(A). MKK4cko-TAC mice are more susceptible to ventricular arrhythmias and slowed conduction velocity. (B). Most activation maps from MKK4F/F hearts showed a sequential activation pattern, beginning with a localized activation of one region of the matrix followed by its successive spread to the remaining area from which recordings were made. However, the old MKK4CKO hearts often showed a more disordered excitation sequence.

References:

1. Zi M, Kimura T E, Liu W, et al. Mitogen-activated Protein Kinase Kinase 4 Deficiency in Cardiomyocytes Causes Connexin 43 Reduction and Couples Hypertrophic Signals to Ventricular Arrhythmogenesis[J]. The Journal of Biological Chemistry, 2011, 286(20): 17821.
2. Davies L, Jin J, Shen W, et al. Mkk4 Is a Negative Regulator of the Transforming Growth Factor Beta 1 Signaling Associated With Atrial Remodeling and Arrhythmogenesis With Age[J]. Journal of the American Heart Association: Cardiovascular and Cerebrovascular Disease, 2014, 3(2).