T wave alternans
![T-wave alternans and prolonged QT interval in a male patient found to be in a narrow-complex tachycardia and ruled in for an acute myocardial infarction. Administered Ibutilide and converted to sinus rhythm but subsequently had an episode of Torsades de Pointes which required DC cardioversion back into sinus rhythm.](/Images/godic/202501/28/T-wave_alternans1712.png")
T wave alternans (TWA) is a periodic beat-to-beat variation in the amplitude or shape of the T wave in an electrocardiogram (ECG or EKG).
TWA was first described in 1908. At that time, only large variations ("macroscopic" TWA) could be detected. Those large TWAs were associated with increased susceptibility to lethal ventricular tachycardias.