The forgotten valve: lessons to be learned in tricuspid regurgitation.

Only limited information is currently available about the prognostic significance of tricuspid regurgitation (TR). The few existing studies, however, suggest a strong impact of TR on clinical outcome. Significant TR is associated with poor prognosis in patients with mitral stenosis after percutaneous balloon valvuloplasty and with a reduction in exercise capacity after mitral valve surgery. A significant increase in mortality among patients with moderate and severe TR has been reported, which was independent of left ventricular ejection fraction or pulmonary artery pressure. In 60 patients with flail tricuspid leaflet due to trauma, significant increases in atrial fibrillation, heart failure, and death were observed. TR was also an independent predictor of increased mortality in 1400 patients with left ventricular systolic dysfunction. TR is only rarely caused by primary abnormalities of the tricuspid leaflets. In most instances it is ‘functional’ in nature and is the consequence of geometric alterations caused by right ventricular dilatation, distortion of the subvalvular apparatus, tricuspid annular dilatation, or a combination of these factors. Significant functional TR most commonly occurs in combination with left-sided heart disease, which often dominates the clinical picture. The development of TR leads to a vicious cycle propagating further right ventricular dilatation and dysfunction, more tricuspid annular dilatation, leaflet tethering, and, consequently, worsening of TR. Although incomplete leaflet closure is the immediate cause of functional TR, the leaflets themselves are usually normal. What leads to such incomplete closure is the currently poorly understood geometrical alteration of the tricuspid apparatus that is caused by interaction between the altered tricuspid annulus size and shape, right ventricular remodelling, and displacement of papillary muscles (Figure 1) which lead to leaflet tethering. Min and co-workers have analysed the tricuspid valve apparatus using real-time three-dimensional echocardiography to predict residual TR after surgical annuloplasty. Tenting volume and anteroposterior tricuspid annulus diameter before surgery were the independent pre-operative predictors of short-term residual TR. In addition, the leaflet tenting angle between the tricuspid annulus line and the septal leaflet was a predictor for operative success. It is noteworthy that annuloplasty led to reduction of annulus size at the expense of an aggravation of leaflet tenting by inward displacement of the annulus. This was accompanied by a reduction of the septal-lateral diameter of the right ventricle, while anteroposterior dimensions remain unchanged. Min’s results are an important step forward as we gain knowledge about new tools for the prediction of immediate surgical success. Nevertheless, two major questions remain unanswered. First, what do these measurements tell us about the long-term success of tricuspid surgery? Follow-up data in this context are sparse. One small study on only 39 patients showed that in addition to tricuspid valve tethering, left ventricular as well as right ventricular function and pressure influence repair durability. Recent data from the Cleveland clinic on .2000 patients report a high recurrence rate of significant TR years after surgery, irrespective of the mode of repair. By 3 months after surgery, 34% of patients had moderate or severe TR, which increased to 45% of patients at 5 years. Risk factors of recurrent TR include higher grade of pre-operative TR, female gender, mitral valve replacement, and left ventricular dysfunction. Echocardiographic measurements were, however, not included in this analysis. Secondly, current ESC and AHA/ACC guidelines on tricuspid valve surgery are based on small retrospective studies as well as on expert consensus, and prospective randomized trials on the benefit of tricuspid valve surgery on outcome are lacking. In functional mitral regurgitation there is growing evidence for adaptive and compensatory mechanisms taking place in the leaflets. Based on the observation that leaflet area is substantially increased in patients with functional mitral regurgitation, DalBianco et al. recently used a sheep model to test the hypothesis