Tricuspid regurgitation (TR) is one of the most common valvular pathologies, being estimated as second of all valvular pathologies in frequency in the Framingham study 
. The following studies found the prevalence of greater than moderate TR to be 0.55% in their study population and strongly associated with female gender and increased age 
, while the OxValve study found that 2.7% of their study population had significant or severe TR 
. In the US, the prevalence of TR was estimated to be 1.6 million, with annual new TR diagnosis being 250,000; however, lower than 8000 TR surgeries were completed 
. More recently, the UK Biobank study reported an incidence rate of 2.0 per 10,000 person–years and a mortality rate of 0.51 deaths per 10,000 person–years 
. Regarding economic burden, a recent study showed that TR, irrespective of heart failure presence, is associated with higher rates of all-cause hospitalization, hospital days, and healthcare-associated expenditure 
It is well established that significant TR is associated with a higher disease burden, and worse cardiovascular outcomes. In a retrospective study 
analyzing 5223 patients, greater TR severity was correlated with higher mortality rates. Furthermore, a subanalysis of the COAPT trial in patients with TR and mitral regurgitation (MR) showed that individuals with MR and moderate or severe TR had higher NYHA class and BNP levels, as well as more severe MR, highlighting the overall worse clinical outcomes in patients with TR and MR coexistence 
. Finally, in the setting of heart failure with reduced ejection fraction, TR was associated with a more severe heart failure presentation as well as worse survival independently of other baseline markers 
2. Pathophysiology of Tricuspid Regurgitation
TR can be pathophysiologically categorized as primary TR, where there is an intrinsic abnormality in the tricuspid valve, and secondary or functional TR, where the regurgitation is a result of the enlargement of the right heart chambers, resulting in a subsequent dilation of the tricuspid annulus and regurgitation 
Primary TR is a result of an either preexisting congenital or acquired defect in the tricuspid valve. The most commonly congenital pathology is Ebstein’s anomaly, a rare disease accounting for 0.3–0.5% of congenital heart defects 
, affecting 0.39–0.72 children per 10,000 births 
. As an embryogenic anomaly, it is characterized by failure of delamination of the tricuspid valve, with the septal and posterior leaflets being displaced towards the apex of the right ventricle, resulting in displacement of the tricuspid functional annulus. The most common cause for primary TR is rheumatic heart disease 
. Rheumatic TR is present in 7.7% of rheumatic heart disease patients, and in most cases, it is associated with a concomitant pathology of the mitral valve 
. A restrictive and regurgitant phenotype is commonly encountered, as a pure stenotic or regurgitant pathology is rare 
. Other causes of primary TR include carcinoid syndrome 
and right-sided infectious endocarditis, which is more rarely encountered (5–10% of all endocarditis cases); however, 90% of its cases develop TR 
. Finally, iatrogenic primary TR is a known complication of the implantation of either a pacemaker or defibrillator device, caused either by direct mechanical damage to the tricuspid valve leaflets or delayed right ventricular activation and alteration of the right ventricular morphology 
Secondary or functional TR is not commonly associated with the valve itself rather than the negative remodeling of the right ventricle, which results in dilation of the tricuspid annulus and misalignment of the valvular leaflets 
. Conditions that could result in this disease are left heart valve pathologies and pulmonary hypertension, which by increasing backward pressure, promote ventricular and atrial remodeling as well as annular dilation. In specific, there is a close relation of TR with other valvular pathologies, as studies show that TR coexists with severe mitral regurgitation in 30–50% of patients and with severe aortic stenosis in 25% of patients 
. Additionally, ischemic mitral regurgitation is strongly associated with development and progression of TR, while TR severity is proportional to the extent of the regurgitation 
. Furthermore, studies showed that coexistence of TR at the time of surgery for mitral or aortic regurgitation adversely affects short- and long-term outcomes 
. Increased risk is also evident in the coexistence of TR and low-flow, low-gradient aortic stenosis with reduced left ventricular ejection fraction 
. Therefore, potential transcatheter management of coexisting valvular pathologies at the same time could be beneficial and improve patients’ outcomes; however, relevant data from clinical studies are still limited. Atrial fibrillation can also be accounted for TR by creating an annular dilation directly and not by negative remodeling of the right ventricle 
. Secondary TR is the most common type of TR, with more than 90% of patients having functional TR, as shown by Mutlak et al. in an echocardiography-based study 
3. Need for Interventional Therapies–Transcatheter Intervention Options
3.1. Leaflet Approximation
Leaflet approximation is the most well-studied procedure thus far. The technique, also known as transcatheter tricuspid edge-to-edge repair (TEER), is aiming to approximate the leaflets of the tricuspid valve via implanting clips and coapting two of the leaflets. There are two TEER devices currently approved for use in TR: The TriClip, as derived by the device used for mitral regurgitation (MitraClip), and PASCAL.
