A 'Foolproof' Way to Diagnose Narrow Complex Tachycardias on EKGs

Bruce Jancin, MDedge News

August 19, 2020

A hospitalist looking at an EKG showing a narrow complex tachycardia needs to be able to come up with an accurate diagnosis of the rhythm pronto. And hospitalist Meghan Mary Walsh, MD, MPH, has developed a simple and efficient method for doing so within a minute or two that she's used with great success on the wards and in teaching medical students and residents for nearly a decade.

"You're busy on the wards. You may have a patient who's unstable. You need to make diagnostic decisions very rapidly. And this is a foolproof way to make the correct diagnosis every time," she promised at the virtual annual conference of the Society of Hospital Medicine.

Her method involves asking three questions about the 12-lead EKG:

1. What's the rate?

A narrow complex tachycardia by definition needs to be both narrow and fast, with a QRS complex of less than 0.12 seconds and a heart rate above 100 bpm. Knowing how far above 100 bpm the rate is will help with the differential diagnosis.

2. Is the rhythm regular or irregular?

"If I put the EKG 10 feet away from you, you should still be able to look at it and say the QRS is either systematically marching out – boom, boom, boom – or there is an irregular sea of QRS complexes where the RR intervals are variable and inconsistent," said Dr. Walsh, a hospitalist at the University of Minnesota, Minneapolis, and chief academic officer at Hennepin Healthcare, where she oversees all medical students and residents training in the health system.

This distinction between a regular and irregular rhythm immediately narrows the differential by dividing the diagnostic possibilities into two columns (See chart). She urged her audience to commit the list to memory or keep it handy on their cell phone or in a notebook.

"If it's irregular I'm going down the right column; if it's regular I'm going down the left. And then I'm systematically running the drill," she explained.

3. Are upright p waves present before each QRS complex in leads II and V1?

This information rules out some of the eight items in the differential diagnosis and rules in others.

Narrow Complex Tachycardias With an Irregular Rhythm

There are only three:

Atrial fibrillation: The heart rate is typically 110-160 bpm, although it can occasionally go higher. The rhythm is irregularly irregular: No two RR intervals on the EKG are exactly the same. And there are no p waves.

"If it's faster than 100 bpm, irregularly irregular, and no p waves, the conclusion is very simple: It's AFib," Dr. Walsh said.

Multifocal atrial tachycardia (MAT): The heart rate is generally 100-150 bpm but can sometimes climb to about 180 bpm. The PP, PR, and RR intervals are varied, inconsistent, and don't repeat. Most importantly, there are three or more different p wave morphologies in the same lead. One p wave might look like a tall mountain peak, another could be short and flat, and perhaps the next is big and broad.

MAT often occurs in patients with a structurally abnormal atrium – for example, in the setting of pulmonary hypertension leading to right atrial enlargement, with resultant depolarization occurring all over the atrium.

"Don't confuse MAT with AFib: One has p waves, one does not. Otherwise they can look very similar," she said.

Atrial flutter with variable conduction: A hallmark of this reentrant tachycardia is the atrial flutter waves occurring at about 300 bpm between each QRS complex.

"On board renewal exams, the question is often asked, 'Which leads are the best identifiers of atrial flutter?' And the answer is the inferior leads II, III, and aVF," she said.

Another classic feature of atrial flutter with variable conduction is cluster beating attributable to a varied ventricular response. This results in a repeated pattern of irregular RR intervals: There might be a 2:1 block in AV conduction for several beats, then maybe a 4:1 block for several more, with resultant lengthening of the RR interval, then 3:1, with shortening of RR. This regularly irregular sequence is repeated throughout the EKG.

"Look for a pattern amidst the chaos," the hospitalist advised.

The heart rate might be roughly 150 bpm with a 2:1 block, or 100 bpm with a 3:1 block. The p waves in atrial flutter with variable conduction can be either negatively or positively deflected.

Narrow Complex Tachycardias With a Regular Rhythm

Sinus tachycardia: The heart rate is typically less than 160 bpm, the QRS complexes show a regular pattern, and upright p waves are clearly visible in leads II and V1.

The distinguishing feature of this arrhythmia is the ramping up and ramping down of the heart rate. The tachycardia is typically less than 160 bpm. But the rate doesn't suddenly jump from, say, 70 to140 bpm in a flash while the patient is lying in the hospital bed. A trip to the telemetry room for a look at the telemetry strip will tell the tale: The heart rate will have progressively ramped up from 70, to 80, then 90, then 100, 110, 120, 130, to perhaps 140 bpm. And then it will similarly ramp back down in stages, with the up/down pattern being repeated.

Sinus tachycardia is generally a reflection of underlying significant systemic illness, such as sepsis, hypotension, or anemia.

Atrial tachycardia: The heart rate is generally 100-140 bpm, and p waves are present. But unlike in sinus tachycardia, the patient with atrial tachycardia lying in bed with a heart rate of 140 bpm is not in a state of profound neurohormonal activation and is not all that sick.

Another diagnostic clue is provided by a look at the telemonitoring strip. Unlike in sinus tachycardia, where the heart rate ramps up and then back down repeatedly, in atrial tachycardia the heart rate very quickly ramps up in stages to, say, 140 bpm, and then hangs there.

Atrial flutter: This is the only narrow complex tachycardia that appears in both the regular and irregular rhythm columns. It belongs in the irregular rhythm column when there is variable conduction and cluster beating, with a regularly irregular pattern of RR intervals. In contrast, when atrial flutter is in the regular rhythm column, it's because the atrioventricular node is steadily conducting the atrial depolarizations at a rate of about 300 bpm. So there's no cluster beating. As in atrial flutter with variable conduction, the flutter waves are visible most often in leads II, III, and aVF, where they can be either positively or negatively deflected.

AV reentrant tachycardias: These reentrant tachycardias can take two forms. In atrioventricular nodal reentrant tachycardia (AVnRT), the aberrant pathway is found entirely within the AV node, whereas in atrioventricular reentrant tachycardia (AVRT) the aberrant pathway is found outside the AV node. AVnRT is more common than AVRT. As in atrial flutter, there is no ramp up in heart rate. Patients will be lying in their hospital bed with a heart rate of, say, 80 bpm, and then suddenly it jumps to 180, 200, or even as high as 240 bpm "almost in a split second," Dr. Walsh said.

No other narrow complex tachycardia reaches so high a heart rate. In both of these reentrant tachycardias the p waves are often buried in the QRS complex and can be tough to see. It's very difficult to differentiate AVnRT from AVRT except by an electrophysiologic study.

Accelerated junctional tachycardia: This is most commonly the slowest of the narrow complex tachycardias, with a heart rate of less than 120 bpm.

"In the case of accelerated junctional tachycardia, think slow, think 'regular,' think of a rate often just over 100, usually with p waves after the QRS that are inverted because there's retrograde conduction," she advised.

She reported having no financial conflicts of interest regarding her presentation.

This article originally appeared in The Hospitalist, an official publication of the Society of Hospital Medicine.


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