Echo-Physiologic Aspects of Dyssynchrony and Resynchronization

The research described in the thesis explores the key mechanisms through which a dyssynchronous electrical activation of the heart leads to cardiac mechanical dysfunktion. It also explores the working mechanisms of a highly effective therapy in these patients, known as Cardiac Resynchronization Therapy (CRT). Hence, the physiology of cardiac dyssynchrony and resynchronization is explored. The technique used for this exploration is a new echocardiographic technique (speckle tracking deformation imaging), which examines th timing and amount of myocardial shortening (contraction) and stretching. Applying known physiologic aspects to improve our echocardiographic approach in the field of dyssynchrony and CRT, and inversely improving our physiologic knowledge from the results of the study, has led to the development of new indices of dyscoordination. Dyscoordination of the heart, and abnormal stretch in the septum following early shortening (septal rebound stretch), are found to have major impact on the functional consequences of cardiac dyssynchrony, but simultaneously represent the substrate to CRT. Comparing to classical dyssynchrony measures that measure only the difference in timing of motion or shortening, measuring stretch-based dyscoordination metrics as septal rebound stretch, improves our capacity to predict who exactly will respond to CRT, and who will not.