Anodal and cathodal thresholds during transthoracic stimulation

A physiological mechanism is proposed for a phenomenon observed in experimental studies: the ventricular threshold during transthoracic stimulation is slightly lower if the electrode closer to the heart is a cathode rather than an anode. This result can be attributed to the discrete structure of the myocardium. In such a structure, the end of each cardiac bundle proximal to the cathode is depolarized, while the distal end is hyperpolarized. Since the transmembrane potential depends upon the gradient, which decreases between proximal and distal ends, the magnitude of the transmembrane potential is somewhat smaller at the distal end. Thus a larger stimulus is required to raise the distal end above the threshold.<>