USMLE (United States Medical Licensing Examination) Step 1 Practice Exam

In which condition is there a risk of sudden death due to a saddle embolus blocking the pulmonary arteries?

1. Caplan syndrome

2. Asthma

3. Pure Red Cell Aplasia (PRCA)

4. Pulmonary infarction

The correct answer is: Pulmonary infarction

Saddle embolus refers to a large blood clot that lodges at the bifurcation of the pulmonary arteries, leading to a significant blockage of blood flow to both lungs. This situation can cause acute right heart failure and is often associated with sudden death. Pulmonary infarction occurs when this blockage prevents oxygenated blood from reaching the lung tissue, resulting in tissue death. The critical risk of sudden death arises due to the massive obstruction caused by the saddle embolus, which can quickly lead to cardiovascular collapse. In the context of the other conditions mentioned, neither Caplan syndrome, asthma, nor Pure Red Cell Aplasia (PRCA) poses the same direct risk of sudden death from a pulmonary embolism. Caplan syndrome involves the formation of nodules in the lungs due to coal dust exposure and is not primarily characterized by acute, life-threatening pulmonary blockage. Asthma is a chronic inflammatory disease of the airways and does not typically involve the type of acute embolic event that leads to sudden death. PRCA is a type of anemia resulting from a reduction in red blood cell production and does not directly relate to sudden vascular events. Therefore, recognizing that a saddle embolus primarily poses the greatest immediate risk of sudden death aligns with the characteristics and dangers associated