Pearls of Knowledge: Acute Inferior Wall MI
Wednesday, March 12, 2025
12-Lead ECG Interpretation: Acute Inferior Wall MI
Pearls of Knowledge © BrainyNurses.com
A lot of information can be gleaned from a 12-Lead ECG and using systematic steps will help to identify all the components. Considering the patient’s history and clinical presentation can provide some helpful clues as to what to look for, especially if you are more of a novice in 12-Lead interpretation. The focus for this 12-Lead interpretation is to look for evidence of ischemia, injury, or infarction.
History and clinical correlation
56-year-old male presenting to the ED having chest pain for the past 20 minutes while at work. Also, complains of feeling lightheaded and nauseated. BP 160/100.
Systematic steps in interpretation
Steps when chest pain is present.
- Identify the rhythm.
- Determine axis (Memory Hint: “Right together, Left apart” using leads I and aVF).
- Look for signs of an acute MI (ST segment elevation of 1 mm or more).
- Look for signs of ischemia (ST segment depression and symmetrically inverted T waves).
- Look for signs of myocardial necrosis (Q wave more than 1/3 the height of the R wave).
Using this guide, evaluate axis and the leads identified for the above changes.
Interpretation
Sinus rhythm with a first-degree AV block.
Lead I and Lead aVR are both more positive (point up). Normal axis.
Axis is important to look at with an acute MI. A conduction defect, such as fascicular blocks will cause an axis shift, and failure to recognize the block could be lethal.
ST segment elevation of ≥ 1 mm is seen in II, III, aVF. Inferior wall MI.
ST segment elevation in Lead III is higher than in Lead II. Possible right ventricular MI.
There is no ST segment depression or symmetrical T wave inversion.
Pathological Q waves are present in Lead III.
Summary
A systematic approach to 12-Lead ECG interpretation is essential in detecting changes and applying them to the clinical setting. Changes occur with numerous conditions including acute coronary syndrome, other pathological disorders, conduction disturbances, electrolyte and acid base imbalances, and with medications.
To enhance care provided for cardiac patients, check out Clinical Application and Interpretation of the 12-Lead ECG. It is on-line, on-demand, with voice-over-power-point, and a comprehensive review to use at the bedside.
The extensive handout is easy to follow and includes a composite reference sheet to use in the session and post on the clinical unit afterwards. In addition, “In My Pocket” cards are included as a ready reference tool.
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