T-wave alternans is a test that is currently being used to risk stratify patients with
structural heart disease for sudden cardiac death. The mechanism of T-wave alternans is
unclear, but may share a common abnormality with conditions of cardiac fluid overload such
as heart failure, which is altered intracellular calcium handling. Current Medtronic
implantable defibrillators have the capability of monitoring cardiac fluid status via
transthoracic impedance measurements.
The purpose of this study is to determine if a correlation exists between T-wave alternans
status and cardiac volume status, as determined by transthoracic impedance measurements.
Secondarily, the study seeks to examine the relationship between arrhythmia frequency and
T-wave alternans or cardiac volume status.
- Class III or IV heart failure patients with a chronically implanted Medtronic
biventricular defibrillator system capable of monitoring intrathoracic fluid volume.
- no active ischemia or pulmonary edema, atrial fibrillation, complete heart block