CRM and Fusion Beats: Effects of Progressive Fusion on Intra-left Ventricular Mechanical Function

Study Summary

This study is looking at cardiac rhythm management (CRM) and fusion beats in patients who have a pacemaker or implantable cardioverter-defibrillator (ICD), to determine if there is a correlation between the time between the contraction of the upper chambers of the heart (atrium) and the lower chambers of the heart, (ventricle) and heart function. Some studies of people with pacemakers have been done to determine if shortening the time of contraction between the atrium and ventricle could benefit the function of the left ventricle. These studies have shown that there is no benefit in heart function.There have been other studies which have shown that chronic pacing of the right ventricle, especially with the lead placed at the tip of the right ventricle, can lead to a decrease in the function of the left ventricle and congestive heart failure. In some patients long term pacing of the right ventricle has also been associated with a reduction in the ability of the left ventricle to pump blood. This is know as a reduced left ventricular ejection fraction, which can be documented by an echocardiogram. This study proposes to evaluate the acute effects of progressive paced fusion beats on the left ventricle to answer the question whether there is an delay between the atrium and ventricle that is "too long" or "too short".