E

Fig. 6.19b. Medtronic HancockĀ® porcine valve.

become available in the United States for about a decade. St. Jude's has developed a new "HP" valve standing for "Hemodynamic Plus" valve, which permits a greater flow orifice for any given valve size. This is because the sewing ring is placed further up the annulus rather than in the annulus, meaning that less of the sewing ring is needed to seat the valve, thus the orifice can be bigger. Each size of the St. Jude's HP valve corresponds to one size up of the regular St. Jude's valve, i.e. a 19 mm HP St. Jude's valve corresponds to a 21 mm regular St. Jude's valve. This corresponds to approximately 25% greater flow through any given valve using the HP valve.

Tissue valves on the market include the Carpentier-Edwards porcine bioprosthesis and bovine pericardial bioprosthesis (Fig. 6.19a), the Hancock porcine valve (Fig. 6.19b), the Ionescue-Shiley bovine pericardial prosthesis, and the Medtronic Intact valve. The Edwards bovine pericardial aortic bioprosthesis appears to have superior long-term results to the porcine valve, with overall freedom of valve dysfunction at 91% over 12 years of study. It is now the most frequently implanted aortic bioprosthesis in the United States and is the tissue valve of choice at Harbor-UCLA. The mitral version of the pericardial valve is now on the market. The Intact valve uses nonpressure fixation of the valve, decreasing the chance of tearing by eliminating the collagen pattern responsible for making the leaflet stiff.

TECHNIQUES OF COMBINED VALVE PROCEDURES

Combined valve or valve-coronary procedures are commonplace. A systematic, routine approach is a requirement for optimizing outcomes. Our techniques at Harbor-UCLA are presented here.

Combined Mitral valve Replacement and Aortic Valve Replacement

Combined mitral and aortic valve replacement is performed using antegrade and retrograde intermittent cold blood cardioplegia. Although we have used continuous warm blood cardioplegia, we find that the aortic valve region is flooded from retrograde flow from the coronary orifices, making the procedure more difficult. Cardiopulmonary bypass is performed as previously described using bi-caval cannulation. The aorta is cross-clamped, cardioplegia given antegrade and the heart arrested. The aorta is opened and the aortic valve removed. The left atrium is opened in standard fashion. A mitral valve replacement is done. The left atrial vent is then placed in the left ventricle and the left atriotomy closed. Deairing of the atrium is not necessary at this point as the aorta, still open, communicates with the left heart. After the left atrium has been closed, pledgetted sutures are applied to the aortic annulus and the annulus is sized. The conduct of the operation, therefore, is to perform the aortic valve resection first, then the mitral valve resection and replacement, and then the aortic valve replacement last. This is to prevent manipulation of a replaced aortic valve while trying to replace the mitral valve, which could lead to dehiscence of the aortic prosthesis from the annulus.

Combined Mitral Valve Replacement and Tricuspid Valve Replacement

Intermittent antegrade and retrograde cold blood cardioplegia is administered and a left atrial vent is used. Cardiopulmonary bypass is initiated using bi-caval cannulation with caval tapes. The cross-clamp is applied and the heart arrested using antegrade then retrograde cardioplegia. The left atrium is opened and a mitral valve replacement is performed. The left atrial vent is then placed in the left ventricle and the left atrium is closed. Prior to finishing the closure, the left ventricular vent is shut off and 10 cm pressure applied to the lungs for deairing of the left heart. When the left atrium is closed, the LV vent is turned on again, the root vent is turned on, the aortic cross-clamp is released, and the patient is placed in Trendelenburg. The vents are shut off and air is aspirated from the dome of the left atrium and left ventricular apex. The right atrium is then opened and the tricuspid valve is replaced or repaired. Alternatively, one can do the tricuspid valve replacement in the arrested heart with the cross-clamp on to improve visualization, but in general it is better to have the cross-clamp off to have reperfusion of the heart.

Combined Coronary Bypass/Valve Replacement

The conduct of the operation is to perform the distal anastomoses first with the coronaries attached to a turkey-foot perfusion cannulae for continuous infusion. Then the valve replacement is done, either aortic or mitral or both. The proximal anastomoses are next performed. Combined coronary/valve procedures are generally done using antegrade and retrograde cold blood cardioplegia in an intermittent fashion.

ENDOCARDITIS

Endocarditis of a cardiac valve can be one of the most devastating infections a physician must manage. Native valve endocarditis may occur in patients who are intravenous drug abusers; in these patients the tricuspid valve is usually involved. The aortic and mitral valves may be involved. Typically, intravenous drug abusers have Staphylococcus aureus as the primary organism. This generally represents acute bacterial endocarditis. Patients with valvular endocarditis who are not drug abusers may obtain their infections from dental abscesses, tooth extraction or oral surgery. The organism is frequently Streptococcal and represents subacute bacterial endocarditis.

Prosthetic valve endocarditis occurs in a post-surgical infection of a heart valve. Early on in the perioperative period and even up to 1 year, Staph epidermidis and gram-negative organisms are the most common. Late prosthetic valve endocarditis usually involve Streptococcal organisms. Patients who have native valve endocarditis may present in a number of ways. These include fever, chills, night sweats and signs of systemic bacteremia, or they may present with shortness of breath, heart failure and signs of hemodynamic compromise. Patients suspected of having endocarditis should undergo an echocardiogram which can be invaluable in assessing valve function and determining if there are vegetations attached to the valve. Cardiac catheterization and cineangiography may be indicated. The patient should be stabilized by afterload reduction in the case of aortic insufficiency and mitral insufficiency and admitted to the Intensive Care Unit if necessary. Blood cultures should be taken and the patient empirically treated with broad-spectrum antibiotics. The antibiotic regimen should be modified according to culture results.

