The production of reversed cardiac mechanism in the dog

Abstract

In a series of experiments, which were published with Kessel and Mason, 1 on the excised perfused hearts of dogs, we were able to show that “excision of the sinus node results in an immedate cessation of the contractions of the whole heart,” that “after excision of the sinus node and the ensuing stoppage, the rate of the whole heart falls and does not again reach the original rate,” and that “the function of the secondary pacemaker devolves on no special portion of the heart.” The results of experiments performed by others and differing from ours were mentioned at that time. I have continued the experiments on dogs, anesthetized with ether, the hearts of which were left in situ and normally nourished. After sufficient controls were registered electrocardiographically, the sinus node was clamped with a specially constructed T clamp, 5 cm. long and 1 mm. wide. In the perfused hearts the rate fell 10 to 70 beats, usually 30 to 50 beats, after the node was excised. In the present series the fall in rate was 10 to 90, usually about 50. Stoppage, which is a usual phenomenon in excised hearts, occurred also in these, but very rarely. The site of the secondary pacemaker varied in these, as it did in the perfused hearts. Photographs of three hearts showing the areas of the auricular surfaces which had been included in the jaws of the clamp, and a series of curves from each of the corresponding experiments and of one in addition were demonstrated. The relation of the disturbed function of the heart to the area clamped will be investigated histologically and reported in detail later. The curves indicate that in each of these cases, there was a dislocation of the pacemaking function from the site responsible for it, and that, after clamping had taken place, this function devolved upon the ventricles, the junctional tissues or another portion of the auricle.