Lack of effect of conduction direction on action potential durations in anisotropic ventricular strips of pig heart

introduction: The influence of activation sequence on the rate of rise of the depolarization phase of action potentials in atrial or ventricular muscles has been well established. However, whether myocardial fiber orientation is important in modulating the repolarization process is unclear. Methods and Results: We examined the influence of activation sequence on the repolarization phase of action potentials in epicardial tissues from the right and left ventricles of domestic pigs. Whereas cells from the right ventricle exhibited direction-dependent differences in action potential duration at 30%, 50%, and 90% of full repolarization (190.6 +/- 31.1 msec vs 181.8 +/- 32.8 msec, 240.3 +/- 23.5 msec vs 236.7 +/- 25.4 msec, and 291.3 +/- 23.7 msec vs 287.4 +/- 25.1 msec for longitudinal and transverse propagation, respectively; P < 0.001), a similar duration of repolarization during both directions of propagation was observed in cells from the left ventricle at 50% and 90% of full repolarization (241.4 +/- 39.4 msec and 285.5 +/- 39.5 msec vs 240.4 +/- 38.9 msec and 284.9 +/- 39.6 msec for longitudinal and transverse propagation respectively; P = NS). A slight but significant difference was found at 30% of full repolarization in cells from the left ventricle (190.4 +/- 39.0 msec vs 187.0 +/- 38.0 msec for longitudinal and transverse propagation, respectively; P < 0.05). In the left ventricle, the duration of repolarization did not change as the distance between the recording site and stimulation site increased. Conclusion: The direction of wavefront propagation with respect to fiber orientation may not play an important role in modulating the duration of repolarization in epicardial cells from the left ventricle.