3.1.1. TriClip (Previously MitraClip)
Nickenig et al. 
were the first to study use of a tricuspid leaflet approximation technique for TR using the MitraClip device. They included 64 patients with symptoms of heart failure (HF) and severe tricuspid regurgitation (TR) and implanted a MitraClip device with a 97% success rate. No intraprocedural deaths or major complication occurred. At 30 days after the procedure, TR was significantly reduced, with TR grade being reduced by at least 1 grade in 91% of the patients. NYHA class and a 6-minute walking test (6MWT) were also improved in this cohort, suggestive of the positive impact of the intervention in the functional status of the patients. Following studies from Orban et al. 
and Braun et al. 
, both examining the use of MitraClip in small cohorts of patients with severe TR, also showed significant improvements in TR grade and functional status, as indicated by the improvement of NYHA class and 6MWT distanced.
Mehr et al. 
studied 249 patients from the TriValve registry receiving a MitraClip for TR. The technical success rate was 96% while the acute procedural success, defined as a TR grade lower or equal to 2, was achieved in 77% of patients. The procedure decreased the proportion of patients with a TR grade greater than 3 from 97% pre-procedurally to 23% before discharge (p
< 0.001), while TR reduction of at least 1 grade was reported in 89% of patients and improvement by at least 1 NYHA class was observed in 72% of patients. At 1 year, patients with a TR grade greater than 3 were significantly lower (baseline 97%; follow-up 28%; p
< 0.001), while 69% of patients were NYHA class I/II. The estimated rate of combined mortality and rehospitalization for heart failure was 34.7%.
Lurz et al. 
, in the TRILUMINATE trial, studied a total of 85 patients, receiving a TriClip for symptomatic TR. At follow-up, 87% of subjects had a sustained TR reduction of at least 1 grade after 1 year, with 70% of subjects having moderate or less TR, as compared to 8% at baseline and 60% at 30 days. Specifically, 56% (22 of 39) of subjects with baseline massive or torrential TR achieved moderate or less TR at 1 year, with 90% achieving at least a 1-grade reduction in TR. Subjects classified as NYHA functional class I/II increased from 31% at baseline to 83% at 1 year (p
< 0.0001). The 6MWT distance was also significantly increased. Among all subjects at 1 year follow-up, the hospitalization rate decreased from 1.30 to 0.78 events/patient–year (p
More recently, undergoing clinical trials presented their preliminary results in the clinical trial sessions of cardiology congresses. Specifically, Lurz et al. 
presented at PCR London Valves 2021 the 30-day results of the bRIGHT study, the first real-world study, having enrolled 300 patients. In the preliminary results presented, the implantation success rate is 98%. At the 30 days follow-up, 71% of patients had moderate or less TR (p
< 0.0001) and 78% were NYHA class I/II (p
< 0.0001). In terms of safety, the procedure was found to be safe, as 1% of patients experienced a major adverse event during the 30 days follow-up. At PCR London Valves 2022, the 1-year results of bRIGHT were also presented 
. At 1 year, 86% of patients had moderate or less TR, while the improvement in NYHA class and KCCQ was maintained throughout the year. A total of 11.5% of patients experienced a major adverse event. The mortality rate was 11.0%, while a 44% reduction in heart failure hospitalizations was noted. Moreover, D. Adams presented at TCT 2022 the results of 30 days of the device arm of TRILUMINATE-Pivotal trial 
. In specific, 97 patients received a TriClip and were followed up for 30 days. The implantation success rate was 99%, while at 30 days, 74% had less than moderate TR and 67% had a reduction in TR class ≥ 2 grades. Moreover, 76% of patients were NYHA I/II at 30 days, in comparison to 32% at baseline (p
< 0.0001). The procedure was safe, with a 1% mortality rate. A total of 7.2% of patients presented major bleeding. Finally, the 1-year results of TRILUMINATE-Pivotal, which were announced and simultaneously published at ACC 2023, included 350 patients, with 175 in the intervention and 175 in the medical therapy arm. The study showed that, regarding the primary composite endpoint of death from any cause or tricuspid-valve surgery, heart failure hospitalization and improvement of the Kansas City Cardiomyopathy Questionnaire (KCCQ) score of at least 15 points, this composite was favored in the TEER arm, with a win ratio of 1.48 (p
= 0.02). Specifically, KCCQ score change was significantly higher in the TEER arm compared to the medical therapy arm; however, there was no significant difference in the incidence of death, tricuspid valve surgery or hospitalization for heart failure. In terms of procedural outcomes, 87.0% of the patients in the TEER arm and 4.8% of those in the control group had TR of no greater than moderate at 30 days (p
< 0.001), while the intervention was found to be safe, as at 30 days follow-up, 98.3% of the patients who underwent the procedure were free of major adverse events 
Fam et al. 
