About implantable cardiac devices
Implantable cardiac devices can sometimes be used to help manage problems with a person’s heart rate or heart rhythm.
The heart has an electrical system (conducting system) that regulates the heart rate, made up of nodes (special clusters of conducting cells) and conduction pathways.
Problems with the electrical circuitry of the heart can include blocked signals or signals taking an abnormal path through the heart.
A special cluster of cells located in the upper right chamber of the heart (right atrium) called the sinus node, is the natural pacemaker that controls your heartbeat (60–100 bpm). To ensure that the heart beats regularly and at the right pace, the sinus node communicates with the heart’s collecting chambers (atria) and the heart’s pumping chambers (ventricles), along nervous system pathways called the atrioventricular node, and the heart’s electrical system. If this system is damaged, it may send unreliable messages to the heart chambers.
An artificial pacemaker is an implantable device that mimics the actions of the nodes and conducting system, and helps to regulate the heart rate.
An artificial implantable cardioverter defibrillator (AICD) can recognise a dangerous heart rhythm and send messages to the heart to try and slow the rhythm and return it to normal.
How a healthy heart works
The heart is a double pump that circulates blood around the body. It has four chambers. The upper right chamber (right atrium) and lower right chamber (right ventricle) take in deoxygenated blood from the body and send it to the lungs. The upper left chamber (left atrium) and the lower left chamber (left ventricle) take in oxygenated blood from the lungs and send it around the body.
The atria are responsible for collecting blood and filling the ventricles. The ventricles pump blood out of the heart. The heart’s electrical system (nodes and conducting system) is responsible for the heart rate and coordinating the heart's contraction or pumping action.
Sick sinus syndrome
‘Sick sinus syndrome’ is when the sinus node in your heart malfunctions and ‘fires’ too slowly, telling your heart to beat slowly. It can be caused by ageing or by coronary heart disease.
Common symptoms include:
- a heart rate which is too fast or too slow
- loss of consciousness.
‘Heart block’ is when there is a block or delay in the electrical signal from your heart’s collecting chambers (atria) to its pumping chambers (ventricles). It often results from damage to your heart’s electrical pathways, caused by coronary heart disease and ageing.
The most common symptom of this serious disorder is dizziness or loss of consciousness. Artificial pacemakers are used successfully to treat both sick sinus syndrome and heart block.
How an artificial cardiac pacemaker works
An artificial cardiac pacemaker is a small battery-operated computer, called a pulse generator. It’s connected to the heart by one or more ‘pacing’ leads. These leads are made of a coiled metal conductor, insulated with plastic and fixed to the inner wall of the heart. The pulse generator sends an electrical signal down the lead to an electric conductor attached to the heart, causing the heart chamber to contract (squeeze).
The system relies on feedback, which means the artificial pacemaker 'listens' to the heart and increases the heart's natural rate. For example, the heart rate of a person with sick sinus syndrome may not increase during physical exertion. The artificial pacemaker recognises this and boosts the heart rate to an appropriate level. To do this, the pulse generator may have sensors to detect physical activity or changes in breathing.
The two major types of artificial cardiac pacemakers include:
- single chamber – only one chamber is regulated, usually the ventricles.
- dual chamber – two leads are used. Information from the atria regulates the contractions of the ventricles.
Implanting an artificial cardiac pacemaker
The typical hospital stay for artificial cardiac pacemaker implantation is between one to two days. The procedure is usually done under local anaesthesia.
The pulse generator, which is about the size and weight of three 50 cent coins, is generally implanted under the skin just below the collarbone on either the right or left side.
The leads are inserted using x-ray control, via a vein found in this area, and positioned in the appropriate right-sided heart chamber. The leads are tested before the pulse generator is attached and the incision is closed.
There are other pacing systems, used in special circumstances, that require more than two leads and may involve pacing the left-sided chambers. Usual activities such as working, driving a car and light exercise can resume after one to two weeks recovery.
Living with an artificial cardiac pacemaker
A person with an artificial cardiac pacemaker can live a normal life and can still perform moderate to strenuous activities, such as sex and (preferably) non-contact sports.
Medications and household electrical appliances won't affect the pacemaker. Mobile phones, portable phones and microwave ovens are also safe to use. If you are concerned about the effect of any electrical appliance, such as welders, talk to your pacemaker specialist.
Certain body imaging tests, such as magnetic resonance imaging (MRI) scans, should not be performed in someone with an artificial cardiac pacemaker, unless the person has an MRI-safe device.
Some pacemakers (and implantable cardioverter defibrillators – see AICD on this page) can be scanned safely in some circumstances, but special precautions are likely to be necessary, and only some MRI sites will be able to support these. If you need to have an MRI and you have an artificial cardiac pacemaker, be sure to discuss this with the MRI facility in advance.
A person with an artificial cardiac pacemaker will require one or two pacemaker checks per year. These are generally conducted in specialised clinics. Adjustments to the pacemaker can be made non-invasively using a specially designed radio frequency programmer, with a wand placed on the skin over the implanted device.
Most pacemakers last longer than five years. However, the life of the battery is dependent on how it’s used. Most pacemakers can calculate the remaining life of the battery and this information is available at testing. Well before the pacemaker fails, a battery depletion indicator suggests that the pacemaker should be replaced. This is again performed under local anaesthesia.
Artificial implantable cardioverter defibrillator (AICD)
Some rapid and very dangerous heart rhythms, such as ventricular tachycardia and ventricular fibrillation, are potentially fatal. One treatment option includes an artificial implantable cardioverter defibrillator (AICD).
This is a complex device that can recognise a dangerous heart rhythm and send messages to regulate the heart. If this doesn't work, the AICD can send an electric shock to jolt the heart out of its fibrillation. In Australia, there was an increase in AICD usage, with 4212 new implants in 2017.
Where to get help