Pacemakers are devices that deliver electrical impulses to the heart to regulate its rhythm. They are used in patients with bradycardia (slow heartbeat) to speed it up and prevent tiredness, breathlessness, dizzy spells and blackouts. Up till recently, all pacemakers consisted of a pulse generator including a battery and clever circuitry that produces an electrical signal. One or two leads (special wires) used to connect the generator with the heart muscle. The whole device is implanted under the skin, usually under the left collar bone. If the pacemaker is needed only temporarily, an external device is used. The implantation procedure is normally straightforward, but as with any operation, there is a risk of complications such as bruising, infection, pneumothorax (collapsed lung), tamponade (collection of blood outside the heart) and damage to the leads.

The recent invention of the leadless pacemaker has the potential to make things much easier. It has the size of a small battery and is implanted via one of the big veins and delivered directly inside the heart so that no leads are necessary. So far, there is only a limited experience with these new devices, but they look very promising. The advantages of leadless pacemakers include less invasive implanting procedure, reduced risk of infection and the elimination of complications related to leads.

Most bradycardic (slow pulse) heart rhythm problems - apart from atrial fibrillation with a slow ventricular response - require the stimulation of both top and bottom right heart chambers (right atrium and right ventricle), but the current leadless pacemakers can deliver impulses only to the right ventricle. There are some other problems, and leadless pacemakers will require further improvements before widespread clinical use. Nonetheless, the preliminary results are very promising, and the new technology has enormous potential.