Most will thought of a premature ventricular complex (PVC) as a nuisance. However, a PVC can unmask or help in arrhythmia diagnosis.
A PVC can unmask hiding P waves
Figure 1 - A PVC in the middle of a regular wide-QRS complex rhythm.
It might look like sinus tachycardia with right bundle branch block (RBBB)
Figure 2 - Organized atrial activities or P waves are marked with red arrows
A properly-timed premature ventricular beat (PVC) can unmask hidden P waves. The 2 P's are marked in red. The atrial rate is about 250 bpm.
When I showed this to nurses, they thought there was a block. Yes, there is but this is physiologic block. The AV node is like a filter or "gatekeeper". It can accommodate only certain number of beats. If it is bombarded with a lot of supraventricular impulses, some of the impulses will be blocked as you can see during atrial flutter or AFL (atrial rate of 250-350 bpm) and atrial tachycardia or AT (150-250 bpm). So, during atrial flutter or atrial tachycardia we see 2:1 or something AV block or AV conduction.
So, our mystery ECG is not sinus tachycardia.
AT vs AFL until confirmed with electrophysiologic study
There has much argument on using the atrial rate to differentiate tachycardias. It is not a good practice to use rate to differentiate tachycardias.
In our case, we are stuck if we call this AT or AFl. You will get several range from different sources. Some would say that AT is 150 - 250 bpm and AFL is 250-350 bpm. Some would say that AT is 100-240 bpm and AFL is 240-340 bpm.
TYPICAL atrial flutter will have an atrial rate of about 240-340 bpm but the atrial rate will slow down with use of antiarrhythmics (amiodarone) and progression of atrial myopathy. Atrial tachycardia will also manifest like atrial flutter in patients who had catheter ablation for atrial fibrillation, maze procedure and prior cardiac surgery with atrial scar.
So, the typical saw-tooth ECG finding can also be seen in fast AT and the presence of isoelectric baseline can be seen in slow atrial flutter. According to Das and Zipes, "...it becomes a matter of semantics to define an AT or an atypical AFL".
Going back to the case, the ventricular rate was in the 120's because the atrial rate was around 250 bpm. There is a 2:1 AV conduction. This case can be interpreted as AT vs AFL with 2:1 AV conduction.
Not all PVC would unmask the arrhythmia
Figure 3 - Not all PVC can unmask a rhythm mystery
Not all PVC can unmask a hidden P wave
Going further, this strip above is not much of help even if there is PVC. It is hard to convince more than 90% of people that there is a P wave in the ST complex. Only the geeks will be convinced.
After several hours, a medication was given and slowed down the rate and revealed the answer to the mystery - atrial flutter. There is group-beating suggesting there is a Wenckebach periodicity and a probable multilevel block. Most readers would interpret it as AFL with variable block.
The take home message for this case:
· Use all leads to interpret a rhythm (full disclosure).
· Make use of the PVC to unmask P waves.
· Fast atrial rates will create a physiologic block.
Figure 4 - Atrial flutter revealed
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