were the first to study the effectiveness of the PASCAL system in TR. They included in their study 28 patients with severe TR, in whom a PASCAL device was implanted. The patients were followed up for 30 days. At the time of the follow-up, mortality rate was 7.1%. No major adverse cardiac and cerebrovascular events were observed. A total of 88% of patients were in NYHA functional class I or II, with TR grade ≤ 2+ in 85% at 30 days. In terms of safety, there were two single-leaflet device attachments, which were managed conservatively. The 6MWT distance was significantly improved. Another study by Kitamura et al. 
, in a similar size of patients, also found an improvement in TR severity, as 82% of patients had less than moderate TR after PASCAL implantation, as well as significant NYHA class and 6MWT distance improvement.
Kordali et al. 
, in the CLASP TR EFS, studied the PASCAL device in 34 patients with severe TR. A total of 97% of the patients had severe or greater TR, and 79% were NYHA III/IV at baseline. A total of 29 patients (85%) received PASCAL implants, and at 30 days follow-up, 85% of them achieved at least 1 TR grade reduction, with 52% having moderate or less residual TR (p
< 0.001). A total of 89% of the patients were NYHA class I/II after the procedure (p
< 0.001), while the mean 6MWT distance was significantly improved and the mean (KCCQ) score was improved by 15 points (p
< 0.001). The rate of major adverse events was 5.9%. None of the patients experienced cardiovascular mortality, stroke, myocardial infarction, renal complication, or reintervention.
Recently, preliminary results from ongoing trials were also released for studies currently assessing the use of PASCAL in TR. Specifically, in EuroPCR 2022, the results of the 30 days of the TriCLASP study were reported 
, while the 6 months results were presented at PCR London Valves 2022 
. The study involved 74 individuals with severe symptomatic TR that received a PASCAL device and were followed up for 30 days and 6 months. A total of 72 patients finally underwent the procedure and 97% successfully received the device. At 30 days, 88% of patients had at least 1 TR grade reduction and 90% had moderate or lower TR. The composite major adverse event rate was 3.0%. At six months follow-up, 88% of patients had moderate or less TR, while 83% had at least 1 TR grade reduction. Furthermore, 61% of patients were NYHA I/II, while significant improvements were noted in both KCCQ score and 6MWT distance. The major adverse event rate at six months was 4.0%, while all-cause mortality was 5.1%. Moreover, Davidson presented the results of 30 days of the CLASP II TR trial from the roll in cohort 
in TCT 2022. The trial included 73 patients followed up for 30 days. Data were available at the time of the follow-up for 68 patients. At 30 days, 83.0% of patients improved by 1 or more TR grade, 62.3% by 2 or more grades, and 73.6% had a TR class lower or equal to moderate TR. Statistically significant improvement was also noted in the NYHA class and the KCCQ score. In terms of safety, the composite major adverse event rate was 8.7%, with no mortality or heart failure hospitalizations reported. Finally, results of 1 year of the CLASP TR study 
were also presented at EuroPCR 2022. The study originally enrolled 65 patients, however, 1-year follow-up data were available for 46. At the time of the follow-up, all patients improved by at least 1 and 75% by at least 2 TR grades, while 86% had moderate or lower TR. Significant improvement in the patients’ functional status were sustained at 1 year, as depicted by NYHA class and KCCQ score. The composite of major adverse events rate at 1 year was 16.9%, while all-cause mortality rate was 10.8%. With the use of the device, the annual rate of heart failure hospitalizations was reduced by 56.4%.
Transcatheter annuloplasty aims to improve TR taking into advantage the same mechanism of surgical annuloplasty, considering the pathophysiology of secondary TR; specifically, the annular dilation caused by the increased left heart pressures. Therefore, by reducing the annular diameter, this procedure aims to decrease the pathologic dilation and subsequently the regurgitation through the valve, providing the same clinical benefit of surgical annuloplasty via a transcatheter procedure. Several devices were tested, with either suture-based or ring/non sutured devices, with Cardioband being the only device approved for use at the moment (CE Mark 2018).
