A bizarre ECG

I was asked for an opinion on this ECG.

The rate is 86 bpm and the QRS complexes are broad. In this situation it is desirable to review the tracings as rhythm strips; prefer 4 as 12 leads are crowded and confusing.

Regular spikes can be seen at the peak of the T waves. A ventricular ectopic breaks up the rhythm. Look at the compensatory pause (the pause is always very helpful particularly for the diagnosis of atrial tachyarrhythmias). Clearly now the rhythm is atrial pacing (AAIR). I have further amplified the tracing using two leads (yellow highlight).

In the compensatory pause and following the atrial stimulus artefact, there is a P wave, but only after a latency period of 120 ms (yellow highlight). The AV delay is 360 ms. Such a latency suggests severe atrial disease (Consider amyloid disease with marked conduction delay in the atrium and AV node). I suspect the atrium is doing little ventricular filling anyway.

Normally, when we see an atrial stimulus artefact lying on or near the previous T wave in patients with a prolonged AV delay, we think of the atrium contracting against closed AV valves; a variant of the pathophysiologic pacemaker syndrome with venous cannon waves in the neck (and lungs). To take the stimulus artefact out of the T wave we need to shorten the AV delay. To achieve this, we require atrial contraction to occur immediately after stimulation as shown in the next figure.

In this illustration, there is marked first degree AV block (480 ms) as well as bifascicular block. The rate is 62 bpm and with a modest increase in atrial rate with rate adaptive pacing, the P wave will lie in the T wave of the previous cycle possibly causing marked symptoms. Such patients require ventricular pacing to shorten the AV delay.

Here is the conundrum!

In our case (figures 1 to 3), shortening the AV delay with ventricular pacing will push the P wave into its QRS and create the same clinical scenario as with the previous T wave in figure 4. Normally we would recommend upgrade to or program DDDR. For physiologic reasons, this may not work as we want the P wave before the QRS which it is where it is now. Shortening the AV delay with ventricular pacing may make things worse.

You learn something new every day!

Dr Harry Mond