Artery Commonly Affected in Lateral Myocardial Infarction
The circumflex artery (option C) is the artery most commonly affected in a lateral myocardial infarction. 1
Anatomical Basis
The left main coronary artery (LMCA) typically bifurcates into two major branches:
- Left anterior descending artery (LAD) - supplies the anterior wall and apex of the left ventricle
- Left circumflex artery (LCx) - supplies the lateral wall of the left ventricle
In approximately two-thirds of patients, the LMCA bifurcates into these two branches, while in one-third of patients, it trifurcates into the LAD, LCx, and ramus intermedius 1. The circumflex artery specifically supplies blood to the lateral wall of the left ventricle, making it the primary vessel involved in lateral myocardial infarctions.
ECG Findings in Lateral MI
Lateral myocardial infarction has distinctive ECG patterns that reflect circumflex artery occlusion:
- ST-segment elevation in leads I, aVL (high lateral leads)
- ST-segment elevation in leads V5-V6 (lateral precordial leads)
- Sometimes isolated ST elevation in aVL and aVR with a superior axis of injury current vector 2
- Often ST depression in inferior leads (II, III, aVF) as reciprocal changes
Importantly, lateral MIs due to circumflex occlusion can be challenging to diagnose because:
- They may present without classic ST-segment elevations (56.6% present as NSTEMI rather than STEMI) 3
- The circumflex artery is the least frequently identified culprit vessel in acute myocardial infarction patients treated invasively 4
Clinical Significance
The circumflex artery is responsible for supplying a significant portion of the left ventricular myocardium, particularly its lateral wall. When occluded, it can lead to:
- Lateral wall infarction
- Sometimes posterior wall involvement (when the circumflex is dominant)
- Potentially life-threatening complications including cardiac rupture in severe cases 5
Recent research shows that patients with circumflex artery occlusion often have delayed treatment because they frequently present without ST-segment elevation, leading to later percutaneous coronary intervention compared to occlusions in other territories 4.
Diagnostic Challenges
Electrocardiographic evidence of myocardial ischemia in the distribution of the left circumflex artery is often overlooked and is best captured using posterior leads at the fifth intercostal space (V7-V9) 1. This is particularly important when initial ECG is non-diagnostic or shows ST-segment depression in leads V1-V3, which may indicate posterior involvement.
In patients with suspected lateral MI, careful attention to ECG patterns is essential, as circumflex occlusions may not always meet traditional STEMI criteria despite complete vessel occlusion 6, 3.