Yes, there are three main types:
- The most common causes of autopsy-negative sudden death, namely, the cardiac channelopathies that include long QT syndrome and catecholaminergic polymorphic ventricular tachycardia
- Sudden infant death syndrome (SIDS)
- The most common cause of autopsy-positive sudden death in young people, especially athletes, namely, hypertrophic cardiomyopathy
Congenital long QT syndrome (LQTS) comprises a distinct group of cardiac channelopathies characterized by delayed repolarization of the myocardium, QT prolongation and increased risk of syncope, seizures and sudden cardiac death in the setting of a structurally normal heart and otherwise healthy person.
This repolarization abnormality usually is without consequence. However, infrequently, when caught off guard by such triggers as exertion, swimming, emotion or auditory stimuli, the heart can spiral out of control electrically into a potentially life-threatening and sometimes lethal dysrhythmia.
The heart’s rhythm typically returns to normal spontaneously after an episode of syncope. But in 5% of untreated and unsuspected cases of LQTS, the person dies of a fatal arrhythmia as the sentinel event.
Long QT syndrome is a genetically heterogeneous disorder most often inherited in an autosomal dominate mode.
To date, hundreds of mutations have been identified, with approximately 75% of clinically robust LQTS cases due to mutations in three genes — KCNQ1 (LQT1), KCNH2 (LQT2), SCN5A (LQT3) — encoding for critical cardiac ion-channel subunits that are responsible for the orchestration of the cardiac action potential.
Hypertrophic cardiomyopathy is one of the most common heritable cardiovascular diseases and the most common cause of sudden death in young people, especially in young athletes. Hypertrophic cardiomyopathy is a disease underscored by profound phenotypic and genetic heterogeneity.
Since the sentinel discovery of mutations in MYH7-encoded beta myosin heavy chain as a pathogenetic basis for HCM, hundreds of mutations scattered over at least 20 genes that encode essential sarcomeric, calcium regulation and structural proteins have been identified.
Some genetic testing is done post mortem such as in unexplained drowning or SIDS. Lethal and unexpected, long QT syndrome (LQTS) and catecholaminergic polymorphic ventricular tachycardia (CPVT) represent ideal arrhythmogenic assassins able to escape suspicion, detection and apprehension by either a standard medicolegal autopsy or a careful evaluation of surviving first- and second-degree relatives.