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Fig. 6.13. Tricuspid valve and its relationship to the AV node and Bundle of His. Danger points for injury to AV node and bundle of His indicated by row of Xs.

Combinatorial Topology

from tricuspid regurgitation. The most common type of tricuspid regurgitation is secondary tricuspid regurgitation, i.e. a functional disorder rather than an organic disorder of the tricuspid valve itself. This functional disorder of the tricuspid valve results from annular dilation as a result of elevated right ventricular pressure usually resulting from mitral valve disease or left heart failure. The functional dilation of the tricuspid usually involves dilation of the anterior two-thirds of the tricuspid annulus, especially in the region of the p osterior leaflet. The septal leaflet is fixed between the trigones and does not dilate because it is part of the fibrous skeleton in the heart. In a similar fashion, the anterior leaflet of the mitral valve is fixed in position and usually does not dilate, whereas the posterior portion of the annulus mitral valve does dilate. The other type of tricuspid regurgitation is of rheumatic etiology.

When the tricuspid valve has rheumatic pathologic changes, the rheumatic process nearly always is associated with mitral and aortic valve disease as well. The tricuspid valve is the least common of these three valves to be involved with rheumatic disease. Rheumatic tricuspid regurgitation is usually associated with a variable amount of tricuspid stenosis. The hemodynamic effect of a moderate tricuspid stenosis is equivalent to a tight mitral stenosis because the right-sided pressures are low compared to left-sided pressure. Another etiology for tricuspid regurgitation is endocarditis. Intravenous drug abusers frequently develop vegetations on the tricuspid valve leading to valvular insufficiency.

When there is organic tricuspid pathology, as with rheumatic tricuspid disease or endocarditis, tricuspid valve surgery is indicated. Indications for operation on a functional tricuspid regurgitation are less clear. If a mitral valve replacement is being performed and the patient also has tricuspid valve regurgitation, then the indications for tricuspid valve replacement or repair are as follows: 1) The tricuspid regurgitation preoperatively has been important and constant, (i.e. not intermittent with periods of no tricuspid regurgitation during adequate medical management of the mitral disease); 2) Right ventricular dilation is longstanding; or

3) Pulmonary hypertension is evident. These would lead one to conclude that the likelihood of the functional tricuspid regurgitation resolving spontaneously after the mitral valve procedure is unlikely and that a tricuspid procedure is indicated.

Whether a replacement or repair of the tricuspid valve should be done depends on the status of the valve itself. If there is organic disease, generally replacement should be done. If the leaflets themselves are normal and the process is functional dilation, then repair can be performed. This can be one of several types: A Kay annuloplasty basically involves plication of the annulus in the region of the posterior leaflet (Fig. 6.14a). This narrows the annulus and basically obliterates the posterior leaflet of the tricuspid valve. The other procedure is annuloplasty of the tricuspid valve using a Duran ring (Fig. 6.14b). The size of the ring is estimated either by the diameter between the commissures of the anterior leaflet of the tricuspid valve, or by actually measuring the area of the anterior leaflet of the tricuspid valve and using this as the appropriate size for the Duran ring.

The DeVega annuloplasty is a tricuspid repair in which two limbs of a pledgetted stitch are brought around the annulus of the septal and anterior leaflet. The stitch is tightened such that only two gloved fingers may be passed through the tricuspid orifice. The conduction tissue adjacent to the septal annulus is totally avoided (Fig. 6.14c).

In tricuspid valve replacement, a portion of the valve leaflets are removed if they are in the way, otherwise, they may be simply plicated out of the way using the annular sutures. It is important to remember that when using the sutures at the septal portion, the suture should not actually be placed into the annulus of the

Tricuspid Valve Tissue Replacement

Fig. 6.14. Tricuspid valve repair.

(a) Kay plication annuloplasty of posterior leaflet.

(b) Duran tricus-pid annuloplasty ring. (c) DeVega tricuspid annu-loplasty. The septal leaflet is avoided.

Fig. 6.14. Tricuspid valve repair.

(a) Kay plication annuloplasty of posterior leaflet.

(b) Duran tricus-pid annuloplasty ring. (c) DeVega tricuspid annu-loplasty. The septal leaflet is avoided.

septal portion but rather within the base of the septal leaflet. This is to prevent injury to the conduction tissue. The base of the septal leaflet serves as a useful buttress and will hold the valve in position. Generally a Carpentier-Edwards bioprosthetic valve is used rather than a St. Jude's valve, although if a mitral valve replacement with a St. Jude's valve has been performed and the patient needs to be anticoagulated anyway, then there is some justification for placing a mechanical valve. However, this is suboptimal because a Swan-Ganz catheter cannot be placed through the St. Jude's valve in the tricuspid position but it can be when a Carpentier-Edward's bioprosthesis is placed. Triscuspid valve replacement is shown in Figure 6.15.

Technique of Tricuspid Valve Surgery

A median sternotomy is performed in the standard fashion, and the aorta is cannulated followed by bi-caval cannulation in both the superior vena cava and inferior vena cava. Caval tapes are passed around the superior and inferior vena cava. Isolated bicaval cannulation is required to prevent air from entering the ca-vae with the right atrium open, lest an air lock develop which would shut off the pump machine. Also without the caval tapes, there would be blood rushing into the right atrium obscuring the operating field. After the aorta and cavae have been cannulated, an antegrade plegia line is placed (in case cardioplegia is needed), cardiopulmonary bypass is initiated and caval tapes snared. The right atrium is opened and surgery is done on the tricuspid in the open, beating heart. Remember that surgery can be done on a beating heart on the right side only, and that the left side should never be opened while the heart is beating lest air be sucked into the left heart and then embolize out of the beating heart through the aorta. With

Fig. 6.15. Tricuspid valve replacement. A Carpentier-Edwards tissue valve is seated into the tricuspid annulus.

