A 65 year-old male was brought in by EMS after he suffered a cardiac arrest at a public place. Bystanders performed immediate CPR for five minutes. Patient was also defibrillated x1, as AED showed a "shock advised" rhythm. After defibrillation patient had ROSC and was brought in to our ED.

Upon arrival in ED, patient was confused, oriented to self only, answering only "yes" or "no" questions. Vitals signs: 92/50, 105, 18, 96% RA

The following ECG was obtained:

The ECG shows ST segment elevations in lateral leads (I and aVL), which are in LAD distribution. There are also reciprocal changes in the expected inferior leads: ST segment depressions in II, III, aVF.

A STEMI alert has been called, and patient went to cath lab.

A subsequent catheterization showed a 100% obtuse marginal artery occlusion. Pt received a stent and is doing well.

Teaching points:
- The lateral wall of the LV is supplied by branches of the LAD and left circumflex (LCx) arteries. The obtuse marginal (OM) artery is a branch of the LCx, originating at the left atrioventricular sulcus, traveling along the left margin of heart towards the apex of the heart.
- Most LAD occlusions cause large territory infarcts, involving both septum/anterior wall and lateral wall.

- Isolated lateral wall MIs are rare, unless the smaller branches of LAD are occluded (OM, D1-first diagonal branch, or ramus intermedius), as in our case.
- Those patients who present with OM occlusions as STEMI, as opposed to NSTEMI, have worse prognosis and outcomes¹.
- The interventional cardiologist believes, that occlusion of OM in this case was enough to cause a life-threatening arrhythmia, such as ventricular tachycardia or ventricular fibrillation, which put our patient into a cardiac arrest.

References:
1. Stribling WK, Kontos MC, Abbate A, Cooke R, Vetrovec GW, Lotun K. Clinical outcomes in patients with acute left circumflex/obtuse marginal occlusion presenting with myocardial infarction. J Interv Cardiol. 2011 Feb;24(1):27-33. PMID: 20958792

Keywords:
myocardial infarction, MI, lateral wall, isolated lateral wall, ECG of lateral wall MI

Courtesy of Karima Sajadi, MD

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