Pacemakers: Technology and exercise

A pacemaker is an implantable device designed primarily to compensate for an abnormally low heart rate or an inadequate heart rate response to exercise. The capabilities of such devices range from simple ventricular back-up pacing at a fixed rate, to sophisticated devices that pace the atrium and the ventricle sequentially and also vary their rates automatically to match the physiologic needs of the patient. To be truly physiologic, a pacemaker should maintain atrioventricular synchrony as well as increase heart rate with exercise. However, heart rate is a much more important factor in increasing cardiac output during exercise than atrioventricular synchrony. When a patient's own sinus node can no longer vary its rate as necessary in response to metabolic demand, pacemakers can act as a substitute, using alternative sensors such as body activity or minute ventilation. The choice of an appropriate pacemaker for a patient depends on a number of factors, including the indication for pacing, the status of the atrium, the presence of underlying heart disease or arrhythmias, and the exercise tolerance of the patient. Exercise programs for patients with implanted pacemakers should be based primarily on the patients' underlying medical condition. Patients with pacemakers who cannot increase their heart rates with exercise, and who exhibit exercise intolerance, may occasionally need upgrading of their pacemakers to a more physiologic, rate-responsive model. Patients with rate-responsive pacemakers already implanted can achieve a nearly normal heart rate response to exercise with proper programming.