Differential Diagnosis for Fainting

• Single most likely diagnosis:
  • Vasovagal syncope: This is the most common cause of fainting, often triggered by stress, pain, or prolonged standing, leading to a sudden drop in blood pressure and heart rate.
• Other Likely diagnoses:
  • Orthostatic hypotension: A drop in blood pressure upon standing, which can be due to dehydration, medication, or autonomic nervous system dysfunction.
  • Cardiac arrhythmias: Abnormal heart rhythms, such as atrial fibrillation or ventricular tachycardia, can lead to fainting by disrupting normal blood flow.
  • Hypoglycemia: Low blood sugar can cause fainting, especially in diabetic patients or those with other metabolic disorders.
• Do Not Miss diagnoses:
  • Cardiac tamponade: Fluid accumulation in the sac around the heart can compress the heart and impede its function, leading to fainting and potentially death if not promptly treated.
  • Pulmonary embolism: A blood clot in the lungs can cause sudden fainting, along with other symptoms like chest pain and shortness of breath, and is life-threatening if not immediately addressed.
  • Aortic dissection: A tear in the aorta's inner layer can lead to fainting among other severe symptoms and is highly lethal without urgent medical intervention.
• Rare diagnoses:
  • Subclavian steal syndrome: A rare condition where there's a reversal of blood flow in the subclavian artery, potentially leading to fainting due to decreased blood flow to the brain.
  • Micturition syncope: Fainting that occurs during or immediately after urination, often due to a sudden drop in blood pressure.
  • Defecation syncope: Similar to micturition syncope but occurs during or after defecation, also related to a sudden drop in blood pressure.