NKX2-5 and atrial fibrillation: In order to further understand the occurrence of SCD in carriers of NKX2-5 mutations, electrophysiological studies were performed on two patients with truncating NKX2-5 mutations (B II:6 and B III:1), and revealed non-sustained ventricular tachycardia (NSVT) [Figure 4A] and an atrial tachycardia that degenerated into atrial fibrillation (Figure 4B) requiring synchronized electrical cardioversion in one patient, and a short His-ventricular (HV) interval at 26 ms suggesting pre-excitation in another patient (Figure 4C) [Normal HV interval: 35–55 ms].