Surgical Treatment of Valvular Heart Disease

41 Surgical Treatment of Valvular Heart Disease



Michael E. Bowdish, Michael R. Mill, Brett C. Sheridan


Competency of the atrioventricular valves allows blood to enter the ventricles, where pressure is generated. When adequate systolic blood pressure is generated, the aortic and pulmonary valves open, allowing blood to enter the arterial system. The atrioventricular valves close, preventing the flow of blood into the atria. During diastole, the aortic and pulmonary valves close, the atrioventricular valves open, and the ventricles fill and ultimately begin the cycle of pulsatile blood flow through the systemic and pulmonary vascular tree.


Malfunction of any of the cardiac valves results in a less efficient circulatory system. Valvular dysfunction causes work overload in one or both ventricles. In extreme cases, resultant congestive heart failure can cause death. More information about etiology, pathogenesis, differential diagnoses, and diagnostic approaches used for evaluation of valvular diseases can be found in Chapters 34 to 40.


Rheumatic heart disease was commonplace before the discovery of penicillin. Astute physicians recognized that mitral valve stenosis frequently occurred many years after an episode of rheumatic fever. As mitral valve “stenosis” progressed, medications provided symptomatic relief but did not interrupt the stenotic process, and a need to relieve the obstruction surgically was apparent. The first successful attempt at surgical treatment involved incising the left atrial appendage, placing a finger through the incision into the left atrium, feeling the stenotic mitral valve, and relieving the obstruction by simple finger pressure. Soon after these initial therapeutic approaches, special knives and dilators were developed to relieve mitral valve stenosis. In the early days of cardiovascular surgery these procedures were all performed on the beating heart.


The use of the anticoagulant heparin allowed blood to circulate outside a patient’s vasculature without clotting and led to the development of cardiac and pulmonary bypass machines in the 1950s. It was then possible to keep the patient alive while stopping the heart for surgical repair. The ability to stop the heart, examine valve pathology, and attempt repair stimulated surgeons’ collaboration with mechanical engineers to develop prosthetic valves to replace those that were too diseased to repair.



First-Generation Prosthetic Valves


Initial attempts to duplicate valve leaflets with flexible, nonbiologic materials failed. The leaflets of these valves were too stiff in comparison with normal valve leaflets. Efforts at using nonflexible leaflets by constructing hinged-valve leaflets resulted in hinge thrombosis and malfunction. Design engineers then focused on free-floating occluders, such as disks or balls retained in a cagelike housing. This general valve design produced the first clinically useful valves, including the Hufnagel, Starr-Edwards, Smeloff-Cutter, and Beall valves (Fig. 41-1). In 1958, the Starr-Edwards valve was used in the first clinically successful valve replacement.


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Figure 41-1 First generation of synthetic prosthetic valves.


Although these early designs functioned as intended, the first caged-ball valves had major shortcomings: (1) they were bulky in design and did not fit well into a small ventricle or aorta; (2) they had a small internal orifice, making them relatively stenotic; and (3) they stimulated thrombus formation, which precipitated thromboembolic events, necessitating long-term anticoagulation therapy.



Second-Generation Prosthetic Valves


The disadvantages of early prosthetic valves led to the development of two divergent lines of valve design using synthetic materials (mechanical valves) or biologic tissue (bioprosthetic valves). The caged-ball valves were modified, and pivoting hingeless disk valves, such as the Lillehei-Kaster, Medtronic-Hall, and Björk-Shiley valves, were developed. The St. Jude and Carbomedics valves were the first successful hinged-leaflet valves (Fig. 41-2, top).


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Figure 41-2 Second generation of synthetic prosthetic valves and biologic valves.


Homograft valves harvested at autopsy and preserved in antibiotic solution or frozen were the first nonsynthetic valves to be implanted successfully. Their limited availability prompted the use of porcine valves procured from slaughterhouses. Porcine valves were preserved with glutaraldehyde and mounted on modified nylon-covered plastic or metal stents. Valves made of pericardium were also developed and used successfully (Fig. 41-2, bottom). Porcine and bovine pericardial valves are commonly used bioprosthetic valves today, whereas the hinged-leaflet valves are the commonly used mechanical valves.



Etiology and Pathogenesis


Cardiac valve pathology comprises two broad categories, congenital valve deformity and acquired valvular dysfunction. Congenital deformity can occur in one or more cardiac valves (see Section VIII). Patients with severe congenital valvular dysfunction can die if prompt surgical intervention is not undertaken. In patients with normally developed hearts, infection can cause valvular dysfunction at any age. Rheumatic heart disease secondary to untreated streptococcal infection and bacterial endocarditis can destroy a normal heart valve (Chapter 39

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Jun 12, 2016 | Posted by in CARDIOLOGY | Comments Off on Surgical Treatment of Valvular Heart Disease

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