Mehlman Cardiology Practice Exam

Carcinoid syndrome triggers a fibrous endocardial reaction on right-sided heart valves from circulating serotonin and other vasoactive substances. Because the lungs quickly metabolize these substances, the right heart is affected first, making left-sided lesions uncommon unless there are hepatic metastases or a bronchial carcinoid bypassing lung metabolism. The most frequent valve involvement is the tricuspid valve, whose fibrous thickening causes regurgitation during systole. Pulmonary valve involvement with stenosis can also occur, but tricuspid regurgitation is the classic and most common lesion.