Question 26.2

Please note: The following ECGs have all been recorded at 25 mm/sec and gain setting of 10 mm/mVe 26.1

A 64-year-old male is admitted to the ICU following coronary artery bypass surgery. His rhythm strip and central venous pressure waveform is shown on page 9 (Figure 2).

Give the likely cause of the abnormality shown.        (20% marks)

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College Answer

Epicardial (atrial & ventricular) pacing leads reversed. 


The image used here is from an article by Aktas et al (2007), where this phenomenon is discussed. Specific feature is the fact that pacer spikes both precede and follow each QRS complex (one is the atrial lead pacing the ventricle, the other is the ventricular lead pacing the atrium after the ventricle has already depolarised).

Additional information can be derived from the (not to scale) CVP waveform:

atrioventricular lead reversal CVP waveform

The first wave is the ventricular contraction, which ejects blood out of the tricuspid valve before it closes (as the atria had not contracted yet, the annulus is not "tight" enough). The second ave is the poor atriumcontracting against a closed tricuspid valve, which increases the venous pressure.


Aktas, Mehmet K., Abrar H. Shah, and Toshio Akiyama. "Atrioventricular Pacemaker Leaf Reversal." Journal of Arrhythmia 23.1 (2007): 69-72.