KCNH2 and Jervell and Lange-Nielsen syndrome: Figure 1 shows the resulting APs obtained at 1 Hz stimulation frequency. Heterozygous LQT1 mutation prolonged APD by only 8 ms in PFC, in contrast to VM, in which a 36 ms APD prolongation is seen. Mutation in LQT2 prolongs PFC APD by 28 ms and VM APD by 46 ms. Clinically, homozygous LQT1 mutation leads to the Jervell-Lange-Nielsen syndrome[1], which is characterized by severe QT prolongation.