Fainting syncope, commonly known as fainting

Situational syncope
Syncope may be caused by specific behaviors including coughing, urination, defecation, vomiting, swallowing (deglutition), and following exercise.^[3] Manisty et al. note: "Deglutition syncope is characterised by loss of consciousness on swallowing; it has been associated not only with ingestion of solid food, but also with carbonated and ice-cold beverages, and even belching."^[14] Fainting can occur in "cough syncope" following severe fits of coughing, such as that associated with pertussis or "whooping cough."^[15] Neurally mediated syncope may also occur when an area in the neck known as the carotid sinus is pressed.^[1] A normal response to carotid sinus massage is reduction in blood pressure and slowing of the heart rate. Especially in people with hypersensitive carotid sinus syndrome this response can cause syncope or presyncope.^[9]

Cardiac[edit]

Heart-related causes may include an abnormal heart rhythm, problems with the heart valves or heart muscle, or blockages of blood vessels from a pulmonary embolism or aortic dissection, among others.^[1]

Syncope from bradycardia

Cardiac arrhythmias[edit]

The most common cause of cardiac syncope is cardiac arrhythmia (abnormal heart rhythm) wherein the heart beats too slowly, too rapidly, or too irregularly to pump enough blood to the brain.^[9] Some arrhythmias can be life-threatening.^[9]
Two major groups of arrhythmias are bradycardia and tachycardia. Bradycardia can be caused by heart blocks. Tachycardias include SVT (supraventricular tachycardia) and VT (ventricular tachycardia). SVT does not cause syncope except in Wolff-Parkinson-White syndrome. Ventricular tachycardia originate in the ventricles. VT causes syncope and can result in sudden death.^[16] Ventricular tachycardia, which describes a heart rate of over 100 beats per minute with at least three irregular heartbeats as a sequence of consecutive premature beats, can degenerate into ventricular fibrillation, which is rapidly fatal without cardiopulmonary resuscitation (CPR) and defibrillation.^{[citation needed]}
Long QT syndrome can cause syncope when it sets off ventricular tachycardia or torsades de pointes. The degree of QT prolongation determines the risk of syncope.^[16] Brugada syndrome also commonly presents with syncope secondary to arrhythmia.^[16]
Typically, tachycardic-generated syncope is caused by a cessation of beats following a tachycardic episode. This condition, called tachycardia-bradycardia syndrome, is usually caused by sinoatrial node dysfunction or block or atrioventricular block.^[17]