This article is the third in our latest series, The 12 Rhythms of Christmas, where each day we examine a new rhythm disorder. It’s a continuation of the theme behind last year’s 12 Leads of Christmas.
This is a new edit of the first article I ever published on my personal blog, so it may seem familiar to some readers.
Finally, if you were curious about the mystery rhythm in Fig. 16 of the first post on sinus tachycardia, you might be surprised to know that it shows atrial flutter with 2:1 conduction. The same tracing pops up in Fig. 23 of this article.
Have you slammed adenosine to cure a patient’s SVT with a fluorish?
*PUSH* â€“ *FLUSH* â€“ â€œYouâ€™re gonna feel funny.â€
…only to see the saw-tooth waves of atrial flutter marching across the monitor?
While you may have performed a successful diagnostic test, your unsuspecting patient has just been given a sneak peek of the day their heart quits beating with no relief from the arrhythmia actually causing their symptoms.
Well, you need-not make that mistake again, because Iâ€™ve put together a rough list of (almost) every tip out there for diagnosing subtle atrial-flutter with 2:1 conduction. In the end youâ€™ll be talented enough to recognize this arrhythmia with your monitor upside-down (hint)!
There’s three things you need to understand about the physiology of atrial flutter:
- Most flutter is caused by a re-entrant circuit that travels around the annulus of the mitral valve. The best way to visualize the mechanism is to watch the animation in the “Atrial Flutter” section of this tutorial (but it’s worth your time to run through all the other chapters).
- Because the flutter circuit does not utilize the AV-node, adenosine almost never has an effect on the atrial portion of the arrhythmia; it just temporarily interrupts conduction to the ventricles (and bothers the patient).
- New-onset or untreated atrial flutter most often presents with 2:1 conduction ratios, with two flutter waves occurring for every QRS complex.
Flutter isn’t always easy to spot
Basic dysrhythmia classes make it seem like atrial flutter is a simple arrhythmia to identifyâ€”just look for prominent saw-tooth waves.
That isn’t always the case. Here’s an extraordinarily subtle case of of atrial flutter with 2:1 conduction.
Consider 2:1 flutter in anyone with a heart rate of 100â€“200 bpm
Itâ€™s going out on a limb, but Iâ€™m going to boldly state that you’re unlikely to come to the correct diagnosis unless you think of it first. Atrial flutter is said to be fairly uncommon, but my personal experience begs to differ. It is indeed less prevalent than atrial fibrillation, but I see an example almost every day in my emergency department, so itâ€™s still very common in its own right. It may seem like overkill to think about it almost every time you encounter a tachycardic patient, but I guarantee itâ€™s an easy habit to pick up and youâ€™ll 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 the next sign…
The heart rate in 2:1 flutter is extremely stable
Atrial fibrillation is usually fairly easy to identify because it is truly irregularly-irregular, but both a-flutter with uniform conduction and sinus tach are described as being regularly-regular. While this may be true if youâ€™re feeling a manual pulse, watch the heart rate generated by the monitor and sinus tachycardia will almost always show at least some variation over the course of a few minutes. In atrial flutter with fixed conduction, while the rate displayed may occasionally vary by a beat or two, it will hardly move (Fig. 8). Sinus tach wonâ€™t do that. Every rule has an exception, however, and there are plenty of times when the rate will vary with a-flutter, leading to our next tip…
Look for breaks in the regular rhythm
Occasionally even untreated flutter may waver from 2:1 conduction for a beat or two, and those moments should be used to scrutinize the strip for signs of atrial activity. PVC’s in particular can provide a brief glimpse of the underlying rhythm. Vagal maneuvers are an option but arenâ€™t always successful. Additionally, flutter tends to crop up in elderly patientsâ€”a population famous for passing out if they bear-down too hardâ€”so maybe having them Valsalva is not the slickest choice. On the other hand, if the only other route is adenosine, vagal maneuvers may be easier to tolerate. Unfortunately, vagal maneuvers often fail or are not a option, and cases where the rhythm shows gaps without provocation are pretty uncommon, so knowledge and experience really are the key to identification.
Scrutinize every lead
The standard ECG has 12-leads so quit relying on just monitoring lead II for arrhythmia identification! While flutter waves typically show up well in lead II, they tend to show up best in III and aVF. Also, weâ€™re not talking about easy cases here, so use all of the information available to you. V1 is an excellent lead for detecting atrial activity, especially flutter waves (or the â€œLewis leadâ€ if youâ€™re monitoring), and donâ€™t discount less common views of the heart like aVR. Flutter waves usually appear upright in V1 and aVR, sometimes making them easier to spot than the inverted F-waves in II, III, and aVF.
The Bix rule
Harold Bix, a cardiologist from Vienna, noted that if a P-wave is located halfway between two QRS complexes, thereâ€™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. In the EKG above there is a slight â€œnotchâ€ or â€œslurâ€ at the tail end of each QRS complex, confirming that there is indeed atrial activity hidden there.
