Differential Diagnosis for LOC Episode and New Onset Atrial Fibrillation

Single Most Likely Diagnosis

• Cardiovascular causes leading to cerebral hypoperfusion: The new onset atrial fibrillation can lead to a reduction in cardiac output, resulting in cerebral hypoperfusion and a subsequent loss of consciousness (LOC). This is a common and plausible explanation given the presentation.

Other Likely Diagnoses

• Dehydration or electrolyte imbalance: Although the patient has normal vitals, dehydration or electrolyte imbalances can sometimes present subtly and contribute to both atrial fibrillation and LOC.
• Acute pulmonary embolism: While less common, an acute pulmonary embolism could cause both atrial fibrillation (due to the stress it places on the heart) and a LOC episode, especially if it leads to significant hypoxia or hypotension that is not immediately apparent.
• Seizure: A seizure could cause a LOC episode, and in some cases, the stress of a seizure can precipitate atrial fibrillation, especially in patients with underlying heart conditions.

Do Not Miss Diagnoses

• Cardiac tamponade: Although rare and less likely given the normal physical exam, cardiac tamponade can cause atrial fibrillation and LOC due to impaired cardiac filling and subsequent hypoperfusion. It's critical to consider this diagnosis due to its high mortality if untreated.
• Hypertrophic cardiomyopathy: This condition can lead to atrial fibrillation and, in severe cases, to obstructive shock or arrhythmias causing LOC. It's essential not to miss this diagnosis due to its potential for sudden cardiac death.
• Toxic or metabolic causes: Certain toxins or metabolic derangements (e.g., hyperkalemia) can cause both atrial fibrillation and altered mental status. These conditions require prompt identification and treatment.

Rare Diagnoses

• Neurocardiogenic syncope with secondary atrial fibrillation: This is a less common scenario where a neurocardiogenic syncope episode could potentially trigger atrial fibrillation, although this would be more of an association rather than a direct cause.
• Arrhythmogenic right ventricular cardiomyopathy (ARVC): A rare condition that can lead to life-threatening arrhythmias, including atrial fibrillation, and potentially LOC episodes due to ventricular arrhythmias.
• Pheochromocytoma: A rare tumor that can cause episodic hypertension, arrhythmias (including atrial fibrillation), and potentially LOC due to severe blood pressure fluctuations or cardiac effects.