Pacemaker-Ventricular Block

Unlike pacemaker-atrial block, the various ECG appearances of pacemaker-ventricular block are well defined and easily identified.

In summary:

• First degree pacemaker-ventricular block – ventricular latency
• Second degree pacemaker-ventricular block – Wenckebach sequences
• Third degree pacemaker-ventricular block – loss of capture with asystole

First degree pacemaker-ventricular block

Ventricular stimulus artefact (red vertical arrows) followed by a latency period (red highlight) and a wide QRS. The appearance suggests very severe ventricular dysfunction. Latency should be identified in numerous leads and are often overlooked. Together with a very broad QRS, it indicates a poor prognosis.

Pacemaker-ventricular block can be seen immediately prior to death and also requires gross electrolyte imbalance.

Ventricular pacing followed by latency and a very wide QRS/T.

Second degree pacemaker-ventricular block

There is further deterioration in the ECG appearance with Wenckebach sequences.

ECG monitoring immediately prior to death. The ventricular latency increases (red highlight) as a Wenckebach sequence, followed by exit block (red vertical arrow). The next sequence is 2:1 block (yellow highlight). Again the QRS/T wave complexes are very wide.

With clinical deterioration, the ECG appearances become more bizarre.

Ventricular latency, a very broad QRS and 2:1 pacemaker-ventricular block.

Third degree pacemaker-ventricular block

This can only be diagnosed in association with lesser degrees of block.

Sequential changes in the ECG immediately prior to death.

This ECG of temporary pacing was diagnosed as ventricular latency (red highlight).

The 12-lead ECG demonstrates a number of lessons we have covered in the last few “Fun with ECGs” and emphasizes the “fun” part of ECG interpretation.

Try to interpret the 12-lead ECG:

• Latency (or pseudo-latency) is only seen in the rhythm strip (red highlight).
• Leads I, II and III (yellow highlight) also show possible ventricular latency, but careful inspection identifies this as atrial pacing with a short conduction period to the ventricle and the P wave axis suggests low atrial pacing at the mouth of the coronary sinus.
• The paced complex before this (blue highlight) also demonstrates low atrial pacing, but with failure of AV conduction.
• Leads V1 to V3 demonstrate left ventricular pacing (green highlight).

How do we put this all together?

Let us review the rhythm strip.

Within the ventricular pseudo-latency, there is an amalgam of both low atrial (blue highlight) and delayed left ventricular (red highlight) pacing. At other times, there is atrial pacing with and without AV conduction (blue highlight).

How can we explain this?

The temporary lead lies in the mouth of the coronary ostium. Probably depending on respiration, it will pace the atrium (yellow highlight and arrow) with and without AV conduction and at other times both the atrium and later the ventricle (yellow and red highlight and red arrow).

Easy!

Understanding the ECG of atrial and ventricular pacing, together with the different features depending on the site of the cathode, allows us to interpret even the most bizarre pacing ECGs.

Harry Mond