Andersen–Tawil syndrome (ATS) is a rare arrhythmia disorder combining a signature arrhythmia phenotype, consisting of a pronounced U-wave and frequent ventricular extrasystoles (Figure 1) with extracardiac features including periodic paralysis and dysmorphic features. Occasionally, complex ventricular arrhythmias including bidirectional ventricular tachycardia and ventricular fibrillation occur.
The pronounced U-wave can easily be distinguished from the ST segment, and the QT interval itself is actually not prolonged
Delannoy E et al. Cardiac characteristics and long-term outcome in Andersen–Tawil syndrome patients related to KCNJ2 mutation. Europsace 2013