Threshold values of the vena contracta area for grading secondary tricuspid regurgitation and its association with outcomes

Background In secondary tricuspid regurgitation (STR), the regurgitant orifice is typically non-circular, developing along the line of coaptation of the leaflets. Vena contracta area (VCA) using three-dimensional echocardiography (3DE) has been recommended to improve the severity assessment of STR. Current TVARC recommendations suggest that a VCA between 0.75 and 0.949 cm2 indicates severe STR,and a simple mathematical addition of the 0.2 cm2 difference to the lower cut-off has been applied. However, the relationship of 3DE VCA with clinical outcomes in patients with STR, as well as the optimal threshold values of VCA remain unclear. Purpose Accordingly, we sought to: 1) determine the VCA threshold associated with increased risk of the composite endpoint (death from any cause or heart failure hospitalization, HHF); 2) identify threshold values of VCA for a five-grade STR severity grading scheme, using the guideline-recommended quantitative criteria as reference; and 3) evaluate whether VCA can improve the risk stratification in comparison to the conventional quantitative parameters of STR severity. Methods From a single-center, consecutively enrolled STR population, we analyzed the patients with good-quality transthoracic 3DE color datasets appropriate for VCA planimetry. (Figure 1A) To determine the VCA threshold values allowing to distinguish between adjacent TR severity grades, we used a non-parametric approach based on kernel density estimate intersections and pairwise comparisons between STR severity grades, utilizing the VCA values at the intersections. Results According to the multiparametric quantitative approach, among the 204 patients (77±12 years, 55% women), there were 9% mild, 38% moderate, 32% severe, 9% massive, and 11% torrential STR. The mean VCA was 0.69 cm² (95%CI 0.41-1.02 cm²). A threshold of VCA >0.65 cm2 identified by spline curve analysis conferred a 3.6-fold risk increase for the composite endpoint (IC 95%: 1.87-6.94) (Figure 1B,C). A VCA ≥0.65 cm2 was associated with an increased risk of events also in the STR patient subgroup with an effective regurgitant orifice (EROA) < 0.4 cm2. The optimal VCA threshold values for STR severity grading were: <0.43 cm2 for mild STR, 0.43 cm2-0.67 cm2 for moderate STR, 0.67 cm2-0.88 cm2 for severe STR, 0.88 cm2-1.26 cm2 for massive STR, and >1.26 cm2 for torrential STR (Figure 1D). When added to a multivariable model, VCA by 3DE significantly increased the model’s predictive power and maintained its independent association with outcomes (HR: 1.011, CI 95%: 1.003-1.019, P=0.007; c2 of models: 44 vs 39, p value <0.001) (Table 1). Conclusion VCA by transthoracic 3DE showed independent and incremental prognostic value over quantitative parameters of STR severity. Proposed threshold values of VCA for severe and massive STR are lower than those recommended by TVARC. A VCA ≥0.65 cm2 helped stratify the risk of events also in patients with non-severe STR according to EROA <0.4 cm2.