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
"a" wave in JVP indicates: 
Select and explain. 
A. Atrial systole, B. Ventricular systole, C. Atrial relaxation, D. Tricuspid regurgitation
A: Atrial systole
Answer: A: Atrial systole 
Explanation: A wave: Arc positive waves due to distention producedby right atrial contraction Large a waves: Indicate atrium is contracting against increased resistance tricuspid stenosis, pulmonary stenosis, pulmonary hypertension.
Cannon S waves
Regularly: During junctional rhythm. Irregularly: complete Heart Block. Absent a waves: Atrial Fibrillation