Atrial rate-responsive pacing in sinus node disease

Patients with sinus node disease (SND) who are unable to achieve an adequate increase in heart rate during exercise are candidates for atrial rate-responsive pacing (AAI-R). We have implanted 40 AAI-R systems in SND patients with an average follow-up of 12.5 +/- 8 (range 3-30) months. All the patients received an activity-sensing pulse generator (Activitrax, Medtronic or Sensolog, Siemens-Pacesetter) with a single atrial lead. Only patients with an intraoperative AV nodal block cycle-length above 100 beats min-1 were included. During follow-up, one patient was observed to have transient asymptomatic 2:1 AV-block during sleep. No patient developed persistent AV-block or chronic atrial fibrillation. Twelve patients with persistent chronotropic incompetence were assigned for a randomized double-blind crossover study, comparing exercise treadmill capacity in AAI-R with conventional atrial inhibited pacing (AAI). During AAI-R pacing the maximum heart rate during exercise was 120 +/- 1 beats min-1 compared with 97 +/- 21 beats min-1 during AAI pacing (P less than 0.01). The average exercise time increased from 11.2 +/- 2 min during AAI-pacing to 13.4 +/- 3 min during AAI-R pacing (P less than 0.01). AAI pacing should be considered for patients with SND and chronotropic incompetence.