Three-dimensional reconstruction of the functional strain-line pattern in the left ventricle from 3-dimensional echocardiography.

A dvances in 3-dimensional (3D) echocardiography offer a rapid, effective imaging technique with adequate temporal and spatial resolution for left ventricular motion assessment. 3D multidirectional tracking of the endocardial left ventricular layer has shown that the functional pattern of directional strain arrangement during cardiac contraction closely relates with the structural architecture of the myocardial heli-cal muscle fiber orientation. 1 In a similar manner, we carried out segmentation tracking of the endocardial-epicardial layers in 10 healthy young athletes (nonprofessional athletes, enrolled at the Sport Medicine Center of the University of Florence, Italy, training 2–3 days a week for 2 hours daily; all exhibiting an excellent echographic window) to evaluate the 3D strain pattern over the whole myocardium thickness and to compare with the hypothesized underlying fiber architecture. An echocardiographic 3D full-volume image of the left ventricular was recorded by a Philips IE33 machine (frame rate, 15–30 Hz). Imaging data were processed by 3D feature tracking (4DLVA 3.0; TomTec Gmbh, Unterschleissheim, Germany), and the endocardial and epicardial tracked surfaces were exported for the following principal strain analysis. 1 Principal strain analysis allows to define the direction along which the main contractile strain (S1) develops, accompanied by a secondary strain (S2) that is typically of much lower intensity and by a thickening (positive strain, S3, that is a consequence of tissue incompressibility S1+S2+S3≈0). The analysis identifies the directions along which such strains act, such that, relative to such directions, shear deformations are absent. Therefore, this approach gives a physics-based synthesis of the overall 3D deformation pattern into 1 principal strain (S1) and 1 secondary strain (S2), with the third strain following from incompressibility. Figure 1 depicts the principal end-systolic strain pattern on the subendocardial, subepicardial layers and short axial slices along the left ventricle (left and right images, respectively; see also Video I in the online-only Data Supplement for the time course). All the images are an average of the volunteers to reduce the noise that results from the echography and the inaccuracies of the 3D echocardiography tracking. Besides noise, individual cases within this homogeneous group did not deviate much from the shown pattern. Results show similar directions of the principal end-systolic strain to those reported by magnetic resonance diffusion tensor imaging. 2 The principal strain lines showed a remarkable relation with the reported orientation and activation sequence of the muscle fibers reported with combined displacement encoding with stimulated echoes and cine strain …