Inferior myocardial infarction (MI) accounts for 40-50% of all MIs. It generally has a more favourable prognosis than anterior myocardial infarction (in-hospital mortality only 2-9%), however certain associated features indicate a worse outcome Show ECG diagnostic criteria
Associated features, all of which confer a worse prognosis, include:
Don’t neglect aVL
Which Artery is the Culprit?Inferior STEMI can result from occlusion of any of the three main coronary arteries:
While both RCA and LCx occlusion may cause infarction of the inferior wall, the precise area of infarction and thus ECG pattern in each case is slightly different:
These differences allow for electrocardiographic differentiation between RCA and LCx occlusion. RCA occlusion is suggested by:
Circumflex occlusion is suggested by:
ECG ExamplesExample 1Early inferior STEMI:
Note how the ST segment morphology in aVL is an exact mirror image of lead III. The concept of reciprocal change can be further highlighted by taking lead aVL and inverting it. Notice how the ST morphology now looks identical to lead III:
(For more about lead aVL and its utility in diagnosing subtle inferior STEMI, check out this post from Dr Smith’s ECG Blog) Example 2Inferior STEMI:
Inferior STEMI:
Hyperacute inferior STEMI:
Inferior STEMI:
Example 6Massive inferolateral STEMI:
In patients with inferior STEMI, ST elevation of 2mm or more in leads V5 and V6 is predictive of extensive coronary artery disease and a large area of infarction. Example 7Recent inferolateral STEMI:
NB. If this patient had ongoing chest pain you would still treat them as an acute STEMI! Bradycardia and AV Block in inferior STEMIUp to 20% of patients with inferior STEMI will develop either second- or third-degree AV block. There are two presumed mechanisms for this:
The conduction block may develop either as a step-wise progression from 1st degree heart block via Wenckebach to complete heart block (in 50% of cases) or as abrupt onset of second or third-degree heart block (in the remaining 50%). Patients may also manifest signs of sinus node dysfunction, such as sinus bradycardia, sinus pauses, sinoatrial exit block and sinus arrest. Similarly to AV node dysfunction, this may result from increased vagal tone or ischaemia of the SA node (the SA nodal artery is supplied by the RCA in 60% of people). Bradyarrhythmias and AV block in the context of inferior STEMI are usually transient (lasting hours to days), respond well to atropine and do not require permanent pacing. Example 8
Example 9
References
Advanced ReadingOnline
Textbooks
LITFL Further Reading
ECG LIBRARYElectrocardiogram
Robert ButtnerMBBS (UWA) CCPU (RCE, Biliary, DVT, E-FAST, AAA) Adult/Paediatric Emergency Medicine Advanced Trainee in Melbourne, Australia. Special interests in diagnostic and procedural ultrasound, medical education, and ECG interpretation. Editor-in-chief of the LITFL ECG Library. Twitter: @rob_buttner Ed BurnsEmergency Physician in Prehospital and Retrieval Medicine in Sydney, Australia. He has a passion for ECG interpretation and medical education | ECG Library | What is Inferolateral wall myocardial infarction?Inferior wall myocardial infarction (MI) occurs from a coronary artery occlusion with resultant decreased perfusion to that region of the myocardium. Unless there is timely treatment, this results in myocardial ischemia followed by infarction.
What is acute ST elevation myocardial infarction?An acute ST-elevation myocardial infarction (STEMI) is an event in which transmural myocardial ischemia results in myocardial injury or necrosis. [1] The current 2018 clinical definition of myocardial infarction (MI) requires the confirmation of the myocardial ischemic injury with abnormal cardiac biomarkers.
What is the best treatment for ST elevation MI?What are the treatment options for a STEMI?. Option 1: Percutaneous coronary intervention (PCI) First, we look for where the blockage is located. ... . Option 2: Thrombolysis. ... . Option 3: Medications. ... . Option 4: Coronary bypass surgery.. Does ST elevation mean heart attack?An ST-elevation myocardial infarction (STEMI) is a type of heart attack that is more serious and has a greater risk of serious complications and death. It gets its name from how it mainly affects the heart's lower chambers and changes how electrical current travels through them.
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