By Ken Grauer, MD
Professor Emeritus in Family Medicine, College of Medicine, University of Florida
How would one interpret the ECG in the figure, obtained in the ED from a middle-aged man with new chest pain?
Is it possible to predict the “culprit” artery from the 12-leads shown on this tracing, or are additional leads needed? The ECG shows sinus rhythm, with normal intervals and axis and no chamber enlargement. There is dramatic ST-segment elevation in each inferior lead, with equally dramatic reciprocal ST depression in lead aVL (and to a lesser extent in lead I). In a patient with new chest pain, this ECG picture is diagnostic of acute inferior ST-elevation myocardial infarction (MI).
Interpretation of ECG findings in the chest leads is less obvious. Inferior lead ST elevation may be seen with acute occlusion of either the right coronary artery (RCA) or the left circumflex coronary artery (LCx). In either case, there often is associated acute posterior involvement because both vessels also supply the posterior wall of the left ventricle. The finding of ST-T wave depression in lead V2 in the figure strongly suggests there is acute inferior-posterior infarction.
Normally, with acute posterior infarction, ST depression also will be seen in lead V1, as well as in lead V2. The fact the ST-T wave in lead V1 is flat rather than depressed strongly suggests “something else” must be attenuating ST depression that otherwise would be seen as a result of acute posterior MI. This strongly suggests that in addition to acute infarction of the inferior and posterior walls of the left ventricle, there also is acute right ventricular (RV) involvement.
Although ST elevation in right-sided leads is the usual way the diagnosis of acute RV MI is made, right-sided lead V1 occasionally shows either unexpected ST segment flattening or slight ST elevation. Recognition of probable RV involvement localizes the “culprit” artery to the proximal portion of the RCA because the LCx does not supply the right ventricle.
For more information about and further discussion of this case, please click here.