Relationship Between &OV0312;max and Conduction Velocity in Uniform Anisotropic Canine Ventricular Muscle: Differences Between the Effects of Lidocaine and Amiodarone

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Abstract
The purpose of these experiments was to determine if .ovrhdot.Vmax in anisotropic myocardium varies approximately as the square of the conduction velocity (.theta.) after the addition of lidocaine (6.5 .mu.g/ml) and amiodarone (20 .mu.g/ml). We measured .ovrhdot.Vmax and .theta. in 16 epicardial strips of uniform anisotropic ventricular muscles, over a wide range of stimulation frequencies. The relationship of .ovrhdot.Vmax to .theta.2 was evaluated by linear regression analysis. We found that the decrease in .ovrhdot.Vmax was proportional to the square of the decrease in .theta. in the presence of lidocaine both during longitudinal (LP) and transverse (TP) propagation (mean slope .+-. SEM; 0.961 .+-. 0.047 and 0.918 .+-. 0.068, respectively). The changes in .ovrhdot.Vmax, in the presence of amiodarone, were not predicted by the quadratic changes in .ovrhdot.Vmax and .theta. were well fitted by the predicted relationship. The slope was significantly different from that of licocaine (2.399 .+-. 0.673 vs. 0.961 .+-. 0.047, p < 0.05). On the other hand, the predicted values of .theta., assuming .theta. = .sqroot..ovrhdot.Vmax .times. k, were significantly more depressed than the measured values. We conclude that in uniform anisotropic ventricular muscle, when the changes in .ovrhdot.Vmax and .theta. are solely due to a decrease in sodium conductance, a quadratic relationship between the changes in both variables is seen and the slope of the regression line should be 1, such as we have shown for lidocaine. In contrast, when a decrease in junctional resistivity in addition to a decrease in sodium conductance are responsible for the changes observed in these variables, such as we showed for amiodarone, an increase of the slope or even a complete alteration of the relationship should be expected to occur.