Four-dimensional geometric assessment of tricuspid annulus movement in early functional tricuspid regurgitation patients indicates decreased longitudinal flexibility.

OBJECTIVES Functional tricuspid regurgitation (FTR) is generally caused by the dilation of the tricuspid annulus (TA) and the tethering of tricuspid leaflets; however, it also occurs in patients without dilatation of the TA. The aim of this study was to develop and to use a four-dimensional tracking system, utilizing cardiac magnetic resonance imaging (MRI), and to assess TA flexibility in patients with early FTR without right ventricle dilation as a preliminary investigation for the mechanism of early FTR. METHODS The structure and movement of the TA were examined in 20 healthy subjects and 19 FTR patients whose right ventricle was not dilated. We analysed the short axis and longitudinal movement of a mid-septal point (S), a mid-lateral point (L), a mid-anterior point (A) and a mid-posterior point (P) on the TA throughout the cardiac cycle. The tethering distance of the tricuspid leaflets and the integrated orbiting volume of the TA were also measured. RESULTS The TA area (mm(2)) and AP and LS distances (mm) did not differ significantly between the two groups, but the longitudinally moving distances (mm) of the four points were significantly shorter in patients with FTR than in healthy subjects. Also, the mean tethering distance (mm) was significantly longer in patients with FTR than in healthy subjects (9.0 ± 1.5 vs 4.0 ± 1.3, respectively; P < 0.001), and the integrated volume (mm(3)) of the annular moving track, throughout the cardiac cycle, was significantly larger in healthy subjects than in patients with FTR (40 428 ± 10 951 vs 22 967 ± 6079, P < 0.001). CONCLUSIONS The longitudinal flexibility of the TA in FTR patients was significantly less than that in the healthy subjects, and the tethering of the tricuspid leaflets occurred in FTR patients despite the absence of TA and RV dilation, which can be one triggering factor of early FTR. Four-dimensional geometric assessment, using cardiac MRI and the tracking program that we have developed, is capable of determining TA structure and flexibility.