Cardiac Medicine Certification (CMC) Practice Exam

What is the reciprocal change observed in V1 during a posterior wall MI?

1. ST elevation

2. ST depression

3. Normal sinus rhythm

4. Inverted T-waves

The correct answer is: ST depression

In the context of a posterior wall myocardial infarction (MI), the reciprocal changes observed in the electrocardiogram (ECG) can include ST depression in the leads that are oriented towards the anterior wall, particularly V1. During a posterior wall MI, which primarily affects the posterior portion of the left ventricle, changes like ST elevation will be seen in the posterior leads, but the anterior leads (such as V1) demonstrate ST depression as a compensatory mechanism. This ST depression in V1 is considered a hallmark sign when assessing for a posterior MI. It indicates that there is a divergence in electrical activity; while the posterior wall is experiencing injury and shows elevation in appropriate leads, the anterior leads reflect a more negative change, such as ST depression. Thus, the identification of this reciprocal change is crucial for diagnosing posterior MIs effectively.