Why your heart can suddenly start racing

THERE are many reasons why electrical signalling through the heart can go wrong. These include issues with the heart’s natural pacemaker, conduction problems with the system of ‘wires’ (specialised muscle cells), or damage to the heart muscle that blocks the electrical signal to certain parts of the heart wall. Malfunction of the nervous system can also lead to problems.

And some arrhythmias can be inherited, caused by chemical imbalances in the heart muscle cells which interfere with their battery function.

But most rhythm disorders are associated with ageing and normal ‘wear and tear’. These are what affect the bulk of the more than two million Britons with arrhythmias, according to NHS Choices.

‘Just like the wiring in your home, wiring in your heart can start to fail,’ says Professor Chris Gale, a cardiologist at Nuffield Health York Hospital.

ATRIAL FIBRILLATION: This is the most common arrhythmia, affecting around one million Britons. It makes the heart beat irregularly and often abnormally fast — in some cases, much faster than 100 beats per minute (the upper end of the normal resting rate), which can cause dizziness, breathlessness, pounding or fluttering.

Wear and tear in the electrical ‘wiring’ of the body is the typical cause, but it is often seen in patients with hypertension, heart valve disease, heart failure, heart attack, chronic lung disease and diabetes.

‘ Many of these lead to enlargement or damage of the heart muscle, causing the electrical system to stretch and start to pull apart,’ says Professor Gale, who believes that atrial fibrillation will become more common as our ageing population lives longer.

It’s also linked to an overactive thyroid, as too much thyroid hormone can shorten the electrical signals’ length.

Atrial fibrillation may also be triggered temporarily by caffeine — more than five cups of tea or coffee a day for most people.

SUPRAVENTRICULAR TACHYCARDIA: This arrhythmia leads to an abnormally fast resting heart rate — up to 250 beats per minute, instead of the normal 60 to 100. It can last for minutes, hours or days.

It is usually caused by faulty electrical connections in the heart and may be linked to medications, such as asthma drugs, too much alcohol, or even emotional upset.

These effects are temporary, but unpleasant, as in ‘ holiday heart’ syndrome, where heavy drinking can cause arrhythmias in otherwise healthy patients.

A study in the European Heart Journal found around a third of revellers at the 2015 Munich Oktoberfest who bingedrank suffered a cardiac arrhythmia during the festive season.

When medication is to blame, lowering the dose of drugs can prevent symptoms, but this should only be following the advice of a doctor.

BRADYCARDIA: This is where the heart beats more slowly than usual (less than 60 beats per minute) and usually starts in the sinus node. It can be due to ageing, low thyroid hormone levels, or an imbalance in electrolytes, such as too much potassium in the blood. Some heart drugs, such as betablockers, may also slow the heart rate. ‘Heart block — where the heart beats too slowly because the electrical signals telling it to contract are partially or totally blocked — can also occur due to ageing, a heart attack or heart surgery and occurs when scarring or damage to the heart wall damages the electrical conduction system,’ says cardiologist Dr Chris Pepper.

‘It often requires a permanent pacemaker to be fitted, to keep the heart beating above a minimum rate.’ VENTRICULAR FIBRILLATION: This is a very serious arrhythmia, where the heart’s electrical rhythm becomes chaotic and the bottom pumping chambers no longer beat effectively. It can be genetic or due to scars or damage from a heart attack.

Without help within minutes, in the form of emergency defibrillation, a person will rapidly lose consciousness and die.