By Ken Grauer, MD
Professor Emeritus in Family Medicine, College of Medicine, University of Florida
The ECG in the figure below was obtained from a middle-aged man with chest pain. What can one say about the cardiac rhythm? How can one determine the “culprit” artery?
Although definitive diagnosis of the cardiac rhythm is not possible from the limited period of monitoring seen in the figure, the rhythm is supraventricular, as all QRS complexes are narrow. It looks like the atrial rhythm is regular at an increased rate, and it looks as if some form of group beating is present. Some P waves appear to be conducting, as judged by the repetition of similar PR intervals (best seen in lead V6). But some P waves are not conducted. This suggests there is some type of second-degree AV block.
Regarding the rest of the 12-lead ECG, there is ST segment elevation in leads II, III, and aVF. Considering the tiny size of the QRS complex in lead III, a relatively large Q wave is seen in this lead. Reciprocal ST depression is seen in leads I and aVL. The ST segment in lead V1 is flat. Peaked T waves with significant ST depression are seen in the other five chest leads.
Considering the history of new chest pain, the ECG findings are diagnostic of recent or acute infero-postero occlusion-based myocardial infarction (OMI). The anterior lead ST depression (that is maximal in leads V2 through V4) indicates acute posterior involvement. The fact that the ST segment in lead V1 is flat rather than depressed (as it is in other chest leads) suggests there is associated acute right ventricular involvement. This localizes the acute occlusion to the proximal right coronary artery because neither the left circumflex nor the left anterior descending artery supplies the right ventricular wall. Additionally, the fact that the QRS complex is narrow and the rest of the 12-lead ECG is diagnostic of acute inferior MI strongly suggests the conduction disturbance is a type of AV Wenckebach (Mobitz I), second-degree AV block.
For more information about and further discussion on this case, please click here.