Some Causes of Syncope
Cause | Suggestive Findings | Diagnostic Approach* |
|---|---|---|
Cardiac outflow or inflow obstruction | ||
Valvular disease: Aortic stenosis, mitral stenosis, tetralogy of Fallot, prosthetic valve dehiscence or thrombosis | Young or old patient Syncope often exertional; recovery prompt Heart murmur | |
Hypertrophic cardiomyopathy (HCM), restrictive cardiomyopathy | Young or old patient Syncope often exertional; recovery prompt Heart murmur (in hypertrophic cardiomyopathy) S4 (in restrictive cardiomyopathy) | Echocardiography |
Cardiac tumors or thrombi | Syncope may be positional Usually a murmur (possibly variable) Peripheral embolic phenomena | Echocardiography |
Pulmonary embolism, amniotic fluid embolism, or, rarely, air embolism | Usually from large embolus, accompanied by dyspnea, tachycardia, or tachypnea Often risk factors for pulmonary embolism | Sometimes D-dimer Sometimes POCUS or echocardiography CT angiography or nuclear scan |
Cardiac arrhythmia | ||
Bradyarrhythmias (eg, due to sinus node dysfunction, high-grade atrioventricular block, medications†) | Syncope occurring without warning; recovery immediate on awakening May occur in any position Bradyarrhythmias more common in older adults Patient taking medications, especially antiarrhythmics or other medications that block AV nodal conduction in susceptible patients Structural heart disease | If ECG unclear, consider Holter monitor, event recorder, or occasionally an implantable loop recorder (duration of monitoring determined by frequency of symptoms) Electrophysiologic testing if abnormalities detected or strongly suspected Serum electrolytes if clinical reason for abnormality (eg, diuretic use, vomiting, diarrhea) |
Tachyarrhythmias, either supraventricular or ventricular (eg, due to ischemia, heart failure, myocardial disease, medications†, electrolyte abnormalities, arrhythmogenic right ventricular cardiomyopathy, long QT syndrome, Brugada syndrome, preexcitation) | Syncope occurring without warning; recovery immediate on awakening May occur in any position Patient taking medications, especially antiarrhythmics or other medications that prolong the QT interval Structural heart disease | If ECG unclear, consider Holter monitor or event recorder, or occasionally an implantable loop recorder (duration of monitoring determined by frequency of symptoms) Electrophysiologic testing if abnormalities detected or strongly suspected Serum electrolytes if clinical reason for abnormality (eg, diuretic use, vomiting, diarrhea) |
Ventricular dysfunction | ||
Acute myocardial infarction, myocarditis, systolic or diastolic dysfunction, cardiomyopathy | Syncope a rare presenting symptom of myocardial infarction (most such patients are older), with arrhythmia or shock | Serum troponin ECG Echocardiography (traditional, POCUS, or both) Sometimes cardiac MRI |
Pericardial tamponade or constriction | Jugular venous elevation; pulsus paradoxus > 10 | Echocardiography (traditional, POCUS, or both) Sometimes CT |
Vasovagal (neurocardiogenic) | ||
Increased intrathoracic pressure (eg, tension pneumothorax, cough, straining to urinate or defecate, Valsalva maneuver) | Warning symptoms (eg, dizziness, nausea, sweating); recovery usually prompt but not immediate (5 to 15 minutes) although can be prolonged in rare cases Precipitant usually apparent | Clinical evaluation |
Strong emotion (eg, pain, fear, sight of blood) | Warning symptoms (eg, dizziness, nausea, sweating); recovery prompt but not immediate (5 to 15 minutes, but sometimes up to hours) Precipitant usually apparent | Clinical evaluation |
Carotid sinus pressure | Warning symptoms (eg, dizziness, nausea, sweating); recovery prompt but not immediate (5 to 15 minutes, but sometimes up to hours) Precipitant usually apparent (eg, turning head, button collar, shaving) | Clinical evaluation |
Swallowing (rare) | Warning symptoms (eg, dizziness, nausea, sweating); recovery prompt but not immediate (5 to 15 minutes, but sometimes up to hours) Precipitant usually apparent | Clinical evaluation |
Medication administration, insect bite, allergy history, other signs of anaphylaxis (eg, rash, wheezing, hypotension) | Allergy testing | |
Medications† | Symptoms developing within several minutes of assuming upright position Drop in BP with standing during examination | Clinical evaluation Sometimes tilt table testing |
Autonomic dysfunction | Symptoms developing within several minutes of assuming upright position Drop in BP with standing during examination | Clinical evaluation Sometimes tilt table testing |
Deconditioning caused by prolonged bed rest | Symptoms developing within several minutes of assuming upright position Drop in BP with standing during examination | Clinical evaluation Sometimes tilt table testing |
Anemia | Chronic fatigue, sometimes dark stools, heavy menses | Complete blood count or hematocrit |
Endocrine disorders (eg, adrenal insufficiency, hypothyroidism) | Symptoms developing within several minutes of assuming upright position Often associated symptoms of underlying endocrine disorder | Basic metabolic panel Morning cortisol measurement Thyroid stimulating hormone (TSH) |
Cerebrovascular | ||
Basilar artery transient ischemic attack, or stroke | Sometimes cranial nerve deficits and ataxia | MRI or CT |
Aura with visual symptoms, photophobia; often unilateral, but may be bilateral | Clinical evaluation | |
Other | ||
Prolonged standing | Apparent by history; no other symptoms | Clinical evaluation |
Pregnancy | Healthy female of childbearing age; no other symptoms Usually an early or unrecognized pregnancy | Urine pregnancy test |
Hyperventilation | Often tingling around mouth or on fingers prior to syncope Usually in context of an emotional situation | Clinical evaluation |
Altered mental status until treated, onset seldom abrupt, sweating, piloerection Usually history of diabetes or insulinoma | Fingerstick glucose Response to glucose infusion | |
Psychiatric disorders | Not true syncope (patient may be partially or inconsistently responsive during events) Normal examination Often history of psychiatric disorder | Clinical evaluation |
* ECG and pulse oximetry are done for all. | ||
† See table Some Medications That Cause Syncope. | ||
AV = atrioventricular; BP = blood pressure; POCUS = point-of-care ultrasound; S4 = fourth heart sound. | ||