aka ECG Exigency 016.2
The following tracing can be found in our ECG library, allegedly as an example of Wenckebach AV block. However, as one of our readers, Jan Štros has pointed out, there is something not entirely right about this ECG tracing…
Can you spot the “deliberate” mistake?
Q2. What features of Wenckebach are notably ABSENT?
Q3. What possible explanations could exist to explain this tracing?
Here is my impression of the ECG (by no means the “correct” answers) is as follows…
1. The presence of a progressively prolonging PR interval that abruptly shortens (i.e. resets) after a pause in the rhythm is strongly suggestive of Wenckebach AV block.
2. Notably absent is the lack of a non-conducted P wave. While it is tempting to assume (as I did) that the non-conducted P wave must be hidden in the preceding T wave, there is no evidence of this – the P waves are too tall to be superimposed on the T waves without producing an obvious “bump”.
3. The frequently dropped P waves occurring in a regular pattern are suggestive of second degree SA block (type I). Features that are supportive of this: (1) Grouping of the QRS complexes, and (2) The duration of the each sinus pause is less than double the preceding PP interval
(See our ECG library page on SA block for an explanation of the different types http://lifeinthefastlane.com/ecg-library/sa-exit-block)
Possible causes of this ECG pattern would include conditions that suppress both SA and AV node function, e.g.
- Sick sinus syndrome
- Increased vagal tone
- Inferior MI
- Drugs: digoxin, beta-blockers, verapamil
So, the final diagnosis: