When is it usually invalid to diagnose an infarct using an EKG?

When is it usually invalid to diagnose an infarct using an EKG?

• A. Right bundle branch block
• B. Left bundle branch block
• C. Ventricular hypertrophy
• D. Atrial fibrillation

Answer: (B)

Diagnosing an infarct using an EKG can be challenging in the presence of a left bundle branch block. This is primarily because a left bundle branch block alters the typical pathway of electrical conduction through the ventricles, which can mask or obscure the characteristic changes seen in the case of a myocardial infarction. The typical ST-segment elevation or depression associated with infarcts may not be reliably interpreted when this conduction abnormality is present, as the altered depolarization can present with similar patterns that could be misinterpreted as ischemic changes.

Furthermore, criteria for recognizing ischemia or infarction in the context of left bundle branch block are more complex than in a normal conduction pattern, and often the well-established criteria for ST elevation or depression must be modified. This necessitates a careful evaluation and often correlating clinical findings and additional diagnostic strategies beyond just the EKG readings to make an accurate diagnosis of a myocardial infarction in such cases.