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: Physiology
Which of the following condition is associated with giant 'a' wave in a JVP? 
Select and explain. 
A. ASD, B. Tricuspid stenosis, C. SVC obstruction, D. Complete hea block
B: Tricuspid stenosis
Answer: B: Tricuspid stenosis 
Explanation: 'a' wave in a JVP reflects right atrial presystolic contraction and occurs just after P wave on ecg and precedes first hea sound. Giant a waves occur in tricuspid stenosis and right ventricular hyperophy. Giant a waves are produced when right atrium contracts with increased force due to the increase in resistance to the flow of blood from right atrium to right ventricle. Reference: Harrison's Principles of Internal Medicine 18th edition chapter 227.