This ECG shows a common manifestation with inferior wall M.I., BRADYCARDIA. We see the signs of acute inferior wall M.I. in the inferior leads: II, III, and aVF all have ST segment elevation. There almost appear to be pathological Q waves in Leads III and aVF. There are still VERY tiny r waves, and the downward deflections are not wide, but should full-blown Q waves develop in these leads, they would signify necrosis in the area. A repeat ECG would certainly be warranted.
Another sign that there is an inferior wall STEMI is the ST segment depression in Leads I and aVL, which are reciprocal to Lead III. ST depression can have many meanings, but when it is localized in the leads which are opposite ST elevation, it is reciprocal. There is also ST depression in Leads V1 and V2. These leads are reciprocal to the POSTERIOR wall, otherwise known as the upper part of the inferior wall. If an inferior wall M.I. is large enough, it can produce ST elevation in the posterior leads (not performed in this case), and ST depression in the anterior leads, especially V1, V2, and V3.
The rhythm is a marked sinus bradycardia, at just under 40 beats per minute. Sinus bradycardia is very common in inferior wall M.I., because the inferior wall and the sinus node are usually both supplied by the right coronary artery. AV blocks can also occur because the AV node is also supplied by the RCA in most people.
It is important to remember that bradycardia does not always need to be treated. In patients with acute M.I., a well-tolerated bradycardia may actually be beneficial to the injured heart, reducing supply/demand ischemia. A well-tolerated bradycardia is a rate that does not produce low blood pressure and poor peripheral perfusion. Some people tolerate rates in the 40’s quite well. If the patient shows signs of poor perfusion: low BP, decreased mentation, pallor, shortness of breath, the rate should be cautiously increased with medication or electronic pacing.
Patients who present with acute inferior wall M.I. should be screened for right ventricular M.I. Right-sided chest leads, especially V3 through V6 can reliably detect right ventricular M.I. Other signs which may or may not be present, and have less accuracy, are: Lead III with higher ST elevation than Lead II, aVL with ST depression of 1 mm or more, and ST elevation in V1 on the 12-Lead ECG. For more about the prognostic implications and treatment of RVMI, we refer you to Drs. Wang and Poponick.
For a more detailed look at this ECG, and a thorough discussion of inferior wall M.I. ECG changes, please refer to the comment below from our Consulting Expert, Dr. Ken Grauer, MD.