Three-dimensional apex-seismocardiography

Traditional apex-cardiography measures chest wall vibrations at the apex beat using an air-coupled microphone. To provide additional insight in apexcardiography and chest vibrations we estimated the three dimensional displacement of the apex beat. A 3-axis accelerometer was placed at the location of the apex beat in 5 healthy subjects in left lateral decubitus position. ECG, echo Doppler of the carotid artery and phonocardiography were recorded simultaneous. The 3D displacements of the apex beat were estimated by twofold integration of the accelerometer signal. The most dominating displacement direction was estimated as the largest eigen vector in a principal component analysis (PCA). The peak-to-peak displacements in the longitudinal, transverse and perpendicular dimensions were O.39±O.35 mm, O.28±O.15 mm and O.38±O.12 mm (mean+Std). The dominating displacement direction changed largely from subject to subject, the average deviation from the downward perpendicular axis was 3.8±41 degrees toward the superior direction and with 18.4±30 degrees towards the medial line. The longitudinal and transverse displacements show that single axis measurement along the perpendicular axis only reveals a part of the complex movements at the apex beat.