Differential Diagnosis for Syncope

The differential diagnosis for syncope is broad and can be categorized based on the likelihood and potential impact of missing a diagnosis. Here's a structured approach:

• Single Most Likely Diagnosis

  • Vasovagal Syncope: This is the most common cause of syncope, especially in young individuals. It is characterized by a sudden loss of consciousness due to a decrease in blood flow to the brain, often triggered by stress, pain, or prolonged standing. The diagnosis is typically made based on a classic history of prodromal symptoms such as nausea, sweating, and pallor before the syncopal episode.

• Other Likely Diagnoses

  • Orthostatic Hypotension: This condition occurs when there is a significant drop in blood pressure upon standing, leading to reduced blood flow to the brain and potential syncope. It is more common in the elderly and those with dehydration, bleeding, or certain medications.
  • Cardiac Arrhythmias: Conditions like supraventricular tachycardia (SVT), ventricular tachycardia (VT), and atrioventricular (AV) block can lead to syncope due to inadequate cardiac output. A history of heart disease or palpitations before syncope increases the likelihood.
  • Obstructive Cardiac Causes: Aortic stenosis, hypertrophic cardiomyopathy, and pulmonary embolism can cause syncope by obstructing blood flow. Symptoms such as chest pain, dyspnea, or a history of similar episodes can guide towards these diagnoses.

• Do Not Miss Diagnoses

  • Myocardial Infarction or Acute Coronary Syndrome: Although less common as a cause of syncope, missing a myocardial infarction can be fatal. Syncope in the context of chest pain or electrocardiogram (ECG) changes suggestive of ischemia should prompt immediate evaluation.
  • Pulmonary Embolism: Syncope can be the presenting symptom of a large pulmonary embolism, especially if it leads to a significant obstruction of the pulmonary arteries. Risk factors for thromboembolism, such as recent travel, surgery, or cancer, increase suspicion.
  • Aortic Dissection: This is a life-threatening condition where the inner layer of the aorta tears. Syncope can occur due to involvement of the aortic arch or obstruction of major arteries. Severe, tearing chest pain and unequal blood pressures in arms are red flags.
  • Subarachnoid Hemorrhage: Although rare, syncope can be the initial presentation of a subarachnoid hemorrhage, often followed by a severe headache. The sudden onset of a "thunderclap" headache should prompt immediate imaging.

• Rare Diagnoses

  • Long QT Syndrome: A genetic disorder affecting the heart's electrical system, leading to potentially life-threatening arrhythmias and syncope. It is often diagnosed after a syncopal episode, especially in young individuals without structural heart disease.
  • Brugada Syndrome: Another genetic condition that affects the heart's electrical activity, increasing the risk of dangerous arrhythmias and syncope. It is diagnosed based on characteristic ECG patterns.
  • Neurocardiogenic Syncope with Prolonged Asystole: A form of vasovagal syncope where the asystolic pause is prolonged, potentially leading to more severe symptoms or complications.

Each of these diagnoses requires careful consideration of the patient's history, physical examination, and diagnostic tests to determine the underlying cause of syncope.