FIGURE 5.

MKK4^cko-TAC mice are more susceptible to ventricular arrhythmias and slowed conduction velocity. A, subjected to a train of eight stimuli (S1 at 100 ms) with a premature stimulus at 90 ms (S2). No episodes of arrhythmias were induced in the MKK4^f/f-TAC heart (upper panel); however, ventricular tachycardia was induced in the MKK4^cko-TAC heart (lower panel) (scale bar: 200 ms). B, the ventricular effective refractory period was measured using the same S1-S2 protocol, showing a prolonged ventricular effective refractory period in the MKK4^cko-TAC heart (n = 6–13 per group). C, representative epicardial activation maps recorded from the MKK4^f/f and MKK4^cko hearts of TAC-treated mice. Earliest activation is found in red, the latest activation is shown in blue, and numbers indicate activation time (ms). The slowing of conduction and propagation of excitation was seen in the MKK4^cko-TAC heart. D, summary data illustrate that both longitudinal CV and transverse CV were significantly slower in the MKK4^cko heart (n = 3 per group). Data are presented as mean ± S.E.