SyncopeEtiology & Pathophysiology

– Harrion’s Manual of Medicine

Transient loss of consciousness and postural tone due to

reduced cerebral blood flow.

Syncope

Etiology

Cardiogenic

Neurocardiogenic

Metabolic

Cardiogenic• Lesion or structural abnormalities of the heart

• Also, cardia arrhythmias

Cardiac Output

Blockage of Blood flow

• Hypertrophic cardiomyopathy

• Aortic Stenosis

Arrhythmias

Bradycardia Tachycardia

Bradycardia Tachycardia

Sinus node abnormalities AV block

Ventricular / Supraventricular muscle’s signal overrides

Pump fast, but not effectivePump slow

Cardiac Output

Syncope

Neurocardiogenic

• Known as Vasovagal syncope

• Caused by pain, fear, anxiety, close quarters and excessive heat

• The most common cause of syncope

Pathogenesis • Cardioinhibitory response

Sensory input NTS

vagal afferent

pain pathway

central pathway

Sympathoinhibtion& vagal efferent

Prolonged Standing Venous Pooling Pain/ Anxiety

Sympathetic surge

Vigorous cardiac contraction

Decreased venous return

Markedly reduced end-systolic volume

Vagal reflex

Hypotension & syncope

Bradycardia Vasodilation

Mechanoreceptor

Pathogenesis• Carotid sinus syndrome

Carotid sinusTuring head, looking up

and…

This may cause syncope.

Is It Really Pathologic?

Or a mean of protection…

Threat/fear Central hypovolemia

High sympathetic activity

Vasovagal reflex

Fear and threat bradycardia Hypotension

Bradycardia and hypotension during central hypovolemia

Decrease in myocardialO2 demand and

improvement in diastolic filling

Possible defense mechanism for heart

Metabolic

95%

5%

metabolic syncope

RARE.

Cause

• Hypoxia

• Hypoglycemia

• Hyperventilation

So How Did It Happen?

Reference• Alboni P., Alboni M., Bertorelle G.. The origin of vasovagal syncope: to

protect the heart or to escape predation? Clin. Auton. Res. 2008 Aug;18(4)

• Mohamed HA. Syncope: Evaluation and management. Libyan J Med

•

• Harrison’s Manual of Medicine

•

• Problem-oriented Medical Diagnosis

• Patient information: Syncope (fainting) (Beyond the Basics) In: UpToDate, Post TW (Ed), UpToDate, Waltham, MA. (Accessed on September 23, 2015.)

Reference • http://

www.fda.gov.tw/MLMS/H0001.aspx

• http://140.112.125.99/phar/intranet/druginfo/index.asp

• Micromedex® 2.0, (electronic version). Truven Health Analytics, Greenwood Village, Colorado, USA. Available at: http://www.micromedexsolutions.com/ (cited: Sep./23/2015).

• Acquired long QT syndrome. In: UpToDate, Post TW (Ed), UpToDate, Waltham, MA. (Accessed on September 23, 2015.)

• Sinus bradycardia. In: UpToDate, Post TW (Ed), UpToDate, Waltham, MA. (Accessed on September 23, 2015.)