A pacemaker is a small, battery-operated device that senses when your heart is beating irregularly or too slowly. It sends a signal to your heart that makes your heart beat at the correct pace.A pacemaker is a small device about the size of a matchbox that weighs 20-50g. It consists of a pulse generator – which has a battery and a tiny computer circuit – and one or more wires, known as pacing leads, which attach to your heart
The pulse generator emits electrical impulses through the wires to your heart. The rate at which the electrical impulses are sent out is called the pacing rate.
Almost all modern pacemakers work on demand. This means they can be programmed to adjust the discharge rate in response to your body's needs.
Implantable cardioverter defibrillators (ICDs)
If the pacemaker senses that your heart has missed a beat or is beating too slowly, it sends signals at a steady rate. If it senses that your heart is beating normally by itself, it doesn't send out any signals. Most pacemakers have a special sensor that recognises body movement or your breathing rate. This allows them to speed up the discharge rate when you're active. Doctors describe this as rate responsive.
An implantable cardioverter defibrillator (ICD) is a device similar to a pacemaker. It sends a larger electrical shock to the heart that essentially "reboots" it to get it pumping again. Some devices contain both a pacemaker and an ICD.
ICDs are often used as a preventative treatment for people thought to be at risk of cardiac arrest at some point in the future. If the ICD senses the heart is beating at a potentially dangerous abnormal rate, it will deliver an electrical shock to the heart. This often helps return the heart to a normal rhythm.
A conventional ICD has a pacing lead that's implanted along a vein (transvenously). There's also a newer type of ICD where the pacing lead is implanted under the skin (subcutaneously).