AN ALGORITHM FOR AUTOMATIC-MEASUREMENT OF STIMULATION THRESHOLDS - CLINICAL-PERFORMANCE AND PRELIMINARY-RESULTS

We have developed an algorithmic method for automatic determination of stimulation thresholds in both cardiac chambers in patients with inta ct atrioventricular (AV) conduction. The algorithm utilizes ventricula r sensing, may be used with any type of pacing leads, and may be downl oaded via telemetry links into already implanted dual-chamber Thera (R ) pacemakers. Thresholds are determined with 0.5 V amplitude and 0.06 ms pulse-width resolution in unipolar, bipolar, or both lead configura tions, with a programmable sampling interval from 2 minutes to 48 hour s. Measured values are stored in the pacemaker memory for later retrie val and do not influence permanent output settings. The algorithm was intended to gather information on continuous behavior of stimulation t hresholds, which is important in the formation of strategies for progr amming pacemaker outputs. Clinical performance of the algorithm rt as evaluated in eight patients who received bipolar tined steroid-eluting leads and were observed for a mean of 5.1 months. Patient safety was not compromised by the algorithm, except for the possibility of pacing during the physiologic refractory period. Methods for discrimination of incorrect data points were developed and incorrect values rt ere di scarded. Fine resolution threshold measurements collected during this study indicated that: (1) there were great differences in magnitude of threshold peaking in different patients; (2) the initial intensive th reshold peaking was usually followed by another less intensive but lon ger-lasting wave of threshold peaking; (3) the pattern of tissue react ion in the atrium appeared different from that in the ventricle; and ( 4) threshold peaking in the bipolar lead configuration rt as greater t han in the unipolar configuration. The algorithm proved to be useful i n studying ambulatory thresholds.