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Wednesday, 29 January 2014

Spring 2 - Can we trust our machine analyses?


'Keeping  ECGs Simple' is an educational blog which runs alongside Twitter.

A new ECG case "quizz" is launched most Wednesday evenings in term time, via @ecgclass, and a conversation/discussion around the case evolves on #ECGclass during the course of the evening. Don't forget the follow the hashtag for the updates during the course of the evening!

Each term will be divided into 5 'classes' or 'cases' to discuss:



Cases are generally aimed at Primary Care.  All scenarios are completely fictitious, but based on commonly occurring presentations in General Practice. 
This is an educational site, intended for healthcare professionals and shouldn't be construed as patient advice. 

Please use the Hashtag #ECGclass on Twitter, if you want to ask the patient any questions, or request any further investigations. Alternatively, please join in discussion and leave comments below.

Remember there are no right or wrong answers!  

ECG interpretation is often open to debate, and will usually evolve and change as new information becomes available.  Everyone's opinion is valid, and useful for others, as the evolution process takes place.  Together we will try and form an interpretation based on the trace, and information, we have in front of us.  Don't worry if you disagree - shout up and share your thoughts - the diagnosis is often arguable on the basis of a 12 lead trace, and may only become more obvious when a longer rhythm strip is available. 

Please feel free to join in, but most important of all, have fun! :-)


Today we're doing a confidence test. Will you challenge your ECG machine?

It's Saturday morning and your Practice flu-clinic is in full swing. 
Your practice nurses recently went on a course which suggested to them the importance of screening for AF in the wll over 65yr olds. As such they have been checking for 'irregular pulses' with each flu-jab given.  Five asymmtomatic people are invited back, the following week for an ECG

Let's look the recordings, one by one.
Assuming they all each fulfil the CHA2DS2-Vasc criteria for treatment, and have no contraindications, who are you going to initiate on anticoagulation and rate control?


The machine says this is AF.
Is it?


 Not AF - Ignore your machine - P waves are clearly visible.

 Study the rhythm strip...

P waves are clearly visible, but don't have a consistent relationship to the QRS. i.e. The PR interval is variable
The Rhythm is irregular. 
Starting with the 3rd complex on long lead II: This QRS complex is preceded by a P wave, but the PR interval is prolonged (>5 small squares). 
The following complex has an even longer PR interval. 
The P wave of the subsequent complex is so premature that it is lost in the previous T wave. (Note the distorted shape of T wave). 
This series of 4 complexes is then followed by a pause, before the cycle repeats itself. 

It's a bit tricky without a longer rhythm strip, but on this 12 lead, it looks like Mobitz Type 1, second degree Heart Block - Wenckebach

Features of Wenckebach:
  • P-R interval progressively lengthens until P waves fails to conduct
  • P-R interval then resets to normal
  • The R-R interval progressively shortens
  • Cycle repeats
  • Usually benign - Observe, check medications. (The patient above actually required pacing - symptomatic during prolonged pauses on 24hr ECG)


a.   Is this AF?
b.   If not, what it is?


2a). This is Not Sinus Rhythm - Ignore your machine! 
Neither has this patient got ventricular trigeminy, multifocal extrasystoles (that's bizarre pattern in the rhythm strip is probably movement artefact - seen in a limb lead but not mirrored in the chest leads), nor a short PR interval (un-measureable without P waves).

2b). Can you see P-waves? 
If you are ever uncertain about P waves, look carefully at V1 and V2 - these are the two leads in which P waves are usually best seen. 
I can't see them on this ECG. 
The rhythm is irregularly irregular. You guessed it. This is barn door AF - missed by the machine. 


a.  Is this AF?
b.  If not, what it is?


Now this is a bit more tricky. You definitely need an element of suspicion, and a piece of paper to map the complexes here. 

This is infact atrial flutter with variable atrioventricular conduction, with cycles of both 2:1 and 3:1 AV conduction being present.
The flutter waves are positive in II, III and aVF which suggests that this may be a “clockwise” atrial flutter. The flutter cycle length is close to 200 msec, and the flutter waves can be seen lining up close to each major grid line in lead V1.

