Hypertrabeculated <i>Nkx2-5</i> mutant hearts exhibit QRS defects, BB blocks and high susceptibility to fibrillation.

<p>(A) Representative tracings from surface ECG measured in lead II in anaesthetized mice at 3-, 6- and 9-month old. In control mice, QRS complexes are normal regardless of the age at which they were recorded. Tracings from <i>Nkx2-5</i>^{<i>ΔTrbE10</i>} and <i>Nkx2-5</i>^{<i>ΔTrbE14</i>} mice demonstrated bundle branch block-like appearance with widened QRS complex and a characteristic pattern with Notched R, R' wave and fragmented QRS. (B) Dobutamine caused a marked increase of heart rate in control mice and only a small effect in <i>Nkx2-5</i>^{<i>ΔTrbE10</i>} and <i>Nkx2-5</i>^{<i>ΔTrbE14</i>} mice. (C) Severe susceptibility to ventricular fibrillation was found in <i>Nkx2-5</i>^{<i>ΔTrbE10</i>} and <i>Nkx2-5</i>^{<i>ΔTrbE14</i>} mutants but not in control mice. Cardiac frequency and quantification of arrhythmias and fibrillation before and after Dobutamine injection are summarized in the table. (D) Plots of QRS duration in lead II from 9-month old mice against Ejection Fraction (EF) recorded during echocardiography (N = 27) and MRI (N = 11) or against LV mass from MRI (N = 11). Red and green dots represent mice with fluctuating EF overtime. Linear relationships were observed and R² and p-values were indicated for each graph.