Table 3.11-5. Probable location of myocardial infarction based on ECG findings

ECG leads

Location of MI

V1-V4

LV anterior wall, ventricular septum, apex

I, aVL, V5-V6

LV lateral wall, apex

II, III, aVF

LV inferior wall

V1-V3 (tall R waves),
V7-V9 (ST-segment elevation ≥0.05 mVa and Q waves)

LV posterior wall

Vr4-Vr6 (ST-segment elevation ≥0.05 mV)b

Right ventricle

a ≥0.1 mV in male patients aged <40 years.

b ≥0.1 mV in male patients aged <30 years.

In 50%-70% of cases of inferior wall ST-segment elevation myocardial infarction, so-called mirror ST-segment depressions are found in the anterior or lateral leads; this is also true for 40%-60% of anterior wall MIs with mirror elevation in the inferior leads. This finding is associated with more extensive infarction and a worse prognosis. ST-segment depression in anterior leads may also represent posterior MI.

ECG, electrocardiography; LV, left ventricle; MI, myocardial infarction.