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Minimally invasive as it applies to aortic valve surgery refers to the exposure required to perform the aortic procedure, because total cardiopulmonary bypass is still required. Initial experience used the anterior thoracotomy, but recent series report the ministernotomy or "J" incision as the preferred technique for exposure. Though pain, blood loss, and length of stay may not be significantly different when compared with the conventional technique, lower costs and earlier recovery may be achieved. Minimally invasive aortic valve surgery is a technique that is still evolving.

The introduction of the Toronto stentless porcine valve (SPV) (St. Jude, Minneapolis, MN), recently approved by the Food and Drug Administration following a 6-year multi-institutional clinical trial from 1991 to 1997, reflects an evolutionary pursuit of an ideal valve substitute, namely, low thrombogenicity, freedom from anticoagulation, durability, easy availability, resistance to infection, and easy implantability. Currently, four different types of valve replacement have been time tested: mechanical valves, cryopreserved aortic homograft, stented heterograft, and pulmonary autograft (Ross procedure), and none of the available valve substitutes meet all the criteria of an ideal valve. The mechanical valve's favorable properties of durability and easy implantability are susceptible to thrombus formation, which requires lifelong anticoagulation. Although the aortic homografts are durable, with low incidence of infection and thrombogenicity, their widespread application has been limited by the lack of availability. The pulmonary autograft, with its native aortic valve properties, has been shunned by some surgeons because it requires a demanding technical expertise in implantation and needs an allograft in the pulmonary position. Stented xenografts are characterized by "off-the-shelf" availability, freedom from anticoagulation, easy implantability, and low incidence of infection. Its major drawback has been its limited durability. Another limitation is its residual transvalvular gradient. A modified version, a stentless xenograft, has been introduced to improve hemodynamic profiles in the hope of subsequent superior structural durability and patient survival. Two valves have been approved by the Food and Drug Administration, the Toronto SPV and the Freestyle valve (Medtronic, Minneapolis, MN). At The Methodist Hospital and the Baylor College of Medicine, the Toronto SPV stentless valve has been our stentless xenograft valve of choice. We therefore review the historical evolution, design advantages, surgical techniques, and clinical outcomes of this valve.

Bacterial endocarditis is an important cause of cardiac valvular problems. The diagnosis of bacterial endocarditis can be difficult, and, often, an aggressive clinical evaluation including serial blood cultures is necessary. The pathophysiology of endocarditis is changing with the rise of intravenous drug use; staphylococci are an increasingly common cause. Endocarditis often warrants surgical intervention. Operations for bacterial endocarditis range from valve repair to valve replacement to homograft replacement. The operations are technically challenging, but new methods of myocardial protection have markedly improved the surgical outcomes. Valve excision is an option for intravenous drug users with tricuspid valve endocarditis. Surgical management of endocarditis is a technically challenging but rewarding procedure that should be offered to appropriate patients.

Replacement of the diseased aortic valve represents one of the triumphs of cardiac surgery; however, the perfect valve substitute continues to elude surgeons after almost four decades of clinical experience. The characteristics of the ideal valve substitute include the following: central flow capacity, low transvalvular gradient, low thrombogenicity, durability, easy availability, resistance to infection, non-immunogenicity, and easy implantability. The pulmonary autograft first performed by Ross (Lancet 1967, 2:956-958) came closest to achieving these goals, but creates a double valve procedure for single valve disease. Aortic valve replacement (AVR) with homograft aortic valve was introduced by Ross in 1962 (Lancet 1962, 2:487) and Barratt-Boyes in 1964 (Thorax 1964, 19:131-150). Like the pulmonary autograft, homograft AVR results in an excellent hemodynamic outcome but suffers from limitations of graft availability, lack of durability, and difficulty with implantation. Mechanical valves and stented tissue valves allow "off the shelf" easy availability as well as easy implantability. These valves are unfortunately intrinsically obstructed to some extent because of the space occupied by the stent and sewing ring. Stent mounted tissue valves also continue to exhibit limited durability. Stentless xenograft aortic valves have been developed as a compromise between these ends of the valve spectrum to allow excellent hemodynamics and hopefully improved durability while allowing "off the shelf" availability in a variety of standard sizes. We examine the rationale for use of the stentless xenograft aortic valve, the clinical development of this valve, and the surgical techniques of implantation.

The introduction of the Starr-Edwards valve allowed complete replacement of diseased left-sided heart valves. With improved cardiopulmonary bypass, myocardial protection, and surgical techniques the mortality rate from aortic valve replacement decreased substantially, whereas the mortality rate from mitral valve replacement remained high, largely because of low cardiac output syndrome. Increasing use of mitral valve repair techniques resulted in a marked decrease in short-term and long-term morbidity and mortality when treating patients with mitral regurgitation. Some believed that this resulted from maintenance of the mitral annular papillary muscle continuity during mitral valve repair. Subsequent experimental and clinical studies have validated the positive short-term and long-term effects of maintaining the integrity of the mitral valve subvalvular apparatus. This article considers the history of the clinical use of preservation of the subvalvular apparatus, the physiologic studies examining this concept, and the clinical data available on its use. It also examines the following: 1) mitral stenosis versus mitral regurgitation and the preservation of the subvalvular apparatus; 2) whether the anterior, posterior, or both areas of the subvalvular apparatus should be preserved; and 3) the surgical techniques for the preservation of the subvalvular apparatus and valve implantation.

Allograft valves have been used for aortic valve replacement (AVR) for 35 years with excellent results. Early attempts at mitral valve replacement (MVR) with mitral valve allograft were unsuccessful mainly due to technical issues of measurement of appropriate graft size, difficulty of reimplantation, and early dehiscence of the papillary muscle anastomosis. Recently, interest in this procedure has been rekindled by successful laboratory experiments with mitral valve allograft implantation and improved understanding of the mitral valve apparatus from extensive mitral valve repair experience. In this article, we discuss the rationale for allograft use, the historical perspective of allograft use, and technical problems, along with current solutions and clinical outcomes of MVR with mitral valve allograft. Tricuspid valve replacement (TVR) with allograft mitral valve also is briefly discussed.

Minimally invasive surgical techniques have proliferated at a staggering rate in the last decade. Cardiac surgery has been a late entrant in this process but is currently experiencing a surge of interest in and techniques for minimally invasive approaches. Cardiac valve surgery has seen a rapid and ongoing evolution of minimally invasive approaches that, it is hoped, will decrease patient discomfort, operative morbidity, length of hospitalization, and cost, improve cosmetic healing, and facilitate return to normal function while not compromising short- or long-term outcomes of the surgical procedure. This article examines the evolution of recent experience with minimally invasive valve surgery and emphasizes the surgical considerations surrounding 1) the choice of incision, 2) access techniques for cardiopulmonary bypass (CPB), 3) methods of myocardial protection, 4) techniques for aortic occlusion, and 5) atrial incisions for exposure of the mitral valve. The results of early and currently available series are also reviewed.

Allograft valves have been used in cardiac valve replacement for 35 years. During much of this time, certain centers have used allograft aortic valves for aortic valve replacement and have reported excellent long-term results. After an initial period of failure using allograft mitral valves for mitral valve replacement, the technical problems of papillary muscle dehiscence and mitral regurgitation appear minimized by current investigators who now report encouraging early results. The current status of allograft use for aortic and mitral valve replacement is reviewed.