Syncope (Fainting)

The episodic and unpredictable nature of syncope makes its study and differential diagnosis difficult. Because syncope includes rather disparate disease process the diagnostic evaluation requires specialized knowledge in different fields including cardiac electrophysiology, blood pressure and blood flow regulation (hemodynamics, biology of blood vessels), hormone regulation (endocrinology), and integrative neurophysiology (peripheral and central nervous system, brain research). Therefore the diagnosis and management of syncope demand teamwork by specialists. However, a prudent approach is for the patient to consult a clinical cardiac electrophysiologist who has the knowledge and tools to rule out life-threatening arrhythmias.

Numerous conditions associated with loss of consciousness are often thought to be part of differential diagnosis, but are not true syncope. Disease processes characterized by sustained low blood pressure (hypotensive states or shock syndromes) include aortic dissection (aortic rupture), shock due to heart attacks or failure (cardiogenic shock), cardiac tamponade (compression of the heart by acute fluid accumulation in the pericardial cavity), massive pulmonary embolism, and others are not associated with rapid spontaneous recovery. In these syndromes, impairment of consciousness and reduction in brain blood flow are sustained. Brain function and consciousness may be perturbed when the blood contains low concentrations of oxygen (hypoxemia), glucose (hypoglycemia), calcium (hypocalcemic tetany), or hydrogen ions (alkalotic tetany). An excess of hydrogen ions (acidosis, hypercapnia) may also affect consciousness. With some exceptions, such as hypoglycemia or low carbon dioxide due to voluntary hyperventilation, loss of consciousness associated with changes in blood chemistry are neither transient nor acutely reversible. When the blood composition is therapeutically corrected, one characteristically observes gradual recovery in brain function over minutes to hours.

Consciousness depends upon the normal activity of the lower brain (brain stem). Therefore, transient loss of consciousness independent of changes in brain blood flow or chemistry may be caused by disturbances in the activity of brain cells themselves. In some seizure disorders that are often first manifest in childhood, the child may appear to be temporarily unconscious but seldom loses postural tone, a cardinal feature of syncope. These "Petit Mal" or "absences" seizures might simulate syncope due to a circulatory disturbance. However, the diagnosis is often reasonably clear after careful questioning of the patients and witnesses of the attacks. "Grand mal" seizures with loss of consciousness combined with a loss of motor tone is associated with gradual but spontaneous recovery. As a rule, one should never ascribe spells with syncope-like features to a rare seizure disorder until a cardiac electrophysiologist rules out a cardiac arrhythmia. Prevention of sudden arrhythmic death is possible by appropriate treatment. This is particularly important in elderly persons with heart disease.