A 56-year-old man presented with an episode of syncope. An ECG showed sinus rhythm with complete heart block, where the atrial rate was 80/min and ventricular rate was 43/min. The dissociation between the P waves and QRS complexes indicated complete heart block. The narrow QRS complexes and normal axis suggested the escape pacemaker was in the AV junction, resulting in an escape junctional rhythm controlling the ventricles. The ECG was otherwise normal.

1. Stepwise interpretation of ECG
ID 111

2. ID #111 – 56 year old man who had an episode of syncope

3. ID #111 – 56 year old man who had an episode of syncope
Can you see P waves?

4. ID #111 - 56 year old man who had an episode of syncope
Yes, there are sinus P waves, rate 80/min.
Are the waves followed by QRS complexes?

5. ID #111 - Sinus rhythm with complete heart block –P rate 80/min, QRS rate 43/min
No – The rhythm of the P waves and the rhythm of the QRS complexes are regular, but the two
rhythms are dissociated. The atrial rate is 50/min, the ventricular rate 83/min
There is complete heart block
As atria and ventricles are dissociated, where is the activation of the ventricles coming from?

6. ID #111 - Sinus rhythm, with complete heart block – Sinus rate 80/min.
Escape junctional rhythm. Ventricular rate 43/min.
The QRS complexes are narrow – The escape pacemaker is in the area of the AV junction

7. ID #111 - Sinus rhythm, with complete heart block – Sinus rate 80/min.
Escape junctional rhythm. Ventricular rate 43/min.
The QRS axis is normal (near 0 degrees). There is no bundle branch block or non-specific block
No LVH or QRS signs of myocardial infarction. The ST segment and T waves are normal.

8. ID #111 Final diagnosis: Sinus rhythm, with complete heart block –
Escape junctional rhythm. Ventricular rate 43/min.