A 48-year-old woman with episodic flushing and secretory diarrhoea has hepatomegaly and elevated 24-hour urinary 5-HIAA. Examination reveals a pansystolic murmur increasing with inspiration and an ejection systolic murmur over the left second intercostal space. Echocardiography shows thickened, retracted tricuspid and pulmonary valve leaflets with normal mitral and aortic valves. Why are the left-sided valves spared?

• A Left-sided valves have higher endothelial serotonin receptor density that is protective
• B Serotonin is inactivated by monoamine oxidase in the lungs before reaching the left heart ✓
• C Higher left-sided pressures prevent platelet aggregation on these valves
• D The left-sided valves are anatomically distant from hepatic venous drainage

Explanation

Carcinoid heart disease results from circulating serotonin and other vasoactive substances elaborated by a tumour metastatic to the liver, reaching the right heart via the hepatic vein and vena cava. They induce endocardial fibrous plaques that retract the tricuspid and pulmonary valves. The left heart is usually protected because monoamine oxidase in the pulmonary vascular endothelium degrades serotonin before it reaches the systemic arterial side; left-sided disease appears only with a patent foramen ovale or bronchial carcinoid.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.