What are the causes and treatments of syncope?

Causes and Management of Syncope

Definition and Pathophysiology

Syncope is transient loss of consciousness caused by global cerebral hypoperfusion, requiring as little as a 20% drop in cerebral oxygen delivery or systolic blood pressure falling to 60 mmHg. 1

The mechanism involves failure of protective cerebrovascular autoregulation, baroreceptor reflexes, or vascular volume control, with older patients and those with hypertension or diabetes at highest risk due to altered autoregulatory ranges and diminished chemoreceptor responsiveness. 1

Primary Causes of Syncope

Neurally-Mediated Reflex Syncope (Most Common)

Vasovagal syncope is the most frequent cause, triggered by emotional stress, pain, or prolonged standing, characterized by inappropriate vasodilation and bradycardia. 2, 3

• Vasovagal (common faint): Emotional triggers, pain, prolonged standing 1
• Carotid sinus syncope: Mechanical manipulation of carotid sinuses 1, 2
• Situational syncope: Specific triggers including 1, 2:
  • Acute hemorrhage
  • Cough, sneeze
  • Gastrointestinal stimulation (swallow, defecation, visceral pain)
  • Micturition (post-micturition)
  • Post-exercise
  • Post-prandial
  • Brass instrument playing, weightlifting
• Glossopharyngeal and trigeminal neuralgia 1

Orthostatic Hypotension

Orthostatic syncope results from impaired peripheral vasoconstriction or reduced intravascular volume, typically occurring immediately after rising from supine or sitting position. 4

• Primary autonomic failure syndromes: Pure autonomic failure, multiple system atrophy, Parkinson's disease with autonomic failure 1
• Secondary autonomic failure: Diabetic neuropathy, amyloid neuropathy 1
• Drugs and alcohol 1
• Volume depletion 1

Cardiac Arrhythmias (High Mortality Risk)

Cardiac syncope carries a 24% one-year mortality rate, making identification of arrhythmic causes critical for preventing sudden cardiac death. 2

• Sinus node dysfunction (including bradycardia/tachycardia syndrome) 1, 2
• Atrioventricular conduction system disease 1, 2
• Paroxysmal supraventricular and ventricular tachycardias 1, 2
• Inherited syndromes: Long QT syndrome, Brugada syndrome 2
• Frequent ventricular extrasystoles (>10,000-20,000/day) can trigger malignant arrhythmias 2

Structural Cardiac/Cardiopulmonary Disease

Multiple pathophysiological mechanisms often contribute in structural heart disease, including restricted cardiac output, inappropriate reflex vasodilation, and primary arrhythmias. 1, 2

• Valvular disease: Aortic stenosis, left ventricular outflow tract obstruction 1, 2
• Acute myocardial infarction/ischemia 2
• Obstructive cardiomyopathy 2
• Atrial myxoma 2
• Acute aortic dissection 2
• Pericardial disease/tamponade 2
• Pulmonary embolus/pulmonary hypertension 2

High-Risk Features Requiring Urgent Evaluation

Hospitalization is mandatory for patients with suspected significant heart disease, ECG abnormalities suggesting arrhythmic syncope, syncope during exercise, syncope causing severe injury, or family history of sudden death. 2

• Underlying structural heart disease (ischemic, cardiomyopathy, valvular, congenital) 2
• LVEF ≤40% 2
• EVF with complex or polymorphic morphology 2
• EVF occurring during exercise or post-exercise recovery 2
• Survivors of cardiac arrest 2

Diagnostic Approach

Essential Initial Evaluation

• ECG: Identify arrhythmias, conduction abnormalities, morphology of ventricular extrasystoles, QRS duration, evidence of structural disease 2
• Echocardiography: Evaluate ventricular function, structural anomalies, diastolic dysfunction, pulmonary hypertension 2
• 24-hour Holter monitoring: Quantify arrhythmia burden (>10,000-20,000 EVF/day suggests cardiomyopathy risk) 2
• Head-up tilt test (60-70 degrees): Diagnose orthostatic and neurally-mediated syncope, with pharmacological provocation (isoproterenol) or lower body negative pressure to improve sensitivity 4

When to Avoid Testing

Neurological evaluation is only necessary when loss of consciousness cannot be attributed to syncope; avoid unnecessary neuroimaging, EEG, or CT/MRI without head trauma or specific neurological signs. 2, 5

Treatment Strategies

Non-Pharmacological Management (First-Line)

Non-pharmacological interventions should be considered first for all syncope patients. 4

• Avoid rapid position changes from supine to standing 4
• Avoid high room temperature or situations inducing peripheral vasodilation 4
• Increase sodium and fluid intake 4
• Mild physical exercise 4
• Postural counter-maneuvers 4

Pharmacological Treatment for Orthostatic/Neurally-Mediated Syncope

• Mineralocorticoids: Fludrocortisone 4
• Vasoconstrictor agents: Ephedrine, midodrine 4
• Beta-blockers: First-line for symptomatic EVF and arrhythmic risk reduction 2
• Adenosine receptor blockers: Theophylline 4
• Anticholinergic agents: Scopolamine, disopyramide 4
• Serotonin reuptake inhibitors: Fluoxetine, sertraline (specific cases) 4
• Desmopressin: Increases intravascular volume 4
• Erythropoietin: Improves anemia and augments blood pressure 4
• For post-prandial hypotension: Octreotide, indomethacin, ibuprofen, metoclopramide, or two cups of coffee daily 4

Cardiac-Specific Treatments

For Arrhythmias

• Beta-blockers: First-line for symptomatic ventricular extrasystoles 2
• Amiodarone: For recurrent ventricular tachycardia or fibrillation when beta-blockers insufficient 2
• Verapamil: For idiopathic left ventricular fascicular tachycardia 2

Catheter Ablation (Class I Indication)

Catheter ablation is strongly recommended for EVF triggering recurrent ventricular fibrillation with ICD discharges, electrical storm due to EVF triggers, and left ventricular fascicular tachycardia. 2

• EVF-induced cardiomyopathy (burden >10,000-20,000/day with ventricular dysfunction) 2
• Frequent or complex EVF in repaired tetralogy of Fallot with unexplained syncope 2

ICD Implantation

ICD implantation is mandatory for survivors of cardiac arrest due to ventricular fibrillation or tachycardia with LVEF ≤40%, and for secondary prevention in patients with symptomatic sustained ventricular tachycardia. 2

Structural Heart Disease Treatment

• Valvular disease: Valve repair/replacement 2
• Ischemic heart disease: Revascularization 2
• Obstructive cardiomyopathy: Surgical myectomy or alcohol septal ablation 2
• Cardiac masses: Surgical removal 2
• Vascular steal syndromes: Direct corrective angioplasty or surgery 2

Acute Management

For acute ventricular tachycardia or fibrillation, cardioversion/electrical defibrillation is the intervention of choice, followed by early intravenous beta-blockers to prevent recurrence. 2

• Consider immediate angiography for recurrent polymorphic ventricular tachycardia or fibrillation indicating incomplete revascularization or recurrent ischemia 2

Critical Clinical Pitfalls

• Cardiac pacemakers are often recommended without adequate indication 4
• Multiple mechanisms may contribute to syncope in structural heart disease patients; do not assume single etiology 1, 2
• Older patients and those with hypertension or diabetes have altered autoregulatory ranges, increasing syncope risk at higher blood pressures than expected 1
• Recurrence rate is 35% with 29% risk of physical injury, necessitating preventive counseling 3