In vitro estimation of the electrical performance of bipolar pacing electrode systems.

With the current interest in bipolar stimulation, there is a need for greater understanding of the electrical contributions of the two electrodes in this type of pacing. This has been investigated using a specially designed cell in which an electrode under test was immersed in a buffered saline solution (pH 7.42) at 37-38 degrees C. Four electrode types were studied: a single stimulating electrode (6 mm2 dish tip, Pt-black coated) and three indifferent electrodes. The indifferent electrodes were a 41 mm2 polished Pt ring, a Pt-black coated version of the same electrode, and a titanium pacemaker enclosure which was included to allow comparison with the unipolar situation. These electrodes were tested individually against a chlorided silver reference electrode of negligible (1-2 omega) impedance, the results being processed in such a way as to allow estimation of the properties of the stimulating electrode taken in combination with each of the indifferents. Constant current pulses (1-10 mA amplitude, 0.5 and 1.0 ms duration) were applied and measurements made from the resulting voltage waveforms. These were v1 and v2, the potential at the leading and trailing edge of the pulse, and v3, the post-pulse potential at 20 ms following the trailing edge. The potential v2--v1 is electrode dependent and allows the determination of the energy loss due to polarization to be calculated. Sinusoidal AC signals (0.1 Hz-10 kHz, 20 microA maximum amplitude) were also employed, allowing determination of sensing impedance. Under all conditions, the calculated performance of the stimulating electrode with the coated ring was nearly equivalent to that with the pacemaker enclosure.(ABSTRACT TRUNCATED AT 250 WORDS)