Mechanistic Insights into Tricuspid Regurgitation Secondary to Pulmonary Arterial Hypertension.

The simultaneous presence of pulmonary arterial hypertension (PAH) and secondary tricuspid regurgitation (STR) portends particularly poor outcomes. However, not all patients with PAH develop significant STR, and the mechanisms and clinical implications underlying this phenomenon remain unclear. We sought to describe the functional, anatomic, hemodynamic, and clinical characteristics of patients with PAH with and without STR. Patients diagnosed with PAH between 2007 and 2013 were included. STR, defined by absent primary tricuspid valve disease on transthoracic echocardiogram, was considered significant if ≥ moderate in severity. The characteristics of right-sided chambers and tricuspid valve annuli and leaflets were compared between patients with significant versus nonsignificant STR using a transthoracic echocardiogram, cardiac computed tomography, and right-sided cardiac catheterization. These features were then correlated with the composite outcome of all-cause mortality and PAH hospitalization. Of 88 included patients, 52 had significant STR. No baseline clinical differences, including atrial fibrillation, were observed. Patients with significant STR had worse right ventricular dysfunction (tricuspid annular planar systolic excursion = 1.5 vs 2.1 cm; p = 0.02) and increased right ventricular sphericity (sphericity index = 1.8 vs 2; p = 0.004), with similar annular dimensions/shape, lengths/angles of the mural and septal leaflets, and tenting height. After a median of 54 months, right atrial mean pressure was independently associated with the composite outcome on multivariable analysis (hazard ratio = 1.07, p = 0.02). In conclusion, anatomic and functional alterations in the right ventricle rather than the tricuspid valve are implicated in developing significant STR in PAH. Multimodality imaging provides mechanistic insight, and hemodynamic assessment may offer prognostic guidance in this population.