Ever given a patient adenosine to cure their SVT with a flourish,
*PUSH* – *FLUSH* – “You’re gonna feel funny,” ¹
only to see the tell-tale saw tooth waves of atrial flutter marching across the screen? While you may have performed a successful diagnostic test, your patient has been given a sneak peek of the day their heart quits beating with nothing to show for it. Well you need not make this mistake again, because I’ve put together a rough list of (almost) every tip out there for diagnosing atrial-flutter with 2:1 conduction. In the end you’ll be talented enough to recognize this arrhythmia with your monitor upside-down (hint)!
2:1 conduction of atrial flutter is the most common manifestation of untreated (i.e. new-onset) atrial flutter, making it doubly difficult to diagnose because the patient will often have no history. This post was originally going to include a primer on the pathophys of atrial flutter, but even when I gutted the extemporaneous info it was too much. Instead, all you need to do is look at the atrial flutter section of this animation from blaufuss.org. It’s simply the best resource I’ve come across for visualizing the phenomena behind most forms of narrow-complex tachycardia. Onto the tricks…
0 – Be systematic.
This one doesn’t pertain specifically to flutter, but develop a systematic way of approaching every ECG. It may initially seem redundant for easy tracings, but you’ll never see subtle findings if you don’t look. Additionally, it will prove necessary to be well-practiced if you want to dissect very complicated cases. Here’s a good method for general 12-leads interpretation from my heroes at EMS 12-Lead, but I’ll have to do a post on specifically how to approach rhythm diagnosis since they don’t have one (yet).
1 – In anyone with a heart rate of 130-170, consider the possibility of atrial flutter.
It’s going out on a limb, but I’m going to boldly state that you’ll never come to the correct diagnosis unless you think of it first. When compared to sinus tachycardia and atrial fibrillation, atrial flutter is relatively rare. It may seem like overkill to think about it almost every time you encounter a tachycardic patient, but I GUARANTEE it’s an easy habit to pick up. You will look like a rock-star picking up flutter that otherwise would have been missed. Now a lot of things can cause a rate in that range, including sinus tach and a-fib, so that brings us to trick #2:
2 – The rate WILL NOT BUDGE from 149 bpm (or whatever half of that person’s particular atrial rate is).
Atrial fibrillation is usually fairly easy to rule out because it is irregularly-irregular, but both a-flutter with uniform conduction and sinus tach are usually described as being regularly-regular. While this may be true if you’re feeling a manual pulse, watch the heart rate generated by the monitor and a sinus rhythm will almost always show at least some variation over the course of a few minutes. If the patient is experiencing atrial flutter with constant conduction, while the rate displayed may occasionally vary by a beat or two, it will hardly move. I’ve been able to identify flutter without an ECG by simply placing the patient on a portable pulse ox, noting the rate was 153, getting a very cursory history, stepping aside for a couple of minutes to arrange further care, then returning to note that even after resting, the patient’s rate was still exactly 153 bpm. Sinus tach won’t do that. Every rule has an exception, and there are plenty of times when the rate will vary with a-flutter, leading to tip #3:
There’s a lot of videos on the net of unwavering flutter from a rhythm generator, but that’s cheating, so if anyone comes across a clip from an actual patient please let me know.
3 – Look for breaks in the regular rhythm.
Occasionally even untreated flutter may waver from 2:1 conduction for a beat or two, and these moments should be used to scrutinize the strip for signs of atrial activity. Vagal maneuvers are an option but aren’t always successful. Additionally, flutter tends to crop up in elderly patients, a population famous for passing out if they bear-down too hard, so maybe having them Valsalva is not the slickest option. On the other hand, if the only other route is adenosine, vagal maneuvers may have a place (noting, of course, if they are allowed in your scope of practice). Unfortunately vagal maneuvers often fail or are not a possibility, so knowledge and experience will be the key to identification. The ECG below varies quite a bit between 2:1 conduction and higher ratios, making diagnosis easy, but sometimes the biggest break you’ll get is a single 3:1 cycle in an otherwise steady stream of 2:1.
4 – Scrutinize EVERY lead.
The standard ECG has 12-leads, so quit relying on monitoring lead II for arrhythmia identification. While flutter waves do typically show up well in lead II, we’re not talking about easy cases, so use all the information available to you. V1 is an excellent lead for detecting atrial activity (or the “Lewis lead” if you’re monitoring), and don’t discount less common views of the heart like aVR. While I’m bad-talking monitors, if you’re using a Lifepack-12 you should rarely trust what you see. The filter used in monitor-mode grossly distorts the ST-segments and T-waves, making tricky rhythm analysis even more difficult. Thankfully even ACLS has started to encourage obtaining a 12-lead for rhythm identification unless the patient is in extremis, so don’t be slower to evolve than the AHA.
