This document summarizes the ECG findings for a 58-year-old man presenting to the emergency department with 2nd degree AV block, Mobitz type 1. The ECG shows regular sinus rhythm at a rate of 88 beats per minute with intermittent conduction block such that every third P-wave is not followed by a QRS complex, resulting in a ventricular rate of 59 beats per minute. Further analysis of the ECG found normal QRS axis, duration and morphology with no signs of infarction, hypertrophy, or other abnormalities. The final diagnosis was sinus rhythm with Mobitz type 1 2nd degree AV block and a ventricular rate of 58 beats per minute.

1. Stepwise interpretation of ECG ID 108 2 nd degree AV block Mobitz 1

2. ID 108 – 58 year old man in the emergency department

3. ID 108 – 58 year old man in the emergency department Can you see P waves?

4. Yes: there are regular P waves, that originate from the sinus node (rate 88/min) Are the P waves followed by QRS complexes? ID 108 – 58 year old man in the emergency department - Sinus rhythm, 88/min.

5. Yes, however, there is 2 nd degree AV block: 2 P waves are conducted with progressive PR prolongation and the third P wave is blocked ( Mobitz 1 second degree AV block ) Ventricular rate 59/min. ID 108 Sinus rhythm with 2 nd degree AV block (Mobitz 1) Ventricular rate 59/min

6. ID 108 – Sinus rhythm with 2 nd degree AV block (Mobitz 1) – Ventricular rate 59/min . Following diagnostic steps: - QRS axis is normal – The QRS duration is normal (no BBB or nonspecific block) - No right or left ventricular hypertrophy – No QRS signs of infarction- Normal ST segment and T waves

7. ID 108 Final diagnosis: - Sinus rhythm with Mobitz 1 second degree AV block (3:2 AV conduction) Ventricular rate 58/min. No other abnormalities