Answer:
The correct answer is option A. right atrium.
Explanation:
The sinus node is located in the right atrium of the heart which is a bunch of specialized cells that present near the vena cava junction. The sinus node has the role of a cardiac pacemaker that generates an impulse on its own in between 60 to 100 impulses per minute.
If a patient has irregular pulse the right atrium should be assessed as left ventricle or the right ventricle or left atrium has no role of generating impulse.
Thus, the correct answer is option A. right atrium.