Sudden arrhythmic death syndrome

What is SADS?

Sudden arrhythmic death syndrome is when someone dies suddenly and unexpectedly from a cardiac arrest, but the cause of the cardiac arrest can’t be found.

A cardiac arrest is when your heart suddenly stops pumping blood around your body. This stops your breathing and starves your brain of oxygen.

The rhythm of your heart (which controls your heartbeat) is controlled by electrical impulses. If the electrical impulses go wrong, it can cause an abnormal heart rhythm known as an arrhythmia. Some arrhythmias can be dangerous if they’re left untreated, they can cause a cardiac arrest. Your heart’s rhythm and electrical impulses are no longer there after death, this means an abnormal heart rhythm can’t be found and the heart’s structure will appear normal. This is why the cause of the cardiac arrest can’t be found and SADS might be diagnosed.

Sudden arrhythmic death syndrome affects around 500 people in the UK every year.

You may also see sudden arrhythmic death syndrome, or SADS, being called sudden adult death syndrome.

What causes SADS?

SADS usually happens when an abnormal heart rhythm, known as an arrhythmia, goes untreated and leads to a cardiac arrest. An arrhythmia usually causes the heart to beat too fast, too slow or irregularly. It is usually caused by a heart condition that affects the heart’s electrical system.

Sometimes, the heart condition that causes the arrhythmia can be inherited. Inherited heart conditions are often the cause of SADS if they are left undetected and untreated. These conditions include:

• long QT syndrome (LQTS)
• Brugada syndrome
• catecholaminergic polymorphic ventricular tachycardia (CPVT)
• progressive cardiac conduction defect (PCCD).

A condition that causes SADS is undetectable after death because the heart will appear normal. But there are a few conditions that can cause SADS because of very subtle changes to the heart. SADS may still be diagnosed because the structural changes are too small to be seen when the heart is examined after death.

These conditions include:

• hypertrophic cardiomyopathy (HCM)
• dilated cardiomyopathy (DCM)
• arrhythmogenic right ventricular cardiomyopathy (ARVC)

Thanks to research, we now know that these conditions are caused by changes (or mutations) in one or more of our genes. We can sometimes discover these changes with genetic testing for family members, known as cascade testing. In some cases, this is the only way of telling if someone has an inherited heart condition or if they are at risk of developing one.

How is SADS diagnosed?

After an unexpected and sudden death, a coroner (someone who is responsible for investigating deaths) will usually ask for a post-mortem examination to be carried out to find out the cause of death. A post-mortem usually happens within two to three working days after the death.

During the post-mortem examination, a pathologist (a doctor trained in the study of disease) will look for conditions that could have caused the death, such as:

• coronary heart disease
• heart attack
• heart failure
• clots on the lungs

If the pathologist can’t find an obvious cause of death, they may do further tests such as:

• look at organ tissue
• test for medications or drugs in the body
• ask for an assessment by an expert heart pathologist.

The coroner will then decide on a cause of death. SADS is declared if the death is still unexplained after these tests.

When this happens, the coroner will usually recommend that family members are tested for inherited heart conditions. Some people might not feel ready to be tested after losing a loved one which is understandable, but the tests are usually simple for most people. The earlier you and your family are tested, the less you risk a family member possibly leaving a heart problem untreated.

How do they test for inherited heart conditions?

An inherited heart condition is usually tested for with a genetic test. A genetic test is usually done with a simple blood test. It can also be carried out on a sample of hair, skin or bodily tissue.

Genetic tests can find genetic faults. A fault could mean you are at risk of developing the same inherited heart condition that your family member has.

If someone has a heart condition or has died from SADS, the immediate family (their parents, siblings and children) might be referred for genetic tests. The tests are normally done in an inherited heart condition clinic at a hospital or genetics centre.

During your appointment, you might also be asked about your health, family history and if you have any symptoms. It’s helpful to bring information about any family members who have passed away unexpectedly or have been diagnosed with heart and circulatory diseases.

What's the difference between sudden cardiac death and SADS?

Sudden arrhythmic death syndrome (or SADS) is diagnosed when the cause of death can’t be explained in a post-mortem examination because the structure of the heart appears normal.

Sudden cardiac death (SCD) is when the cause of death can be found in a post-mortem examination because something is wrong with the structure of the heart. Such as, partially or fully blocked arteries after a heart attack.

Emotional support

If someone you love has passed away due to SADS, this may be an extremely difficult time for you. It’s understandable to be confused about what’s happened and wonder if there were symptoms that were missed. You might also be concerned about your own health, or the health of other close family members.

Some people don’t feel ready to go to a specialist genetics centre for assessment straight away but the earlier you’re seen, the sooner a heart problem can be diagnosed or your risk of developing a heart problem in the future can be assessed. If you have an inherited condition, your condition can be monitored and you’ll be given treatment if you need it.

Whatever you’re feeling, there is support available and it can be helpful to talk to family, friends and support services:

• it may be that hospital staff can offer support
• you can access local bereavement services through your GP and you can visit our bereavement page for support if you’ve sadly lost a loved one
• join our online community platform, HealthUnlocked, and talk to people who have been through similar experiences

Beating heartbreak caused by heart disease

We’ve made vital discoveries into tests and treatments, but more needs to be done.

We’re currently funding research into the genes and proteins that control the spread of electrical currents across the heart. That research is helping us understanding the heart rhythm problems that cause SADS.

With research we hope to diagnose people before it’s too late. 

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Last updated September 2021

Next update due September 2024