Drug cabinet: Anti-arrhythmics

Dr Martin Lowe

Some abnormal heart rhythms can be treated with medication. Consultant cardiologist and electrophysiologist Dr Martin Lowe explains all to Doireann Maddock.

An arrhythmia is an abnormal heart rhythm and it happens as a result of a problem with the electrical impulses that regulate your heart. It can make your heart beat too quickly, too slowly or in an irregular way.

The symptoms of an arrhythmia will depend on what type you have and how it affects the functioning of your heart. Arrhythmias are a common problem and can range from being a minor inconvenience to a life-threatening condition.

What are anti-arrhythmic drugs?

Anti-arrhythmic drugs are designed to treat an abnormality of the heart rhythm. They may be used to terminate the abnormal rhythm, prevent it happening or slow the heart rate during the abnormal rhythm to make it more tolerable.

Why would I be prescribed an anti-arrhythmic?

Anti-arrhythmics are generally the first treatment offered, because most abnormal heart rhythms respond to them

Anti-arrhythmic drugs are generally the first treatment that a person is offered, because they can be started straight away and most abnormal heart rhythms respond to them.

There are two approaches to drug dosing. One is a ‘pill in the pocket’ method when people carry a supply of the medication and take a tablet when an episode of arrhythmia happens. This is often recommended when the episodes are less frequent and a benefit of this is that you can minimise the potential side effects from taking long-term medication. If you’ve been advised to take this approach, it can be a good idea to keep the pill in your wallet or purse so that you always have it on you.

The second method is to take medication on a regular basis to try to prevent the change in rhythm occurring in the first place.

Your specialist or GP will advise which option is most suitable for you.

What are the different types of anti-arrhythmic drugs available?

There are many different types and some of them, such as beta blockers and calcium channel blockers, are also commonly prescribed for other uses, for example in the treatment of high blood pressure. When treating a heart rhythm problem, sometimes it’s more appropriate to control the rate and frequency of the rhythm problem rather than seek to cure it.

When treating a heart rhythm problem, sometimes it’s more appropriate to control the rate and frequency of the problem rather than seek to cure it

This can be a complex decision and involves considering factors such as the type and severity of the arrhythmia you have, how long you’ve had it, your age and how it is affecting (or likely to affect) your life.

The most common arrhythmia is atrial fibrillation (AF), which is commonly treated with beta blockers such as atenolol, bisoprolol and metoprolol. Beta blockers may stop the arrhythmia occurring but, more often, are useful for slowing down the heart rate during the arrhythmia without actually terminating it. Calcium channel blockers such as verapamil and diltiazem work in a similar way. Digoxin is also commonly prescribed for AF to help control the rate.

Flecainide, sotalol (also a beta blocker) and amiodarone are also commonly prescribed for arrhythmias. They have the ability to terminate an arrhythmia and are usually given to prevent the abnormal rhythm from occurring or reduce its frequency or duration.

What are the possible side effects and how are they managed?

Many side effects are not too troublesome and you can usually carry on taking your medication.

Beta blockers have a general slowing effect on metabolism and can cause lethargy, which can be more noticeable with the first few doses and then often settles with time.

Many side effects are not too troublesome and you can usually carry on taking your medication

Amiodarone, although very effective as an anti-arrhythmic drug, has a number of potential side effects including making your thyroid over- or underactive, affecting liver function and making your skin more sensitive to sunlight. Skin sensitivity to sunlight with amiodarone requires use of a high-factor sun cream to prevent sunburn. For many people, amiodarone-related thyroid effects can be treated with medication to control thyroid function, but some may need to stop taking the drug. If this happens, dronedarone, which is structurally similar to amiodarone, may be substituted as it has no adverse effects on thyroid function.

Anti-arrhythmic drugs such as flecainide are usually well tolerated but can cause stomach upset and, very occasionally, induce Brugada syndrome – a more dangerous arrhythmia, which can increase the risk of sudden cardiac death. Flecainide-induced Brugada syndrome is uncommon but you’d need to stop taking the medication and further investigation in a specialist arrhythmia clinic would be required.

As with all medication, it’s important that you discuss any side effects with your GP or specialist. Do not suddenly stop taking your medication unless your doctor has instructed you to do so.

Are there instances where I wouldn’t be prescribed an anti-arrhythmic?

If you have heart muscle damage from a previous heart attack or have a type of heart muscle disease and you have been diagnosed with a life-threatening arrhythmia, it may be more appropriate to have an ICD implanted because drugs have not been shown to be effective at preventing sudden cardiac death (caused by the dangerous arrhythmia) in these cases.

Is there an alternative option to taking anti-arrhythmic drugs?

Many abnormal rhythms, such as AF, can be treated with a technique called ablation, which involves burning or freezing the abnormal tissue in the heart that is responsible for the arrhythmia. However, this may not be suitable for everyone. Although this is a commonly performed procedure and has the potential to cure the rhythm abnormality, it’s not always successful with a single procedure (and may need to be repeated at a later date), especially when used for AF.

Open heart surgery is rarely required to treat an arrhythmia, but if the patient is having coronary artery bypass surgery or valve surgery, the surgeon may take the opportunity to treat the arrhythmia at the same time.

For those with a heart problem that puts them at risk of a life-threatening arrhythmia, an ICD can be implanted to manage this.

Your specialist will be able to discuss what treatment options are best for you.

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