Syncope (fainting)

FAINTING (SYNCOPE) Steph Parish
Transient loss of consciousness due to inadequate cerebral blood flow is termed syncope, and may be due to a variety of causes.

VASCULAR CAUSES
The most common cause of syncope is the vasovagal attack, also known as neurocardiogenic or situational syncope, or as a simple faint. It may be triggered by prolonged orthostatic stress, or strong emotion. The mechanism begins with peripheral vasodilation and venous pooling of blood leading to a reduction in the amount of blood returned to the heart. The near-empty heart responds by contracting vigorously, which in turn stimulates mechanoreceptors (stress receptors) in the inferoposterior wall of the left ventricle. These in turn trigger reflexes via the central nervous system, which act to reduce ventricular stress (ie. further vasodilation and sometimes profound bradycardia), but this causes a drop in blood pressure and therefore syncope. These episodes are usually associated with a prodrome of dizziness, nausea, sweating, tinnitus, yawning and a sinking feeling.

OBSTRUCTIVE CAUSES
A restriction of blood flow from the heart into the rest of the circulation, or between the different chambers of the heart can cause syncope. Causes include aortic stenosis, hypertrophic obstructive cardiomyopathy, pulmonary stenosis, pulmonary hypertension/embolism, defective prosthetic valve.

ARRHYTHMIAS
Stokes-adams attacks have been defined as sudden loss of consciousness unrelated to posture. It is usually due to intermittent high-grade atrioventricular block, profound bradycardia or ventricular standstill. Without warning, the patient falls to the ground, pale and deeply unconscious. The pulse is usually very slow or absent. After a few seconds the patient flushes brightly and recovers consciousness as the pulse quickens. Often there are no sequelae, but patients may injure themselves during falls.

SOURCES
Most of this is taken straight from Kumar and Clarke. None of our other textbooks (notably Saladin and Guyton) had any relevent info that I could find.