Although, sodium channel blockers have the ability to suppress nonsustained ventricular arrhythmias, an excessive drug-associated arrhythmic death rate has been reported in patients with coronary heart disease (CHD). Sodium channel blockers should prevent initiation of reentry activation by reducing directional differences in cardiac conduction (anisotropy). However, in vitro data demonstrated, that reduction of membrane excitability, e.g. by lowering the inward Na+ current, increases the risk for conduction failure and associated reentry arrhythmias. In 11 dogs the effects of myocardial ischemia, premature epicardial stimulation (PES) and propafenone on anisotropic conduction properties were tested using three-dimensional mapping techniques. The epicardial (longitudinal and transverse to fiber orientation) and transmural (oblique and straight) spread of activation was reconstructed during constant and PES. At baseline, conduction velocities (CV) were higher along (1.20 +/- 0.41 m/s) than across (0.91 +/- 0.19 m/s; p < 0.05) epicardial muscle fibers as well as along oblique (1.77 +/- 0.75 m/s) compared to straight (0.39 +/- 0.09 m/s, p < 0.05) transmural pathways. Acute ischemia did not significantly reduce tissue anisotropy. PES and additional administration of propafenone epicardially eliminated and transmurally profoundly reduced tissue anisotropy (longitudinal 0.58 +/- 0.09 m/s, transverse 0.69 +/- 0.08 m/s, oblique 0.69 +/- 0.28 m/s, straight 0.27 +/- 0.07 m/s). However, reduced anisotropy was associated with a higher probability for conduction block along myocardial fibers in the epicardium and along oblique transmural pathways. Our data show, that propafenone exhibits both potential pro- and antiarrhythmic effects in dogs with acute myocardial ischemia. These results possibly provide more insights in mechanisms underlying the excessive drug-associated arrhythmic death rate in patients with CHD.
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