Effects of propafenone on anisotropic conduction properties within the three-dimensional structure of the canine ventricular wall

Background Structural complexities of the intact ventricular wall cause a v ery complex spread of activation. The effects of regional tissue damage and of antiarrhythmic drugs on directional differences in activation should he lp to further elucidate intramural conduction patterns. Methods and results In 10 healthy dogs and in 5 dogs with subacute anterior wall infarction, 6 parallel rows of 6 needle electrodes with 4 bipolar ele ctrode pairs per needle were inserted into the left anterior ventricular wa ll. Using a computerized multiplexer-mapping system, the spread of activati on in epi-, endo- and midmyocardial muscle layers and in the surviving epic ardium, respectively, was reconstructed. Marked differences in conduction v elocities relative to fiber orientation were evident in the surviving epica rdium of infarcted hearts. Directional differences in conduction velocities , although less pronounced, were still preserved throughout the intact vent ricular wall. Epicardial transverse conduction in intact hearts was signifi cantly faster than transverse conduction in infarcted hearts (0.87 +/- 0.11 m/s vs 0.68 +/- 0.1 m/s). In normal hearts, propafenone (2 mg/kg) decrease d conduction velocities primarily in longitudinal directions (-27 +/- 10 %) , but also moderately in transverse directions (-13 +/- 7 %) of all muscle layers, with no significant effect on straight (-4 +/- 8 %), but on oblique transmural conduction (-33 +/- 18 %). In infarcted hearts propafenone decr eased conduction particularly in longitudinal direction (-23 +/- 14 %) with out affecting conduction transverse to the fiber orientation (+3 +/- 6%). Conclusions Longitudinal intramural shortcircuits reduce directional differ ences in activation. Transmural infarction results in a loss of alternative intramural pathways, unmasking marked anisotropy in the surviving epicardi um. Conduction delay in intramural pathways explains the effects of propafe none on transverse and oblique transmural conduction. Primarily longitudina l conduction delay results in reduced tissue anisotropy.