M.Sc Thesis

M.Sc StudentSpeizman Shay
SubjectExploring the Dependence of the Atrio-Ventricular Delay on
the Loading Conditions
DepartmentDepartment of Biomedical Engineering
Supervisor ASSOCIATE PROF. Amir Landesberg


Congestive heart failure, despite significant advances in therapy, is still associated with high morbidity and mortality rates and is the leading cause of death in the western world. Cardiac Resynchronization Therapy (CRT) has emerged as an effective treatment option for patients with moderate to severe heart failure. The therapeutic objective of CRT is to correct electrical and mechanical abnormalities by providing a more coordinated ventricular contraction pattern. Nonetheless, up to 30% of the patients receiving the treatment are not responding to it.

There is clinical evidence that the atrioventricular delay has a significant role in the cardiac output and that there is an optimal atrioventricular delay. Several methods for determining the optimal AV delay exist. However, all of them are performed at rest in supine position. The study investigates whether a continuous (dynamic) adaptation of the AV delay to the loading conditions is required for optimizing the cardiac function.

A large animal model (sheep) was utilized in order to test role of the loading conditions. Following left thoracotomy and pericardiectomy the heart was exposed. Left ventricle Pressures, left ventricle volume and epicardial electrical activity were measured. Loading conditions were changed by generating partial aortic occlusions and transient inferior vena cava occlusions.

Data analysis was performed offline. The atrioventricular delay, heart rate, maximal left ventricle pressure and total peripheral resistance were calculated. Despite significant changes in the total peripheral resistance, left ventricle pressure and the end-diastolic volume (preload) the AV delay did not change. The ratio between the AV delay and the cycle time remained constant for all the animals as well. In transient inferior vena cava occlusions changes in the AV delay occurred sometimes but with no clear pattern. In an attempt to explain these findings a model of the left atria and ventricular was created and quasi static analysis was performed. The study carries potential merits for the future development and optimization of resynchronization therapy.