Background The development of carcinoid heart disease (CaHD) is still relatively unclear. It is difficult to define an optimal follow‐up for patients without any cardiac involvement at baseline. The aim of this study was to assess the prevalence and natural history of CaHD by annual echocardiographic examinations. Methods and Results We studied 137 consecutive patients (61±12 years, 53% men) with proven digestive endocrine tumor and carcinoid syndrome between 1997 and 2017. All patients underwent serial conventional transthoracic echocardiographic studies. Right‐sided and left‐sided CaHD were systematically assessed. We used a previous validated echocardiographic scoring system of severity for the assessment of CaHD. An increase of 25% of the score was considered to be significant. Mean follow‐up was 54±45 months. Prevalence of CaHD was 27% at baseline and 32% at 5‐year follow‐up. Disease progression was reported in 28% of patients with initial CaHD followed up for >2 years (n=25). In patients without any cardiac involvement at baseline, occurrence of disease was 21%. CaHD occurred >5 years from the initial echocardiographic examination in 42% of our cases, especially in patients presenting with new recurrence of a digestive endocrine tumor. An increase of urinary 5‐hydroxyindoleacetic acid by 25% during follow‐up was identified as an independent predictor of CaHD occurrence during follow‐up (hazard ratio [HR], 5.81; 95% CI, 1.19–28.38; P =0.03), as well as a maximum value of urinary 5‐hydroxyindoleacetic acid >205 mg/24 h during follow‐up (HR, 8.41; 95% CI, 1.64–43.07; P =0.01). Conclusions Our study demonstrates that in patients without initial CaHD, cardiac involvement may occur late and is related to serotonin. Our data emphasize the need for cardiologic follow‐up in patients with recurrence of the tumor process.

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