RESUMEN
UNLABELLED: Automatic mode switching (AMS) is absolutely dependent on atrial tachyarrhythmia detection. The effects of programming several features that could influence tachyarrhythmia detection were assessed in 18 patients (six women; mean age 64 years) with pacemakers having AMS capability. The atrial electrogram amplitude in sinus rhythm at implant (SR-EGM), last measured atrial sensing threshold prior to tachycardia (A-SENS), and atrial sensing threshold for effective AMS during atrial tachyarrhythmia (AMS-SENS) were obtained. Additionally, ten patients had AV intervals increased from 60 to 200 ms, while seven patients had detection algorithms made more stringent from 5 beats at 150 beats/min to 11 beats at 200 beats/min to assess their effects on AMS efficacy. RESULTS: Sensitivities:Mean SR-EGM = 3.55 mV; mean A-SENS = 2.06 mV; and mean AMS-SENS = 1.46 mV. Fourteen patients developed atrial fibrillation and four atrial flutter. Thirteen of 14 patients who developed atrial fibrillation sensed adequately at > or = 1.0 mV in normal sinus rhythm (NSR), but only six patients had effective AMS at these settings in atrial fibrillation. Three of four patients who developed atrial flutter had effective AMS at > or = 2.0 mV. AV Interval:AMS was effective in eight of ten patients at AV intervals up to 200 ms. One patient lost AMS at an AV interval of 120 ms. Algorithm: In two of seven patients, AMS was not effective if the detection algorithm was more stringent than five beats at 150 beats/min. CONCLUSIONS: (1) In atrial fibrillation, effective AMS requires more sensitive atrial settings than in NSR; (2) AV intervals as short as 120 ms can interfere with AMS function; and (3) More stringent detection algorithms may be inappropriate for effective AMS function.
