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Wednesday, 17 April 2013

18 Intelligent Comments about any ECG - #ECGclass 28

Good evening and welcome back, to old and newcomers alike!
Hope you all enjoyed a relaxing Easter Break. :-)

Given the time of year, I thought we'd work through systematic ECG interpretation tonight - as if we would for our medical student finals......yikes.  
Good luck to all those out there doing exams this term!

As always, if you decide to join in on Twitter,  don't forget to use the hashtag #ECGclass in your replies, so that others can follow the thread and thought evolution process. 

For the benefit of newcomers, here's the usual spiel:

#ECG Class is an educational blog which runs alongside Twitter.
A new ECG "quizz" is launched most Wednesday evenings, in term time. 

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! :-)

#ECGclass Case 28

OK, so here's the ECG we're going to systematically work through. (Apologies, if some of this seems too basic for you.) Today's class is about method and logic.

I don't know what the history is here, but lets imagine this ECG was done on a 60yr old man, without any symptoms. When he attended for his routine flu jab, the diligent nurse (who was screening for AF) noted his irregular pulse and duly arranged the ECG:

 Always STATE the obvious and simply describe what you see. 

Start by diving the ECG up into the  following 6 considerations. 
Each has 3 points to think about, and state: 

  • The Technicalities.

So lets start the ball rolling by stating a couple of facts to the examiner.  This is so easy, and will serve to limber you up.  
You've been handed a bit of paper. What does it show? 

  1.  Electrical activity is seen (important to state, as not seen in asystole!)
  2.  This particular trace shows a standard 12 lead ECG, with a long lead II rhythm strip.
  3.  The trace is calibrated with standard paper speed of 25mm/sec and a gain of 1cm=1mV

Bingo!  3 points already in the bag, and you've started the ball rolling.  ;-)
Now think about the various components of the ECG, and consider each one in turn:

  • Rate and Rhythm.  (use the long lead II strip)

  1. Is it regular, or irregular? (look at the atrial and ventricular rhythms separately).  If it is irregular,   is it irregularly irregular or regularly irregular? 
  2. What is the atrial rate? 
  3. What is the ventricular rate?

  • P Waves 

  1. Are P waves present?
  2. What is their appearance? i.e Are they morphologically normal? Describe the shape & size and  comment on the normal intervals. (Remember, because of the orientation, the P wave morphology is usually best seen in the V1 and V2 chest leads). Finally,Are they consistent in appearance?
  3. Relationship to QRS. Is there a P wave associated with every QRS complex? 

  • QRS Complex.
  1. Are QRS complexes present?
  2. Are they normal in appearance/morphology, and is their shape consistent in appearance within  each lead view?
  3. What is the QRS cardiac axis? (Only possible on 12 lead ECGs)

  • T waves and ST segment.

  1. Are T waves present?
  2. How would you describe them (shape, size) in each lead?
  3. For each lead view, describe the orientation of the T waves and whether the ST segment is isoelectric; or depressed or elevated in any lead?

  • Intervals (Durations)

  1.  What is the PR interval. Is it normal and is it consistent?
  2.  What is the QT interval? Is it normal?
  3.  What is the duration of the QRS complex?  Is it normal? (determines whether or not there is any conduction delay). 

There you have it. 
18 intelligent statements you can make about any ECG, without even coming up with a diagnosis. 


ECG Technicalities.  

  1. Trace shows electrical activity
  2. This is a 12 lead ECG, with a long lead II rhythm strip
  3. The ECG is of standard paper speed and calibrated to a gain on 1cm=1mV

Rhythm and Rhythm.
  1. It looks irregular doesn't it. It is in fact, regularly, irregular. (If you missed this, we'll come back to it in a moment).
  2. The background atrial rate = 75 bpm (Choose any two consecutive but normal looking complexes, and divide 300 by number large squares between the P waves)
  3. The background ventricular rate is the same.

  1. Yes, P waves are seen.
  2. Yes, they are morphologically normal. i.e. they are small, domed and rounded with a height of  <3mm, and a duration of 2-3 small squares (0.08 - 0.11 seconds). But, are they all the same? Not quite. There are occasional P waves which look slightly smaller than the rest (Note the ones before the 3rd, 7th and 11th QRS complexes on the long lead II). 
  3. Yes. There appears to be a P wave before every QRS. 

