Filed under: Tachyarrhythmia
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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
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Patient: Woman, 69 y/o with no significant medical history. Presented in the ER with grave sepsis due to unknown focus of infection. Rectal temperature is 40.5°C, BP 170/100, pulse irregular at ca. 150 bpm, SAT 93 % w/O2 3 l/min, RF >50/min, peripher cyanosis, lip cyanosis, marmorated skin over the abdomen and thorax, serum glucosis 8.7. Arterial blood gas analysis showed a minor electrolyte imbalance and a respiratory alcalosis.
ECG interpretation: Multifocal / Chaotic Atrial Tachycardia with Variable Degree of AV Block, incomplete RBBB and Left Ventricular Hypertrophy
ECG description:
- Supraventricular Tachycardia / Narrow Complex Tachycardia
- Atrial ectopic rhythm with highly irregular rate
- Incomplete Right Bundle Branch Block (QRS 120ms)
- Varying P wave morphology and axis. Three or more morphologically distinct P’ waves in the same lead.
- Variable AV Block. P:QRS ratio ranges from 1:1 to 2:1. Several P’ waves buried in QRS complexes.
- Probable Left Ventricular Hypertrophy from Sokolow’s Criteria (RV5 + SV2 >35mm)
Note that there is a:
- Highly varying PP interval, which is due to a varying atrial rate. Mean A-rate is around 135 bpm
- Highly varying RR interval, which is due to a varying ventricular rate. Mean V-rate is around 150 bpm
- Highly varying PR interval, which is due to varying ectopic atrial foci.
- Isoelectric baseline between every ectopic P’ wave.
- No obvious dominant atrial pacemaker, ruling out sinus rhythm with multiple PACs.
Further observations:
- Cardiac axis pointing downwards at approx 90°
- Probable Left Ventricular Hypertrophy according to Sokolow-Lyon Index
- T wave inversion in leads V1-V3
Measured intervals, counting from the first (leftmost) P wave:
- PP (millimetres): 18, 22, 24, 19, 26, 12, 28, 18.5, 17.5, 22, 18
- PR (milliseconds): 80, 100, 80, 65, 100, 60, 70, 115, 120, 115, 80, 65
- RR (millimetres): 19. 21.5, 23.5, 20, 24, 18, 28, 19, 19.5, 19, 18
- All intervals are irregularly irregular.
Multifocal Atrial Tachycardia (MAT)
Term: MAT is also known as chaotic atrial tachycardia, and describes rapid firing of several ectopic atrial foci at a rate faster than 100 bpm.
Occurrence: MAT is often associated with COPD or CHF , but can also occur in the presence of hypokalemia, hypomagnesemia, hypoxia, acute myocardial infarction and mitral stenosis.The condition usually occurs in seriously ill patients, mostly elderly people.
Mechanism: Characterized by P waves of varying morphology, assuming that distinct P waves originate from ectopic atrial foci. The ectopic P waves may be called P’ (P Prime). Due to different automaticity foci, both P wave morphology and axis will vary. The PR interval will also vary, depending on the proximity of each atrial focus to the AV node and the prematurity of each ectopic impulse. Some P waves may be nonconducted, and some may be aberrantly conducted if they get conducted into the ventricles while they are still partially refractory. MAT is often preceded or followed by frequent PACs, sinus tachycardia, AF, A-flutter, ectopic AT or PAT. Compared to WAP (Wandering Atrial Pacemaker), the ecg findings and rhythm characteristics are the same, but in MAT the atrial rate is higher.
ECG characteristics: 1) Three or more morphologically distinct P waves in the same lead. 2) The absence of one dominant atrial pacemaker, in disctinction to sinus rhythm with multiple premature atrial complexes. 3) An isoelectric baseline. 4) Varying PP, PR and RR intervals. Ventricular rate is usually 100 to 150 bpm.
Ladder diagram for lead V1 (click to view larger)
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Ladder diagram description: The ladder diagram shows ectopic atrial foci firing at varying rate and with varying proximity to the AV Node, resulting in varying PR intervals and varying ventricular rate (RR intervals).
January 5, 2009
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Patient: Ca. 70 y/o woman with long history of paroxysmal atrial fibrillation, that has been successfully electroconverted earlier. She presents in the ER with a fresh onset of atrial fibrillation, with palpitations and dyspnea.
