Fainting syncope, commonly known as fainting

Obstructive cardiac lesion[edit]

Blockages in major vessels or within the heart can also impede blood flow to the brain. Aortic stenosis and mitral stenosis are the most common examples. Major valves of the heart become stiffened and reduce the efficiency of the hearts pumping action. This may not cause symptoms at rest but with exertion, the heart is unable to keep up with increased demands leading to syncope. Aortic stenosis presents with repeated episodes of syncope.^[9] Rarely, cardiac tumors such as atrial myxomas can also lead to syncope.^[9]

Structural cardiopulmonary disease

Diseases involving the shape and strength of the heart can be a cause of reduced blood flow to the brain, which increases risk for syncope.^[3] The most common cause in this category is fainting associated with an acute myocardial infarction or ischemic event. The faint in this case is primarily caused by an abnormal nervous system reaction similar to the reflex faints. Women are significantly more likely to experience syncope as a presenting symptom of a myocardial infarction.^[18] In general, faints caused by structural disease of the heart or blood vessels are particularly important to recognize, as they are warning of potentially life-threatening conditions.^[9]
Among other conditions prone to trigger syncope (by either hemodynamic compromise or by a neural reflex mechanism, or both), some of the most important are hypertrophic cardiomyopathy, acute aortic dissection, pericardial tamponade, pulmonary embolism, aortic stenosis, and pulmonary hypertension.^[9]

Other cardiac causes[edit]

Sick sinus syndrome, a sinus node dysfunction, causing alternating bradycardia and tachycardia. Often there is a long pause (asystole) between heartbeats.^[9]
Adams-Stokes syndrome is a cardiac syncope that occurs with seizures caused by complete or incomplete heart block. Symptoms include deep and fast respiration, weak and slow pulse, and respiratory pauses that may last for 60 seconds.
Subclavian steal syndrome arises from retrograde (reversed) flow of blood in the vertebral artery or the internal thoracic artery, due to a proximal stenosis (narrowing) and/or occlusion of the subclavian artery.^[9] Symptoms such as syncope, lightheadedness, and paresthesias occur while exercising the arm on the affected side (most commonly the left).
Aortic dissection (a tear in the aorta) and cardiomyopathy can also result in syncope.^[19]
Various medications, such as beta blockers, may cause bradycardia induced syncope.^[17]
A pulmonary embolism can cause obstructed blood vessels and is the cause of syncope in less than 1% of people who present to the emergency department.^[20]