Fainting, known as syncope, is a brief loss of consciousness from lack of blood flow to the brain that results in a person falling or collapsing. According to the American Heart Association, cardiac, non-cardiac and idiopathic (unknown) causes can lead to syncope. Inefficient pumping of the heart is the overarching cardiac reason for a lack of blood supply to the brain. The reasons for inefficient pumping, in turn, can be grouped by the components that come together to make the heart go: the conduction system, vasculature, valves and muscle tissue. According to Thomas H. Miller, M.D. and Jerry E. Kruse, M.D., M.S.P.H. in their article in the Oct. 15, 2005 issue of the American Family Physician, cardiac causes of syncope are linked to higher rates of morbidity and mortality than non-cardiac causes.
Conduction System Delays
Arrhythmias are related to problems with the heart's electrical conduction system that cause it to beat in irregular rhythms or rates. This leads to the heart's inability to coordinate the order and rate of squeezing of its chambers. One fairly common example is atrial fibrillation, but there are many others. Delays in conduction, such as heart block and long QT syndrome, are additional examples.
Narrowing of Arteries
The coronary arteries, which supply blood to the heart muscle, can become narrowed from cholesterol plaques and can lead to myocardial infarction (heart attack) or cardiac ischemia (temporary lack of blood supply to the heart). This also leads to ineffective pumping from the heart that can lead to fainting. Aortic dissection, in which the large aortic vessel ruptures, can lead to fainting (or death if not urgently repaired).
Defects in Valves
Structural heart disease, such as valvular disease, can lead to syncope. Most often, mitral stenosis or aortic stenosis are the culprits, but any defect in one of the heart's valves--the aortic, pulmonic, tricuspid, or mitral--can potentially lead to syncope. When congenital or acquired damage occurs to one or more of these valves, blood can leak back into parts of the heart that it shouldn't, causing less blood to get pumped to the brain and body. Defects could also cause the valves to become narrowed, making it difficult for the heart to pump blood through the great vessels to the rest of the body.
Diseases of the Heart Muscle
The muscle tissue making up the heart can become impaired from chronic disease, infection, certain medications or illicit drugs. This results in cardiomyopathy, or disease of the heart muscle. The heart muscle walls may become stiffened or enlarged from prolonged hypertension, inherited disorders, or from autoimmune disease that attacks the heart. Because of less than ideal heart muscle tissue, the heart can't squeeze the blood around effectively, which can lead to syncope. The three main types of cardiomyopathy are classified as restrictive, hypertrophic and dilated.
Miscellaneous Cardiac Issues
The heart can develop rare tumors, such as an atrial myxoma, which can obstruct the vessels exiting the atria. This leads to reduced blood flow to the brain. Pericardial disease, such as pericarditis, pericardial effusion or hemopericardium--in which pus, fluid or blood, respectively, collect in the outermost layer surrounding the heart--may compress the chambers of the heart and lead to inefficient pumping and, potentially, syncope.
References
- "Robbins Pathologic Basis of Disease, 8th Edition"; Vinay Kumar, M.B.B.S., M.D., P.R.C.Path, Abdul K. Abbas, M.B.B.S., Nelson Fausto, M.D., Jon C. Aster, M.D., Ph.D., editors; 2010.
- American Family Physician: Evaluation of Syncope
- American Heart Association: Syncope
- American Heart Association: Cardiomyopathy
- Johns Hopkins Medicine: Valvular Heart Disease
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