The indications for surgery for native valve endocarditis are as follows:

1) Hemodynamic compromise with heart failure. This typically occurs as sudden and severe aortic or mitral regurgitation in a heart that has not been accustomed to chronic and slowly worsening regurgitation pattern.

2) Persistent bacteremia after at least 1 week of adequate antibiotic therapy, or resistant organism.

3) Massive destruction of the valve with an annular abscess.

4) Recurrent embolization by the vegetation or a persisting vegetation which may embolize at any time.

It is important to perform a CT scan of the brain and spleen since optimally other septic organs are managed before the heart surgery, although this is not always feasible.w In general, if at all possible, the patient should undergo at least 1 week of intravenous antibiotics prior to cardiac surgery intervention.

For prosthetic valve endocarditis, surgery has been shown to significantly improve survival compared to medical management. Prosthetic valve endocarditis usually involves a periprosthetic leak. For a periprosthetic infection, antibiotics are given preoperatively, then the valve is replaced. Replacement is particularly compelling if there is evidence of periprosthetic leak, septic embolization, or refractoriness of the infection. In selected patients, if there is good response to antibiotics and there is no periprosthetic leak or other complications, one may simply manage the infection with antibiotics.

In the case of a destroyed aortic annulus due to an abscess in either a native valve endocarditis or prosthetic valve endocarditis, one could do a Bentall type ascending aortic and aortic valve replacement with deep seating of the valve in the left ventricular outflow tract and reimplantation of the coronary arteries. Alternatively a homograft valve with its attached aorta may be deeply seated into the left ventricular outflow tract with reimplantation of the coronary arteries.

For tricuspid valve endocarditis a similar protocol may be followed as with the aortic and mitral valves with the exception that tricuspid valve excision alone without replacement may be a management option. Patients who present with tricuspid valve endocarditis once again should be treated with antibiotics, and if there is poor response to the antibiotic treatment or if there are other compelling reasons for surgery the patient may simply undergo tricuspid valve excision. The patient is carefully watched in the perioperative period. If there are signs of severe tricus-pid regurgitation with ascites, massive hepatomegaly, lower extremity edema and inadequate hemodynamics because of poor volume loading of the left heart, then reoperation may be necessary and the tricuspid valve replaced with a bioprosthesis.

More and more surgeons appear to be performing primary tricuspid valve replacement rather than simple tricuspid valve excision as the initial surgery to prevent the frequent hemodynamic sequelae of tricuspid valve excision alone.

AORTIC ALLOGRAFT AND AUTOGRAFT PROCEDURES

Many cardiac surgeons are developing increased interest in the use of aortic allograft (homograft) and pulmonary autograft to manage a wide variety of aortic valve and root pathology. Allografts procured from organ donors are cryopreserved and commercially available in a variety of sizes. Because anticoagulation can be avoided and because of the low incidence of valve failure, throm-

boembolic events, and endocarditis, the use of allograft and native pulmonary tissue is particularly attractive. One of the most compelling indications for allograft procedures is in acute aortic endocarditis with massive tissue destruction resulting in aortic ventricular discontinuity. Being a biologic device, these alternative methods are not expected to surpass or equal the longevity of most mechanical aortic valves. There is increasing evidence that the longevity of homografts and autografts is superior to porcine bioprostheses, although the comparison to bovine pericardial bioprostheses is not complete at present.

Allograft aortic procedures can be summarized as freehand allograft (subcoronary) technique, complete root replacement, and inclusion cylinder technique. In the freehand allograft technique, the graft is trimmed to include only the valve leaflets and commissures. Three tissue "posts" are left remaining between which is left enough room to avoid obstructing the patient's native coronary ostia (Fig. 6.20a). The allograft is sewn into position in the aortic annulus and the tissue "posts" are sewn to the native aortic wall, avoiding the coronary ostia.

The most important factor in determining short and long term success for the freehand allograft technique is the precision of insertion. Slight technical errors which may not be apparent at the initial operation lead to geometric imperfection, distortion and increased failure rate. This has led many to abandon the freehand technique in place of complete allograft root replacement which eliminates

Fig. 6.20a. Freehand (infracoronary) allograft. (b) Allograft for complete root replacement with coronary ostia holes constructed. (c) Inclusion cylinder technique.

Fig. 6.21a. Ross pulmonary autograft procedure. Aorta is opened and aortic valve removed. Courtesy of Dr. Jeff Milliken, Harbor-UCLA.

Fig. 6.21b. The pulmonary valve is excised en bloc with portions of the right ventricular outflow tract and pulmonary artery. A large residual defect in the right ventricle is left remaining. Courtesy of Dr. Jeff Milliken, Harbor-UCLA.

Fig. 6.21d. The pulmonary autograft is sutured to the aortic annulus. Courtesy of Dr. Jeff Milliken, Harbor-UCLA.

errors of geometric misalignment (Fig. 6.20b). Short and long term studies clearly demonstrate that such complete root replacement procedures have lower pressure gradients and lower incidence of aortic insufficiency than the freehand technique. One technical modification is the inclusion cylinder technique, in which the allograft root replacement is performed within the walls of the native aorta, which is then wrapped around the allograft (Fig. 6.20c). Advantages of this tech-

Your Heart and Nutrition

Your Heart and Nutrition

Prevention is better than a cure. Learn how to cherish your heart by taking the necessary means to keep it pumping healthily and steadily through your life.

Get My Free Ebook


Post a comment