocardiogram

Abstract

The purpose of this work is to define fiducial points in the seismocardiogram (SCG) and to correlate them with physiological events identified in ultrasound images. For 45 healthy subjects the SCG and the electrocardiogram (ECG) were recorded simultaneously at rest. Immediately following the SCG and ECG recordings ultrasound images of the heart were also obtained at rest. For all subjects a mean SCG signal was calculated and all fiducial points (peaks and valleys) were identified and labeled in the same way across all signals. Eight physiologic events, including the valve openings and closings, were annotated from ultrasound as well and the fiducial points were correlated with those physiologic events. A total of 42 SCG signals were used in the data analysis. The smallest mean differences (±SD) between the eight events found in the ultrasound images and the fiducial points, together with their correlation coefficients (r) were: atrial systolic onset: −2 (±16) ms, r = 0.75 (p < 0.001); peak atrial inflow: 13 (±19) ms, r = 0.63 (p < 0.001); mitral valve closure: 4 (±11) ms, r = 0.71 (p < 0.01); aortic valve opening: −3 (±11) ms, r = 0.60 (p < 0.001); peak systolic inflow: 13 (±23) ms, r = 0.42 (p < 0.01); aortic valve closure: −5 (±12) ms, r = 0.94 (p < 0.001); mitral valve opening: −7 (±19) ms, r = 0.87 (p < 0.001) and peak early ventricular filling: −18 (±28 ms), r = 0.79 (p < 0.001). In conclusion eight physiologic events characterizeing the cardiac cycle, are associated with reproducible, well-defined fiducial points in the SCG.

A Novel Adaptive Recursive Least Squares Filter to Remove the Motion Artifact in Seismocardiography

“…Constant values -0.007 and 0.01 in Equation (11) are the maximum amplitude of the IM envelope peaks and minimum amplitude of the AO envelope peaks respectively [32]. In addition, the time interval between val_max and val_min should be restricted shorter than 0.02s [33]. When loc_min, val_min, loc_max and val_max meet the restrictions in Equation (11), loc_max and val_max are the timestamp and the value of the extracted AO peak respectively.…”

A Clinical Method for Estimation of VO2max Using Seismocardiography

“…As the alignment to the ECG R-peak can result in a smoothed second heart sound (S2) with inaccurate fiducial points around S2, due to variation in the systolic to diastolic time interval, the individual beats were aligned to the S2 as follows: The acceleration signal recorded from IC4 was forward-backward filtered with a Butterworth bandpass filter of 1 st order with cutoff frequencies of 50 and 500 Hz to obtain a proxy for heart sound. Using this filtered signal, the individual beats were aligned to the location of the peak envelope of the S2-sound as described in [14].…”

“…The first description of the SCG was by Mounsey in 1956 and the technique has since been investigated in different settings, although SCG is not used by clinicians today [11,13]. The fiducial points in the SCG signal are correlated to events such as heart valve opening and closings in the cardiac cycle [14]. Time intervals have previously been correlated with those obtained by echocardiography in both healthy subjects and heart failure patients [12,[15][16][17].…”

“…Therefor we investigate the correlation between VO2max and the timing and amplitudes of SCG fiducial points [14]. Besides investigating these parameters by them self, we also include the parameters in a linear model together with demographic data for estimation of VO 2 max.…”

Visualization of the Multichannel Seismocardiogram

“…Single segments of either one or three second length where used for the visualization methods. The SCG signals were filtered with a forwards-backwards low and high-pass Butterworth filter of 90 Hz and 0.05 Hz [8].…”