Assessment of the work capacity and relationship between rate response and exercise tolerance associated with...

The relationship between rate response and exercise tolerance was studied by measuring the symptom-limited maximum treadmill time (MTT)both during fixed rate VVI pacing and during VVI + activity mode pacing (RRP) in 15 patients (mean age, 73 years) who had received rate-responsive ventricular pacemakers. Their indications were atrioventricular block, sino-atrial block, and atrial fibrillation with slow ventricular response. Basic rate was programmed to 60 ppm in both pacing modes; rate response and activity threshold were programmed to 5 and medium, respectively. The order in which the two pacing modes were tested was randomly determined. The MTT was, on average, 29% longer in RRP than in VVI mode with a mean of 12 minutes in VVI and 14.8 minutes in RRP (p less than 0.001). For the subgroup of eight patients with paced-only rhythm the average increase in MTT was 38% with a mean of 9.5 minutes in VVI and 12.8 minutes in RRP (p less than 0.01). Seven patients who showed episodes of spontaneous rhythm, increased their average MTT by 17% (mean in VVI, 14.9 minutes; in RRP, 17.1 minutes; p less than 0.02). During RRP, a significant positive correlation existed between MTT and the increase in heart rate (N = 15; r = 0.83; p less than 0.001). In 12 patients with paced-only rhythm, the pacing rate remained at the programmed basic rate when the patients were lying, sitting, and standing and increased to 86 +/- 4 ppm during casual walking, and to 101 +/- 4 ppm during jumping up and down with the pacemaker programmed to the above-mentioned parameters. The maximum pacing rate during jumping corresponded with the maximum pacing rates measured from Holter recordings during normal daily activities.