4.5 – UPDATE – Really try the “Lewis Lead”
In tip #4 I mentioned using the “Lewis lead” for detecting hidden atrial activity, but I just wanted to share a case that reinforces the utility of this lead when searching for hidden atrial flutter.
5 – The Bix rule.
Harold Bix, a cardiologist from Vienna, noted that if a P-wave is located halfway between two QRS complexes, there’s a good chance there is also a P-wave buried inside the QRS as well. Since flutter waves tend to be somewhat wide and rarely fall perfectly inside a narrow QRS complex, you can often find signs of buried waves as slurring in the upstroke or downstroke of the QRS. His advice leads well into tip #6:
6 – Non-specific ST or T-wave abnormalities can actually be useful.
In almost every case of 2:1 atrial flutter I’ve seen, the computer interpretation has included a statement regarding non-specific ST or T-wave changes (or often outright claims of ischemia). This is because flutter waves (henceforth called “F-waves”) are relentless and will barrel through everything on a tracing. QRS complexes are relatively powerful deflections and not easily affected (except as noted in #5), but ST-segments and T-waves end up being fairly susceptible to distortion, and the effects of F-waves usually manifest as ST-depression. Any unusual ST-depression, T-wave shapes, or unexpectedly biphasic T-waves should tip you off to search for signs of more buried deflections approximately 200 ms later (1 large box, corresponding to the usual atrial rate of 300 bpm). Since we’re mentioning the computerized interpretation…
7 – Never trust the computerized interpretation.
It’s fairly well-known that the GE Marquette 12-lead algorithm is a poor diagnostician of rhythm abnormalities, but when it comes to 2:1 atrial flutter it is especially flawed, and in my experience an incorrect interpretation is the norm.
8 – It just doesn’t look right.
When it comes to odd wide complex rhythms, hyperkalemia should always pop into your mind. In the same vein, if you see a narrow complex tachycardia that just doesn’t look like a typical AVNRT (“SVT” if you prefer the vernacular), consider atrial flutter. As in tip #6, those F-waves can screw with every aspect of the tracing.
9 – Turn the beat around.
This is probably my favorite trick of the bunch so I’m not sure why it’s buried way down at #9.
Most people don’t realize this, but disco singer Vicki Sue Robinson was not an actual electrophysiologist. Lacking an MD, her rendition of the hit song “Turn the Beat Around,” which instructed cardiologists to, “turn the beat around, turn it upside-down,” still made waves in the diagnosis of atrial flutter.
Flutter waves tend to show up best as negative deflections in the inferior leads (II, III, aVF), so if you’re considering the diagnosis, flip the ECG upside down and look at these leads. You’ll be amazed how much easier it is to identify the regular F-waves of flutter once they’re upright. It also makes it easier to see how those ST and T-wave distortions mentioned in #6 really are the predictable result of atrial activity.
10 – Faster paper speeds are your friend
The standard ECG is recorded with a paper speed of 25 mm/sec, but most machines have an option for 50 mm/sec. In fact, it is often the preferred setting for electrophysiologists trying to diagnose tachyarrhythmias; those guys are the experts so we can probably learn a thing or two from them. While it does take a little practice to get comfortable looking at complexes double their normal width, it also enhances small features that might have otherwise slipped your notice.
11 – If it’s less than 150 bpm, it still might be 2:1 flutter.
Many anti-arrhythmic medications (I’ve always thought mostly class I and III, but apparently at least some, if not all beta-blockers as well) can slow down the rate of the circus movement of the atria, consequently slowing down ventricular response. Of note, this can lead to a very dangerous state if the atrial rate slows down enough for the AV node to begin conducting 1:1 rather than the default 2:1.
12 – A saw-tooth pattern is not necessary to seal the diagnosis
Go back and look at the ECG in #11, taking note of how subtle the F-waves are. Very often this loss of typical F-wave amplitude and morphology is linked to a decrease in atrial rate, making very slow F-waves exceptionally easy to confuse with sinus rhythm. There’s no easy way to get around these tough cases and your best tool will be keen observation. Keep an eye open for repeating patterns in the baseline with a consistent relationship to the QRS complexes that could easily be written off as artifact.
