 The purpose of this study is to collect and analyze electrical measurements, timing, and signals from a CRT-D device in heart failure patients who either already have an implanted left atrial pressure sensor or will undergo a simultaneous implantation of a left atrial pressure sensor and a CRT-D device. These devices may be placed at the same time or separately staged procedure at the discretion of the investigator. A comparison will be made between the information gathered from the CRT-D system and the information gathered by the left atrial pressure sensor. 