The RV apex has historically been used as the site for ventricular pacing in cases of sinus node dysfunction or atrioventricular block because of its relatively accessible location for lead implantation. Initial studies showed RV pacing improved symptoms, exercise capacity, quality of life, and survival in these patients.11-13 However, more recent studies have illustrated that chronic RV pacing may actually impair LV systolic function and increase the risks of heart failure, hospitalization, and death in some patients.
The primary hypothesis is that patients upgraded to CRT from a RV pacemaker respond better than those receiving CRT as a first time device. To test this hypothesis the investigators will compare changes in cardiac size and function, and hospitalization and survival rates between the two patient groups.
The second hypothesis will investigate whether changes in septal dyssynchrony are correlated with changes in ejection fraction in previously RV paced patients. The investigators believe that the patients with the most improvement in septal dyssynchrony due to RV pacing will see the greatest improvement in LV function following upgrade to CRT. A significant correlation between change in IM-S and change in EF will support the hypothesis.
