Baseline electrical differences between different LQTS genotypes in vivo and ex vivo. (A) Heart-rate corrected QTc interval. (B) Action potential duration at 75% of repolarization. (C) Action potential triangulation in transgenic LQT1. (D) Short-term variability of QT. (A–D) LQT1: green, in vivo n = 8, ex vivo n = 7; LQT2: red, in vivo n = 6, ex vivo n = 6; LQT2–5: violet, in vivo n = 8, ex vivo n = 9; and LQT5: blue, in vivo n= 8, ex vivo n = 9; WT littermates: grey, in vivo n = 6, ex vivo n = 7. Differences are indicated as * for P-value < 0.050, ** for P-value < 0.010, and *** for P-value < 0.001. All data are presented as mean ± SEM. The WT (grey) bars are shown next to each LQTS genotype bar to better indicate the difference to WT for each individual genotype. LQTS, long QT syndrome; LQT1, long QT Type 1; LQT2, long QT Type 2; LQT5, long QT Type 5; LQT2–5, combined form of long QT Types 2 and 5; SEM, standard error of the mean; WT, wild type.