Which statement about posterior MI assessment is true?

• A. Posterior MI is best confirmed with posterior leads V7-9
• B. Posterior MI is diagnosed by ST elevation in V1-V3
• C. Posterior MI never shows R waves in V1
• D. Posterior MI is diagnosed only via echocardiography

Answer: (A)

Posterior MI involves the back wall of the heart, so the abnormal electrical vector points away from the standard chest leads. That often makes the infarct appear as ST depression in the anterior leads (V1–V3) rather than the expected ST elevation. To directly visualize the posterior wall, you add posterior leads (V7, V8, V9) placed on the back. ST elevation in these posterior leads confirms posterior involvement, which is why this approach is the best way to diagnose posterior MI.

The other statements aren’t reliable: ST elevation in V1–V3 isn’t typical for posterior MI; posterior MI can show prominent R waves in V1–V2 due to the posterior-facing vector; and while echocardiography helps assess function, it isn’t the sole method to diagnose MI on its own.