What is the Culprit’ Artery?
By Ken Grauer, MD
Professor Emeritus in Family Medicine, College of Medicine, University of Florida
Dr. Grauer is the sole proprietor of KG-EKG Press, and publisher of an ECG pocket brain book.
Figure — ECG obtained from a patient with new-onset chest pain.
Scenario: Interpret the ECG in the Figure — obtained from a patient with new-onset chest pain. Localize the area(s) of acute infarction. Which coronary artery is likely to be acutely occluded?
Interpretation: The rhythm is sinus. Intervals and axis are normal. No chamber enlargement. Regarding Q-R-S-T Changes:
- Small q waves are seen in leads II, III, aVF; and in leads V5, V6.
- Transition is normal (occurs between lead V2-to-V3) — albeit the R wave is taller-than-expected in leads V2, V3.
- There is subtle-but-real ST elevation in each of the inferior leads (II, III, aVF) — with suggestion of hyperacute T waves (especially in lead II). A similar pattern of slight J-point ST elevation is seen in leads V5, V6 — with suggestion of hyperacute T waves in these leads.
- There is marked ST depression in leads V1 through V4.
Impression: Sinus rhythm with acute infero-postero-lateral ST elevation myocardial infarction (STEMI). The cardiologist on call should be notified of the need for immediate cardiac catheterization and reperfusion. We suspect acute LCx (Left Circumflex Artery) occlusion.
- The ECG picture in leads V1, V2, V3 strongly suggests associated acute posterior infarction. Although none of the standard 12 leads directly visualize the posterior wall of the left ventricle, the anterior leads provide a mirror-image of ongoing posterior events. Turning the tracing over and holding it up to the light (performing a "mirror test") suggests that rather than taller-than-expected R waves and marked ST depression in anterior leads, there are deepening Q waves and increasing ST elevation in posterior leads. Alternatively — one could apply posterior leads (V7, V8, V9) directly.
In most patients (~85%), the right coronary artery (RCA) is a dominant vessel that supplies the right ventricle before continuing as the posterior descending artery (PDA) that runs along the undersurface of the heart to supply the inferior and posterior walls of the left ventricle. Acute occlusion of the RCA therefore may result in acute infero-postero infarction. RCA involvement is suggested on ECG by the finding of ST elevation that is more marked in lead III than in lead II and by marked reciprocal ST depression in lead aVL. Neither of these signs is seen in the Figure. Instead we see inferior, posterior, and lateral precordial involvement with ST elevation in leads V5, V6. This distribution of changes (with minimal ST elevation in lead III, and significant ST elevation in lead V6) is much more suggestive of acute LCx occlusion. In ~15% of patients, rather than the RCA, it is the LCx that is dominant and gives rise to the PDA to supply the posterior and inferior walls of the left ventricle. Acute occlusion of a dominant LCx is the situation we suspect in this case.