Ph.D Thesis

Ph.D StudentRappaport Dan
SubjectReconstruction of the Electrical Activation Sequence in the
Left Ventricle Based on Motion Analysis Computed
from B-mode Echocardiograms
DepartmentDepartment of Biomedical Engineering
Full Thesis textFull thesis text - English Version


Asynchronous cardiac activation leads to decreased pumping efficiency. Quantifying the activation sequence may optimize the selection of patients for Cardiac Resynchronization Therapy (CRT) and its efficacy. The feasibility of assessing the directivity and the degree of synchronous activation with ultrasound was examined.

A tissue tracking method estimates the regional motions along a curved ROI and computes various mechanical parameters, such as strain, strain rate and curvature, which reflect the time of activation.

Numerous reconstruction methods based on either of the regional mechanical parameters were examined on a simulation platform. A 2D finite element model (Femlab) simulated a cross section of the left ventricle. Physiological passive and active mechanical properties were regionally assigned to allow induction of an activation sequence followed by a contraction pattern. The first peak strain after activation onset showed superior ability to reconstruct the true activation sequence under various simulated physiological conditions.

The developed method was validated in vivo, by reconstructing the activation maps in 6 open-chest sheep. Initially, the reliability of the tissue tracking method was examined. Concurrent measurements of the shortening of the diameters by implantable sono-crystals were compared to those made by the tissue tracking method. The correlation coefficient of 0.99 +- 0.004 proves the accuracy of the tissue tracking method. 

The sequence of activation was analyzed during normal activation as well as during induced pacing from the anterior and the lateral left ventricle free wall. A vector sum of the regional activation times (SDV) was calculated whose magnitude and angle describe the degree of the synchrony and the directivity of the sequence of activation. The magnitudes and angles of the delay vectors obtained from lateral and septal pacing and the normal activation were statistically different (P<0.05) using paired-t-test. The shift of the estimation of the pacing site from the true position was 20 +- 17°.

The clinical experiments and the computed SDV provided a new evidence of the maximal contraction synchrony, independent of the regional physiological properties.

To summarize, the ability to assess the directivity and the degree of synchronous activation with ultrasound was proved. A method was developed which successfully quantifies the sequence of activation in ultrasound B-mode short-axis cross-sections, which is suitable for further development within the clinical settings.