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Syncope

Syncope is defined as a sudden, transient loss of consciousness characterized by unresponsiveness and loss of postural tone. The prognosis for most persons with syncopal episodes is good; however, persons with syncope caused by a cardiac disorder have a one-year mortality rate of 20-30% and a 33% incidence of sudden death over 5 years. Persons with noncardiac causes or syncope of unknown origin have a relatively benign prognosis. Hospitalization is generally not necessary, unless a cardiac etiology or a significant injury during the syncopal event.

Pathophysiology

Vasovagal attacks, cardiac disorders and pulmonary outflow obstruction produce syncope because of a reduction of cerebral blood.

Hypoxia, hyperventilation and hypoglycemia, increased intracranial pressure, seizures and hysteria can cause syncope.

Vasovagal episodes cause reflex syncope secondary to underfilling of the right side of the heart.

Cardiac syncope is caused by inadequate output from the left ventricle. Mechanical causes of cardiac syncope include aortic stenosis, hypertrophic cardiomyopathy, myocardial infarction and pulmonary embolus. Tachyarrhythmias, especially ventricular tachycardia, account for most of the arrhythmias that result in cardiac syncope. Syncope of cardiac origin results in markedly increased rates of mortality and sudden death.

The cause of syncope can not be determined in 38-47% of

      Differential Diagnosis of Syncope

      Non-cardiovascular

      Cardiovascular

      Metabolic

        Hyperventilation

        Hypoglycemia

        Hypoxia

      Neurologic

        Cerebrovascular insufficiency

        Normal pressure hydrocephalus

        Seizure

        Subclavian steal syndrome

      Increased intracranial pressure

        Psychiatric

        Hysteria

        Major depression

        Reflex syncope (heart structurally normal)

        Vasovagal

        Situational

        Cough

        Defecation

        Micturition

        Postprandial

        Sneeze

        Swallow

        Carotid sinus syncope

      Orthostatic hypotension

      Drug-induced

        Cardiac

        Obstructive

        Aortic dissection

        Aortic stenosis

        Cardiac tamponade

        Hypertrophic cardiomyopathy

        Left ventricular dysfunction

        Myocardial infarction

        Myxoma

        Pulmonary embolism

        Pulmonary hypertension

        Pulmonary stenosis

        Arrhythmias

        Bradyarrhythmias

          Sick sinus syndrome

          Pacemaker failure

          Supraventricular and ventricular tachyarrhythmias

Clinical Evaluation

The history and physical examination can identify potential causes of syncope in 50-85% of cases in which a successful diagnosis is made. A young, healthy patient with a history compatible with vasovagal syncope.

History

A complete description of the syncopal episode, prodromal circumstances and symptoms following the syncopal episode should be obtained. The relationship of fainting to micturition, defecation, cough, swallowing or postural change.