Rhythm Nation, June Answer!

by eabram • June 20, 2014 • 6 Comments

Rhythm Nation – Answer!

Well done Nathan and Carl! This week’s winner is Nathan for the first, most correct answer.

This patient has an inferior myocardial infarction with ST elevation in II, III and aVF, and reciprocal depression in aVL. In this case, the culprit artery is the RCA (80% of inferior MIs) which demonstrates a pattern of ST elevation greater in III than II. If it had been LCx then there would have been ST elevation in I and V5-V6.

This patient also had marked bradycardia which occurs about 20% of the time, due to a second or third degree AV block. The exact mechanism is unknown, but there are two predominant theories:

Impaired blood flow from the AV nodal artery which commonly arises from the RCA and thus leads to AV node ischemia
Bezold-Jarisch reflex – which is an increased vagal response due to ischemia

In a patient with inferior MI, it is necessary to consider if a right ventricular infarction (about 40%) has also occurred. In a regular EKG, if ST elevation in V1 is greater than V2 or if V1 is isoelectric and V2 is ST depressed, consider RV infarction. In order to confirm, do a right-sided EKG – the ST elevation in V4R (V4 right) is the most sensitive finding for RV infarction.

When the RV is infarcted, it has poor contractility and thus heavily preload sensitive. Treatment is with bolus IVF to maintain preload. Nitrates are contraindicated as they reduce preload, which can lead to profound hypotension and death. Treatment can include inotropes with pacing if needed until PCI or thrombolytic therapy are available. The bradycardia, however, is often transient and these patients do not necessarily get rushed to the EP lab.

For a more in-depth review with pretty pictures, please see the excellent review from Life in the Fast Lane:

http://lifeinthefastlane.com/ecg-library/basics/inferior-stemi/

The views expressed on this blog are the author's own and do not reflect the views of their employer. Please read our full disclaimer here. Any references to clinical cases refer to patients treated at a virtual hospital, Janus General Hospital.