Syncope - Clinical Symptoms

Syncope

Syncope is defined as a transient loss of consciousness due to inadequate cerebral blood flow. Cerebral perfusion is dependent on the heart rate, the arterial blood pressure as well as the resistance of the whole vasculature. Changes in any of these may result in syncope. There may be no warning, or patients may describe feeling faint, cold and clammy prior to the onset. They may have blurred vision, tinnitus and appear very pale prior to the loss of consciousness. Whilst unconscious they are hypotonic with a very slow or difficult to feel pulse. Within a few seconds they spontaneously recover, they tend to be flushed and sweaty but not confused (unless prolonged hypoxia leads to a tonicclonic seizure).

·        Vasovagal syncope is very common and occurs in the absence of cardiac pathology. Predisposing factors include prolonged standing, fear, venesection, micturition or pain. There is peripheral vasodilation causing a reduced ventricular filling. The heart contracts force-fully, which may lead to a reflex bradycardia via vagal stimulation and hence a loss of consciousness.

·        Postural syncope (fainting on standing) is seen in patients with autonomic disorders, salt and water depletion, hypovolaemia or due to certain drugs especially antianginal and antihypertensive medication.

·        Cardiac arrhythmias may result in syncope if there is a sudden reduction of the cardiac output. This may occur in bradycardias or tachycardias (inadequate ventricular filling time). The loss of consciousness occurs irrespective of the patient’s posture. A Stokes–Adams attack is a loss of consciousness related to a sudden loss of ventricular contraction particularly seen during the progression from second to third degree heart block.

·        Carotid sinus syncope is a rare condition mainly seen in the elderly. As a result of hypersensitivity of the carotid sinus, light pressure, such as that exerted by a tight collar, causes a severe reflex bradycardia and hence syncope.

·        Exertional syncope occurs in aortic valve or subvalve stenosis. The syncope results from an inability of the heart to increase cardiac output in response to in creased demand.

The immediate management of syncope or impending syncope is to lie the patient down and raise their legs increasing cerebral blood flow.