Electrical Stimulation and Digitalis Drugs

Summary

In the nondigitalized animal, a unipolar stimulus to the endocardium or myocardium discharged during diastole resulted in a single response unless energies greater than 5 J were used. During digitalization employing ouabain, the diastolic threshold energy for a repetitive ventricula response (RVR) was reduced by 6 orders of magnitude. RVR was first noted after 70% of the toxic dose of ouabain had been given and consisted of 2 ventricular ectopic beats. With advancing degrees of digitalization, a single stimulus evoked paroxysms of ventricular tachycardia. The most sensitive part of the cardiac cycle followed immediately after inscription of the T wave. As toxicity was approached, the zone of lowered threshold extended throughout most of the diastolic interval.