QRS complex.
  1. Yes. QRS complexes are present.  
  2. They appear consistent in   size and shape within each lead.  The morphology is appropriately  narrow, with a duration of  less than 3 small squares (i.e. < 0.11 seconds).
  3. To 'eyeball it', the axis on this ECG, it is between 0 and -30 degrees (i.e. slightly leftward, but within normal limits). You are allowed to +/- 15 degrees to this rough estimate.  So we could estimate more accurately at -15 degrees. Here's My noddy guide to axis calculation if you need it. (For the more geeky out there it is more accurately around -19 degrees on the above ECG)

T waves and ST segment.
  1. T waves can be seen.
  2. They are all of rounded and normal morphology and size in all leads. 
  3. They are upright in all leads except aVR, V1 and III (not clear in aVF) where they are inverted. (acceptable normal pattern). The ST segment is neither depressed or elevated. ( isoelectric in every lead). 

Intervals (durations).
  1. The PR interval. They are normal, but not quite consistent. Whilst most P waves are consistent in shape and size, with a PR interval of just under 5 small squares (0.11 sec), you will see that the 3rd, 7th and 11th QRS complex on the long lead II, are preceeded by a slightly smaller P wave, with a slightly shorter PR interval than the others.

    Even if you don't know what this means...Just describe it in this way to the examiner. It helps pass time, and collects points, while you think!

  2. The QT interval. The QT interval is about 10 small squares (0.4 seconds).  This falls within the normal range of 9-11 small squares (0.36-0.44 secs)
  3. The QRS durationThe morphology of each QRS is appropriately  narrow, with a duration of  less than 3 small squares (i.e. < 0.11 seconds)
Note i: Choose any nice clear QRS-T complex for your 'duration' calculations. If they are all different, just state which one you are using. (I always look for one where the R wave falls nicely on a large well-defined line to help me!)

Note ii: if the Ventricular rate falls outside that of sinus rate (ie tachycardic or bradycardic) then you would need to state that the QT interval would need correcting for rate.  

You've made some great observations. Now all you have to do is sum up.

In Summary:

So, we have now established 18 statements of fact in summarising this ECG...

First state the Obvious, then, consider each wave-form, describe what you see, and sum up as follows

  • This is a 12 lead ECG showing electrical activity, with standard paper speed, and gain calibrated. (the 3 compulsory statements of fact)
  • It is regularly irregular, with an atrial and ventricular rate of around 75bpm. 
  • P waves are present and whilst normal in size, shape and duration, some do appear smaller (prior to the 3rd, 7th and 11th complexes in the long rhythm strip). There is a P wave preceeding every QRS complex
  • Whilst the PR interval is mostly consistent, once again, it is shorter in the complexes listed above 
  • QRS complexes are present and of consistent uniform morpholgy within leads. Their size and shape are within normal limits. The QT interval is 0.4seconds which is within normal limits for an ECG at this rate.
  • T waves are present, with a normal rounded morphology and size. Mostly upright buy inverted in leads aVR, v1 and III which can be normal. 
  • There is no significant depression, or elevation, of the ST segment.
  • The axis is between 0 and -30 which is within normal limits.

Now to plump for an interpretation...
We know the answer lies somewhere in the 3rd, 7th and 11th complexes of the rhythm strip. So now it's just a matter of mathematical patterns. 

Taking only the long lead II rhythm strip now:
The 1st and 2nd QRS complexes have the same interval between them as between the 4th and 5th, 5th and 6th, 8th and 9th, 9th and 10th complexes. So these are the regular background complexes.
Complexes 3, 7 and 11  actually result from premature early atrial beat which much originates very close to the SA given (Given the P wave and it's almost normal morphology).

Every 4th beat is an Atrial Ectopic. 
If every second beat is an atrial ectopic, it is known as Atrial Bigeminy. 
Every third is known as Atrial Trigeminy.  
Beyond that, it is described as "Frequent, regular, premature atrial activity"

This ECG shows benign atrial ectopy, and is most likely of no significance.
He can go home, at last.

Tah dah! Easy, no?

Well done, and thank you all. See you next week. 
H. :)

Learning point - ECG skeleton memo:

  • Technical:                  Electrical activity? Which leads? Calibration?
  • Rate and Rhythm:    Regular or irregular? Atrial rate? Ventricular Rate?
  • P waves:                     Present? Shape? Relationship to QRS?
  • QRS:                          Present? Shape? Axis?
  • T waves:                    Present? Shape? Orientation?
  • Intervals:                   PR? QT? QRS?

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