This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.V.S., Subject name: Medicine
[{'content': 'Which of the following is associated AV block? \nSelect and explain. \nA. Hypothyroidism, B. Hyperthyroidism, C. Pheochromocytoma, D. Cushing syndrome', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. a. HypothyroidismRef: Harrisons Principle of Internal Medicine 19th Ed; Page No-1471ETIOLOGY OF AV BLOCKAutonomic Carotid sinus hypersensitivityVasovagalMetabolic/Endocrine HyperkalemiaHypermagnesemiaHypothyroidism Adrenal insufficiencyDrug-related Beta blockersCalcium channel blockersDigitalisAdenosineAntiarrhythmics (class 1 and III) LithiumInfectious Endocarditis Lyme disease Chagas disease SyphilisTuberculosisDiphtheriaToxoplasmosisInflammatorySLERheumatoid arthritis InfiltrativeAmyloidosisSarcoidosisMCTDSclerodermaHemochromatosisNeoplastic/TraumaticLymphomaMesotheliomaMelanomaDegenerativeLev's diseaseRadiation Catheter ablationLenegre's diseaseCoronary artery diseaseAcute Ml Abbreviations: MCTD, mixed connective tissue disease; Ml myocardial infarction; OMIM, Online mendelian Inheritance in Man (database; designations: , phenotypic description, molecular basis known; % phenotypic description); SLE, systemic lupus erythematosus", 'role': 'assistant'}]