Hedinger Syndrome: What it is and why the right heart is more affected than the left heart
Hedinger syndrome, also known as carcinoid heart disease, refers to cardiac involvement in carcinoid syndrome and is marked by fibrotic damage predominantly affecting the right-sided heart valves—most commonly the tricuspid and pulmonary valves. The underlying mechanism involves prolonged exposure of the endocardium to vasoactive substances, chiefly serotonin, secreted by metastatic neuroendocrine tumors. These mediators promote valvular thickening, retraction, and dysfunction, leading primarily to regurgitation and occasionally stenosis.
Do you know why the right heart is more commonly affected than the left heart?
Its because Serotonin and related vasoactive products are degraded by the lung primarily through active uptake into pulmonary endothelial cells via the serotonin transporter (SERT), followed by intracellular metabolism by monoamine oxidase (MAO) to 5-hydroxyindoleacetic acid (5-HIAA). This rapid uptake and metabolism in the pulmonary vasculature prevent significant amounts of serotonin and related products from reaching the left heart, explaining the right-sided predominance of valvular involvement in Hedinger syndrome.
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References
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Jardine B, Bassingthwaighte JB. Modeling serotonin uptake in the lung shows endothelial transporters dominate over cleft permeation. Am J Physiol Lung Cell Mol Physiol. 2013 Jul 1;305(1):L42-55. doi: 10.1152/ajplung.00420.2012. Epub 2013 May 3. PMID: 23645496; PMCID: PMC3726944.
Adnot S, Houssaini A, Abid S, Marcos E, Amsellem V. Serotonin transporter and serotonin receptors. Handb Exp Pharmacol. 2013;218:365-80. doi: 10.1007/978-3-642-38664-0_15. PMID: 24092348.
Bayer H, Müller T, Myrtek D, Sorichter S, Ziegenhagen M, Norgauer J, Zissel G, Idzko M. Serotoninergic receptors on human airway epithelial cells. Am J Respir Cell Mol Biol. 2007 Jan;36(1):85-93. doi: 10.1165/rcmb.2006-0151OC. Epub 2006 Jul 27. PMID: 16873768.
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