The influence of mechanical conditions of the circulation on the electrocardiogram

Previous Work .—As a preliminary to the investigation of the effect of work on the mammalian heart it was advisable to carry out experiments on the cold-blooded heart in order to determine the relations of the electrical deflections to the amount of work performed. Special attention was paid to the duration of the electrical response and the constancy of the heart rate. The isolated ventricle of the tortoise (Testudo grœca ) was used. In the frog’s heart Straub (1) measured the effect on the electrogram (direct leads) of increasing the filling and initial tension. Under these conditions he noted that the R' and T' waves were diminished in size. Seeman (2), working on the same animal but using a slightly different method, found that with increased venous pressure R' and T' diminished in the same ratio; little or no change in the electrogram was noticed on raising the pressure against which the heart contracted. If The heart was allowed to beat under isometric conditions, R' and T' diminished as the venous pressure was raised, until a certain level was reached; at this point the amplitude of the deflections showed no further alterations. Seeman concluded that these changes were not brought about by the augmented work of the heart muscle but by the adjustment of tension differences during contraction. Working on the frog’s heart, Dale and Mines (3) demonstrated the balance between the frequency of beat, the duration of electrical response, auriculo-ventricular and intraventricular conduction; they also showed the effects of nervous influences on these factors.