Pearls of Knowledge: Acute Inferolateral Wall MI
Monday, February 24, 2025
12-Lead ECG Interpretation: Acute Inferolateral 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
50-year-old male with a history of hypertension and smoking 1 pack per day for 30 years presents to the ED complaining of vague chest discomfort and shortness of breath. He had not been feeling well for the past few hours but wanted to wait until his wife got home before he went to the hospital. On assessment, an S4 gallop is auscultated. Intermittent second-degree, type I AV block has been seen on the monitor but is not present on the 12-Lead.
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 the rhythm, determine axis, the leads identified for the above changes, and the impression.
Interpretation
The rhythm is slight sinus dysrhythmia where the heart rate varies by more than 0.12 seconds.
Lead I is upright (points up) and Lead aVF is negative (points down). Left axis deviation, which is typical for an inferior MI, especially with lateral wall involvement.
ST segment elevation is present in Lead II, III, and aVF. Inferior wall MI. Q waves are also beginning to form which could represent an old infarction with some extension occurring acutely, or more probably, an infarction which is several hours old.
Inferior wall MI can occur in conjunction with lateral wall. ST segment elevation is present in V5-V6 (and extends to V4), but not in Lead I and aVL. Inferolateral wall MI.
Clinical Significance
Significant risk factors are present in this patient including male sex, smoker, and a history of hypertension. Delay in presenting to the hospital for a few hours could account for the development of the Q waves in the inferior leads. An S4 gallop is indicative of resistance to filling and is heard in the acute MI process. The intermittent second-degree, type I block is not a concern. It can be transient with acute inferior and inferolateral MI and is not a progressive type of heart block.
An inferolateral wall MI is caused by an occlusion of the right coronary artery. If the patient is left dominant, it is the circumflex artery. (Dominance refers to the artery that is supplying the posterior descending artery.)
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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