Fig. 6.15. Tricuspid valve replacement. A Carpentier-Edwards tissue valve is seated into the tricuspid annulus.

Onion Plant Diagram

the atrium open, the pump sucker is placed in the coronary sinus to drain blood coming out of the sinus and the tricuspid valve is inspected. If tricuspid valve replacement is required, the orifice is sized and the valve replaced. If the tricuspid valve needs repair only, then a Duran ring may be used with the size based on the area of the anterior leaflet. The right atrium is closed and caval tapes are loosened. Weaning from cardiopulmonary bypass is performed. If too much bleeding occurs during tricuspid valve procedures such that visualization is obscured, antegrade cold blood cardioplegia is given intermittently with the aorta cross-clamped. The valve procedure is done, then the aortic cross-clamp is released and the right atrium is closed with the cross-clamp off.

MECHANICAL AND BIOPROSTHETIC CARDIAC VALVES

A mechanical valve should be expected to last the lifetime of the patient. Bioprosthetic valves are made from porcine or bovine valve or pericardial tissue. They deteriorate with time, either becoming calcified or stenotic, or more commonly, the leaflet tears in the region of the stent post (Fig. 6.16). The advantage of the mechanical valve is that it is permanent. The disadvantage is that it requires anticoagulation for the rest of a patient's life. Even with adequate anticoagulation, there remains a chance of thrombosis.

Overall, there is a 5% chance of thromboembolism in 5 years with a mechanical prosthesis. There is about a 3% chance of developing an anticoagulation related complication in 5 years as a result of hemorrhage from the coumadin.

The advantage of the bioprosthetic valve is that there is no need for anticoagulation with no thrombotic or hemorrhagic complications. The disadvantage is that the valve deteriorates with time such that by 15 years, half of patients will require redo cardiac surgery to replace the valves. Tissue valves deteriorate much faster in young patients. The reason for this is unclear, but it is felt to probably represent differences in calcium metabolism in young people compared to older people. Also, the difference in force of contraction in younger people contributes to valve deterioration. In any event, in patient's under 50, a bioprosthesis deterio-

Fig. 6.16. Explanted Carpentier-Edwards bioprosthesis with a leaflet tear resulting in severe regurgitation.

Fig. 6.16. Explanted Carpentier-Edwards bioprosthesis with a leaflet tear resulting in severe regurgitation.

rates within 10-15 years in about half of patients and has an even worse record for younger patients.

It is interesting that tissue valves placed in the aortic position tend to deteriorate less rapidly than tissue valves placed in the mitral position. This is because when the ventricle contracts and there is high pressure within the ventricle, much greater stress is placed on the mitral valve than on the aortic valve, since during systole the aortic valve leaflets must simply open to permit flow, whereas the mitral leaflets are forcefully brought together leading to an increased rate of deterioration. For aortic valves, as a general rule, patients who are less than 70 years of age should undergo mechanical valve replacement because of the high chance that they will require reoperation at a later time if a tissue valve is placed. On the other hand, for patients who are greater than 70, a porcine or bovine bioprosthesis should be used. However for mitral valves, patients should be greater than 75 before a bioprosthesis is used because of the increased chance of deterioration of the mitral position. Patients less than 75 requiring mitral valve replacement generally should undergo placement of a mechanical prosthesis.

In younger people, exceptions may be made to the rule of using mechanical prostheses. For example, in an athelete who engages in high risk sports where there is a chance of head injury or hemorrhage, anticoagulation is a poor idea and a tissue valve should be placed, knowing full well that the patient patient will require another operation, perhaps quite early on. Also, a lady in childbearing age who wishes to have more children may be advised to have a tissue valve placed, again knowing that she will require reoperation for replacement of the tissue valve. If a patient with a mechanical valve does become pregnant, she should bear her children. The main problem with coumadin is the chance of teratogenicity. Therefore, coumadin should be stopped during the first trimester and the patient given heparin. Coumadin can be resumed the second trimester but then stopped again in the third trimester and the patient heparinized until the time of childbearing, at which time the heparin is stopped.

The mechanical valves that one can choose from include bi-leaflet and tilting disk mechanical valves (Fig. 6.17). St. Jude manufactures the valve with the most clinical experience and has basically remained unchanged since its inception over quarter-century ago. It is the valve used most commonly at our institution. The Medtronic-Hall, while not being in clinical use as long as the St. Jude's valve, is reported to be reliable as well. The Starr-Edwards valve was the original heart valve and works as a ball-in-cage type mechanism. It was altered to include a cloth covering over the struts which worsened the quality of the valve because cloth could embolize. This version is no longer being used. The Bjork-Shiley tilting disc and Duromedics bileaflet valves have both been pulled during their history because of the risk of fracture of the valve with embolizaton of the leaflets (Fig. 6.18). A modified Duromedics valve, however, has recently been introduced. Another valve, Carbomedics, is similar to the St. Jude's valve with the exception of a hinge modification and the fact that the valve can be rotated to allow for different orientations of the valve within the annulus once seated. Newer St. Jude's valvesm however, also can rotate. Although used in other countries previously, it has only

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