THE RELATIVE CONDUCTIVITY OF THE TISSUES IN CONTACT WITH THE HEART

Abstract

Observations were made on 16 nem-butalized dogs in studying the effects of insulation of various regions around the heart on the voltage of the QRS of the standard limb-lead electrocardiograms. All animals were breathing normally with chests closed at the time records were taken. "Mock" operation had no appreciable effect on the strength of the peripheral electrical field of the heart. Insulation between the lungs and the lateral surfaces of the heart produced no apparent change. Insulation of the heart from the posterior muscle mass resulted in an approximate reduction of voltage of 34%. Insulation of the heart from the ant. chest wall reduced the voltage by 14%; insulation from the diaphragm decreased the voltage by 25%. Liga-tion close to the heart of all the vessels of the larger circuit (except the coronary circuit) reduced the voltage by 10%, while separating the cut ends of these vessels reduced it 40%. By elimination of the other surfaces, therefore, the region immediately cephalad to the base of the heart carries roughly 27% of the current generated by the heart to the body. The heart itself, because of the absence of any effect on the electrocardiogram save that of decrease in voltage, must be an excellent conductor.