The following ECG is from a 76 yr old male who presented with a 3 week history of progressive shortness of breath and occasional chest heaviness.
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- Mean ventricular rate 36 bpm
- Mean atrial rate 72 bpm
- Irregular ventricular rate
- R-R varies between 1520 – 1680 ms (~36 – 39 bpm)
- Variability in P-P interval
- PR prolonged before QRS ~260ms
- Apparent 2:1 conduction
- Voltage criteria for LVH – aVL >11mm
- 2:1 AV block
- This is what this ECG appears to show at initial review
- There is P-P and R-R variability
- Could represent ventriculophasic sinus arrhythmia although pattern is not entirely predictable
- Possible CHB
- QRS Morphology unusual
- May represent multi-level conduction system pathology
- ? Isorhythmic dissociation – apparent temporal relationship between P & QRS
What is Ventriculophasic Sinus Arrhythmia
This phenomenon can be seen in up 40% of case of complete AV block and, as in this case, can be seen with 2nd degree AV block also.
You get a shorter P-P interval when there is an associate QRS complex with a longer P-P when there is no QRS between the P waves. Several mechanisms have been proposed including alterations in sinus node perfusion related to ventricular contraction and the mechanical effects of atrial stretch.
To make things more confusing there is a much rarer paradoxical phenomenon when the P-P is longer when a QRS is contained between them.
It is important to recognized as the P-P variability may be mistaken for other ECG features such as U waves for example.
You can read more about ventriculophasic sinus arrhythmia in this nice case report of the paradoxical version here:
What happened ?
There was no reversible cause identified for the AV block.
The patient was admitted under cardiology and underwent an uneventful PPM insertion.
References / Further Reading
- Chan TC, Brady WJ, Harrigan RA, Ornato JP, Rosen P. ECG in Emergency Medicine and Acute Care. Elsevier Mosby 2005.
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