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: Medicine
[{'content': 'QT depression is seen in ? \nSelect and explain. \nA. Hypokalaemia, B. Hyperkalaemia, C. Hypocalcaemia, D. Hypercalcaemia', 'role': 'user'}, {'content': "Answer: A \nExplanation: In vitro, hypokalemia not only prolongs the QT interval in the absence of drug but also potentiates drug block of ion\xa0channels that results in QT prolongation. Drugs (i.e., certain antiarrhythmics and erythromycin) and electrolyte disorders (i.e., hypokalemia, hypocalcemia, hypomagnesemia) can prolong the QT' interval and predispose to torsades de\xa0pointes.\nHypercalcemia can result \xa0in significant electrocardiographic changes, including bradycardia, AV block, and short QT interval; changes in serum calcium can be monitored by following the QT interval\nHyperkalemia, or drugs such as flecainide) tend to increase QRS duration. Conditions that prolong phase 2 (use of amiodarone, hypocalcemia) increase the QT interval.\nHypocalcemia typically prolongs the QT interval (ST portion), while hypercalcemia shortens it", 'role': 'assistant'}]