CAUTION – MATH! – If there is variable conduction to the ventricles, atrial fibrillation becomes a common misdiagnosis. Measure a bunch of R-R intervals and look for a lowest-common-denominator. For example, if the atria are contracting at 300 bpm, meaning F-waves are 200 ms apart (1 large box), even with variable conduction every RR interval should be a multiple of 200. This means that 2:1 conduction would result in R-waves exactly 2 large boxes apart (400 ms); 3:1 conduction leads to R-waves 3 large boxes apart (600 ms); and 4:1 conduction would exhibit 4 large boxes between R-waves (800 ms). It’s minutiae for a diagnosis that probably won’t change the treatment plan, but who cares about patient outcomes when you can prove to everyone that you’re smarter than them.²
13 – F- waves are not exclusive to flutter.
If you see what appear to be F-waves at a rate exceeding 350 bpm, they’re probably “f-waves” associated with atrial fibrillation (note the clever use of lower-case in this case). The key to this distinction is that in atrial flutter with regular conduction (be it 2:1, 3:1, or 7:1), the QRS complex will typically appear at a regular interval in comparison to the F-waves. In fibrillation the QRS will vary in its relationship to the f-waves. The morphology of f-waves will often vary, however I have also seen cases of very regular appearing fibrillatory waves.
There’s also a rare form of atrial flutter (type II) that can generate flutter waves at 340-440 bpm, but in contrast to a-fib, all the tracings I’ve come across exhibit clear F-waves in the inferior leads (if you have any cases contradicting this, please let me know). The f-waves of atrial fibrillation are usually confined with the right precordial leads (V1 and V2), with minimal evidence in the inferior leads, where flutter waves dominate.
On the other hand, if the rate is less than 250 bpm, it may be an entity known as “atrial tachycardia.” In A-Tach you will see distinct P-waves at a rate exceeding the normal physiological rate of sinus rhythm, often with 2:1 or 3:1 conduction, except they don’t have the saw-tooth pattern of flutter waves and are slower. As I stated in #9, there can be some overlap with slow a-flutter and atrial tach, leaving a diagnostic grey-zone. Thankfully they’re still treated the same acutely.
14 – Too fast to be possible is not impossible.
(Sigghhhhhh. For fear of being accused of being unsafe, I have to note the obvious: My whole blog, and this section in particular, in no way endorses trying to get fancy and pull out a zebra to diagnose an unstable patient; just follow ACLS. It is simply intended to act as water for your mind-grapes.³)
I noted in the pathophys section (before it was gutted) that if you combine a rapid atrial rate with Wolff-Parkinson White syndrome (WPW), you can get some truly astounding ventricular rates. If you encounter a wide-complex tachycardia faster than 220 bpm, it may be worth considering the existence of either atrial fibrillation or flutter with WPW. The key to distinguishing the two is that in flutter you will see a (mostly) regular, (mostly) consistent QRS morphology – as you should expect by now, at around 300 bpm. If the patient has a-fib, the rhythm will be irregularly irregular (as in normal a-fib, but extra fast) and the QRS morphology may vary wildly. Actual study of this topic would require a couple of posts unto itself, but I figured it was at least worth a cursory mention.
15 – Read a lot of ECGs.
If you’ve spent any time studying ECGs beyond the simplistic introduction to arrhythmias we all start with, it has probably become apparent that there is a lot of gray surrounding the many distinct electrophysiologic abnormalities recognizable on a 12-lead. This post is not intended to act as a hard framework for making the diagnosis of atrial flutter, but is merely a collection of the thoughts that cross my mind when I’m dissecting a difficult tracing. In these cases there will always be a lot of overlap with atrial fibrillation, AVNRT, atrial tachycardia, and several other dysrhythmias. The best advice I can offer is just to read LOTS of ECGs. There are scores of algorithms and diagnostic criteria to aid in making an electrocardiographic diagnosis, and while they have their place and can be of great utility (e.g. the aVR algorithm for ruling-in V-Tach, or the Sgarbossa criteria for recognizing STEMI w/ LBBB), the most useful tool is a well-trained eye capable of noticing when something on a tracing just doesn’t fit.
Well congratulations if you’ve made it all the way through. There’s a chance I’ll distill this information down to a much shorter reference card (à la Paucis Verbis cards) or add more tips at a later date. If you have any ideas of your own, please let me know and I’ll be glad to include them, with due credit, of course.
1. Don’t do this.2. Sarcasm, don’t fight me please.
3.“Jack Welch has such unparalleled management skills they named Welch’s Grape Juice after him, because he squeezes the sweetest juice out of his workers’ mind grapes.” — Jack Donaghy