Please choose one of the answers above, then review the video below with the answers and explanation.

An important reminder/message from this case: it is not enough to see a "P" wave before each QRS complex to call it "sinus rhythm". These P waves should have the correct axis (typically upright in leads I and II) to call them "sinus P waves".

Just to complicate things a bit, if there is an ectopic atrial rhythm (or atrial tachycardia) originates from the top-part of the right atrium (i.e., same neighborhood of sinus node) it may have the same axis as the sinus P wave, and hence it will be almost impossible to differentiate between it and sinus tachycardia based on the EKG axis only. However, there are other things you to help differentiate the two (beyond the scope of this quiz).

If you are not familiar with what we mean by "P wave axis", let me know and we can explain more.