Ectopic (unifocal) atrial tachycardia arises from an independent focus within the atria, distinguished by a consistent P-wave of abnormal shape and/or size that falls before a narrow, regular QRS complex. It can be caused by automaticity, which means that some cardiac muscle cells, which have the primordial (primitive, inborn, inherent) ability to generate electrical impulses that are common to all cardiac muscle cells, have established themselves as a rhythm center with a natural rate of electrical discharge that is faster than the normal SA node. Some atrial tachycardias, rather than being a result of increased automaticity may be a result of a micro-reentrant circuit (defined by some as less than 2 cm in longest diameter to distinguish it from macro-reentrant atrial flutter). Still other atrial tachycardias may be due to triggered activity caused by after-depolarizations. Multifocal atrial tachycardia (MAT) is tachycardia arising from at least three ectopic foci within the atria, distinguished by P-waves of at least three different morphologies that all fall before irregular, narrow QRS complexes. This rhythm is most commonly seen in elderly people with COPD. Atrial fibrillation meets the definition of SVT when associated with a ventricular response greater than 100 beats per minute. It is characterized as an "irregularly, irregular rhythm" both in its atrial and ventricular depolarizations and is distinguished by its fibrillatory atrial waves that, at some point in their chaos, stimulate a response from the ventricles in the form of irregular, narrow QRS complexes.
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 survey of records showed that 230 otherwise healthy Thai foreign workers living in Singapore died suddenly of unexplained causes between 1982 and 1990. Causes
A sudden death in 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), PCCD (progressive cardiac conduction defect), 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 attributed to night time hypoglycemia triggering abnormal heart rhythms or cardiac autonomic neuropathy, a 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.