Isolated tricuspid regurgitation: a new entity to face Prevalence, prognosis and treatment of isolated tricuspid regurgitation

In recent years the tricuspid is no longer considered the "forgotten valve," but nowadays, specialists focused the treatment of tricuspid regurgitation (TR) especially at the time of left heart valve (LHV) surgery, overlooking the emerging entity of isolated TR. Its incidence appears to be rising along with the higher prevalence of atrial fibrillation (AF), intracardiac devices and intravenous drug users. Hence, the aim of the present review is to summarize the available evidences in terms of natural history, clinical presentation and treatment of isolated TR. Tricuspid regurgitation is commonly classified into primary and secondary etiology. Primary or organic TR is relatively uncommon (10%) and may be due to either acquired or congenital diseases. Conversely, secondary or functional TR, caused by dilatation and flattening of the tricuspid annulus along with increase of leaflet tethering due to the remodeling of the right ventricle (RV) has become in last decade an emerg-ing entity. Secondary TR may be due grade progression after left heart valve surgery, to previous TV surgery failure, RV remodeling or permanent AF. Primary TR causes pure volume overload on initially normal right-sided cardiac chambers. Conversely, RV enlargement is the major finding of secondary TR; RV systolic area, RV spherical index and right atrial area were identified as independent factors correlated with TV tethering height. The RV has less muscle mass than the left ventricle, and RV systolic function is therefore more load sensitive. Thus, pulmonary hypertension results in an early fall in RV ejection fraction and associated RV enlargement. An interesting entity is isolated TR related to AF, whose prevalence is estimated to be 14% in recent studies. It is known to cause dilation of the mitral and tricuspid annulus, together with changes in the dynamic mechanisms that govern the variation in area size during the cardiac cycle; as a matter of fact the relative change in TA area was significantly lower in AF (13.5%) than in sinus rhythm (SR) (33.1%). In isolated TR, medical therapy (MT) is indicated only in patients with secondary TR having also severe RV/LV dysfunction or severe pulmonary hypertension. Diuretics are the main MT in case of isolated TR in the presence of right HF in carefully selected candidates, surgery can be performed safely with good long-term survival and it should be considered early at first stages. In the treat-ment of isolated TR we had two diametrically opposed approaches so far, such as medical therapy, based almost exclusively on diuretics, and surgical therapy. In this scenario, trans-catheter approach is gaining momentum, including repair or re-placement treatment. The former sees the use of devices for direct or indirect annuloplasty, or leaflet approximation. The second consists of orthotopic or heterotopic replacement devices (transcatheter tricuspid valve replacement devices). Evi-dences from randomized studies and longer follow-up will help clarify the best patient selection and treatment strategies.