Introduction
It is difficult to separate discussion of the tricuspid valve (TV) from that of the right ventricle (RV) because abnormalities of TV function are usually associated, or even caused by, degrees of right ventricular dysfunction. In the normal circulation, the low pressure in the RV allows the TV to function under low stress with low afterload and so even moderate degrees of TV dysfunction are generally well tolerated. In considering the abnormalities of the TV, it is best to consider them under the following four headings:
1. The TV in the setting of biventricular circulation
2. The TV in the systemic RV
3. The TV in the functionally univentricular circulation
4. Ebstein’s anomaly of the TV
Tricuspid Valve in Biventricular Circulation
Congenital isolated abnormalities of the TV are rare. Tricuspid stenosis is more commonly a surrogate marker of a small RV and so is rather a degree of ‘hypoplasia’ of the valve rather than valvular narrowing. Tricuspid regurgitation (TR) is commoner, but the majority is functional regurgitation secondary to volume overload of the RV (such as with large atrial septal defects (ASDs) or due to chronic pulmonary regurgitation after repair of Fallot’s tetralogy) or right ventricular strain (such as with pulmonary stenosis with no VSD). Primary valvar causes of TR include isolated dysplasia of the leaflets, leaflet clefts (most commonly in the anterior leaflet) and flail/elongated chordae. Acquired TR is commoner than primary valve dysplasia and is most likely to be due to damage or tethering of the septal leaflet after VSD (or Fallot) repair or damage to the valve leaflet during an interventional catheter procedure or secondary to an endocardial pacing wire across the valve (see Table 15.1).
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Clinical Presentation and Investigation.
Hypoplasia of the TV and small/borderline RV is dealt with in Chapter 13; however, isolated stenosis of the TV can cause liver engorgement and exercise intolerance in severe cases. If there is a small ASD, then there may be right-to-left shunting causing a degree of cyanosis – this may be the presenting feature. TR in the absence of other lesions is usually very well tolerated, especially in childhood, and rarely causes any symptoms. Trans-thoracic echocardiography is the mainstay of investigation and gives excellent anatomical and functional assessment of the valve. The Carpentier principles of valve assessment should be applied, looking at annular dilatation, leaflet motion and sub-valvar apparatus in turn. Secondary causes of regurgitation are very common, and care should be taken to look for any associated lesions or cause for right ventricular dysfunction. 3D echo can be helpful in understanding the mechanism of regurgitation, but investigation modalities other than echo are rarely needed. In cases of secondary TR, the investigations will be guided by the nature of the underlying lesions (e.g. ASD may need MRI and cardiac catheter to assess right ventricular volume and Qp:Qs).
Surgical Management.
In the rare cases of isolated valvar stenosis with a normal-sized annulus, surgical commissurotomy may be possible, but thickened and dysplastic stenosed valves may require replacement. Regurgitant valves are generally very amenable to repair because the low-pressure environment of the right-sided circulation and compliance of the RV will provide a good setting to accommodate durable repair. Additionally, the aetiology of regurgitation is usually secondary – and surgery will usually involve concomitant repair/correction of the primary problem, which then optimizes the chance for successful repair.
Annuloplasty.
Circumferential annuloplasty using a double-layered suture (De Vega annuloplasty) is the most commonly used technique for symmetrical dilatation of the TV annulus. The sutures follow the true annulus at the hinge points of the valve and avoid the septal component of the annulus in the triangle of Koch to avoid risking injury to the A-V node and bundle. Sutures are reinforced with soft pledgets and tied down with a dilator passed through the valve orifice of a size equivalent to the predicted size for the patient’s weight/body surface area (BSA) (Figure 15.1A). Partial annuloplasties for more asymmetrical valves or correcting more localized jets of regurgitation include commissural annuloplasties or the Kaye annuloplasty, which is predominantly based on the inferior leaflet (Figure 15.1B). Choice depends on the symmetry of the valve and is guided by the echo assessment. Adolescents or adults with no need to accommodate for growth could have an annuloplasty ring to provide a sturdier support for the valve. However, since most patients are younger and are also having the primary lesion addressed, a fixed ring is not always necessary. There is some evidence that older adult patients (>30 years) with severe regurgitation will have a more durable result with a ring rather than simple annuloplasty suture.
Leaflet Repair.
True clefts are unusual but most commonly seen in the anterior leaflet. These can be closed primarily and are often combined with a simple annuloplasty. Localized regurgitation due to natural crenulations in the leaflets has been described, and closing these areas together in a similar fashion can be effective.
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