atrial flutter
First Glance:
From across the room it looks like a supraventricular rhythm with grouped beats of three.
Discussion:
Grouped beats could mean all kinds of things. A second degree block, regular premature ectopy (bigeminy, trigeminy, etc), various supraventricular rhythms with variable blocks, and then a few really unusual entities. This particular strip is tricky- partly because it is tricky, and partly because it has (per usual) diminutive voltages which makes analysis of the atrial activity tricky. What a shame that this lead is gained down to 30%.
Did you see any regularity in the baseline? Your best bet of discovering something subtle is looking at the flat sections of baseline before the first QRS of a group (where the leftover T’s and U’s from the last group will no longer be present).
Here’s what I see:
There are regular negative deflections (green triangles) in the baseline. The rate is around 300. This could be atrial flutter, with the rest of the F waves overrun by the QRS’s and the T waves that follow those QRS’s. In that case, this would be aflutter with a variable block. Usually it’s 2:1, but then occasionally it jumps up to 4:1 every third beat. This is actually a common pattern in my experience, although usually it is alternating 2:1 -> 4:1 -> 2:1 -> etc.
This is where the hidden F waves are:
They are hard to pick out because they are slathered on top of the T waves and QRS’s, but the correlation seems consistent and the interval between the preceding F wave and the first QRS of each group is very regular.
Here’s more strip:
Do you see it? It’s hard to be 100% sure from this strip. If you could see longer pauses you might seal the diagnosis, so you could try some vagal maneuvers to try to get some transient 6:1 or longer block, or you could give adenosine, or you could stop messing around, gain the strip up, and get a 12L!
The P waves are probably not ectopic atrial tachycardia as they are the fast side for that rhythm. It’s still a possiblity though, but flutter just fits better here.
What’s the heartrate? Count 3 second blocks. I count 11 beats in 2 blocks which makes about 110 a minute– for once the monitor and I agree.
Final Impression?
Atrial flutter with 2:1 -> 2:1 -> 4:1 variable block, ventricular rate is 110.
Management implications:
Increase the gain to see the P waves. Confirm with 12L. A lewis lead could clarify atrial activity if still in doubt.
The Take-home Point:
Atrial flutter, in my experience, is the great imitator. A classic flutter strip might be easy, but if you have a 2:1 block (common) or the F waves are not visible or obvious (common) or the block is variable than it can look like all manner of supraventricular rhythms, and can be irregularly irregular.
I have read somewhere that atrial flutter seems to be predisposed to even-numbered blocks (2:1, 4:1) although not every expert agrees. In my experience aflutter with variable block tends to be regularly irregular (as we see here, or with the alternating 2:1 -> 4:1 pattern mentioned earlier), but often there are odd-numbered and variably variable blocks which can look just like afib if the F waves aren’t obvious.
Of note: if you are seeing aflutter with a high-grade block (think 4:1 or above), consider dig toxicity. Dig is especially likely to cause flutter with a high-grade block because it both predisposes to supraventricular ectopy/flutter, and slows the AV node.
It’s worth keeping atrial flutter on the differential because it’s treatment and prognosis is significantly different from most of the other supraventricular tachycardias.
Three star strip. Devious stuff.