Acquired<unk>  Many people with<unk>  have no signs or symptoms. When symptoms occur, they are generally caused by abnormal heart rhythms (arrhythmias), most commonly a form of ventricular tachycardia called Torsades de pointes (TdP). If the arrhythmia reverts to a normal rhythm spontaneously the affected person may experience lightheadedness (known as presyncope) or faint which may be preceded by a fluttering sensation in the chest. If the arrhythmia continues, the affected person may experience a cardiac arrest, which if untreated may lead to sudden death. Those with<unk>  may also experience seizure-like activity (non-epileptic seizure) as a result of reduced blood flow to the brain during an arrhythmia. Epilepsy is also associated with certain types of<unk> . The arrhythmias that lead to faints and sudden death are more likely to occur in specific circumstances, in part determined by which genetic variant is present. While arrhythmias can occur at any time, in some forms of<unk>  arrhythmias are more commonly seen in response to exercise or mental stress <unk> 1), in other forms following a sudden loud noise <unk> 2), and in some forms during sleep or immediately upon waking <unk> 3). Some rare forms of<unk>  affect other parts of the body, leading to deafness in the Jervell and Lange-Nielsen form of the condition, and periodic paralysis in the Andersen–Tawil <unk> 7) form. Risk for arrhythmias While those with<unk>  have an increased risk of developing abnormal heart rhythms the absolute risk of arrhythmias is very variable. The strongest predictor of whether someone will develop TdP is whether they have experienced this arrhythmia or another form of cardiac arrest in the past. Those with<unk>  who have experienced syncope without an ECG having been recorded at the time are also at higher risk, as syncope in these cases is frequently due to an undocumented self-terminating arrhythmia. In addition to a history of arrhythmias, the extent to which the QT is prolonged predicts risk. While some have QT intervals that are very prolonged, others have only slight QT prolongation, or even a normal QT interval at rest (concealed<unk> . Those with the<unk> est QT intervals are more likely to experience TdP, and a corrected QT interval of greater than 500 ms is thought to represent those at higher risk. Despite this, those with only subtle QT prolongation or concealed<unk>  still have some risk of arrhythmias. Overall, every 10 ms increase in the corrected QT interval is associated with a 15% increase in arrhythmic risk. As the QT prolonging effects of both genetic variants and acquired causes of<unk>  are additive, those with inherited<unk>  are more likely to experience TdP if given QT prolonging drugs or if they experience electrolyte problems such as low blood levels of low potassium (hypokalaemia). Similarly, those taking QT prolonging medications are more likely to experience TdP if they have a genetic tendency to a prolonged QT interval, even it this tendency is concealed. Arrhythmias occur more commonly in drug-induced<unk>  if the medication in question has been rapidly given intravenously, or if high concentrations of the drug are present in the person's blood. The risk of arrhythmias is also higher if the person receiving the drug has heart failure, is taking digitalis, or has recently been cardioverted from atrial fibrillation. Other risk factors for developing torsades de pointes among those with<unk>  include female sex, increasing age, pre-existing cardiovascular disease, and abnormal liver or kidney function.
Long QT syndrome
Brugada syndrome
Short QT syndrome
Arrhythmogenic cardiomyopathy
Catecholaminergic polymorphic ventricular tachycardia
Opitz G/BBB syndrome
Jervell and Lange-Nielsen syndrome
Familial atrial fibrillation