TOWARD OPTIMIZING A PRESHAPED CATHETER AND SYSTEM PARAMETERS TO ACHIEVE SINGLE-LEAD DDD PACING

P wave electrogram amplitudes and atrial stimulation thresholds were d etermined in eight Hanford miniature swine using a preshaped catheter with an ''S'' curve in the SVC, and a major lobe in the atrium to enha nce electrode contact with the atrial wall. The catheter was designed for pacing and sensing in the DDD mode. P wave amplitudes were also as certained with two commercially available VDD leads and compared to th e data from the experimental catheters, The preshaped catheter used tw o 6-mm(2) platinum iridium atrial electrodes with a 7-mm separation. B oth atrial electrodes are on the same side of the catheter, facing out ward on the major atrial lobe formed in the catheter. The P wave ampli tudes were tested only in the differential bipolar configuration. For the eight preshaped catheters, the mean was 6.6 +/- 3.8 mV while for t he conventional leads it was 2.9 +/- 1.6 mV. The mean atrial stimulati on thresholds ranged from 1.1 +/- 0.2 V to 2.3 +/- 1.2 V, with still l ower thresholds of 0.9-1.3 V when using the parallel unipolar atrial e lectrode configuration, in which both parts of the bipolar atrial elec trode are configured as a unipolar electrode. The data suggest that bi polar stimulation may be effective if sequential reverse polarity puls es are used to achieve cathodal stimulation from each electrode of the bipolar pair, on a beat-to-beat basis.