Secondary tricuspid regurgitation: neglected no more!

This editorial refers to ‘Prognostic validation of partition values for quantitative parameters to grade functional tricuspid regurgitation severity by conventional echocardiography’, by D. Muraru et al., pp. 155–165.

Secondary tricuspid regurgitation (STR) has been living in the shadow of its left-sided counterpart for too long. As time progresses, this trend appears to change—certainly fuelled by the success of modern transcatheter therapies. STR is frequently occurring across the heart failure spectrum^1,2 and, as community-based studies indicate, STR is strongly tied to the ageing population. Most commonly, STR develops as a consequence of left-sided structural heart disease or pulmonary hypertension.³ Societal guidelines recommend grading according to a traditional system (mild, moderate, and severe). The terminology, however, is not clearly defined with respect to the associated risks-partly because its relationship to quantitative measurements remains unknown.

In this issue, Muraru et al.⁴ assessed this relationship between quantitative measures of STR severity and the composite endpoint of death and hospitalization for congestive heart failure. Moreover, they identified cut-off values for echocardiographic parameters of STR severity, based on patients’ outcome. The authors enrolled a cohort of 269 patients with at least mild STR and performed two- and three-dimensional echocardiographic assessment of STR severity according to semiquantitative and quantitative parameters. The results confirm that STR severity is independently associated with mortality and morbidity. The authors elegantly advance the current concept of STR grading by highlighting the continuous increase in risk with rising STR severity. This approach strengthens the currently unmet clinical need to understand quantitative metrics of STR severity as a tool for risk stratification beyond the three-grade scale and enhances risk stratification in the sense of an individual patient-centred approach. The recently proposed expansion of the grading scheme with the two additional grades ‘massive’ and ‘torrential’⁵ is certainly an important step towards diversification of the tail end of the STR spectrum specifically with the recent advances in transcatheter repair techniques. The present data from Muraru et al., however, drives the attention towards the most important aspect of the disease: the threshold when STR evolves from a surrogate of disease severity towards a critical contender driving heart failure progression, morbidity and mortality. Based on their results, the authors defined cut-off values indicating severe functional tricuspid regurgitation for vena contracta width (VCW > 6 mm), the effective regurgitant orifice area (EROA) (>0.3 cm²), the regurgitat volume (RegVol) (>30 mL), and the regurgitant fraction (RegFr) (>45%), thereby questioning current guidelines standards (VCW ≥ 7 mm, EROA ≥ 0.4 cm², RegVol ≥ 45 mL).

Several technical difficulties have to be addressed to provide reproducible and consistent echocardiographic measurements. Image acquisition of sufficient quality and underestimation of the EROA by two-dimensional echocardiography due to the sphericity assumption of the proximal isovelocity surface area method limit the applicability in STR grading. The RegFr, a measure of regurgitant volume relative to right ventricular stroke volume is specifically challenging due to the more complex right-ventricular shape. In their study, however, Muraru et al. acquired and analysed three-dimensional echocardiographic data, providing the most accurate solution for calculating the RegFr by echocardiographic acquired datasets. Of note, the RegFr threshold indicating severe STR by echocardiography (45%) is almost identical to the recently published cut-off for cardiac magnetic resonance imaging (50%).⁶ Additional risk-levels that might need attention when assigning the terms mild, moderate, and severe are the risk of STR progression^7,8 and the potential benefit of an intervention⁹ specifically opposed to the inherent procedural risk. While these risk-levels are evolving and subject to prospective and randomized trials, the observations by Muraru et al. provide a solid basis for the echocardiographic assessment of STR.

In summary, the study by Muraru et al. contributes in an important way to the pathophysiologic understanding of STR, emphasizing its significance at even lower VCW, EROA and RegVol thresholds than previously expected. Moreover, it validates for the first time, partition values for the RegFr strengthening the clinical role of three-dimensional echocardiography. Future directions will need a constant refinement of STR grading that recalibrates to the evolving risk-benefit ratio of STR intervention, advances in medical therapy, and the risk of STR progression. Furthermore, development of an integrated quantification might add the necessary flexibility to account for the morphological, pathophysiological, and functional variability of STR. The current data by Muraru et al. lays the foundation to further advance such a personalized diagnostic approach in order to offer holistically tailored therapies and collaboratively master the challenge of STR.

Conflict of interest: none declared.

The opinions expressed in this article are not necessarily those of the Editors of EHJCI, the European Heart Rhythm Association or the European Society of Cardiology.

References