The patient should be anticoagulated and considered for atrial flutter ablation.

An ECG rhythm strip with carotid sinus massage or adenosine could be used to confirm the presence of flutter non-invasively when there is doubt.

The LVH suggestion is also believable (voltage criteria met in Lead I, and possibly aVL - see earlier blog on LVH).


a.   Is this AF
b.   If not, what it is?


4a). This is NOT AF.  

4b) This ECG as seen, may well be Multifocal Atrial Tachycardia, ideally we need a longer rhythm strip to help sort it out. (Read on below for more detail on MAT, or skip to Case 5)

Like many of you, when I first looked at this ECG, I was quite confused. It's not an easy one.  
The machine's 'AF diagnosis' made me question myself. 
It is clearly irregularly-irregular, with no fixed pattern, but there are some very clear P-waves which seem appropriately associated with a normal QRS complex....
I considered an altering PR interval, perhaps Wenckebach, but just wasn't happy with any of my thoughts. 

To make it worse, we asked the patient how she felt (crazy thing to do, I know…;)) - she admitted that the previous night, she had an episode when she felt quite light headed, dizzy with a short burst of palpitations.

If we look at the lead II rhythm strip only:

The 1st QRS seen, looks quite normal, and is preceded by a normal looking P wave. 

The 4th and 6th complexes, likewise, look normal. 
The 2nd complex, certainly looks like an atrial ectopic.
The 5th complex looks like and atrial escape beat (kicking in to compensate after a long pause)
The 8th complex is a nodal ectopic (identified by the inverted preceding p-wave)

So, on this ECG alone, we can see lots of different patterns of atrial activity. 

This could be something called Multifocal atrial tachycardia. 
This is often seen in people with poor lung function, such as severe COPD. 

Multifocal Atrial Tachycardia is characterised by an irregular atrial rate greater than 100 beats per minute, with at least 3 morphologically distinct P waves and irregular P-P intervals.  
It is often short-lived and self-limiting. 
Any underlying condition, such as respiratory failure is the mainstay of treatment. Rate control is not important, and may in fact make her feel less well. 

 I feel this rhythm strip is inadequate, so on this lady I requested a longer lead II strip:

Does this help?

It doesn't help enormously.  

It does however show more 'normal' P waves, and more frequently associated with a normal QRS complex. 
Also, as she has relaxed in the waiting room, her rate has come down, so it's no longer an atrial tachycadia - multifocal, or otherwise. 

But sometimes, a long rhythm strip just isn't long enough.

So, lets see a bit more….

This just goes to show how helpful rhythm strips can be if you wait long enough!

We can now see, at last, a background rhythm. 

The first two beats are sinus beats, followed by an atrial ectopic. 
This pattern then repeats. 
This is NOW a clear Atrial trigeminy rhythm. 

Now we have the benefit of this knowledge, we can more confidently assume that the previous strips seen, just represent a mixture of atrial ectopic activity. 

There is frequent premature atrial activity, but whenever there is a prolonged pause, an atrial escape beat (compensatory beat) kicks in. 
The rest of the time she's in Atrial bigeminy. 

This doesn't need any further action or treatment. She's well in herself and can be reassured that this is often seen in her age group. 

However, patients with this kind of rhythm, do have a higher tendency to progress into AF in the future. So it's wise to remain vigilant. 

The main learning point here is - once again - REMEMBER TO IGNORE your ECG machine's interpretation! 

Had the clinician here just glanced at the report, and not the trace, an unnecessary referral - and possibly inappropriate treatment - may have been initiated.


a.  Is this AF
b.  If not, what it is?


YES!!  This is AF.  Just popped in to remind you how straight forward it is to spot AF! 

So why can't the machines be as reliable as you? 
Switch off the machine analysis and start looking at ECG's yourself. ;-)

Well done everyone. Shall we have a quick and easy one next week?

(Collapses with exhaustion)

Thank you all once again, for your fun and input on Twitter.


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