Tricuspid Valve Repair

Anatomy and Physiology

Of all the valves in the heart, the tricuspid valve (TV) is the largest and most apically placed between the right atrium (RA) and the right ventricle (RV). It consists of three leaflets, namely septal, anterior and posterior, and has a normal valve area of 7-9 cm2.[5] The tricuspid valve complex consists of the leaflets, annulus, chordae, papillary muscles, and attached right ventricle segment.[6][7] The mean pressure gradient across the TV is less than 2 mmHg, and peak velocity across the valve is less than 1 m/s due to the large size of the valve and lower pressures on the right side of the heart. There are reported variants of the TV with two or more than three cusps.[8] 

The anterior (or attitudinally anterosuperior) leaflet is the largest of the three leaflets with the greatest motion. Septal leafet is the least mobile and attached to the septum less than 10 mm apically from the septal insertion of the anterior mitral leaflet, a distinguishing feature helpful in diagnosing Ebstein anomaly when it is tethered to the right ventricular wall giving it an echocardiographic appearance of greater than 10 mm apical attachment and causing atrialization of the RV with severe TR. The posterior (or attitudinally inferior) leaflet is the shortest circumferentially. The coaptation point of the leaflets is at or below the level of the annulus. The coaptation length is 5 to 10 mm, allowing more valve area available in case of annular dilatation before failure to coapt.[9]

Usually, there are two papillary muscles, anterior and posterior, with a third septal papillary muscle, which is variable. Anterior papillary muscle is the largest, and attached chordae support the anterior and posterior leaflets. This papillary muscle sometimes joined by the moderator band. The posterior papillary muscle can be bifid or trifid, and the attached chordae support posterior and septal leaflets. The tricuspid annulus is a dynamic structure and D shaped, with a larger semicircular C-shaped segment correlating with the RV free wall and a shorter and straighter segment correlated to the septum.

Pathophysiology of Tricuspid Regurgitation (TR)

The two main types of tricuspid regurgitation (TR) are primary and secondary (functional). The most common etiology of TR is secondary (functional), and its incidence is approximately 90% among patients with TR.[10] Primary TR is less common and caused by anatomical involvement of TV structures and usually due to a congenital or acquired etiology affecting leaflets or chordae. In secondary (functional) TR, leaflets and chords are normal, and TR occurs due to atrial and ventricular dilatation, annular dilation, and chordal tethering. The most common causes of secondary TR are left-sided valvular or myocardial pathologies and pulmonary hypertension. 

Following are the causes of tricuspid regurgitation:

Primary TR

A. Congenital

• Ebstein anomaly
• TV hypoplasia, clefts
• Double orifice valve

B. Acquired

• Prolapse or flail of TV leaflets due to myxomatous degeneration
• Carcinoid syndrome
• TV endocarditis
• Pacemaker and ICD related
• Rheumatic disease
• Traumatic injury to the valve structures (chest trauma or iatrogenic with right-sided intracardiac procedures)

Secondary TR

• Left-sided valvular heart diseases (mitral valve stenosis/regurgitation)
• Left ventricular dysfunction
• Primary or secondary pulmonary hypertension
• Right atrial enlargement (in atrial fibrillation)
• Right ventricular dysfunction and dilatation (remodeling after right ventricular infarct)
• Tricuspid annular dilatation

Indications

Isolated tricuspid valve repair is uncommon in spite of the fact that tricuspid valve abnormalities can result in significant morbidity and mortality. Most of the tricuspid valve procedures are performed secondarily with other primary cardiac surgical procedures. The current most common indication is to perform tricuspid valve surgery in patients who have symptomatic severe primary tricuspid regurgitation.[11][12] Following are the indications for tricuspid valve repair or replacement:

• Symptomatic severe tricuspid stenosis
• Severe tricuspid stenosis without symptoms when the patient is undergoing left-sided valve surgery
• Symptomatic severe primary or secondary tricuspid regurgitation
• Severe primary or secondary tricuspid regurgitation (symptomatic or asymptomatic) when the patient is undergoing left-sided valve surgery
• Moderate to severe primary tricuspid regurgitation when the patient is undergoing left-sided valve surgery
• Asymptomatic or mildly symptomatic primary tricuspid regurgitation with evidence of progressive right ventricular dilatation and dysfunction
• Mild or moderate progressive functional (secondary) tricuspid regurgitation with a dilated annulus (more than 40 mm or more than 21 mm/m2) when the patient is undergoing left-sided valve surgery 
• Tricuspid valve endocarditis
• Carcinoid involvement of the tricuspid valve 
• Congenital malformations e.g., Ebstein anomaly
• Traumatic or iatrogenic injuries to the valve when taking biopsies or from pacemaker leads