Not all tracings are going to give you a hint of the buried activity. In those instances all you can rely on is Bixâ€™s suggestion, your clinical suspicion, and the other tips presented here.
ST or T-wave abnormalities are the norm
Atrial flutter is excellent at mimicking ST-depression and ST-elevation. It can also leave the T-wave totally unidentifiable in some leads. This is because flutter waves are relentless and will barrel through everything on a tracing. QRS complexes are relatively large deflections andÂ not easily affected, but ST-segments and T-waves end up being fairly susceptible to distortion. Because of the timing and slope of the F-waves in 2:1 flutter, this most often manifests as apparent ST-depression in the inferior leads. 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).
The presence of atrial flutter should also make you question the diagnosis of STEMI. The two can be present at the same time but it is a pretty rare occurrence and most computer-generated statements of STEMI in the setting of flutter are false-positives. Acute MI can sometimes trigger atrial fibrillation but itâ€™s rather unusual for it to present with new-onset flutter. That said, flutter + STEMI is not impossible, especially if the patient has a history of the former, and if the EKG shows a clear STEMI then itâ€™s a STEMI.
Never trust the computerized interpretation
Itâ€™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. In my experience an incorrect interpretation is the norm. The Mortara VERITAS algorithm is much better at considering the possibility of flutter (though it has plenty of other flaws), but itâ€™s still not perfect.
It just doesn’t look right
When it comes to odd-looking rhythms with very wide complexes, hyperkalemia should always pop into your mind. In the same vein, if you see a tachycardia that just doesnâ€™t look like a typical sinus tach, AVNRT, or AVRT (â€œSVTâ€ if you prefer the vernacular for the latter two), consider atrial flutter.
Turn the beat around
This is probably my favorite trick of the bunch so Iâ€™m not sure why itâ€™s buried so far down the list.
Most people donâ€™t realize this, but disco singer Vicki Sue Robinson was not an actual electrophysiologist. Lacking an MD or DO, her rendition of the hit song â€œTurn the Beat Around,â€ which instructed cardiologists to, â€œturn the beat around, turn it upside-down,â€ still managed to make 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 youâ€™re considering the diagnosis, flip the ECG upside down and look at these leads. Youâ€™ll be amazed how much easier it is to identify the regular F-waves of flutter once theyâ€™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.
Zooming in on the leads with the most clear atrial activityâ€¦
If it’s less than 150 bpm it still might be 2:1 flutter
Many anti-arrhythmic medications (Iâ€™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. This becomes a big concern with the use of class I antiarrhythmics, which have a tendency to slow down the rate ofÂ the flutter circuit without actually breaking the rhythm. 300 /min is too fast for the AV-node to conduct, but slow the atrial rate to 220 /min without also blocking the AV-node and the patientâ€™s ventricular rate can suddenly jump from a rate of 150 bpm with 2:1 conduction to 220 bpm with 1:1 conduction.
A saw-tooth pattern is not necessary to seal the diagnosis
Very few of the EKGâ€™s Iâ€™ve shown so far have demonstrated the clear, classic â€œsaw-toothâ€ pattern that is touted as being representative of atrial flutter. The F-waves of flutter can take a variety of morphologies, but most often the bulk of the wave is negative in the inferior leads and upright in V1. Also, as the atrial rate slows with the use of medications, there is a loss of F-wave amplitude and the morphology can become incredibly subtle. This makes slow atrial flutter, at rates that often causes us to omit flutter from our differential, very difficult to identify.
Thereâ€™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 â€“ MATH! â€“ 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). Itâ€™s minutiae for a diagnosis that probably wonâ€™t change the treatment plan, but who cares about patient outcomes when you can prove to everyone that youâ€™re smarter than them.
F-waves are not exclusive to flutter
If you see what appear to be F-waves at a rate exceeding 350 bpm, theyâ€™re probably â€œf-wavesâ€ 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, 4:1, or 7:1), the QRS complex will typically appear at a regular interval in relation to the F-waves. In fibrillation the QRS will vary its relationship to the f-waves. The morphology of fibrillatory f-waves willÂ often vary as well, sometimes by a very small degree, though I have also seen cases of very regular appearing fibrillatory waves.
Thereâ€™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, this should still present with a fairly fixed relationship between the F-waves and QRS complexes.
Confusing things further, if the rate is less than 250 bpm it may be an entity known as â€œatrial tachycardia.â€ In A-tach you will see distinct P-waves of abnormal morphology at a rate exceeding the normal physiological rate of sinus rhythm, often with similar conduction ratios to a-flutter, except they donâ€™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 theyâ€™re still treated the same acutely.
Read a lot of ECG’s
If youâ€™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 Iâ€™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 some 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 doesnâ€™t fit.
Check out the rest of The 12 Rhythms of Christmas (updated as new posts come out)!