American Board of Internal Medicine (ABIM) Certification Practice Exam

What is the recommended action for patients with left bundle branch block undergoing nuclear stress testing?

1. Administer a pharmacologic stressor

2. Perform exercise stress testing without modifications

3. Proceed with imaging without any stress tests

4. Only use vasodilators for stress testing

The correct answer is: Administer a pharmacologic stressor

For patients with left bundle branch block (LBBB) undergoing nuclear stress testing, the recommended action is to administer a pharmacologic stressor. LBBB can obscure the electrocardiographic (ECG) changes typically used to assess for inducible ischemia during traditional exercise stress testing. Because the normal conduction through the heart is altered, the presence of LBBB can lead to false-positive or false-negative results when attempting to interpret the patient's performance during exercise. Pharmacologic stress testing, using agents such as adenosine or regadenoson, induces vasodilation and accordingly increases blood flow to the heart. This method does not rely on patient exercise capacity or the assessment of exercise-induced changes on the ECG, making it a more reliable option for eliciting myocardial perfusion data in the presence of conduction abnormalities like LBBB. Using a vasodilator enhances the ability to visualize blood flow in the myocardium without the confounding effects of abnormal conduction patterns, thereby improving diagnostic accuracy in this specific patient population. Therefore, administering a pharmacologic stressor is considered the best practice for nuclear stress testing in patients with LBBB.