Session MA.1

Ultrasound Echocardiographic Assessment of Transmural Inhomogeneity of the Left Ventricular Contraction during the Heart Cycle

N Bachner, D Adam*, M Lightman, Z Vered

Technion
Haifa, Israel

Objectives: The complex fibrous structure and efficient function of the heart produce transmural inhomogeneities of its mechanical properties. The fibers are wound in a spiral structure around the cavity, generating the rotation of the left ventricle during contraction and relaxation. Mathematical models showed that left ventricular rotation tends to equalize the sarcomere shortening between the myocardial layers. Moreover, pathologies that cause left ventricular hypertrophy, increase this inhomogeneity. The purpose of this study was to measure the transmural changes of left ventricular rotation and circumferential strain in normal subjects, in order to establish the normal behavior. Deviations from these values will allow early detection of different pathologies, e.g. aortic stenosis, or heart failure.
Methods: Circumferential strain and the myocardial rotation were calculated at 3 levels (Apical, Papillary muscle and mitral valve) from short-axis ultrasound echo cines in 11 normal subjects, utilizing 2D-Strain program of speckle tracking imaging (UFI, GE Healthcare Inc., and Technion, Israel) and a novel signal processing method. This new method enabled high temporal and spatial resolution measurements of the myocardial velocities, so that the circumferential strain and the myocardial rotation were evaluated during a full heart cycle for 3 myocardial layers.
Results: A significant transmural difference was found in the myocardial rotation and circumferential strain, at the 3 short axis levels. The rotation is larger in the endocardium and decreases towards the epicardium, while the apex and base rotate in counter directions (apex level: endocardium 7.7±3.4 [deg], midwall 5.0±2.3 [deg], epicardium 3.6±2.0 [deg], Papillary muscle level: endocardium 1.4±2.4 [deg], midwall 1.8±2.1 [deg], epicardium 2.3±1.3 [deg], mitral valve level: endocardium -4.4±2.0 [deg], midwall -1.9±2.4 [deg], epicardium -0.5±2.1 [deg]). Similarly, the circumferential strain is larger at the endocardium than at the epicardium. Furthermore, the circumferential strain is larger at the apex level than at the base level (apex level: endocardium -30.6±10.0 [%], midwall -19.1±7.1 [%], epicardium -10.6±5.5 [%], Papillary muscle level: endocardium -26.9±7.2 [%], midwall -17.1±5.4 [%], epicardium -5.7±4.7 [%], mitral valve level: endocardium -21.1±5.4 [%], midwall -14.0±4.0 [%], epicardium -7.9±2.9 [%] ).
Conclusion: Left ventricular transmural inhomogeneities of the left ventricular rotation and of the circumferential strain are measurable by 2D ultrasound, and may serve as a simple, affordable and commonly available diagnostic modality.

(Abstract Control Number: 233)