Technique or Treatment

Surgical Repair of the Tricuspid Valve

Tricuspid regurgitation is the most common reason for surgical tricuspid valve repair. Patients with secondary (functional) TR most likely undergo repair while patients with primary TR are not considered suitable candidates for repair due to pathology involving multiple leaflets, and replacement has better results. The aim of TV repair is reducing annular diameter, increasing valvular adaptation, and reducing RV afterload. Important anatomic considerations for the surgeon include the presence of the atrioventricular node (AVN) and conducting system within the triangle of Koch demarcated as the base of the septal leaflet, coronary sinus orifice, and tendon of Todaro. The tricuspid annulus is also related to the base of the aortic valve, the membranous interventricular septum, the right coronary artery, the fibrous body, and the lateral atrioventricular junction.

A. Suture Tricuspid Valve Annuloplasty 

The first suture annuloplasty technique was described by Kay to treat secondary TR. In this technique, sutures are placed in a way to completely exclude the posterior tricuspid leaflet and converting the valve into a bicuspid valve.[13] Another technique, introduced by De Vega, is the suture annuloplasty in which two parallel sutures are placed in a counterclockwise fashion, starting from posteroseptal commissure to anteroseptal commissure around the TV annulus and tied together reducing annular diameter.[14] The problem with this technique is that sutures can cut through the myocardium, especially if it is fragile.

B. Ring Annuloplasty of the Tricuspid Valve

Carpentier introduced the technique of using a rigid or semi-rigid ring to reinforce and fixating the tricuspid annulus in systole in an attempt to restore the physiological geometry of the TV. The size of the ring is normally decided by measuring the distance from anteroseptal commissure to posteroseptal commissure.[15] The close proximity of the conduction system aortic root requires careful placement of sutures during the procedure.

C. Clover Technique for Tricuspid Valve Repair

Alfieri proposed stitching together the middle points of all the leaflets (similar concept as Alfieri stitch for mitral valve) and adding ring annuloplasty to decrease TV annular diameter. This technique gives the valve a clover shape, and so the procedure is known as the clover technique. This has been used in both primary and secondary TR.[16] 

Other surgical techniques for tricuspid valve repair are used in primary TR and depend on the mechanism and involved pathology. It ranges from surgical intervention and repair of leaflets when there is a prolapse or flail segment, chordal transposition, or neo chord when there is chordal rupture, and sliding papillary muscle repair when there is a diseased or elongated papillary muscle.[17] In case when the valve is affected primarily by a diseased process and a repair technique is not feasible to correct the valve pathology, like in carcinoid syndrome and endocarditis, valve replacement should be considered. Usually, a bioprosthetic valve is chosen for the tricuspid position due to decrease pressures, increase thrombotic risk, and future chances of pacemaker lead placement.

Transcatheter Repair of the Tricuspid Valve

Though it has been shown that untreated tricuspid regurgitation has adverse outcomes, most of the patients with sole tricuspid pathology still receive conservative treatment due to the high risk involved with the surgery. For this reason and because of the success of treating other valve problems, the percutaneous transcatheter tricuspid repair is gaining attention. There are many innovative technologies under investigation for transcatheter tricuspid valve repair targeting leaflet coaptation, annuloplasty, and prosthetic valve deployment. Currently, the most widely used technique is the off-label use of the edge-to-edge clip repair system.[18] Current surgical tricuspid annuloplasty consists of ring and suture techniques. Of suture techniques, the surgical plication of posterior leaflet making the valve functionally bicuspid and the suturing of the three leaflets edge to edge, are the most common techniques to treat severe tricuspid regurgitation. Transcatheter edge-to-edge TV repair can produce similar results as achieved by these suture techniques. Reports of first cases of transcatheter TV repair were published in 2016 in patients with severe TR and high surgical risk of complications.[19] Intraprocedural guidance to direct the clip at the desired leaflets is a challenge in this technique due to anteriorly located TV and three leaflets.

