These data suggest that serotonin plays a major role in the pathogenesis of the cardiac plaque formation observed in carcinoid patients.

Carcinoid syndrome originates from metastatic carcinoid tumors localized in the gastrointestinal system, pancreas, biliary vessels, bronchi, ovaries, and testes; it is characterized by flushing, telangiectasias, diarrhea, bronchoconstriction, and fibrous endocardial plaques in the heart. Cardiac involvement is detected by echocardiography in over 50% of patients with this syndrome. Right-sided valvular heart disease occurs frequently in patients with carcinoid syndrome, involving most commonly the tricuspid and pulmonary valves. Involvement of the left-sided valves rarely occurs. Medical therapy for carcinoid heart disease includes digitalis and diuretics for congestive heart failure symptoms; the effects of carcinoid syndrome can be treated with the use of somatostatin analogues. Conventional chemotherapy has been of little beneficial value, with response rates of only 10% to 30%. The use of octreotide, a long-acting and potent somatostatin analogue, is a major advance in the management of carcinoid tumors. In addition to providing effective symptom relief in malignant carcinoid syndrome, octreotide can also be used for diagnostic purposes. Despite its expense, octreotide is the current agent of choice for the treatment of this condition. Analogues with different receptor specificities and pharmacokinetics hold promise for the future. Valve surgery is the only definitive treatment for intractable right-sided heart failure. Although cardiac surgery carries high perioperative mortality, marked symptomatic improvement occurs in survivors. Surgical intervention therefore should be considered in the appropriate patients when cardiac symptoms become severe. Balloon valvulotomy in patients with severe pulmonary artery stenosis often results in palliation of symptoms; however, surgery still is required often in these patients.