SINGLE-LEAD DDD SYSTEM - A COMPARATIVE-EVALUATION OF UNIPOLAR, BIPOLAR, AND OVERLAPPING BIPHASIC STIMULATION AND THE EFFECTS OF RIGHT ATRIAL FLOATING ELECTRODE LOCATION ON A TRIAL PACING AND SENSING THRESHOLDS

Single lead DDD pacing using unipolar or bipolar stimulation is limite d by high atrial threshold. Overlapping biphasic (OLBI) waveform stimu lation sia atrial floating ring electrodes may preferentially enhance atrial pacing and avoid diaphragmatic pacing. Single lead DDD pacing w ith OLBI atrial pacing was studied in 12 patients (6 men and 6 women; mean age 74 +/- 7 years) with complete heart block. At implantation, a trial bipolar rings (area 27 mm(2), separation 10 mm) rt ere positione d at radiological defined high, mid, and low right atrial (RA) levels, and P wave amplitude and atrial and diaphragmatic pacing thresholds w ere determined in each position using unipolar, bipolar, and OLBI stim ulation in random order. Although statistically insignificant, both th e maximum and minimum sensed P rr ave amplitudes tended to be lower in the low RA position. Independent of the stimulation modes, minimum at rial pacing threshold occurred in the mid-RA. At mid-RA, the atrial pa cing threshold was significantly lower with OLBI pacing compared with either unipolar or bipolar mode (3.9 +/- 2.2 V vs 6.7 +/- 3.5 V and 6. 9 +/- 3.5 V, P < 0.05). Although the diaphragmatic thresholds were sim ilar, OLBI pacing modes in the mid-RA and final location significantly improved the safety margin for avoidance of diaphragmatic pacing comp ared with unipolar mode. There was no correlation between atrial pacin g and sensing threshold. At predischarge testing all but one patient r r ho developed atrial fibrillation had satisfactory atrial capture and a stable atrial pacing threshold (day 0: 2.6 +/- 1.1V vs day 2:3.2 +/ - 1.3V P = NS). However, diaphragmatic pacing occurred in four of 11 ( 36%) patients, especially in the upright position (sitting and standin g). Our preliminary clinical results suggest that OLBI pacing via atri al floating ring electrodes can reduce the atrial pacing threshold. To optimize atrial pacing and sensing, the bipolar electrodes should be located at the mid-RA level first, although the high RA is an alternat ive. Despite significant improvements in the safety margin for diaphra gmatic pacing with OLBI pacing, diaphragmatic stimulation remains a cl inical problem.