Sorry for not posting much lately, folks! I guess I’ve just been too busy…! Anyway, hope you like this one. It was brought to me by a colleague who thought I might enjoy it. He was perfectly right about that!
The patient: Elderly male, admitted to the CCU for near syncopes and episodic dizziness. He had a known atrial flutter, and was using betablockers and flecainide. I’m afraid I do not have the full list here, nor the dosages. He was sleeping when this episode occured and didn’t notice anything. He also did not pass out.
EKG description: This is atrial flutter (type 1, counter-clockwise) at approx. 260 bpm, with a high and quite varied degree of atrioventricular block. The lowest F-wave/QRS ratio in the top strip, is 4:1, resulting in a ventricular rate of around 65 bpm. Medications might play a part here, but one would suspect the ratio to be lower at this atrial rate. The long blocked period shows ventricular standstill that lasts for almost 6 seconds. This is of course the reason for his episodic dizziness and near syncopes (I’m surprised he didn’t syncope completely). In the lower strip, the blocked periods get even longer, practically resulting in ventricular standstill. With such persisting absence of AV conduction, normally one would expect a ventricular ectopic focus to take over. This however, did not happen here.
Conclusively, this is atrial flutter with a high-degree atrioventricular block and intermittent episodes ventricular standstill. The patophysiology behind this could be AV-node tissue degeneration over time, leading to progressively increasing level of block.
December 16, 2009
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Patient: Woman, 51 y/o. Mitral valve replacement 21 years ago. Known paroxysmal atrial fibrillation. Presents in the ER with nausea, pale skin, mild diaphoresis, palpitations and diffuse chest pain.
Prehospital ECG:
- Supraventricular tachycardia
- Ventricular rate is ca. 120 bpm
- Normal axis at ca. 10°
- Atrial activity best visible in lead V1, showing P waves with a slightly varying and prolonged PR interval.
- Several P waves superimposed and partially hidden in T waves
- Pseudo R waves in lead V1
Interpretation: This faxed ECG shows a supraventricular tachycardia, but right precordial lead V1 shows clear atrial activity. The small, peaked P waves with a slightly changing and prolonged PR interval suggests atrial ectopy. Ectopic Atrial Tachycardia rarely occurs with 1:1 ratio, as the AV node usually blocks half or more of the impulses. A common AV block ratio is 2:1. With a ventricular rate of 120 bpm, a 2:1 AV block would indicate an atrial rate of 240 bpm. This would be a typical atrial rate for ectopic atrial tachycardia. Using a ruler or a caliper and measuring from one of the visible P waves here, we will see exactly that: P waves appear at a rate of 240 bpm. The most visible P waves are right after or superimposed on T waves, and the others are hidden in or appearing right after each QRS, creating what looks like a small S wave, a pseudo S wave.
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To confirm the diagnosis, carotid pressure is applied while a rhythm strip is recorded. Paper speed is set to 50 mm/s in order to discern P waves more easily. When pressure is applied, a larger AV block is induced and 3:1 periods occur intermittently. During these blocks, clearly discernable P waves are seen in the right precordial leads. The P waves show atrial ectopic activity at a rate of 240 bpm, just as we suspected from the previous ECG. By marching out the P waves with a caliper, we’ll see that every other P wave gets completely or partially hidden in the QRS complexes when the ratio changes back to 2:1.
May 17, 2009
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Patient: Woman, 70 y/o. Congestive Heart Failure. 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 approx. 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 EKG shows an Ectopic Atrial Tachycardia (EAT) with variable degree of AV Conduction, and was in the clinical setting mistaken for atrial flutter when the patient was presented in the ER. 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 however, be dangerous for the patient. The pitfall is that paradoxically, atrial flutter is treated with digitalis, which again induces EAT. Which means that if EAT is being mistakenly treated with digitalis, the arrhythmia will be sustained, as well as the degree of AV block could be increased. This will 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 EAT is, of course to remove the digitalis intoxication.
Differentiating Ectopic Atrial Tachycardia and Atrial Flutter
The reason that EAT is often mistaken for atrial flutter, is because of the multiple P waves. Depending on their axis and morphology, they can for the untrained eye 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 EKG. If you understand the underlying electrophysiologic mechanisms of atrial flutter, differentiating it on a surface EKG 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
- 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 counterclockwisely in a circular fashion usually within the right atria, flutter waves are created on the EKG. 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.
- Seldom coexist with ectopic atrial tachycardia in the same patient
Ectopic Atrial Tachycardia with block
- Is characterized by a rapid and regular atrial rhythm at rates from 150 to 250 bpm
- 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. 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 dysmorph, 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.
- Often occurs due to digitalis intoxication
Cherchez le P!
The above are the famous words by EKG master Henry J. L. Marriott, and 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 especially pointed out that one must look for P waves buried in T waves. In both premature contractions, like for instance a PAC, and in other conditions, P waves can get buried in both the preceding T wave, in the QRS and practically anywhere. And as we will see with this EKG, 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. These are however, 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 retrograd P waves shortly after ventricular depolarization. Also, you will note that:
- The baseline is perfectly isoelectric between each P’ wave, ruling out the macro reentry 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 MAT (Multifocal Atrial Tachycardia), there are not multiple ectopic foci here. The P wave configuration is constant and unimorph throughout the leads.
February 3, 2009