In this article, the author describes the creation of “The ECG Blog: Your PQRST-Needs Satisfied,” found at "ecgblog.wordpress.com,” and provides an interesting case study of differentiating ectopic atrial tachycardia from atrial flutter on ECG.

Background

I work as an ER nurse in the emergency department of Stavanger University Hospital, a large regional hospital in Norway. Although obtaining ECGs is a natural part of any ER nurse’s job, it is generally not expected that Norwegian nurses have any interpretive skills whatsoever. Some of course do, but most have gained their wisdom from work practice and self studies. ECG is hardly taught at all in nursing schools, unless one specializes within cardiac care nursing, intensive care nursing or within prehospital services. Even then, it is taught at a very basic level.

When I graduated as a nurse, those pink paper strips all looked the same to me. They reminded me of seismographic recordings or lie detector prints that I had seen on television: randomly scribbled lines, humps and bumps. Whenever I obtained an ECG and had the MD confirm it, I always thought it was amazing how these doodles could contain so much information about the patient’s heart and condition. Luckily, I’ve always felt the need to understand the things I do in order to do them well. That is why I quickly decided and felt obliged to learn the basic concepts of ECG interpretation. Working at the bedside of a patient is a great responsibility, and I felt unsafe not being able to read an ECG. Even though it is the doctor’s responsibility to confirm every ECG, I think it is very important that nurses know how to respond on the ECG that they’ve obtained from their patient.

I’ve had no formal ECG education; I’ve learned ECG interpretation by studying books as well as ECGs that I had xeroxed at work. I started this interest early in late 2006. While my enthusiasm was constantly growing, I became more and more frustrated that there were so few like-minded souls to exchange ideas with, learn from and discuss with. In order not to stagnate and to keep learning, I started searching the Internet for discussion groups, forums and sites where I could meet people who shared my interest for 12-lead interpretation. My first search on Google was for “ECG forum,” and the top result that was displayed was the forum for East Coast Guitars! I was disappointed and on the brim of disillusionment.

Creation of The ECG Blog

Even though there are a lot of Internet resources on electrocardiography and arrhythmia interpretation, I was struck by the fact that were so few sites that were open for discussion among their readers. What I needed was an arena where I could meet and discuss with fellow enthusiasts. I couldn’t find any forums or blogs that were completely dedicated to ECG interpretation that allowed discussions and comments. There was only one thing to do to fill this gap, so in October of 2008, I started The ECG Blog.

A blog is a good medium for presenting and discussing ECGs. First of all, most blog providers offer free hosting and several gigabytes of storage. This means that a large amount of high-resolution ECGs can be stored and presented. Threaded discussions allow users to comment and discuss each case. Additionally, maintaining a blog requires minimal skills, and the publishing is done with a few easy mouse clicks.

Every ECG is posted in high resolution, which allows the user to see things in full detail. Many Internet sites only provide low-resolution images, which makes it sometimes impossible to see and look for the details that often tip the diagnosis in the right direction. Even more important is that an ECG should always be interpreted in light of the patient if possible. Therefore, I present every ECG along with all the available clinical information and anamnesis.

The blog’s main focus is 12-lead interpretation, but telemetry strips or prehospital 3-lead strips are also sometimes presented. All ECGs are from my own private collection, which consists of several hundred ECGs. Every case is first presented with an ECG that is described in detail, followed by a thorough interpretation that walks the reader through every part of the ECG. All relevant differential diagnoses are discussed and ruled out systematically, so that the reader learns how to differentiate arrhythmias from one another. I want the reader to fully understand and not only accept the final diagnosis. So far the blog has been a success; since the start in October 2008, I´ve had a total of 15,000 unique hits from all over the world.

Case Presentation

The following is a case of ectopic atrial tachycardia (EAT) with variable atrio-ventricular block that shows how a case typically is presented in the blog. While perhaps obvious for the experienced interpreter, this is still an interesting case that shows the importance of investigating the details of each lead, as well as understanding the mechanisms of each arrhythmia. The ECG is recorded at 50 mm/s, 10mm/mV. This particular case shows how to differentiate EAT from atrial flutter. (Figures 1 and 2)

Patient Description:

The patient is a 70-year-old female with congestive heart failure who is currently using digitalis.

ECG Description:

• Narrow complex tachycardia of supraventricular origin.

• Variable ventricular rate. Rate varies from 73-105 bpm.

• Right axis deviation. Cardiac axis is at approximately 150°.

• Multiple P’ waves. Atrial rate is 210 bpm.

• Varying AV block. P:QRS ratio ranging from 1:1 to 3:1.

• Ectopic P’ waves, inverted in inferior leads II, III, aVF. P waves superimposed on QRS complexes.

• Prominent Q waves in inferior leads, II, III, aVF.

• T wave inversion in inferior leads, II, III, aVF.

ECG Comments:

This ECG shows an ectopic atrial tachycardia with variable degree of AV conduction. The ECG reading was mistaken as atrial flutter when the patient was presented in the ER. This is a common mistake to make, as atrial flutter is probably the arrhythmia that resembles EAT the most electrocardiographically. Atrial flutter is a common differential diagnosis with EAT, but making the wrong diagnosis here can be dangerous for the patient. The pitfall is that paradoxically, atrial flutter is treated with digitalis, which again induces EAT. This means that if EAT is being mistakenly treated with digitalis, the arrhythmia will be sustained, and the degree of AV block could be increased. This would be like adding fuel to a fire! Untreated EAT with block can at some point compromise the patient’s cardiac output and result in hemodynamic unstability. The treatment for digitalis-induced EAT is, of course, to stop the digitalis treatment of the patient.