Three-dimensional transesophageal echocardiography (TEE) is required for the successful placement of the clips. The other challenge is the steering of the clip system, as it is not designed to be used for the tricuspid valve. Percutaneous transcatheter tricuspid repair techniques can be broadly divided into the following categories:

• Direct suture annuloplasty 
• Direct ring annuloplasty
• Coaptation enhancement

The inferior vena cava is located very close to the tricuspid valve and septum, making it very challenging to steer the system perpendicular to the valve for clip deployment.[20] The main aim is to deploy the clips in a way to reduce the effective regurgitation orifice area (EROA) of the valve. Usually, deploying the valve on septal and anterior leaflets gives the best results.[21] Other techniques are the deployment of two clips, on septal anterior and septal posterior leaflets, and a zipping technique, where two clips are deployed to anteroseptal commissure making the valve bicuspid. This technique is being used in patients considered high risk for surgery. Though there are no set criteria available so far to exclude patients for this procedure, patients with concurrent tricuspid stenosis, EROA more than 1.5 cm2, coaptation defect more than 15 mm, and restricted leaflet mobility due to hardware like implanted leads, are considered not suitable for transcatheter repair.[22]

There are transcatheter annuloplasty devices under investigation for the treatment of functional TR, where transcatheter direct annuloplasty can be performed by anchoring a ring whose size can be controlled according to the desired diameter.[23] In some cases, due to annular dilatation and leaflet involvement, a combined approach using a coaptation device along with an annuloplasty device is warranted for better results.[24]

Complications

The complications involved with tricuspid valve repair, whether surgical or transcutaneous, are generalized to any valvular procedure of the heart. Following complications can occur after tricuspid valve repair:

• Perioperative bleeding and resulting blood products transfusion-related complications
• Arrhythmias and heart blocks
• Heart failure
• Stroke
• Infections of the surgical site and/or the valve prosthesis
• Sepsis
• Pulmonary complications e.g., pneumonia, embolisms 
• Renal failure (higher risk in transcatheter procedures with pre-existing renal disease due to dye use)
• Drug reactions
• Prosthetic valve malfunction

The tricuspid valve has been considered a "forgotten" valve due to hesitation in treating sole tricuspid lesions in the past. Surgical mortality of tricuspid valve replacement is 3-4 times higher, compared to other single valve open procedures. Severe tricuspid regurgitation is associated with a poor prognosis, independent of age, biventricular function, and RV size. Most of the tricuspid valve repair procedures are performed in conjunction with the left-sided cardiac procedure.

The current gold standard for surgical repair is ring annuloplasty with an incomplete semi-rigid annuloplasty ring, but some centers perform the modified bicuspidisation when the annulus is not severely dilated. Since a very small fraction of patients is considered surgical candidates, there has been a renewed interest in developing percutaneous transcatheter devices for tricuspid regurgitation. Percutaneous techniques are likely to increase in the future due to improved technology and increased awareness of tricuspid regurgitation effects on the long-term outcomes.

Clinical Significance

Tricuspid valve repair as a sole procedure is quite uncommon. Historically tricuspid valve incompetence has not been considered significant to affect the outcome, a concept which is questioned in recent studies, showing untreated tricuspid regurgitation, particularly in the presence of other cardiac diseases is associated with increased morbidity and mortality.[25] A moderate to severe tricuspid regurgitation should not be ignored as eventually, it affects the quality of life and survival. Particularly with more options available to perform tricuspid valve repair, surgical valvuloplasty, and percutaneous repair, any significant degree of tricuspid regurgitation should be addressed.

Enhancing Healthcare Team Outcomes

Tricuspid regurgitation is the most common indication requiring tricuspid valve repair. Untreated tricuspid regurgitation leads to increased morbidity and mortality. Severe tricuspid regurgitation is associated with a poor prognosis, independent of age, biventricular function, and right ventricular size. Surgical mortality of tricuspid valve replacement is 3-4 times higher, compared to other single valve open procedures. Functional tricuspid regurgitation frequently coexists with left-sided valve disease, and most of the tricuspid valve procedures are performed secondarily with other primary cardiac surgical procedures. The most common indication for tricuspid repair is secondary (functional) tricuspid regurgitation. Complications of tricuspid valve repair include heart blocks, infections, bleeding, prosthetic valve dysfunction, stroke, and death. 

An interprofessional team should include cardiologists, anesthesiologists, cardiac surgeons, and intensivists. Preoperative echocardiographic evaluation of the tricuspid valve requires coordination between the sonographer and the cardiologist. In the intraoperative environment, closed-loop communication between the surgeon, anesthesiologist, cardiologist, circulating nurse, and srub technician is vital for successful tricuspid valve repair. A detailed handoff to the receiving critical care team is essential in improving the outcomes and minimizing adverse events.