Electrographic Studies of Conductivity in Cardiac Muscle.

Abstract

This abstract presents the results of studies with the string galvanometer which confirm and extend previous observations 1 upon the recovery of conductivity, and the effect of the blocked impulse upon subsequent conduction in the quiescent, excised, atropinized turtle heart. The previous work was with the kymograph.

The observations were incidental to experiments directed toward other ends. They are based upon studies of approximately 30 turtle hearts, from some 15 of which simultaneous myograms and electrograms were obtained. These demonstrate that although the electrical and mechanical conduction intervals may not appear identical, the curves illustrating the recovery of conductivity are parallel. The electrical are more accurate than the mechanical.

The results fall into three divisions. (1) Curves illustrating the recovery of conductivity between auricle and ventricle, with and without compression at the A-V groove. These are similar to those already published, 1 excepting that in some the deviation of the individual points from a smooth curve is less pronounced. They demonstrate that not only are conduction times for all rest intervals increased by compression, but also that the curve returns much less promptly to a resting level. A recovery curve for the human heart was reported by Ashman and Herrmann. 2 (2) Confirmation of the fact that a very premature blocked impulse may have no detectable influence upon the conduction time of a subsequent impulse; that a slightly later blocked impdse has a moderate effect; and that an impulse arriving at the compressed muscle so late as to just fail of transmission to the ventricle, has, on the average, 65 per cent as great an effect as a transmitted impulse. These results are identical with those previously reported. A similar phenomenon has been reported by Lewis and Master3 for the mammalian heart.