Differentiating Atrial Flutter and Ectopic Atrial Tachycardia

The reason that EAT is often mistaken for atrial flutter is because of the multiple P waves. Depending on their axis and morphology, for the untrained eye, they can easily resemble flutter waves (F waves). Also, if one suspects an atypical flutter pattern, one might think that the P waves are due to flutter activity. However, the key is to understand the electrophysiology behind the two mechanisms and how they will appear on a surface ECG. If you understand the underlying electrophysiologic mechanisms of atrial flutter, differentiating it on a surface ECG is much easier. Also, by examining both the P waves and the baseline of the different leads, the correct diagnosis will be easily within reach in most cases.

Atrial Flutter:

• Atrial flutter is characterized by a rapid and regular atrial rhythm at rates from 250 to 400 bpm.

• Due to the macroreentry mechanism of atrial flutter, where an ectopic impulse travels counterclockwise in a circular fashion usually within the right atria, flutter waves are created on the ECG. When the impulse has travelled a full circle, it reactivates the same focus again, creating a reentry loop mechanism. Thus, where one F-wave ends, the next one arises immediately. Several F waves together makes out the hallmark saw tooth baseline.

• Flutter waves (F waves) and the saw tooth pattern are best seen in the inferior leads, II, III and aVF. Sometimes, F waves are more clearly visible in lead V1.

• Atrial flutter seldom coexists with ectopic atrial tachycardia in the same patient.

Ectopic Atrial Tachycardia with Block:

• EAT with block is characterized by a rapid and regular atrial rhythm at rates from 150 to 250 bpm.

• It has abnormal P (or P’) waves whose morphology is different from that of the sinus P waves. P waves are often inverted in inferior leads (II, III, aVF) if the ectopic focus sits distally in the atria.

• Has isoelectric intervals between P waves in all leads.

• When atrial rates become fast, the AV node usually blocks signals. EAT never occurs with first-degree AV block; it always presents with second-degree or third-degree AV blocks. Wenckebach conduction can also occur.

• P waves are often difficult to spot, as they are often small and dysmorphic, and often get buried in or superimposed on the QRS complex. Lead II is often difficult to use, while lead V1 is often a good lead for discerning P waves.

• EAT often occurs due to digitalis intoxication.

Cherchez le P!

The above are the famous words by ECG master Henry J.L. Marriott; it is french for “Look for the P!” What Marriott meant was that finding and evaluating the P waves is the key to understanding and diagnosing arrhythmias. Marriott also pointed out that one must especially look for P waves buried in T waves. In both premature contractions (PAC) and in other conditions, P waves can get buried in both the preceding T wave, in the QRS and practically anywhere. As we will see with this ECG, spotting P waves is what pinpoints the diagnosis.

The rhythm is obviously supraventricular, as QRS complexes are within the normal range (<120 ms). There are multiple, small P waves before many of the QRS complexes. The P:QRS ratio varies from 3:1 in the longest cycles, to what seems like 1:1 in the shortest cycles. However, the latter is actually 2:1. When examining the QRS complexes, there are P waves buried in the QRS complex. The buried P waves appear at the end of the QRS, and are best seen in leads V2-V5, as they create a pseudo S wave at the end of each QRS. By marching out the P waves with a caliper, the buried P waves are easy to spot. With this in mind, and knowing that first-degree AV block doesn’t occur with EAT, we will conclude that where AV block ratio seemed to be 1:1, the block is really 2:1. This means that in those cycles, there are actually two P waves for each QRS, but the second P wave is buried in the QRS itself. However, these are not sinus P waves. They are deflections from an ectopic atrial focus, and should therefore be referred to as P’ waves, which is the correct labelling for ectopic P waves.

By measuring the P’P’ interval, the atrial rate is constant and regular at 210 bpm. In the 2:1 block cycles, the ventricular rate is 105 bpm. The ventricular rate is half the atrial rate, which correlates with a 2:1 block. Now, remembering what Dr. Marriott preached, when examining the T waves, there are clearly P waves buried in their humps. This is best seen in lead V3, where T wave morphology changes throughout the lead. The extra peaks and bumps on the T waves are actually buried P’ waves. If these were not observed, this rhythm could be mistaken for an AV nodal reentry tachycardia, as there would be no P waves preceding the QRS, with seemingly retrograde P waves shortly after ventricular depolarization. Also, you will note that:

• The baseline is perfectly isoelectric between each P’ wave, ruling out the macroreentry impulse rotation mechanism of atrial flutter.

• In inferior leads II, III and aVF, the P’ waves are inverted as the P wave axis is shifted superiorly. This indicates a low atrial focus and is a common sign of atrial ectopy. This again rules out atrial flutter, which would produce F-waves in the same leads.

• Unlike multifocal atrial tachycardia (MAT), there are not multiple ectopic foci here. The P wave configuration is constant and unimorph throughout the leads.

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