Recent research supports the hypothesis that reducing the amount of pacing in the lower right chamber of the heart may prevent the progression of congestive heart failure (CHF) in some implantable cardioverter defibrillator (ICD) patients. CHF refers to symptoms (shortness of breath, fatigue, fluid overload) caused by decreased pumping action of the heart muscle. The ICD can be set to use one wire (top or bottom of the heart) or two wires (top and bottom). Both settings allow the heart to beat more naturally using its own electrical signals. Two device settings will be compared. Managed ventricular pacing (MVP) will allow the ICD to use both wires only as necessary. This setting allows the ICD to send electrical signals to the top and bottom chambers of the heart if needed. The other setting, ventricular pacing (VVI) will allow the ICD to operate the bottom chamber of the heart if it is needed.
The purpose of the study is to compare two device settings (sets of instructions) used by the ICD. The Implantable Cardiac Defibrillator (ICD) can be set to use one wire (top or bottom of the heart) or two wires (top and bottom). The study will compare how much time either ICD wire is used by the ICD and the status of congestive heart failure.