The Stimulating Electrode

The principal method of artificial cardiac pacing involves the transvenous endocardiac placement of electrodes, usually unipolar, which transmit cathodal stimulus pulses to the myocardium as introduced by Furman in 1958 [119]. The response of an excitable cardiac muscle cell to an external stimulus depends on the electrical field strength—that is, on whether the field depolarizes the diastolic membrane potential sufficiently to generate spontaneous depolarization of the cell—an all-or-none AP which propagates excitation of the entire myocardium. Physiological experiments in which intracellular electrodes are used to excite the heart have shown that charge-carrier injection of 10-11As suffices to trigger the AP [120]. Artificial pacing with the electrodes currently in common use requires a greater charge, about 10-6 As.