Let's analyze the ECG strip shown: **Features visible:** - Regular rhythm - Normal P waves before every QRS complex - PR interval is consistently prolonged (>0.20 seconds), but every P wave is followed by a QRS complex - QRS complexes are narrow ### Diagnosis: This is **sinus rhythm with 1st degree heart block**. **Explanation:** - **1st degree heart block** is characterized by a consistently prolonged PR interval (>0.20 s) but with all P waves conducted to the ventricles (no dropped beats). - There are no dropped QRS complexes, and the PR interval does not progressively lengthen (which would suggest 2nd degree, type I or Mobitz I block). - Sinus bradycardia would have a slow rate, but PR interval would be normal. - Junctional rhythm would typically lack normal P waves or have them inverted or after the QRS. ### Correct Answer: **a. Sinus rhythm with 1st degree heart block** It appears the selected answer in the image is incorrect. The correct answer is **a**.