Bradycardia/Tachycardia related to Sotalol: The patient is on Sotalol, a beta-blocker that can cause bradycardia or exacerbate existing bradycardia, potentially leading to near fainting episodes due to decreased cardiac output. Sotalol can also contribute to QT prolongation, increasing the risk of torsades de pointes, a form of tachycardia that can lead to syncope.

Dehydration/Electrolyte Imbalance: Dehydration or electrolyte imbalances, particularly potassium or magnesium deficiencies, can exacerbate arrhythmias and contribute to symptoms of near fainting.
Cardiac Ischemia: Underlying coronary artery disease could lead to cardiac ischemia, especially in the context of atrial fibrillation, which increases the risk of cardiac ischemia due to rapid heart rates or decreased cardiac output.
Hypotension: Sotalol can also cause hypotension, which, combined with atrial fibrillation, might lead to reduced cerebral perfusion and symptoms of near fainting.

Pulmonary Embolism: Although less common, pulmonary embolism can present with near fainting and is a life-threatening condition that requires immediate diagnosis and treatment.
Cardiac Tamponade: This is a life-threatening condition where fluid accumulates in the pericardial sac, compressing the heart and reducing its ability to pump blood effectively, leading to symptoms that can include near fainting.
Aortic Dissection: A tear in the aorta can lead to severe chest pain, hypotension, and reduced cardiac output, potentially causing near fainting.

Vasovagal Syncope: While less likely given the context of atrial fibrillation and medication with Sotalol, vasovagal syncope could still be a consideration, especially if triggered by specific events or stressors.
Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC): A rare heart condition that can lead to life-threatening arrhythmias and might present with symptoms of near fainting, especially during or after physical activity.

ECG to assess for bradycardia, tachycardia, or signs of ischemia
Blood tests for electrolytes (potassium, magnesium), complete blood count, and cardiac biomarkers (troponin)
Echocardiogram to evaluate cardiac function and rule out tamponade
Chest X-ray to assess for signs of pulmonary embolism or cardiomegaly
Holter monitor or event monitor for longer-term rhythm assessment
Consider a stress test or coronary angiography if cardiac ischemia is suspected
CT pulmonary angiogram if pulmonary embolism is suspected
Transthoracic echocardiogram to assess for aortic dissection if suspected