Brugada syndrome

Brugada syndrome (BrS) is a genetic disorder in which the electrical activity within the heart is abnormal. It increases the risk of abnormal heart rhythms and sudden cardiac death. Those affected may have episodes of passing out. The abnormal heart rhythms seen in those with Brugada syndrome often occur at rest. They may be triggered by a fever. About a quarter of those with Brugada syndrome have a family member who also has the condition. Some cases may be due to a new genetic mutation or certain medications. The most commonly involved gene is SCN5A which encodes the cardiac sodium channel. Diagnosis is typically by electrocardiogram (ECG), however, the abnormalities may not be consistently present. Medications such as ajmaline may be used to reveal the ECG changes. Similar ECG patterns may be seen in certain electrolyte disturbances or when the blood supply to the heart has been reduced. There is no cure for Brugada syndrome. Those at higher risk of sudden cardiac death may be treated using an implantable cardioverter defibrillator (ICD). In those without symptoms the risk of death is much lower, and how to treat this group is less clear. Isoproterenol may be used in the short term for those who have frequent life-threatening abnormal heart rhythms, while quinidine may be used longer term. Testing people's family members may be recommended. The condition affects between 1 and 30 per 10,000 people. It is more common in males than females and in those of Asian descent. The onset of symptoms is usually in adulthood. It is named after the Spanish cardiologists Pedro and Josep Brugada who described the condition in 1992. Their brother Ramon Brugada was the first to describe one potential genetic cause in 1998. While many of those with Brugada syndrome do not have any symptoms, Brugada syndrome 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 Brugada syndrome despite a normal heart rhythm due to a sudden drop in blood pressure, known as vasovagal syncope. The abnormal heart rhythms seen in Brugada syndrome 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. Certain medications may also worsen the tendency to abnormal heart rhythms in patients with Brugada syndrome and should be avoided by these patients. The individual cells of the heart communicate with each other with electrical signals, and these electrical signals are disrupted in those with Brugada syndrome. As a genetic condition, the syndrome is ultimately caused by changes to a person's DNA, known as genetic mutations. The first mutations described in association with Brugada syndrome were in a gene responsible for a protein or ion channel that controls the flow of sodium ions through the cell membrane of heart muscle cells – the cardiac sodium channel. Many of the genetic mutations that have subsequently been described in association with Brugada syndrome influence the sodium current in some way, or affect other ionic currents. A long list of factors that can generate a Brugada ECG pattern have been described, including certain medications, electrolyte disturbances such as a decrease in the levels of potassium in the blood, and a reduction in blood supply to key areas of the heart, specifically the right ventricular outflow tract. Drugs that have been implicated include antiarrhythmic medications such as flecainide, verapamil and propranolol, antidepressants such as amitryptiline, and drugs that enhance vagal tone such as acetylcholine. The ECG pattern can also be seen following excessive use of alcohol or cocaine.