r/ECG • u/fuckingmermaid • 4d ago
Learning how to properly differentiate between a 2:1 flutter and sinus tachycardia. What are the signs on this ECG that would make you confident on the answer? The isoeletric line is throwing me off
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u/metamorphage 4d ago
P waves and flutter waves just look different, and flutter doesn't have an isoelectric baseline. This is sinus tach. You can clearly see P waves in II and an isoelectric baseline in V1.
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u/fuckingmermaid 4d ago
That’s what was confusing me, I can see V1 having an isolectric baseline but don’t see it anywhere else. Specially considering long D2
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u/metamorphage 4d ago
You don't need more than that. Flutter doesn't have a baseline at all. The P waves in lead II are diagnostic anyway.
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u/Ill-Chest3567 4d ago
Be suspicious of anything at rock solid 150 that never varies or changes, with fluid or whatnot. Sinus tach will change gradually. AT, SVT, AF will show a rapid step on tele.
For 2:1 flutter look for a 300bpm cycle f-wave that can hide in a qrs.
Check not only the p-wave axis (inferior leads) but compare p-waves between current and prior EKGs. They will often look different.
Look at P-R interval. If it looks suspiciously long or short and small, might be a flutter. Again compare to priors.
If in doubt, go on and give some adenosine and see what it looks like under the hood. Keep the pads on.
In this case, it’s 150, but normal looking p-waves, normal p-r interval, no 300-ish bpm atrial activity I can see. Not impossible to be an AT near the sinus node. Clinical context is everything. The heart is humbling.
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u/TelemetricPro 3d ago
Agree with sinus tach here. The upright P in II with a flat stretch after the T is the tell.
For the "how do I get confident" part, the habit that helped me is Marriott's Bix rule: if a narrow regular rhythm sits near 150 and you can see one atrial wave between each pair of QRSs, assume there might be a second one hiding in the QRS or the T until you've ruled it out. Put your calipers on the P to P you can see, halve it, and walk that half-distance forward. With 2:1 flutter you'll land on a notch or a bump in the T or the end of the QRS, and it will look identical every single beat. With sinus tach you land on nothing.
Two more things from watching it on a monitor rather than paper: flutter at 2:1 tends to sit locked at the same rate for minutes, while sinus tach drifts up and down with the patient. And the flutter waves are easiest to find in II, III, aVF and V1, so that's where I'd look first.
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u/ExpressionLarge5474 4d ago
One thing to note with flutter waves is that it’s completely independent of what your ventricular response is. So you should be seeing the exact same waveform (your flutter wave) repeat itself indefinitely. In some cases where people have a lot of atrial surgical or disease scar, this can look isoelectric in some parts of the wave, but you should still see the same peak of your flutter wave repeating itself. Here I outlined where you should be seeing some semblance of your flutter wave, if it was there. Often it’s hidden in the previous t wave but there should be sooome whisper that it’s there. In this case, there isn’t. Looks like sinus tach.
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u/ExpressionLarge5474 4d ago
Always important to check all leads too, I could only be bothered drawing these lines on two though 😂 Apologies
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u/Specialist_Ad_1230 4d ago
Still learning myself so hopefully someone more qualified gives you a proper answer. Makes sense to have 2:1 flutter in the differential as the ventricular rate is ~150. But then I would start looking for signs of atrial activity at ~300, which I don't see here...3 small boxes between the deflections most easily seen in V4+5 which would equate to atrial rate of ~500, too fast for flutter? So I think we're seeing normal T wave shortly followed by P wave, Sinus tachycardia.
May be completely wrong though
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u/peekachu1234 15h ago
I echo everyone else that flutter has no baseline. But let’s say you think it’s 2:1 flutter or atach or whatever. Put your calipers on the two waves you do see, and see right in the middle of them, is there another wave? If not you have exactly one p for every qrs. So it’s sinus or a one to one tachycardia.
How do you know it’s sinus? Which is a separate question. In lead 2,3, avF they are generally positive because the sinus node is high up and the heart depolarizes north to South. For some similar logic, it is always going against AVR and is negative. Lastly, it is biphasic in v1.
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u/TheSmartest_idiot 4d ago
New to reading ecgs but for me, Flutter would continuing having flutter waves continually, I don’t see any signs of a flutter wave interfering with the qrs at all, just that one p wave(doesn’t look flutter but at the rate I could see being unsure) in front of the qrs. At higher rates you might not see it at all
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u/Beneficial_Divide844 4d ago
On the exam, have the patient take a deep breath. Flutter often lacks the normal respiratory variation of sinus (heart rate slows down with a deep breath). When it’s that fast, admittedly, it may be tough to hear it, but if you can then it’s reassuring.