Rhythm Nation – Answer!
Well done Nathan and Carl! This week’s winner is Nathan for the first, most correct answer.
This patient has an inferior myocardial infarction with ST elevation in II, III and aVF, and reciprocal depression in aVL. In this case, the culprit artery is the RCA (80% of inferior MIs) which demonstrates a pattern of ST elevation greater in III than II. If it had been LCx then there would have been ST elevation in I and V5-V6.
This patient also had marked bradycardia which occurs about 20% of the time, due to a second or third degree AV block. The exact mechanism is unknown, but there are two predominant theories:
- Impaired blood flow from the AV nodal artery which commonly arises from the RCA and thus leads to AV node ischemia
- Bezold-Jarisch reflex – which is an increased vagal response due to ischemia
In a patient with inferior MI, it is necessary to consider if a right ventricular infarction (about 40%) has also occurred. In a regular EKG, if ST elevation in V1 is greater than V2 or if V1 is isoelectric and V2 is ST depressed, consider RV infarction. In order to confirm, do a right-sided EKG – the ST elevation in V4R (V4 right) is the most sensitive finding for RV infarction.
When the RV is infarcted, it has poor contractility and thus heavily preload sensitive. Treatment is with bolus IVF to maintain preload. Nitrates are contraindicated as they reduce preload, which can lead to profound hypotension and death. Treatment can include inotropes with pacing if needed until PCI or thrombolytic therapy are available. The bradycardia, however, is often transient and these patients do not necessarily get rushed to the EP lab.
For a more in-depth review with pretty pictures, please see the excellent review from Life in the Fast Lane:
http://lifeinthefastlane.com/ecg-library/basics/inferior-stemi/
eabram
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6 Comments
andygrock · June 22, 2014 at 12:36 pm
Hello,
Thanks for a great post Liz! Just an additional comment to the viewers, anytime you see an Inferior STEMI, the patient needs cath lab or lytics as soon as possible. If you can do so without delaying either of these, every inferior MI should get a Right Sided EKG.
A posterior EKG is indicated anytime you see ST depressions in V1, V2, or V3 or an R/S wave ratio greater than 1 in V1, V2, V3.
Cheers
andy g
References: Amal Mattu, Jeffery A Tabs, Robert A Barish, Electrocardiology in Emergency Medicine, 2007
jmartind · June 22, 2014 at 10:24 pm
Agreed. ST elevation in lead III > lead II can reflect right ventricular MI (lead III is a right-sided lead). You can also see ST elevation in right-sided precordial leads V1 and V2.
When I see ST-depressions in V1 and V2 in the setting of an inferior MI, I suspect infarction of the posterior wall (infero-posterior MI).
andygrock · June 26, 2014 at 9:55 am
Interesting case report on inferior MI found on cath. EKG is super subtle, but focuses on st depressions in avl. Thoughts?
http://hqmeded-ecg.blogspot.com/2014/06/sudden-left-trapezius-pain-and-syncope.html?m=1
Nathan · June 28, 2014 at 5:41 pm
ST depression in aVR is always abnormal! If you see it, like for subtle elevations in I, II, & aVF. Might be an inferior MI.
Nathan · June 28, 2014 at 5:42 pm
That should read II, III & aVF
Nathan · June 28, 2014 at 5:46 pm
I’m not doing a good job typing on my phone. ST depression in aVL is abnormal and should make you look for ST elevations in II, III & aVF.