ATRIAL RATE-ADAPTIVE PACING - WHAT HAPPENS TO AV CONDUCTION

To investigate if an nonphysiological prolongation of the AV interval is common during activity sensor modulated atrial rate adaptive (AAIR) pacing, 21 patients with sinus node disease treated with fixed rate a trial (AAI) or AAIR pacemakers were examined. Spike-Q intervals were c ompared at different heart rates obtained by overdrive pacing at rest and during exercise (Study I), measured during exercise at unresponsiv e (AAI), optimal (AAIR) and over responsive programming (AAIR +) of th e activity sensor (Study II), and finally examined by 24-hour Holter r ecording in AAI and AAIR pacing modes (Study III). Study I: The spike- Q interval increased significantly with increasing heart rate at rest, but not during exercise. At rest the spike-a interval was significant ly higher at all heart rates compared to exercise. There was a signifi cant positive correlation between the maximal spike-Q interval at rest and the maximal spike-Q interval during exercise (r = 0.63). Study II : The spike-Q interval was shortest in the AAI and longest in the AAIR + mode in all patients. Study III: During AAI or AAIR pacing the spik e-Q interval was longest at night and shortest in the morning. The mea n spike-Q interval was longer in AAIR than in AAI pacing. No statistic al difference between the maximal spike-a intervals observed during th e two modes was, however, found. Variations in spike-Q interval are ge nerally caused by changes in autonomic tone or medication with drugs w ith antiarrhythmic effect. Our results indicate that the risk for an n onphysiological prolongation of the AV interval during AAIR pacing is rather small and can be predicted by studying the spike-Q interval at rest during overdrive pacing.