Effects of tocainide on ectopic impulse formation in isolated cardiac tissue.

The effect of tocainide on enhanced automaticity if Purkinje fibers was studied under the influence of epinephrine (0.2 microgram/ml) by means of intracellular recordings with microglass electrodes. In the presence of tocainide 5 microgram/ml and 10 microgram/ml cycle length of enhanced automaticity was increased in the range of 10.6% and 34.9% and in the range of 26.3% and 108.7% respectively. Repetitive impulse formation in ventricular myocardium was generated by creating a potential difference in a papillary muscle mounted in a partition chamber. One chamber was connected to ground, the potential of the other chamber could be changed in the range of 0 to 500 mV. By progressively increasing the voltage difference across the papillary muscle repetitive rhythmic impulse formation was induced. The threshold voltage gradient increased in the presence of tocainide (100 microgram/ml) from--285 to--335 mV. The results suggest that tocainide is suitable to suppress arrhythmias due to enhanced automaticity of Purkinje fibers.