A Study to Determine if T Wave Alternans is a Marker of Therapeutic Efficacy in the Long QT Syndrome

T wave alternans (TWA), an alteration of the amplitude and morphology of the T wave that occurs every-other-beat, is emerging as an important new marker for identifying patients at risk of developing malignant ventricular arrhythmias. {Rosenbaum, Jackson, et. Al 1994} It is undergoing intense investigation in a number of areas where patients are thought to be at higher risk for Sudden Cardiac Death including heart failure, and hypertrophic cardiomyopathy. However, patients with congenital Long QT have yet to be evaluated. In addition, there appears to be no definitive way to evaluate the efficacy of treatment of the Long QT Syndrome. Finally, the role that the sympathetic nervous system plays in the Long QT Syndrome is not well understood and still controversial. The primary purpose of this study is to evaluate the presence of TWA in patients with Long QT Syndrome, and to assess whether TWA is a predictor of efficacy of treatment. Another purpose of this study is to understand the role of the sympathetic nervous system in the Long QT Syndrome.