Inferior OMI

Inferior MI's account for a little under 1/2 of all MI's. They have a better prognosis than anterior OMI, though a few features that may be found indicate a poor prognosis. The RCA accounts for ~80% of inferior OMIs. Almost all of the rest will be due to a dominant left circumflex artery. Rarely, an inferior OMI is due to a wraparound LAD.

Inferior OMIs can be difficult to initially diagnose as they are covered by a low voltage area. Therefore, the ST elevation is not as large as an anterior or anterolateral OMI. It is common to initially have only T wave inversion in aVL (reciprocal change) before the patient develops any significant ST elevation.

Patients with inferior OMI commonly have bradycardia as the inferior OMI causes vagal stimulation (producing more nausea and diaphoresis). Additionally, the RCA supplies the SA node in about 60% of people and this can lead to sinus node dysfunction. Conduction delays can also result. In fact, up to 20% of patients will develop a 2nd or 3rd degree AV block with inferior OMI. This can be due to increased vagal stimulation or ischemia of the AV node itself (RCA supplies the AV node 80% of the time). The conduction delay can follow a stepwise progression from 1* AV block or develop suddenly. Despite having a high-grade block, these patients sometimes respond to atropine (likely that these patients have high-grade blocks from significant vagal stimulation).

Inferior OMI with 3* AV Block

Examples:

Right Ventricular Involvement

Isolated RV infarction is incredibly uncommon. RV infarction complicates about 40% of inferior OMIs. RV infarction is noteworthy as these patients are particularly preload sensitive and may decompensate when given nitroglycerin.

Standard 12-lead Findings:

ST elevation in V1
ST elevation in V1>V2
ST elevation in V1 + ST depression in V2 (very specific for RV MI)
isoelectric V1 + ST depression in V2
ST elevation in III>>II

One can place right-sided leads to confirm RV involvement, though this is often not necessary if the patient is already going to the cath lab. V3-V6 are placed on the right side of the chest and V1 and V2 are inverted as below. It is important to physically write on the EKG as this will not be included in the computer print out.

Examples:

Aslanger pattern

The Aslanger pattern describes EKG findings in those with an inferior OMI with multivessel disease. The multivessel disease affects the EKG to change the classic findings that are expected with an inferior OMI; specifically, there is lack of contiguous ST elevation in multiple leads. The findings are:

Inferior STE isolated to III

ST segment V1>V2

ST depression in any of V4-V6, with positive or terminally positive T wave

The lack of contiguous elevation occurs due to the subendocardial ischemia pulling the vector towards aVR (where subendocardial ischemia is directed to). The average ST vector then is directed rightward with ST elevation in III and aVR.

Examples: