Assessment of left ventricular twist by 3D ballistocardiography and seismocardiography compared with 2D STI echocardiography in a context of enhanced inotropism in healthy subjects

Abstract

Ballistocardiography (BCG) and Seismocardiography (SCG) assess the vibrations produced by cardiac contraction and blood flow, respectively, by means of micro-accelerometers and micro-gyroscopes. From the BCG and SCG signals, maximal velocities (V_Max), integral of kinetic energy (iK), and maximal power (P_Max) can be computed as scalar parameters, both in linear and rotational dimensions. Standard echocardiography and 2-dimensional speckle tracking imaging echocardiography were performed on 34 healthy volunteers who were infused with increasing doses of dobutamine (5-10-20 μg/kg/min). Linear V_Max of BCG predicts the rates of left ventricular (LV) twisting and untwisting (both p < 0.0001). The linear P_Max of both SCG and BCG and the linear iK of BCG are the best predictors of the LV ejection fraction (LVEF) (p < 0.0001). This result is further confirmed by mathematical models combining the metrics from SCG and BCG signals with heart rate, in which both linear P_Max and iK strongly correlate with LVEF (R = 0.7, p < 0.0001). In this setting of enhanced inotropism, the linear V_Max of BCG, rather than the V_Max of SCG, is the metric which best explains the LV twist mechanics, in particular the rates of twisting and untwisting. P_Max and iK metrics are strongly associated with the LVEF and account for 50% of the variance of the LVEF.

Figure 1

Synchronization of SCG and BCG signals with LV twist. From top to bottom: (a) ECG with the P-Q-R-S-T waves labeled; (b) LV twist, apical and basal rotations; (c) angular rates of LV twist, apical and basal twist rotations; (d) K_Lin SCG; (e) K_Rot SCG; (e) K_Lin BCG; (f) K_Rot BCG. The first of the two main peaks of K_Lin SCG (d) and K_Rot SCG (e) occurs before the aortic valve closure (AVC), during the ejection phase of cardiac cycle and concomitantly with the acceleration of LV twist; the second one occurs after the AVC, synchronously with the deceleration phase of LV twist. With regards to the BCG, waves of K_Lin and K_Rot occur almost exclusively after the AVC, during the diastolic phase of cardiac cycle. The Aortic Valve Closure (AVC) is labeled on the figure. K_Lin kinetic energy in the linear dimension, K_Rot kinetic energy in the rotational dimension, SCG seismocardiography, BCG ballistocardiography, ECG electrocardiogram, LV left ventricle.

Figure 2

Correlations between metrics of BCG and SCG with the LVEF. Mathematical models combining: (A) linear P_Max of SCG and BCG with the LVEF and (B) iK of SCG and BCG with the LVEF (both R = 0.7, p < 0.0001).