Abstract
Various combinations of simultaneous tachycardias have been observed to occur in the human heart. As a rule, the coexisting atrial and ventricular forms are the most frequent. When esophageal leads were used, the incidence of these arrhythmias was found to be greater than that reported by other authors. This greater incidence was due to the fact that without esophageal leads the atrial rhythm in many cases could not be interpreted correctly because the widened QRS complexes sometimes obscured the atrial deflections. Digitalis was the cause of these arrhythmias in over 75 per cent of the cases studied. This was well demonstrated in cases in which the double rhythms were induced by the intravenous administration of short-acting digitalis preparations. Appropriate treatment with potassium and procaine amide usually abolished the tachycardias promptly. Contrary to the usual belief, the prognosis was not necessarily dependent upon the nature of the disorder of the rhythm but chiefly upon the precarious conditions of the myocardium. As a rule, these arrhythmias were most frequently seen in elderly patients with arteriosclerotic heart disease.
A single exception was that of simultaneous tachycardias occurring in a 9-year-old girl with rheumatic fever who died several days after sinus rhythm was restored. Whenever the rate of the lower pacemaker was rapid enough, it was conceivable that the atrial impulses could not transverse the A-V junction because of the refractoriness provoked in the latter by the lower pacemaker. However, it was demonstrated that some degree of abnormal refractoriness or true block was present. Yet, obviously, a complete A-V block did not exist. This impedance to conduction was ascribed mainly to the toxic effects of digitalis.
