Like it? Share it!

Wednesday, 1 May 2013

Posterior MI - #ECGclass case 29

An ECG special request topic tonight.

Slightly out of my field, so I'm relying on you experts out there to add your comments and educate us all at the end please!

#ECG Class is an educational blog which runs alongside Twitter.
A new ECG "quizz" is launched alternate Wednesday evenings, in term time. 
Any discussions generated with be archived for summary and reflection, on the following interim Wednesdays, and stored at  www.storify.com  (Just search #ECGclass or @ECGclass).

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 29

It's first thing Monday morning. The first of your same-day booked appointments wanders in at 9am.

He's a 56yrs man who rarely attends, but he woke in the small hours of the night with 'indigestion'. The pain hasn't got any worse, but it's niggled on for several hours now, so his wife booked the appointment and insisted he came down to see you before work.
He's never really suffered with indigestion before, but has no cardiac history or risk factors.

He looks a little unsettled and restless, but nothing else of note. Apart from a slight tachycardia, his pulse is normal, and BP borderline elevated (he's visibly a bit anxious).
You are really not sure if his symptoms represent anything or nothing so you arrange an immediate ECG:


Now, you too are anxious, and arrange a 999 ambulance for immediate transfer with telemetry.

What does the ECG show? (Stick to describing the ST changes only).



The ECG shows 2-3mm of horizontal/downsloping ST depression in leads V1-4


At a glance, with my GP head, I would have felt this showed anterior ischaemia.
But, bear in mind, he has ongoing pain, at rest.   This has to be assumed to be Acute Coronary Syndrome until proven otherwise.

In accordance with NICE Guidelines for new onset chest pain, and in order appropriate to the circumstances, offer:
  • Pain relief
  • Aspirin
  • Other Therapeutic interventions
  • Pulse oximetry (supplement O2 only if % SAO2 indicates)
  • Monitor until ambulance arrives (GP) or diagnosis confirmed (Hospital)

On arrival at hospital, serial troponins were taken, and the posterior ECG leads (V7-9) were monitored. 
A subsequent diagnosis of Posterior MI was made.




Posterior Myocardial Infarction

With Acute MI, the presence of persistent ischaemic pain, indicates that still viable areas of ischaemic and injured myocardium are in danger of necrosis. 

It is outwith the concept of this forum, to go into management of Acute Coronary Syndrome (ACS) in any detail, but everyone should make themselves familiar with the NICE Guideline "Chest Pain of Recent Onset" (CG95).  
Pages 1-9 of the Quick reference guide linked above, deals with ACS, whereas pages 10 onwards, deal with stable angina.

In STEMI, the ECG leads which are orientated to the area supplied by the affected coronary artery will reveal the ST elevation. And so, the area of infarction can be determined by which leads of the ECG are affected:



And it follows, that the coronary artery affected in Acute Myocardial Infarction, is determined by the location of the MI :



Of course, reliance on ST elevation to diagnose STEMI, assumes we are viewing the affected myocardium from the front. What if the ST elevation is in the posterior myocardial wall?

If ST depression is present in leads V1-V3, with ongoing chest pain, then recording of the posterior leads (V7,V8,V9) will be invaluable. 

The posterior leads are placed on the posterior chest wall:


Of course,the recordings from the 3 posterior leads will therefore be a mirror-image of V1-3 :

                 

And so, the posterior ST elevation becomes obvious.


Posterior MI is often a bit of an enigma to GP's and students, and I'm sure we all recall been told to flip the ECG paper upside down, and view form the back. When lacking precious time/ability to monitor the posterior leads, this method can still be invaluable - it's just remembering to think of it!


Hope that helps a little.
Looking forward to any more gems of education on posterior MI's (for me) from anyone who'd like to add a comment! :)

Thank you.







5 comments:

  1. Just looking at ST segments there is significant st depression across the anterior/septal leads. This could be indicative of a posterior MI and I would do a V6-9 for a further look

    ReplyDelete
  2. Thanks. Can you explain the appearance differences between anterior ischaemia and posterior MI?

    ReplyDelete
    Replies
    1. Sure, ischemia does not localize on the surface ECG; so any localized ST-depression is a reciprocal change until proven otherwise. Ischemia produces diffuse ST-depression and T-wave changes rather than the focal changes we were classically taught.

      Delete
  3. I’m glad you’ve brought this one up. I think it’s an important topic. The main difference between anterior ischaemia and posterior MI is that the latter qualifies for, and would benefit from, PPCI. Where there’s a convincing history of ongoing cardiac sounding chest pain and no STE, and especially if you see that anterior depression pattern, posterior leads are always worth a shot. There's good evidence that we miss a lot of circumflex occlusions which would be amenable to PPCI because posterior leads aren’t taken.

    There’s a decent review of the topic here: http://www.ncbi.nlm.nih.gov/pubmed/22565144

    ReplyDelete
  4. Thanks Mark. That's really helpful. So I guess it's the story behind the ECG changes, which give the game away?
    If the circumstances and history are suggestive of stable angina, then it may be anterior ischaemia (such as might be seen during an ETT), but if the the ST changes accompany prolonged ischaemic sounding pain, at rest, then a posterior MI needs to be considered. is that about right?

    ReplyDelete