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There are other causes of syncope like hypersensitive carotid sinus, which is located in a small, slightly dilated portion of the common carotid artery, at the level of the thyroid cartilage, just below the angle of the jaw, before this blood vessel bifurcates into internal and external carotid arteries. It is present on each side of the neck.

The carotid sinus is very important for controlling the heart rate of a person. In general practice, when a person comes with a very high rate, e.g. in a condition of PAT, when the patient feels marked palpitation, and is in acute distress, the physician may give a mild massage (about five seconds at a time) on the side of the neck, at the level of the upper border of the thyroid cartilage. This stimulates the carotid sinus (involving the cardioinhibitory effect of the vagus nerve), and the heart rate starts decreasing slowly. This method is so effective that if simultaneously the heart rate is not checked, carotid sinus may lower the heart rate to dangerous levels.

Hence, one can imagine the role of the normal carotid sinus in lowering the heart rate with a simple massage, and if the carotid sinus is hypersentitive, a mere jerk/movement of the neck to one side may markedly bring down the normal rate of the heart, leading to the decreased flow of blood to the brain, causing syncope. The same may happen when there is a pressure on the carotid sinus from outside, i.e. from some lesions in the neck such as enlarged glands, etc. Or, this may happen when a person is wearing a very tight collar, etc.

Hence, every case of syncope needs a very thorough check-up for arriving at a definite conclusion, and besides, various investigations for detecting a lesion in the heart, when it is so suspected, tests may also be required to see the hypersensitivity of the carotid sinus, especially when other causes/possibilities are not contributory.

It is true that in spite of a thorough investigation in a well-equipped hospital, the cause of syncope may not be possible to detect. (The author happened to examine an emergency case of syncope in a 73-year old man, who as soon as he stood up from a chair, fell down suddenly. The patient was made to lie down, and when the author reached the spot he was fully conscious. He was then investigated extensively, but no cause of syncope could be determined, and the patient has had no such attack now for the last five years).

As stated earlier, rarely, in some cases, when an attack of syncope is a bit more acute, i.e., when the period of unconsciousness is slightly prolonged, even convulsions may occur. Hence, besides investigations for the heart, an EEG/CT scan, etc., may also be required for the exclusion of epilepsy.

Other causes of syncope

There are some other causes of syncope as well. Even a continuous fit of coughing may cause syncope, as a result of diseases of the lungs, like a severe type of chronic bronchitis. It is often seen in middle-aged persons, due to a low cardiac output (as due to prolonged coughing, there is a low return of blood to the heart, and so the heart output, accordingly, decreases), and hence less blood is supplied to the brain, leading to transitory unconsciousness. The patient recovers as soon as the bout of coughing is over.

Syncope may also occur while passing urine, due to the reflex action of the distended urinary bladder.

It is advisable that one should not immediately stand up while getting up from bed during the night, i.e., after a period of sleep or recumbency, for for any reason, so as to avoid postural hypotension, which may also lead to syncope.

Again, syncope is likely to manifest itself due to the involvement/narrowing of the blood vessels of the brain, caused by atherosclerosis, say, when the involvement of the vertebro-basilar artery responsible for vertebro-basilar insufficiency occurs. Such attacks of syncope are called transient ischaemic attacks (TIA).