Over the past 40 years, permanent pacemakers have become standard treatment for patients with symptomatic sinus node disease and documented, or suspected, high grade atrioventricular (AV) block. Permanent pacemakers were first developed for the treatment of heart block, often in young patients following surgical repair of congenital heart defects. These early pacemakers were primitive devices, allowing only for fixed rate asynchronous pacing in the ventricle (that is, VOO mode). Subsequently, sensing circuits were developed to permit inhibited modes of pacing (that is, VVI mode). Permanent pacemakers were designed primarily to prevent mortality, which was inevitable and often occurred early in patients with complete heart block.

The development of dual chamber pacing and rate responsiveness allowed pacemaker therapy to progress from simply maintaining a minimal heart rate to allowing for restoration of physiologic chronotropy and normal atrioventricular activation. This led to the expansion of this technology from immediate life saving treatment to use aimed at improving haemodynamic function and quality of life, and reducing morbidity. While it is clear that modern dual chamber pacemakers can increase exercise capacity in subjects with chronotropic incompetence and prevent pacemaker syndrome caused by ventricular pacing, the effects on other end points including mortality and arrhythmia prevention remain controversial. With the development of more physiologic pacing, attempts have been made to apply pacemaker technology to the treatment of problems other than symptomatic bradycardia. These problems include pacing to prevent atrial arrhythmias, to improve haemodynamic function and symptoms in patients with hypertrophic or dilated cardiomyopathy, and to prevent neurocardiogenic syncope. Thus, much of the interest in modern pacemakers is for indications other than primary bradycardia. It is these new indications that are the subject of this review.