Abstract
This paper describes a reexamination of the relationship between the electrode area and the threshold current through the use of various types of electrodes (endocardial, myocardial and epicardial disc electrodes), for designing a low-power stimulation electrode of cardiac pacemakers. Results are as follows.
1. As the electrode area is made smaller and smaller, threshold current becomes less and less until a point is reached where the value becomes more or less constant.
2. As the area of the electrode is reduced, the ratio of incremental increase of the threshold current (increased threshold current due to inactive layer interposed under the electrode/threshold current with direct contact to ventricular wall) increases but this also stabilizes itself to a constant value after a certain point is reached. This fact corresponds to the results obtained through long-term implantations of the endocardial electrodes.
3. On the other hand, the resistance of the electrode is inversely proportional approximately to the square root of its area. From these results, we deduced that the design and fabrication of an electrode with minimal threshold energy and highest safety margin of the stimulation current (stimulation current/threshold current) is entirely feasible, if the electrode area is around 10 mm2.