Nickenig et al. 
were the first to study the use of Cardioband in the TRI-REPAIR trial. They enrolled 30 individuals with moderate to severe symptomatic TR unsuitable for surgical intervention, and a Cardioband was implanted in them. In all patients, the device was successfully implanted. Both at 30 days and 6 months, there was a sustained, significant reduction in the annulus diameter from baseline. This result was also significant at the 2 years follow-up 
. Moreover, there was a reduction in the severity of TR, with 76% at 30 days, 73% at 6 months, and 72% at 2 years having less than moderate TR. A total of 88% of patients were NYHA class I/II at the 2 years follow-up. Finally, MWT and KCCQ score were both improved throughout the 2 years follow-up period.
In the TriBAND study 
, the researchers followed up 61 patients with severe functional TR who underwent a Cardioband implantation. The device was successfully implanted in 58 patients. Follow-up echocardiographic results were available for 54 and 42 patients at discharge and at 30 days follow-up, respectively. There was a 19% reduction in the annular diameter at discharge and 20% at 30 days. At least 1 TR class reduction was reported in 78% of patients at discharge and 85% of patients at 30 days, while 2 TR class reduction was achieved in 59% of patients at discharge and 30 days. Furthermore, 74% of patients were NYHA class I/II (p
< 0.001). In terms of safety, all-cause mortality was 1.6%, while the rate of the composite of major adverse events was 19.7%. In PCR London Valves 2022, V. Rudolph presented the one-year results of the TriBAND study 
. The tricuspid annulus diameter was reduced by 22% in one year, while 86% of patients had at least 1 TR grade reduction and 67% had at least a 2 TR grade reduction. A total of 61.1% of patients were NYHA class I/II at 1 year, while there was also a significant improvement in KCCQ score throughout the follow-up period. Cardiovascular mortality was 2.9%, while a major bleeding occurred in 11.5% of patients.
Following this, Davidson et al. 
, in the Cardioband TR Early Feasibility Study, studied 30 patients with a Cardioband and followed them up for 30 days. The device was successfully implanted in 28 patients. Annulus diameter was significantly decreased from baseline both at discharge and at follow-up. Furthermore, at 30 days, 85% of patients had a reduction of at least 1 TR class and 56% of at least 2 TR classes, while 44% had moderate or less TR (p
< 0.001). Finally, 75% of patients were NYHA class I/II, while the KCCQ score at the follow-up was significantly improved.
Finally, the 1-year results of the Cardioband TR Early Feasibility Study 
, including 37 patients, show a sustained reduction in TR as well as a sustained improvement in NYHA class and KCCQ score. In terms of safety, the 1-year cardiovascular-related mortality was 8.1%, while 5.4% of patients required reintervention, and in 35.1%, a major bleeding event was reported.
3.3. Tricuspid Valve Replacement
The first valve system used for transcatheter tricuspid valve replacement was the Gate system. Navia et al. 
were the first to implant the Gate valve in two individuals with severe TR, not candidates for surgical management. The procedure was successful in terms of device implantation and TR reduction, with only mild paravalvular leaks being noted. Hahn et al. 
also showed a significant reduction in TR and in NYHA class. Finally, in the larger up-to-date study of the Gate valve 
, initially including 30 patients, the procedure was successful in 26 patients, while 2 patients (5%) were converted to open heart surgery. Out of the patients that successfully received the valve, all had a reduction in TR by at least 1 grade and 75% by at least 2 grades. At the time of the follow-up (mean follow-up time was 127 ± 82 days), 62% of patients were NYHA class I/II and four patients died. It is noteworthy that the in-hospital mortality rate was increased (10%); however, there were no late adverse outcomes related to the device at the time of the follow-up.
Another device currently being assessed is the Lux-Valve. Lu et al. 
reported the first use of this valve in humans in an observational study including 12 patients with severe TR. Procedural success was 100%. At 30 days follow-up, 90.9% of patients had no to mild residual TR, while 54.5% of patients were NYHA class II. There was one recorded death 18 days post procedurally due to vasospastic myocardial infarction, and one surgical reintervention for bleeding. Sun et al. 
, in a subsequent study, also reported great procedural success as well as echocardiographic and functional improvement at 1 year, with the exception of one mortality event due to heart failure worsening.
