Relationship between Vmax and conduction velocity in uniform anisotropic canine ventricular muscle: differences between the effects of lidocaine and amiodarone.

The purpose of these experiments was to determine if Vmax in anisotropic myocardium varies approximately as the square of the conduction velocity (theta) after the addition of lidocaine (6.5 micrograms/ml) and amiodarone (20 micrograms/ml). We measured Vmax and theta in 16 epicardial strips of uniform anisotropic ventricular muscles, over a wide range of stimulation frequencies. The relationship of Vmax to theta 2 was evaluated by linear regression analysis. We found that the decrease in 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 Vmax, in the presence of amiodarone, were not predicted by the quadratic changes in theta during TP. However, during LP, the changes in Vmax and theta were well fitted by the predicted relationship. The slope was significantly different from that of lidocaine (2.399 +/- 0.673 vs. 0.961 +/- 0.047, p less than 0.05). On the other hand, the predicted values of theta, assuming theta = square root of Vmax x k, were significantly more depressed than the measured values. We conclude that in uniform anisotropic ventricular muscle, when the changes in 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.(ABSTRACT TRUNCATED AT 250 WORDS)