Sudden Death Syndrome: Infants, Adults, Causes, Prevention, More

Sudden death syndrome (SDS) is a loosely defined umbrella term for a series of cardiac syndromes that cause sudden cardiac arrest and possibly death.

Some of these syndromes are the result of structural problems in the heart. Others may be the result of irregularities within the electrical channels. All may cause unexpected and abrupt cardiac arrest, even in people who are otherwise healthy. Some people die as a result of it.

Most people don't know they have the syndrome until a cardiac arrest occurs.

Many cases of SDS aren't properly diagnosed, either. When a person with SDS dies, the death may be listed as natural cause or heart attack. But if a coroner takes steps to understand the precise cause, they may be able to detect signs of one of the syndromes of SDS.

Some estimates report at least 4 percent of people with SDS have no structural abnormalities, which would be the easiest to determine in an autopsy. Irregularities in electrical channels are more difficult to spot.

SDS is more common in young and middle-aged adults. In people of this age, the unexplained death is known as sudden adult death syndrome (SADS).

It can occur in infants as well. These syndromes may be one of the many conditions that fall under sudden infant death syndrome (SIDS).

One particular condition, Brugada syndrome, may also cause sudden unexpected nocturnal death syndrome (SUNDS).

Because SDS is often misdiagnosed or not diagnosed at all, it's unclear how many people have it.

Estimates suggest 5 in 10,000 people have Brugada syndrome. Another SDS condition, long QT syndrome, may occur in 1 in 7,000 people. Short QT is even more rare. Only 70 cases of it have been identified in the last two decades.

It's sometimes possible to know if you're at risk. You may be able to treat the underlying cause of possible SDS if you are.

Let's look more closely at the steps that can be taken to diagnose some of the conditions associated with SDS and possibly prevent cardiac arrest.

People with SDS usually appear perfectly healthy before their first cardiac event or death. SDS often causes no visible signs or symptoms. However, there are some risk factors that increase a person's likelihood of having some of the conditions associated with SDS.

Researchers have found specific genes may increase a person's risk for some types of SDS. If a person has SADS, for example, more than 20 percent of their first-degree relatives (siblings, parents, and children) are likely to have the syndrome, too.

Not everyone with SDS has one of these genes, though. Just 15 to 30 percent of confirmed cases of Brugada syndrome have the gene that's associated with that particular condition.

Other risk factors include:

• Sex. Males are more likely to have SDS than females.
• Race. Individuals from Japan and Southeast Asia have a higher risk for Brugada syndrome.

In addition to these risk factors, certain medical conditions can increase the risk of SDS, such as:

• Bipolar disorder. Lithium is sometimes used to treat bipolar disorder. This drug can trigger Brugada syndrome.
• Heart disease. Coronary artery disease is the most common underlying disease connected to SDS. Approximately 1 of every 2 deaths caused by coronary artery disease are sudden. The first sign of the disease is cardiac arrest.
• Epilepsy. Each year, sudden unexpected death in epilepsy (SUDEP) occurs in about 1 out of every 1,000 people diagnosed with epilepsy. Most deaths occur immediately after a seizure.
• Arrhythmias. An arrhythmia is an irregular heart rate or rhythm. The heart may beat too slow or too quickly. It may also have an irregular pattern. It could lead to symptoms such as fainting or dizziness. Sudden death is also a possibility.
• Hypertrophic cardiomyopathy. This condition causes the heart's walls to thicken. It can also interfere with the electrical system. Both can lead to an irregular or rapid heartbeat (arrhythmia).

It's important to note that despite these identified risk factors, they don't mean you have SDS. Anyone at any age and in any state of health can have SDS.

It's unclear what causes SDS.

Gene mutations have been linked to many of the syndromes that fall under the SDS umbrella, but not every person with SDS has the genes. It's possible other genes are connected to SDS, but they haven't been identified yet. And some SDS causes aren't genetic.

Some medications can cause the syndromes that may lead to sudden death. For example, long QT syndrome may result from using:

• antihistamines
• decongestants
• antibiotics
• diuretics
• antidepressants
• antipsychotics

Likewise, some people with SDS may not show symptoms until they begin taking these certain medications. Then, the medication-induced SDS may appear.

Unfortunately, the first symptom or sign of SDS can be sudden and unexpected death.

However, SDS can cause the following red-flag symptoms:

• chest pain, especially during exercise
• loss of consciousness
• difficulty breathing
• dizziness
• heart palpitations or fluttering feeling
• unexplained fainting, especially during exercise

If you or your child experience any of these symptoms, seek immediate medical attention. A doctor can conduct tests to determine what's the likely cause of these unexpected symptoms.

SDS is only diagnosed when you go into sudden cardiac arrest. An electrocardiogram (ECG or EKG) can diagnose many of the syndromes that can cause sudden death. This test records the electrical activity of your heart.

Specially trained cardiologists can look at the ECG results and identify possible problems, such as long QT syndrome, short QT syndrome, arrhythmia, cardiomyopathy, and more.

If the ECG isn't clear or the cardiologist would like additional confirmation, they may also request an echocardiogram. This is an ultrasound scan of the heart. With this test, the doctor can see your heart beating in real time. This may help them detect physical abnormalities.

Anyone experiencing symptoms associated with SDS may receive one of these tests. Likewise, people with a medical or family history that suggests SDS is a possibility may want to have one of these tests.

Identifying the risk early can help you learn ways to prevent possible cardiac arrest.

If your heart stops as a result of SDS, emergency responders may be able to resuscitate you with life-saving measures. These include CPR and defibrillation.

After resuscitation, a doctor may perform surgery to place an implantable cardioverter defibrillator (ICD) if appropriate. This device can send electrical shocks into your heart if it stops again in the future.

You might still get dizzy and pass out as a result of the episode, but the implanted device may be able to restart your heart.

There's no current cure for most causes of SDS. If you receive a diagnosis with one of these syndromes, you can take steps to help prevent a fatal incident. This may include the use of an ICD.

However, doctors are torn about using treatment for SDS in a person who hasn't shown any symptoms.

Early diagnosis is an important step in preventing a fatal episode.

If you have a family history of SDS, a doctor may be able to determine if you also have a syndrome that could lead to unexpected death. If you do, you can take steps to prevent sudden death. These may include:

• avoiding medications that trigger symptoms, such as antidepressants and sodium-blocking drugs
• quickly treating fevers
• exercising with caution
• practicing good heart-health measures, including eating a balanced diet
• maintaining regular check-ins with your doctor or cardiac specialist

While SDS usually has no cure, you can take steps to prevent sudden death if you receive a diagnosis before a fatal event.

Receiving a diagnosis can be life-changing and cause different emotions. In addition to working with your doctor, you may want to speak with a mental health specialist about the condition and your mental health. They can help you process the news and cope with changes in your medical status.