Prepare for your USMLE Step 1 with a question focusing on Eisenmenger syndrome. Can you summarize the pathophysiology of this condition and recognize its key clinical features? Sharpen your understanding of this critical cardiovascular topic!
A 25-year-old man is referred to a cardiologist for evaluation for intermittent cyanosis and exercise intolerance. Symptoms began around six months ago, and they have progressively worsened. Past medical history is notable for a congenital heart defect, which was diagnosed shortly after birth. However, he was subsequently lost to follow-up and was not treated for this condition. The patient smokes half a pack of cigarettes per day. Physical exam is notable for cyanosis of the lips and clubbing of the fingers. Cardiac catheterization is performed, and oxygen saturation in the cardiac chambers and outflow tracts are shown below:
Which of the following is the most likely explanation of these findings?
A. Impaired growth of the septum primum
B. Impaired closure of the foramen ovale
C. Reversal of long-standing left-to-right shunt
D. Hyperplasia of bronchial mucus-secreting glands
E. Fluid accumulation in the lung parenchyma
Scroll down for the correct answer!
The correct answer to today’s USMLE® Step 1 Question is…
C. Reversal of long-standing left-to-right shunt
Before we get to the Main Explanation, let’s look at the incorrect answer explanations. Skip to the bottom if you want to see the correct answer right away!
Incorrect answer explanations
A. Impaired growth of the septum primum
Incorrect: This pathology would result in an atrial septal defect (ASD). ASDs are a type of left-to-right shunt. Cardiac catheterization will show increased oxygen saturation in the right atrium, ventricle, and pulmonary artery. Even with Eisenmenger syndrome, ASD would lead to a decrease in saturation in the left atrium (not the ventricle).
B. Impaired closure of the foramen ovale
Incorrect: A patent foramen ovale (PFO) can cause transient right-to-left shunting of blood. Cardiac catheterization may show reduced oxygen saturation in the left atrium, ventricle, and aorta. In contrast, this patient’s catheterization does not demonstrate this finding.
D. Hyperplasia of bronchial mucus-secreting glands
Incorrect: This answer describes chronic obstructive pulmonary disorder (COPD). COPD can result in a productive cough, barrel chest, cyanosis, and nail clubbing. Patients with a smoking history are at increased risk. Although this patient has a smoking history, he is relatively young and lacks a history of cough characteristic of COPD.
E. Fluid accumulation in the lung parenchyma
Incorrect: This answer describes pulmonary edema. The accumulation of fluids in the lung parenchyma can reduce oxygen exchange and cause cyanosis. However, blood in this patient’s left atrium has high oxygen saturation, suggesting that gas exchange is normal.
Main Explanation
This patient has Eisenmenger syndrome, which is when an uncorrected left-to-right shunt reverses direction and becomes a right-to-left shunt. In this patient’s case, the condition most likely arose secondary to an uncorrected ventricular septal defect, given the catheterization finding of decreased saturation in the left ventricle.
Eisenmenger syndrome occurs as a result of the constant shunting of blood to the right heart, which increases pulmonary blood flow. This high flow state triggers vascular remodeling in the lungs, which is characterized by increased proliferation of vascular smooth muscle and narrowing of pulmonary artery lumen. As a result, the right heart must pump against greater resistance, so it too undergoes remodeling in the form of right ventricular hypertrophy. This growth causes the pressure in the right heart to increase and exceed that of the left heart, ultimately switching the shunt’s direction.
Clinically, Eisenmenger syndrome presents with cyanosis, hypoxia, and clubbing of the fingers and toes. In addition, patients can develop polycythemia since hypoxia increases kidney erythropoietin production.
Major Takeaway
Eisenmenger syndrome occurs when an uncorrected left-to-right shunt reverses direction and becomes a right-to-left shunt. This switch occurs because, over time, vascular remodeling increases the pressure in the right heart until it exceeds that of the left. Patients can have cyanosis, hypoxia, digital clubbing, and polycythemia.
References
- Chaix, M.A., Gatzoulis, M.A., et al. (2019) Eisenmenger syndrome: A multisystem disorder- Do not destabilize the balanced but fragile physiology. The Canadian Journal of Cardiology. 35(12), 1664-1674. Doi: 10.1016/j.cjca.2019.10.002.
- Nashat, H., Kempny, A., et al. (2017) Eisenmenger syndrome: Current perspectives. Research Reports in Clinical Cardiology. 8, 1-12. Doi: 10.2147/RRCC.S117838.
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