Contraction decreased at higher pacing rates, and optical mapping revealed electrical conduction that was anisotropic with a ratio of approximately 2.0, rate-dependent shortening of the action potential and slowing of conduction, and slowing of conduction by the sodium channel blocker lidocaine.
In marked contrast, when the weight of the hand was inverted, the up-on-the-beat pattern was sustained at higher pacing frequencies than the down-on-the-beat pattern (F 1, 7) = 61.9, p<0.01) (Fig. 1C).
These effects were more marked at higher pacing frequencies and in the RyR2 s/s hearts.
Indeed, at higher pacing rates failing cardiomyocytes with high [Na+]i are prone to diastolic Ca2+ overload and contractile dysfunction.
Accordingly we used a higher pacing rate of 10 Hz to ensure regular atrial stimulation under all the pharmacological conditions.
As the figure shows, the Niederer-model is not able to capture the faster relaxation kinetics of the mouse at higher pacing frequencies.
