This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Unknown
[{'content': 'Most common cardiac adverse effect of lithium is? \nSelect and explain. \nA. Arrythmia, B. Cardiomyopathy, C. Bradycardia, D. Hypotension', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Reference: Katzung, Basic & Clinical Pharmacology, 13th ed., Pg. 748.\nThe bradycardia-tachycardia (“sick sinus”) syndrome is a definite contraindication to the use of lithium because the ion further depresses the sinus node. T-wave flattening is often observed on the electrocardiogram but is of questionable significance.', 'role': 'assistant'}]