M.Sc Thesis

M.Sc StudentHanani Nitai
SubjectEffect of Pacing Lead Position on Ischemic Left-Ventricle
DepartmentDepartment of Biomedical Engineering
Supervisor ASSOCIATE PROF. Amir Landesberg


Background: Although the benefit of Cardiac Resynchronization Therapy (CRT) in the treatment of heart failure is widely recognized, over 35% of the patients undergo CRT don’t exhibit functional improvement and long term left ventricular (LV) reverse remodeling. Many of these patients have ischemic heart disease. We suggest that the current practice, to pace the left lateral wall of the LV regardless of the presence of ischemic myocardial regions, may not be the optimal pacing treatment.

We hypothesize that improvement in local and global myocardial functions will be obtained by pacing the weak ischemic regions, since pacing decreases the generated external work and energy consumption at the pacing site. This will decrease the workload of these weaker sites and increase the preload of the distal normal myocardium.

The study aims to test the local and global short term effects of the opposing strategies: pacing at the lateral wall, the last activated site, as is done currently, or at the ischemic site.

Methods: Myocardial infarction was created in the anteroseptal region, in open chest sheep (n=8) by ligation of a large marginal coronary artery. Local (pressure-length loop) and global LV (external work [EW]) functions were measured during: i) normal sinus activation without pacing, ii) anteroseptal pacing or iii) lateral pacing. Cardiac function was assessed at baseline, before the coronary occlusion and after reaching a stable overt myocardial infarction.

Results: At baseline, pacing on either site didn't significantly affect the global EW. However, vast decrease in the anteroseptal work was observed during local pacing (p=.0001). Anteroseptal infarction decreased the local work and yielded post-systolic shortening where the ischemic region generated active work during diastole. In ischemia, anteroseptal pacing presented two favorable effects; It significantly decreased the work of the ischemic region (p<.005) while the lateral pacing showed no effect on the ischemic region. Furthermore, pacing the ischemic region diminished PSS-work (p<.02).

Conclusions: Pacing the ischemic region decreases the entire work generated by this region and eliminates its PSS-work. Workload redistribution is achievable, by reducing the work of weaker areas while preserving the global heart function. The novel approach presents two advantages that may promote myocardial reverse remodeling and elongate patient survival: It improves the balance between the regional mechanical demands and regional energy supply or energetic capabilities, and improves cardiac diastolic function by reducing the wasted PSS-work. This study introduces the concept of “energetic synchronization” rather than the conventional electrical or mechanical synchronization.