Stimulus Intensity in Left Ventricular Leads

Cardiac resynchronization therapy (CRT) is a device implanted to improve the function of
some people's hearts. CRT involves the placement of 3 wires in the heart through a vein
near the front of your left or right shoulder into three pumping chambers of the heart, the
most important being the left lower chamber (left ventricle). The purpose of CRT is to send
small amounts of energy (called pacing) through the wires to both the left and right lower
chambers of your heart at (or near) the same time. This helps the heart pump in a more
coordinated way and send more blood to your body with each beat. How much energy is used for
pacing is called the stimulus intensity. Increasing the pacing stimulus intensity of the
left ventricular wire can lead to an increase in the volume of heart muscle directly
stimulated. This has previously been shown to produce beneficial effects on the heart
function, like strength of contraction and increased volume of blood pumped. The purpose of
this study is to determine if pacing the wires in the left ventricular chamber of the heart
using higher stimulus intensity improves the strength of the heart's contraction.