Eccentricities of activitrax pulse generators

At present, and on a worldwide basis, the Activitrax (VVI plus activity or VVIR) pulse generator is the most frequently implanted unit that uses signals other than intracardiac electrograms to control the rate of stimulation. Because all pulse generators have eccentricities,1 it is of clinical importance to describe some of the unexpected varieties of normal function observed during the evaluation of these devices.