To evaluate the physiologic benefits of the rate response estimulation, 48 patients were submited to a 24 hours Holter recording and paired tolerance treadmill test (AAI VVI and AAI-R/VVI-R modes, selected in random order) one month after implantation of an activity sensing pacemaker Activitrax 8400. Mean age of the patients was 46 years and indications for pacing included atrial arrhythmias (16 patients) or A-V conduction disturbances (32 patients, including 25 with complete A-V block). The underlying disease was Chagas cardiomiopathy, in 32 patients. Initial pacemaker setting was: basic rate: 60 or 70 ppm; maximum activity rate: 125 ppm; activity threshold: medium, rate response: 5. The 24 hours Holter recording documented appropriate changes in heart during daily activities. Oversensing, which resulted in pacing interval fluctuations, was diagnosed in two patients and required pacemaker reprograming. Treadmill test showed a significant increase in heart rate during exercise: mean control value: 66.9 ppm; 4 min.: 84.6 ppm; 6 min.: 90.5 ppm (P < 0.05). In the paired test, the AAI/VVI-Activity mode enabled the patients to increase heart rate (12.5%) and exercise time (20.2%; P < 0.05). None of the patients presented exercise induced ventricular arrhythmias in mode AAI/VVI-Activity; on the other hand, 12 patients showed ventricular arrhythmia during exercise in mode AAI/VVI. Clinical improvement and more active life was referred by all patients in this short follow-up period. The Activitrax 8400 was effective in improving patients exercise capacity.
pacemakers, cardiac