A 73-year-old man is brought to the Emergency Department after an episode of sudden loss of consciousness that lasted 5-10 minutes. In the previous several weeks he had felt tired and weak:

• Sinus rhythm with complete heart block (see comment)
• Atrial rate 94/min
• Ventricular escape rhythm, rate 31/min, with right bundle branch block, right superior axis pattern

Comment: The ventricular escape rate is 31/min, the sinus rate 94/min (almost 1:3). This explains why the PR interval seems not to change. A diagnosis of high grade AV block (3:1) was made in the Emergency Department. In fact, the interval between the QRS and the following P clearly changes (noted by looking at the P-wave that comes just at the tail end of the QRS complex); thus, there is complete heart block.

ECG 2 is recorded 15 minutes later:

• Sinus rhythm with complete AV block
• Wide QRS escape rhythm, with right bundle branch block, right inferior axis pattern
• Atrial rate 94/min – Ventricular rate 30/min. 

A therapeutic procedure is performed:

• VVI pacemaker
• Underlying sinus rhythm with complete heart block