ECG description:
- Atrial fibrillation with a ventricular rate of 130-170 bpm
- Three premature beats
- Axis normal, at ca. 30°
- Probable LVH due to Sokolow Criteria (S in V2 + R in V5 > 35mm)
ECG interpretation: Paroxysmal atrial fibrillation with rapid ventricular response. Three premature beats, the first one (5th beat) probably representing the Ashman Phenomenon, from matching the Fisch Criteria. Probable LVH due to Sokolow criteria.
Premature Beats during Atrial Fibrillation
Atrial fibrillation makes it difficult to differentiate wide QRS complexes. During atrial fibrillation, what looks like a normal VPB could easily be a supraventricular impulse that is conducted aberrantly through the ventricles. Normally, it is uncomplicated to distinguish a ventricular beat from a supraventricular beat. In normal sinus rhythm, the lack of a preceding p wave would indicate that the broad pattern is due to a ventricular premature beat. In AF, this clue is lost. Also, ventricular aberrancy often occurs in AF because of the varying cycle lenghts. Ashman phenomenon is an aberrant ventricular conduction due to a change in QRS cycle length. The Ashman Phenomenon can cause diagnostic confusion, as such beats can easily be mistaken for VPBs. Understanding the Ashman Phenomenon and aberrant conduction is useful in order to differentiate between wide complex arrhythmias and supraventricular arrhythmias with aberration. Being able to differentiate such premature beats can be critical, because a run of aberrantly conducted supraventricular beats may look like ventricular tachycardia, and the treatment of these two conditions is different. Typically, a premature beat that terminates a short cycle after a long cycle, tends to be aberrantly conducted.
Aberrant Ventricular Conduction
Aberrant ventricular conduction means an intraventricular conduction delay that appears with changes in the heart frequency. This is a reversible phenomenon, that both arises and terminates with changes in heart rate. Aberrant ventricular conduction occurs because of differences in refractory times of the right and the left branch of the His-Bundle. Therefore, a supraventricular impulse can get conducted from the atria to the ventricles at a time when one of the branches has just completed its refractory period, while the other is still refractory. The still refractory branch will act as if it is blocked, and the result is a situation not unlike the usual bundle branch block (BBB). Due this intermittent “block”, the QRS complex will be splitted and broadened as with a bundle branch block.
The duration of the refractory time varies with the length of the preceding RR interval. The longer the preceding RR interval, which means the slower the heart frequency is, the longer the refractory time of the bundle branches gets. Also, the longer the preceding RR interval, often the larger the difference in refractory times of the left and the right bundle gets.
Often, the combination of a long RR interval and then a following short interval to the premature beat, will lead to aberrant ventricular conduction, the so called Ashman Phenomenon.
The Ashman Criteria
Cycle lengths are the classic way to point out Ashman Beats. The classic Ashman Beat is a a wide, premature beat that terminates a short cycle after a long cycle. The Ashman Criteria is commonly described as:
A wide QRS that terminates the short cycle that follows a long cycle.
The problem with this criteria is that it does not prove that the beat is aberrantly conducted. Because when a beat terminates a short RR interval that follows a long RR interval, a VPB could just as easily have occured in the same spot. Depending on only cycle lenghts in differentiation of aberration from VPBs is also unreliable method due to another reason: Let´s say that a bigeminy pattern occurs. Then a relatively long RR interval will be followed by a short interval, which then is terminated by the bigeminy beat. Therefore, a long preceding cycle can occur in both aberration and ectopy, and it cannot be used with certainty to differentiate Ashman Beats from VPBs.
Fisch Criteria
There are several other explanations on how to distinguish Ashman Beats from VPBs. One of the most common approaches is the Fisch Criteria:
- Relatively long cycle (RR interval) followed by a short cycle (RR interval), terminated by a broad QRS complex. A short-long-short interval is even more likely to initiate aberration. The QRS complex can imitate both LBBB and RBBB, even in the same ECG.
- RBBB-form aberrancy with normal orientation of the initial QRS vector. The initial part of the QRS looks like the other normally conducted beats. Also, concealed perpetuation of aberration is possible, such that a series of wide QRS supraventricular beats is possible.
- Irregular coupling interval of aberrant QRS complexes. The coupling interval is the interval between the premature QRS complex and the normal beat before. This interval can be constant or varying througout the ECG.
- Lack of a fully compensatory pause.
December 21, 2008