American Board of Internal Medicine (ABIM) Certification Practice Exam

Which of the following is a baseline abnormality that precludes an EKG stress test?

1. Sinus bradycardia

2. Left bundle branch block

3. Supraventricular tachycardia

4. First-degree AV block

The correct answer is: Left bundle branch block

The presence of a left bundle branch block (LBBB) is a baseline abnormality that precludes the use of an EKG stress test due to its significant impact on the interpretation of the results. In patients with LBBB, the electrical impulses traveling through the heart are altered, which can obscure or mimic changes that would typically indicate ischemia on an EKG during exercise. Specifically, LBBB can mask ST-segment changes that occur during stress tests, making it difficult to accurately assess a patient's cardiac response and potential ischemia. While other conditions such as sinus bradycardia, supraventricular tachycardia, and first-degree AV block may also influence the assessment process, they do not inherently obstruct the interpretation of EKG changes in the same way. For instance, sinus bradycardia can be a normal variant in well-conditioned athletes and may not significantly affect the EKG's diagnostic utility. Supraventricular tachycardia, though it can complicate results, is often manageable during testing and can be recognized. First-degree AV block, a common and usually benign finding, typically does not impact the ability to conduct stress testing effectively. Thus, LBBB represents a unique challenge in terms of EKG stress testing, as