DIZZINESS AND SYNCOPE

Cardiovascular disorders produce dizziness and syncope by transient hypotension, resulting in abrupt cerebral hypoperfusion. Recovery is usually rapid, unlike with other common causes of syncope (e.g. stroke, epilepsy, overdose).

POSTURAL HYPOTENSION

Syncope on standing upright reflects inadequate baroreceptor-mediated vasoconstriction. It is common in the elderly. Abrupt reductions in blood pressure and cerebral perfusion cause the patient to fall to the ground, whereupon the condition corrects itself.

VASOVAGAL SYNCOPE

This is caused by autonomic overactivity, usually provoked by emotional or painful stimuli, less commonly by coughing or micturition. Only rarely are syncopal attacks so frequent as to be significantly disabling ('malignant' vasovagal syndrome). Vasodilatation and inappropriate slowing of the pulse combine to reduce blood pressure and cerebral perfusion. Recovery is rapid if the patient lies down.

CAROTID SINUS SYNCOPE

Exaggerated vagal discharge following external stimulation of the carotid sinus (e.g. from shaving, or a tight shirt collar) causes reflex vasodilatation and slowing of the pulse. These may combine to reduce blood pressure and cerebral perfusion in some elderly patients, causing loss of consciousness.

VALVULAR OBSTRUCTION

Fixed valvular obstruction in aortic stenosis may prevent a normal rise in cardiac output during exertion, such that the physiological vasodilatation that occurs in exercising muscle produces an abrupt reduction in blood pressure and cerebral perfusion, resulting in syncope. Vasodilator therapy may cause syncope by a similar mechanism. Intermittent obstruction of the mitral valve by left atrial tumours (usually myxoma) may also cause syncopal episodes.

STOKES-ADAMS ATTACKS These are caused by self-limiting episodes of asystole or rapid tachyarrhythmias (including ventricular fibrillation). The loss of cardiac output causes syncope and striking pallor. Following restoration of normal rhythm recovery is rapid and associated with flushing of the skin as flow through the dilated cutaneous bed is re-established.