The heart is a hollow muscle that is about the size of an adult fist, and is found to the left of the breastbone. The heart is the most important organ in our body, as it is a complex pump, responsible for circulating blood, oxygen and nutrients around the body. It pumps blood around your body and beats approximately 70 times a minute.
Arrhythmia or irregular heart beats are also known as heart palpitations, and they are any abnormal rhythm of the heartbeat. The heart contains a natural pacemaker that triggers electrical impulses to spread over the heart, causing it to contract (the heart beat).
There are a number of different types of arrhythmia, and most arrhythmias that come from the top of the heart (supraventricular or atrial) may cause symptoms but aren't life threatening. However arrhythmias that arise from the ventricles (ventricular) can be fatal.
Atrial fibrillation occurs when the electrical impulses in the atria become disorganised, overriding the heart's normal rate and rhythm. This type of arrhythmia causes the atria to contract in an irregular manner or 'fibrillate'. You may notice that your heartbeat is irregular or feels uneven. Attacks of atrial fibrillation can last from a few seconds to days. This can lead to a blood clot forming in your heart because your blood isn't able to flow properly through your heart. If a clot forms, it can travel to your brain and cause a stroke.
Another type of arrhythmia is supraventricular tachycardia - most Supraventricular tachycardias are caused by the occurrence of an extra electrical pathway in the heart, between the atria and the ventricles. This allows electrical impulses to 'short-circuit' and re-enter the atria. The impulses end up travelling around the heart in a circle. Supraventricular tachycardia can make your heart beat very quickly, up to 160 beats per minute. An attack of Supraventricular tachycardia may only last for a few seconds or it can last for several hours.
In ventricular tachycardia, the electrical impulses fire too quickly from the ventricles, causing blood to be pumped out quicker than normal. The ventricles may not have enough time to fill up properly with blood. If the ventricular tachycardia attack lasts for 30 seconds or more (sustained ventricular tachycardia), it can progress to a condition called ventricular fibrillation.
With ventricular fibrillation, electrical impulses start firing from multiple sites in the ventricles, very rapidly and in an irregular rhythm. This makes the heart quiver and unable to beat properly. If prompt treatment isn't given, you may have a cardiac arrest, which can be fatal. Someone who has ventricular fibrillation will lose their pulse, and will quickly become unconscious and stop breathing. You should call for emergency help immediately.
The last type of arrhythmia is heart block. If you have heart block, it means there is a problem affecting how the electrical impulses are transmitted through your heart. Heart block can occur in the atrioventricular node or in the muscle fibres that lead into the ventricles.
With some types of arrhythmia you may not get any symptoms, but if you do get symptoms, they will depend on the type and severity of your arrhythmia. They can include:
- palpitations - a palpitation is an unpleasant awareness of your heartbeat, often described as a thumping in your chest
- fainting or collapsing
- chest pain
- fluid in your lungs (pulmonary oedema)
An arrhythmia can be caused by conditions including:
- underlying heart disease
- heart valve problems
- thyroid disease
- high blood pressure
- Wolff-Parkinson-White syndrome - an electrical abnormality in the heart that can cause supraventricular tachycardi and atrial fibrillation
- heart attack
- coronary artery disease
- inflammation of the heart
Some types of arrhythmia may be caused by certain triggers. For example certain medicines can cause heart block or supraventricular tachycard, alcohol can cause atrial fibrillation or supraventricular tachycard, caffeine and smoking tobacco or cannabis can cause supraventricular tachycard. However sometimes there may be no known cause for an arrhythmia.