Inferior Wall MI
When students are learning to recognize ST elevation M.I. (STEMI), they often want to know, "How many blocks does the ST segment have to be elevated for it to be a STEMI?". Counting blocks simply does not work. Depending on the experience level of your students, it is important to introduce other characteristics of the ST elevation.
Even subtle elevations can indicate acute M.I. when other features are present. These include, ST elevation in related leads, a flat or coved upward ST segment, associated signs such as T wave inversion and pathological Q waves, reciprocal depressions, and of course patient presentation.
This ECG shows subtle ST elevations. The LifePak 15 (PhysioControl) has read it as "Meets ST Elevation MI Criteria". LifePak 15 uses the University of Glasgow criteria, which takes into consideration the age and gender of the patient, among other things. The paramedics who cared for this patient were confused because she had chest pain, and the LifePak said she had MI criteria, but they counted blocks and did not find 1 mm ST segment elevation as they were taught. To the experienced eye, of course, this ECG looks like the CLASSIC inferior wall MI, with the classic bradycardia (junctional rhythm) often seen. This patient was evaluated in the cath lab, and treated for acute STEMI.
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.