ECG Review: Which Vessel is Occluded?
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 Which coronary vessel is likely to be occluded?
Scenario: Interpret the the ECG shown above. What area(s) of the heart are involved? Which coronary vessel is likely to be occluded?
Interpretation: The rhythm is sinus. All intervals and the axis are normal. There is no chamber enlargement. The most interesting findings relate to Q-R-S-T changes. These include: 1) presence of a small but deep Q wave in lead III (but no other Q waves); 2) early transition (with a relatively tall R wave already by lead V2); 3) ST elevation in each of the inferior leads (II, III, aVF) as well as in lateral precordial leads (V5, V6); and 4) ST depression in leads I, aVL, and V2. An additional subtle-but-real finding that may be clinically relevant is the presence of an rSr' pattern in lead V1 with slight ST segment elevation and T wave inversion.
The impression is acute infero-posterior infarction, with possible lateral and right ventricular involvement. In most patients, the right coronary artery (RCA) supplies the right ventricle and posterior and inferior walls of the left ventricle. Approximately 15% of patients have a left-dominant circulation, in which the circumflex artery is larger and supplies lateral, posterior, and inferior walls of the left ventricle. Clues to the RCA being the "culprit artery" in this case are: 1) that ST segment elevation in lead III is clearly more than it is in lead II; 2) that ST depression in lead aVL is marked (and more than in lead I); and 3) that there may also be right ventricular involvement. Definitive diagnosis of acute right ventricular infarction requires use of right-sided precordial leads, which show progressively increasing ST elevation as one moves across the right precordium (usually peaking by lead V3R-to-V4R). However, the finding of some ST elevation in lead V1 (but not in V2, V3) in a patient with associated acute inferior infarction suggests likely right ventricular involvement as well.
Acute posterior infarction produces the "mirror image" of Q wave-ST elevation-T wave inversion in anterior leads (V1, V2, and/or V3). This is best seen in lead V2 of the figure. Flipping lead V2 over in one's mind (to produce a mirror image) transforms the tall R wave and associated ST-T wave shape that we see in lead V2 into a Q wave with ST elevation and T wave inversion. Rather than "lateral infarction," it is likely that the ST elevation that we see in leads V5, V6 for this case represents a reciprocal change from this patient's infero-posterior infarction.