Localization of Infarction

It is often possible to determine in a general way which wall of the heart is involved in a STEMI by determining in which leads we see the three hallmarks of STEMI.

You will recall from Chapter 3 and from your knowledge of the hexaxial reference system (Figure 9.4) that leads II, III, and aVF are called the inferior leads because they look up at the heart from below. When the typical evolution of the three hallmarks of STEMI is seen in II, III, and aVF, we label it an inferior wall myocardial infarction.

If the ST elevation, T wave inversion, and Q wave formation are seen in leads I and aVL, we call it a lateral wall infarction because leads I and aVL look at the lateral wall of the heart.

Finally, if we see evolutionary changes across V2-V4, we label it anterior wall infarction because the precordial leads look at the anterior wall of the heart. When lead Vj is also involved it is sometimes called an anteroseptal infarction.

Either inferior or anterior wall infarctions can also sometimes show changes in the far lateral precordial leads (V5 and V6) as well as in leads I and aVL. The descriptive terms inferolateral or anterolateral are then used to locate the infarction.

Electrocardiographers usually require that the changes of STEMI be seen in two or more contiguous leads (adjacent leads) on the hexaxial reference

Figure 9.4. The hexaxial reference system showing those leads that are considered to reflect the inferior and lateral walls of the heart, aVR -150

aVR -150

Lateral ► Wall Leads

Figure 9.4. The hexaxial reference system showing those leads that are considered to reflect the inferior and lateral walls of the heart,

Inferior Wall Leads

Lateral ► Wall Leads

Inferior Wall Leads system or among the precordial leads before a diagnosis of infarction is made. For example, to diagnose an inferior STEMI, one would have to see changes in at least leads II and aVF, or in leads aVF and III, because each of these pairs of leads are contiguous.

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