This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General pathology, Subject name: Pathology
Irreversible injury in myocardium occurs at 
Select and explain. 
A. 2 minutes, B. 30 minutes, C. 2 hours, D. 5 hours
B: 30 minutes
Answer: B: 30 minutes 
Explanation: Only severe ischemia lasting at least 20 to 40 minutes causes irreversible damage and myocyte death leading to coagulation necrosis. Withlonger periods of ischemia, vessel injury ensues, leading to microvascular thrombosis.( Robbins Basic Pathology, 9th edition, page 377 )