Following this, T. Modine presented the one-year results of their multicenter study studying the Lux-Valve 
. The study enrolled 31 patients and had a follow-up period up to one year. At the time of the follow-up, 92.9% of patients had mild or no TR and 100% had a reduction of at least 2 TR grades, while 82.8% were NYHA class I/II. The reported all-cause mortality at 1 year was 3.23%.
Lastly, the Lux-Valve Plus, a new system offering the same type of valve with a new delivery system permitting the transjugular approach, was recently tested in a first-in-man study 
. The trial included 10 patients with a follow-up at 30 days. At the time of the follow-up, all patients had no or trivial TR (n = 90% and n = 10%, respectively) and a significant improvement in NYHA class (p
< 0.05), while in terms of safety, there was no procedure-related, cardiovascular, cerebrovascular, or bleeding adverse events reported and the mortality at 30 days was 0%.
Evoque is another type of valve used for tricuspid valve repair. The first in-human use was reported by Fam et al. in a single case report, which was followed by a first in-human study by the same team 
, including 25 patients. The patients were followed up for 30 days. The procedural success was 92%, and no intraprocedural adverse outcomes were noted. A total of 96% had a TR grade lower or equal to 2, while 76% of patients were NYHA class I/II at the time of the follow-up. The mortality rate was 0%, and in terms of adverse effects, 12% of patients had a major bleeding, and in 8%, a pacemaker was implanted. Webb et al. 
presented the 1-year follow-up results of the first in-human study. At 1 year, 97% of patients had a TR grade lower or equal to 2, while 87% had a TR grade of 1 or lower. A total of 70% of patients were NYHA class I/II at 1 year and the mortality rate was 7%.
Moreover, in the recently published results of 30 days of the TRISCEND trial 
, 56 patients were enrolled and received an Evoque valve. At 30 days, 98% of patients had mild or no TR and 78.8% of patients were NYHA class I/II. Furthermore, the KCCQ score and 6MWT distance were significantly improved. The composite major adverse event rate was 26.8%, with 1 cardiovascular death, 2 device embolization, and 15 severe bleedings that occurred at the time of the follow-up. The one-year results of the TRISCEND, report at PCR London Valves 2022 
, showed that at one year, 97.6% of patients still had mild or no TR, while 93% remained NYHA class I/II. The significant improvements in the KCCQ score and 6MWT distance were sustained. Finally, the composite major adverse event rate was 30.2%, with 10.7% having experienced a major bleeding event.
3.4. Heterotropic Caval Valve Implantation
Hetertotropic caval valve implantation aims to implant a valvular device in the venae cavae system, which will reduce the systematic blood flow regurgitation as a result of the TR. In order for the procedure to apply to the patient, there must be presence of caval flow reversal and an appropriate inferior vena cava (IVC) diameter. There are three devices available, divided in two categories: balloon expandable devices (Sapien) and self-expandable devices (TricValve and Tricento). TricValve consists of two self-expandable valves, one in each vena cava, while Tricento has one valve implanted in the IVC. There is currently a limited number of trials regarding these systems.
In respect to Sapien, the first randomized trial (TRICAVAL) was stopped due to safety concerns regarding valve dislocation62, while another non-randomized trial (HOVER) evaluating Sapien is currently being underwent 
In regards to TricValve, two randomized trials (TRICUS and TRICUS EURO) investigated the effect of TricValve in severe TR patients. TRICUS 
evaluated the use of TR in 6 out of 24 patients, and even when not mentioning specific results for the device, in all patients, there was heart failure symptom relief and significant reduction in IVC and right atrium pressures. A total of 50.2% of patients functionally improved to NYHA class I/II. The thirty-day mortality rate was 8% and in-hospital mortality was 16%. The TRICUS EURO study 
enrolled 35 patients in whom a TricValve was implanted. Thirty-day procedural success was 94% and no periprocedural deaths were recorded. At the six months follow-up, both KCCQ score and NYHA class were significantly improved, with 79.6% of patients being NYHA class I/II. Moreover, the six-month mortality rate was 8.5%.
Finally, in regards to the Tricento system, most experience is documented in case reports 
. However, in a multicenter registry study 
, Wild et al. studied 21 patients receiving a Tricento prosthesis for a year, with a median follow-up of 61 days. The procedural success was 100%. Significant decrease was noted at both right ventricular end diastolic pressures and the NYHA class, with 65% of patients being NYHA I/II at the follow-up. In three patients, asymptomatic fractures of the device are noted. Lastly, the survival rate at one year was 76%.