Pearls of Knowledge: Acute Anterolateral Wall MI
Tuesday, March 18, 2025
12-Lead ECG Interpretation: Acute Anterolateral 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
65-year-old female presents with severe crushing chest pain for the past 45 minutes. She is cool, clammy, restless, and capillary refill is > 2 seconds. A systolic murmur is auscultated at the left 5th ICS, midclavicular line. Lungs are clear. BP 160/96, RR 24/min. Premature atrial contractions are noted on the monitor but were not evident on the 12-lead ECG.
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).
(If the axis is difficult to determine, equiphasic limb lead is often used)
• 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, the leads identified for the above changes, and the impression.
Interpretation
Sinus rhythm with normal intervals. The axis is difficult to determine using the “Memory Hint” because of the distortion caused by the acute MI. Lead I appears to be positive and aVF appears to be positive or equiphasic. Using equiphasic limb lead interpretation (not shown here), the axis is normal.
Axis is important to look at with an acute MI. A conduction defect, such as a fascicular block will cause an axis shift, and failure to recognize the block could be lethal.
ST segment elevation is present in V3-V4 (anterior) and extends to V2, but not to V1. Anterior wall MI.
Anterior wall occurs in conjunction with lateral wall MI. There is ST segment elevation in V5 and V6 (lateral) and Lead I and Lead aVL (high lateral). Anterolateral wall MI.
The ST segment depression in Lead III is a reciprocal change and not concerning.
A small R wave is present in V1. Poor R wave progression is noted across the precordium.
Clinical Significance
Anterior wall MI rarely occurs alone. When there is lateral or septal involvement with the anterior wall, complications may include severe left ventricular dysfunction resulting in heart failure, cardiogenic shock, and high mortality. The clinical presentation indicates early shock as evidenced by normotension, cool, clammy, and restlessness. The presence of PACs on the monitor is indicative of early heart failure. The presence of a systolic murmur at the left 5th ICS, midclavicular line, indicates mitral valve regurgitation and damage because of the MI.
An anterior wall MI is caused by an occlusion of the left anterior 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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