While many of those with<unk>  do not have any symptoms,<unk>  may cause fainting or sudden cardiac death due to serious abnormal heart rhythms such as ventricular fibrillation or polymorphic ventricular tachycardia. Blackouts may be caused by brief abnormal heart rhythms that revert to a normal rhythm spontaneously. If a dangerous heart rhythm does not stop by itself and is left untreated, the person may have a fatal cardiac arrest. However, blackouts can occur in those with<unk>  despite a normal heart rhythm due to a sudden drop in blood pressure, known as vasovagal syncope. The abnormal heart rhythms seen in<unk>  often occur at rest, following a heavy meal, or even during sleep. These situations are linked to periods when the vagus nerve is activated, referred to as periods of high vagal tone. Abnormal heart rhythms may also occur during fever or following excessive alcohol. Sodium channel blocking medications, commonly used to treat cardiac arrhythmia, may also worsen the tendency to abnormal heart rhythms in patients with<unk>  and should be avoided.
Brugada syndrome
Arrhythmogenic cardiomyopathy
Pacak–Zhuang syndrome
Duchenne muscular dystrophy
Woodhouse–Sakati syndrome
Romano–Ward syndrome
Pascual-Castroviejo syndrome type 1
Catecholaminergic polymorphic ventricular tachycardia