Transient blackouts (Syncope)

Blackout

Can transient blackouts be a manifestation of heart disease?

Transient loss of consciousness (TLOC) with a fall is called ‘syncope’. It could be due to a variety of causes including heart disease. Causes other than cardiac ailment could be some forms of epilepsy (seizure), anemia (lowering of hemoglobin content of blood) or even a simple faint. Of the lot, the simple faint (vasovagal syncope or neurocardiogenic syncope) if probably the most common. It is quite common in children, especially while standing in school assembly in hot season. Dehydration can predispose to this form of syncope.

Syncope due to ailments of the heart can be due to several causes. Serious obstruction to any heart valve can cause syncope, especially during exertion as the heart is not able to meet the extra demand for blood supply with exercise. High blood pressure in the blood vessels of the lung (pulmonary hypertension) is a rare by serious cause of syncope. Obstruction to blood flow to the lungs due to sudden migration of blood clots from another part of the body like the legs can sometimes cause syncope. Another important group of cardiac illness which can cause syncope are the disorders of heart rhythm. A very fast heart rhythm or a very slow heart rhythm, both can cause syncope. In both cases, heart is not able to pump sufficient amount of blood to maintain the circulation to the brain well. Diseases of the heart muscle which leads to poor function of the heart as a pump can cause syncope, mostly during exertion. Gross thickening of the heart muscle in certain heart diseases (hypertrophic cardiomyopathy) can cause obstruction to blood flow from the left ventricle (lower muscular chamber) to the aorta (largest blood vessel supplying oxygenated blood to the body) can lead to syncope, typically occurring while taking rest after exertion.

What tests are likely to be done in a person with syncope?

The most important aspect of evaluation of person with history of syncope is the detailed history of the event and the narration from an eye witness in case one is available. Usually evaluation needs a multidisciplinary approach. Most cases would need both cardiac and neurological work up as the cause often not very evident. If the history points to one form of disease, priority is given for that workup. Important general test is a routine blood count to rule out anemia. Basic blood investigations are also often done to rule out associated important illnesses. Specific cardiac (related to the heart) tests may include an electrocardiogram (ECG), echocardiogram (ultrasound imaging of the heart) and ambulatory electrocardiographic monitoring (24 or 48 hour Holter monitoring). Neurological (related to the brain and nerves) tests may include electroencephalogram (EEG) and brain imaging studies (computerised tomographic or CT scan and/or magnetic resonance imaging (MRI) of the brain. Further workup will depend on the results of these initial tests.

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