This interesting and instructive ECG was contributed by Jason Roediger, ECG Guru Extraordinaire, and one of the experts featured on our '"Ask the Experts" page. It is an excellent example of acute inferior wall M.I. with left bundle branch block. Left bundle branch block normally displays ST elevation and depression in a "negative concordance" pattern. That is, when the QRS complex is negative, we may expect ST elevation. When the QRS is positive, ST depression is seen. In this ECG, there is clearly ST elevation in Leads II, III, and aVF, and the ST segments have a distinct coved upward appearance. This shape signals to the experienced ECG interpreter that there is an acute injury.
Unfortunately, the normal deviations of the ST segment seen in left bundle branch block can make diagnosis of acute M.I. difficult. For a good example of a left BBB without acute M.I., please refer to the ECG archives on this site. Often, students are taught that it is IMPOSSIBLE to see an acute M.I. in the presence of LBBB. This is not true, as this ECG clearly illustrates. See the March 4, 2012 blog post on the ECG Guru regarding this topic.