Syncope (Causes and Pathophysiology)

Syncope is defined as loss of consciousness due to decreased cerebral perfusion. Causes of syncope can be classified as Neuroregulatory, Arrhythmias and Hemodynamic.

 

A. Neuroregulatory causes of syncope.

A.k.a.vasovagal syncope this is caused by a sudden decrease in blood pressure. Prolonged standing is a common cause especially is the subject is dehydrated.

 

The low BP is sensed by carotid baroreceptors, that increase cardiac rate and contractility. On the other hand pressure receptors in the walls of the underfilled left ventricle may sense high-pressure and cause paradoxical bradycardia and lower contractility.

B. Arrhythmia as a cause of syncope.

Common arrhythmias causing syncope include supraventricular tachycardia (SVT), ventricular tachycardia (VT), ventricular fibrillation, and severe bradycardia (eg, heart block).

 

C. Hemodynamic syncope

 

The following Structure defects in the heart can cause syncope.

 

•Hypertrophic obstructive cardiomyopathy (HOCM) or aortic stenosis leading to left sided outflow obstruction

•Pulmonary hypertension may cause syncope when the right ventricle fails to pump against the high pulmonary pressure.
•Ischemic heart disease due to anomalous coronary artery origin, hypercholesterolemia, or acute inflammatory diseases such as Kawasaki disease and myocarditis.

•Pericardial tamponade can cause hypotension and syncope secondary to decreased pre-load (ventricles can not fill well).