Sudden arrhythmic death syndrome (SADS) is a term used after an unexpected death in a person older than 1 year when a standard autopsy and toxicology testing do not identify a cause. In these cases, doctors suspect that a dangerous abnormal heart rhythm may have caused the death.
Some people who later experience a serious heart rhythm problem have warning signs such as palpitations, dizziness, unexplained fainting or seizure-like episodes, although others have no symptoms beforehand. When an inherited heart condition is suspected, close relatives may need heart tests and, in some cases, genetic testing.
There is no treatment for SADS itself because the term describes a finding made after death rather than a disease diagnosed in a living person. However, identifying an inherited condition in relatives can allow treatment and preventive measures, such as avoiding certain triggers or medicines, taking specific medications or using an implantable cardioverter-defibrillator (ICD) in selected higher-risk cases.
Main symptoms
Sudden arrhythmic death syndrome itself does not have a defined group of symptoms because it is diagnosed after death, and some people have no warning signs before a fatal event.
Possible warning signs associated with underlying inherited heart rhythm conditions include:
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Heart palpitations;
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Dizziness or near-fainting;
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Unexplained fainting, also called syncope;
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Seizure-like episodes;
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Sudden cardiac arrest;
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Fainting or other symptoms during exercise or strong emotional stress;
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Fainting or cardiac arrest during sleep or rest;
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Symptoms that occur during a fever.
The type of warning sign can depend on the underlying condition. For example, catecholaminergic polymorphic ventricular tachycardia (CPVT) can cause palpitations, near-fainting or fainting during exercise or strong emotion, while Brugada syndrome may cause fainting or cardiac arrest during sleep or rest and can become more noticeable during fever.
In one study of young people whose deaths were classified as SADS, about one-third had previously experienced fainting and 14% had a family history of sudden cardiac death. Unexplained fainting may therefore be especially important to investigate when it happens with exercise, emotional stress, sleep or fever, or when there is a family history of sudden death.
Possible causes
SADS is not one disease with a single cause. It is a post-mortem classification used when the cause of an unexpected death remains unexplained after autopsy and toxicology testing, although an inherited electrical or structural heart condition may later be suspected or identified through genetic and family testing.
1. Long-QT syndrome
Long-QT syndrome is an inherited heart rhythm disorder that can be associated with SADS. It affects the heart's electrical activity and can increase the risk of dangerous abnormal rhythms.
Fainting can occur, and the situations that trigger symptoms may vary according to the type of long-QT syndrome. The condition can sometimes be identified during the evaluation of relatives after an unexplained sudden death.
2. Brugada syndrome
Brugada syndrome is another inherited electrical disorder of the heart that may underlie an unexplained sudden death. Affected people may experience fainting or cardiac arrest, sometimes while sleeping or resting.
Fever can reveal or worsen the characteristic electrical changes seen with this condition. Because of this, fever management and avoidance of certain medications may form part of preventive care after Brugada syndrome is diagnosed.
3. Catecholaminergic polymorphic ventricular tachycardia
Catecholaminergic polymorphic ventricular tachycardia, or CPVT, is an inherited rhythm disorder in which dangerous arrhythmias can be triggered by exercise or strong emotions. Possible symptoms include palpitations, near-fainting and fainting.
A standard resting electrocardiogram, or ECG, can appear normal in people with CPVT. Exercise testing and other specialized assessments may therefore be important when doctors suspect the condition.
4. Arrhythmogenic cardiomyopathy
Arrhythmogenic cardiomyopathy is another inherited condition that may be found during investigation of a family affected by unexplained sudden death. Unlike disorders that primarily affect the heart's electrical channels, cardiomyopathies involve abnormalities of the heart muscle.
Family investigations can sometimes identify cardiomyopathy even when the person who died did not receive a definite diagnosis during life. In one study of families investigated after a young person's unexplained sudden death, cardiomyopathies were the most frequently identified diagnosis.
Diagnosis
Sudden arrhythmic death syndrome is generally classified after death rather than diagnosed in a living person. Doctors consider SADS when an unexpected death occurs in a person older than 1 year and a detailed autopsy and toxicology testing do not identify another cause, leaving a fatal heart rhythm disturbance as a suspected explanation.
The investigation can include review of the person's medical and family history and the retention of blood or tissue for genetic testing. A molecular autopsy, which means genetic testing performed after death, may help identify a gene change linked to an inherited heart rhythm condition and can guide the assessment of relatives.
Close relatives may undergo tests such as an ECG, longer-term ambulatory heart monitoring, exercise testing, medication-provocation testing, heart imaging and genetic testing when appropriate. A living relative is not diagnosed with SADS, but may instead be diagnosed with an underlying condition such as long-QT syndrome, Brugada syndrome, CPVT or arrhythmogenic cardiomyopathy.
Preventative measures
There is no single way to prevent sudden arrhythmic death syndrome because SADS is a classification made after an unexplained sudden death. Preventative measures instead focus on identifying and managing inherited heart conditions that may increase the risk of a dangerous heart rhythm.
After an unexplained sudden death, first-degree relatives, such as parents, siblings and children, may be advised to have a cardiac evaluation. This can include tests such as an ECG, heart monitoring, exercise testing, heart imaging and, when appropriate, genetic testing. Family screening can help identify conditions such as long-QT syndrome, Brugada syndrome, CPVT or cardiomyopathy before a serious event occurs.
Preventative care depends on the condition that is diagnosed. It may include avoiding certain medicines or triggers, taking beta-blockers or other prescribed medications, treating fever promptly in people with Brugada syndrome and following condition-specific lifestyle advice. An implantable cardioverter-defibrillator (ICD) may also be recommended for selected people who have a higher risk of life-threatening arrhythmias.
Genetic counseling may also be useful when an inherited condition is suspected or confirmed. If a disease-causing genetic change is identified, other family members may be offered genetic testing so that those at increased risk can receive appropriate monitoring and preventative care.