Sudden arrhythmic death syndrome (SADS) is a sudden unexpected death of adolescents and adults, mainly during sleep. One relatively common type is known as Brugada syndrome.
The syndrome is rare in most areas around the world but occurs in populations that are culturally and genetically distinct. It was first noted in 1977 among southeast Asian Hmong refugees in the United States and Canada. The syndrome was again noted in Singapore when a retrospective review of records showed that 230 otherwise healthy Thai foreign workers living in Singapore died suddenly of unexplained causes between 1982 and 1990.
Causes
Sudden death of a young person can be caused by heart disease (including cardiomyopathy, congenital heart disease, myocarditis, genetic connective tissue disorders) or conduction disease (WPW syndrome, etc.), medication-related causes or other causes. Rare diseases called ion channelopathies may play a role such as long QT syndrome (LQTS), Brugada syndrome (BrS), CPVT (catecholaminergic polymorphic ventricular tachycardia), progressive cardiac conduction defect (PCCD), early repolarization syndrome, mixed sodium channel disease, and short QT syndrome. In 20% of cases, no cause of death can be found, even after extensive examination.
In young people with type 1 diabetes, unexplained deaths could be due to nighttime hypoglycemia triggering abnormal heart rhythms or cardiac autonomic neuropathy, damage to nerves that control the function of the heart.
Medical examiners have taken into account various factors, such as nutrition, toxicology, heart disease, metabolism, and genetics. Although there is no real known definite cause, extensive research showed victims aged 18 or older were found to have had a hypertrophic cardiomyopathy, a condition in which the heart muscle becomes oddly thickened without any obvious cause. This was the most commonly identified abnormality in sudden death of young adults. Where people have died suddenly, it is most commonly found that they had had CAD (coronary artery disease) or ASCAD (atherosclerotic coronary artery disease), or any level of stress. However, studies reveal that people were known to have had symptoms within the week before the terminal event such as chest pain at ~52% of patients, dyspnea at ~22%, and syncope at ~7%. About 19% are not known to have experienced symptoms. Scientists have also associated this syndrome with a mutation of gene SCN5A that affects the function of the heart. A 2011 autopsy-based study found that sudden death was attributed to a cardiac condition in 79.3% of cases, and was unexplained in 20.7%.
In the Philippines, bangungot (or in their term, sudden adult death syndrome) is mainly caused by the Brugada syndrome.
Diagnosis
By definition, the diagnosis can only occur post-mortem after other causes are ruled out.
Prevention
A 2011 retrospective cohort study using demographic and autopsy data for a 10-year period comprising 15.2 million person-years of active surveillance suggested prevention of sudden death in young adults should focus on evaluation for causes known to be associated with SUD (e.g., primary arrhythmia) among persons less than 35 years old, and emphasise atherosclerotic coronary disease in those older.
A 2003 study found that the only proven way to prevent SADS is with an implantable cardioverter-defibrillator. Oral beta-blockers such as propranolol are ineffective.
Epidemiology
In 1980, a reported pattern of sudden deaths was brought to the attention of the Centers for Disease Control. The first reported sudden death occurred in 1948 when there were 81 similar deaths of Filipino men in Oahu County, Hawaii. However, it did not become relevant because there was no associated pattern. This syndrome continued to become more significant as years went on. By 1981–1982, the annual rate in the United States was high with 92/100,000 among Laotians-Hmong, 82/100,000 among other Laotian ethnic groups, and 59/100,000 among Cambodians.
In a 2008 study it was found that over half of SADS deaths could be attributed to inherited heart disease: unexplained premature sudden deaths in family, long QT syndrome, Brugada syndrome, arrhythmogenic right ventricular cardiomyopathy and others.