Pacemakers are sometimes recommended for people with conditions that cause the heart to beat abnormally.
Each time the heart beats, the heart muscle contracts (pulls inwards) in preparation for pumping blood around the body.
The contractions are triggered by electrical pulses. These are generated by a group of specialised cells known as the sinoatrial node (SA node).
The SA node is often referred to as a natural pacemaker because it generates a series of electrical pulses at regular intervals.
The pulse is then sent to a group of cells known as the atrioventricular node (AV node). The AV node relays the pulse to the two lower chambers of the heart (the ventricles).
A pacemaker or implantable cardioverter defibrillator (ICD) is needed when something disrupts this process and causes an abnormal heartbeat.
An abnormal heartbeat is called arrhythmia. Some of the most common causes of arrhythmias are described below.
Sick sinus syndrome
In sick sinus syndrome, the SA node doesn't work as it should. This can lead to an abnormally slow heartbeat (bradycardia), an abnormally fast heartbeat (tachycardia), or a combination of both.
Symptoms of sick sinus syndrome can include:
Most cases of sick sinus syndrome are thought to be related to age. Over time, the SA node tissue can become hardened and scarred. This can disrupt the normal pattern of electrical pulses released by the SA node.
Some types of medication can also trigger sick sinus syndrome as a side effect. These include calcium channel blockers and beta-blockers.
Atrial fibrillation is a condition that causes the heart to beat abnormally fast. This is usually considerably higher than 100 beats a minute (often 140 beats a minute or more).
Atrial fibrillation can usually be treated with medication, but some people don't respond to treatment, so a pacemaker may be recommended.
Sometimes people with atrial fibrillation can have a much slower pulse rate than normal, which can also be intermittent (not continuous). In these cases, a pacemaker will usually be recommended.
In people with heart block, the pulse that needs to be sent from the SA node to the AV node is either delayed or absent.
Heart block can be caused when the heart is damaged (acquired heart block), or it can occur if a baby is born with one or more defects that affect their heart (congenital heart block).
If you have heart block and it's causing troublesome symptoms, a pacemaker will usually be recommended.
An implantable cardioverter defibrillator (ICD), which is a device similar to a pacemaker, is mainly used to prevent cardiac arrest.
A cardiac arrest is a potentially fatal condition where the electrical activity that controls the heart becomes so disrupted that the heart stops beating. Unless it's treated quickly, a cardiac arrest will be fatal.
An ICD can detect abnormal electrical signals that could indicate that a cardiac arrest is about to happen. If the ICD detects these type of signals, it sends a powerful electrical shock to the heart.
This basically "reboots" the heart. After the shock, the heart should start beating normally again.
An ICD implantation may be recommended if you've had a cardiac arrest in the past or it's thought you have a significant risk of having one in the future.
Factors that increase the risk of a cardiac arrest occurring include: