Chapter 61 – Acquired Heart Disease Valvular

1679 CHAPTER 61 Stenotic or regurgitant cardiac valves create hemodynamic demands on one or both ventricles of the heart. The compensa- tory mechanisms of the ventricles permit the heart to tolerate these lesions for varying periods of time, sometimes years, before surgical intervention is required. Ultimately, however, significant valvular lesions produce systolic and/or diastolic ventricular dys- function, leading to heart failure. As a general rule, surgery for stenotic valve lesions may be deferred until the patient develops symptoms. Regurgitant valve lesions, however, may produce significant ventricular dysfunction before symptoms develop; therefore, surgery in patients who do not have symptoms may be indicated. Among the heart’s valves, the aortic and mitral valves are the most likely to acquire disease; therefore, this chapter focuses on diseases of the aortic and mitral valves. HISTORICAL PERSPECTIVE Heart failure from mitral stenosis was well recognized by the late 19th century, and efforts at surgical correction began well before the heart-lung machine was available.1 In 1897, Samways sug- gested (but never acted on) the possibility of dilating the stenotic mitral valve. Based on his postmortem studies of rheumatic heart disease in London, Brunton in 1902 proposed surgical intervention for mitral stenosis by passing a dilator through the wall of the left ventricle retrograde into the mitral valve orifice. His proposal was shunned by London physicians, and Brunton never tried this maneuver. The concept, however, was applied 20 years later in Boston when the first report of successful surgi- cal correction of mitral stenosis appeared in 1923. Cutler and Levine reported successful relief of mitral stenosis by incision of the valve with a knife introduced through an apical left ventricu- lotomy. In 1925, Soutter performed the first successful closed mitral commissurotomy at the London Hospital by introducing his index finger through the left atrial appendage. Despite Sout- ter’s success, he received no more patient referrals, and another 20 years elapsed before the procedure became widespread. In June 1948, Bailey in Philadelphia and Harken in Boston each performed a successful closed mitral commissurotomy. Thereaf- ter, it became widely used to treat mitral stenosis. By the mid-1970s, the closed technique was supplanted by open mitral commissurotomy. Although closed mitral commis- surotomy achieved good palliation of mitral stenosis for its era, open mitral commissurotomy offered several advantages. First, the valvuloplasty could be performed under direct vision. The primary reason for failure of closed mitral commissurotomy was residual stenosis, not restenosis. In up to 75% of patients, the subvalvular apparatus of the mitral valve contributes signifi- cantly to the stenosis. The open technique permitted precise and maximal division of fused commissures, as well as fused chordae. In addition, calcium could be sharply débrided from the valve, and any residual mitral insufficiency could be corrected at the time of operation. Finally, the closed technique had the disad- vantage of potentially dislodging a left atrial thrombus, resulting in intraoperative embolization and stroke. Today, however, open mitral commissurotomy is rarely performed; it was supplanted by balloon mitral valvuloplasty by the mid-1990s. Surgical attempts to correct aortic stenosis also began in the early 20th century.1 In 1912, Tuffier, in Paris, unsuccessfully attempted transaortic digital dilation of a stenotic aortic valve. In Charleston, South Carolina, in 1948, Smithy performed the first successful aortic valvotomy in a 21-year-old woman from Ohio. Smithy died later that same year of aortic stenosis at the age of 34 years. Three years later, in Philadelphia, Bailey reported successful aortic valvotomy by insertion of a mechanical dilator across the stenotic valve of patients to open fused commissures. In 1952, Hufnagel and Harvey at Georgetown University placed the first prosthetic ball valve into the descending aorta of a patient with aortic insufficiency. Surgery on the aortic valve under direct vision required the development of cardiopulmo- nary bypass by Gibbon in 1954. In 1955, Swann performed the first successful aortic valvotomy using hypothermia and inflow occlusion. Initially, open aortic valve operations were limited to aortic valve commissurotomy and débridement of calcified aortic valve leaflets. Harken, in Boston, in 1960, and Starr, in Portland, Oregon, in 1963, however, reported replacement of the aortic valve with a prosthesis. In 1962, Ross in London suc- cessfully performed orthotopic homograft valve replacement. In 1967, Ross performed the first pulmonary autograft procedure (Ross procedure) for correction of aortic stenosis. In the mid- 1960s, stent-mounted porcine aortic valves were implanted, but these formaldehyde-fixed valves degenerated rapidly. In 1974, Carpentier, in Paris, reported superior longevity of the historical perspective diagnostic considerations mitral valve aortic valve operative technique surgical outcomes choice of prosthetic valves ACQUIRED HEART DISEASE: VALVULAR David A. Fullerton and Alden H. Harken 1680  SECTION XI  CHEST This attachment of the anterior leaflet to the mitral annulus extends to the aortic annulus through fibrous tissue, providing fibrous continuity between the aortic and mitral valves; the left ventricular side of the anterior leaflet of the mitral valve is visible immediately as the surgeon looks down through the aortic valve into the left ventricle. The posterior leaflet is rectangular and its attachment to the mitral annulus extends for approximately two thirds of the circumference of the mitral annulus. The two leaf- lets are separated by two distinct commissures. There are three important surgical landmarks (see Fig. 61-1). First, the circumflex coronary artery runs along the epi- cardial surface of the heart overlying the posterior mitral annulus. Only millimeters of left atrial muscle separate the artery from the annulus, making it susceptible to injury during mitral valve surgery. Second, the aortic valve is in close approximation to the anterior leaflet of the mitral valve (aortomitral continuity). The noncoronary leaflet of the aortic valve is therefore susceptible to injury during mitral surgery. Third, the atrioventricular node is located deep to the posteromedial commissure of the mitral valve. Mitral Stenosis Causes Rheumatic fever is the principal cause of mitral stenosis, and approximately two thirds of patients with rheumatic mitral ste- nosis are female. Rheumatic fever usually occurs in childhood or adolescence (mean age, 8 to 12 years) and creates an inflam- matory infiltration of the myocardium and valves. Perhaps because the disease afflicts young people and many years pass before symptoms are manifest, a prior history of rheumatic fever is often difficult to confirm. As the mitral valve heals after acute rheumatic fever, the mitral apparatus may become deformed slowly and the patient typically remains asymptomatic for at least 10 years. Symptoms most commonly appear during the glutaraldehyde-preserved porcine valve; thereafter, their usage was well established. By 1981, bileaflet mechanical valves were widely implanted in the aortic and mitral positions and largely supplanted the use of ball cage mechanical valves. In the mid- 1990s, bovine pericardial valves were shown to have durability similar to porcine valves and both types of bioprostheses became widely implanted. By 2004, most valves implanted in the United States were tissue valves. In 2002, transcatheter aortic valve replacement was performed by Cribier in Rouen, France. DIAGNOSTIC CONSIDERATIONS Valvular heart disease may be suggested by a patient’s history or by a heart murmur detected on physical examination. Regardless of the valve lesion in question, echocardiography should be used to assess the severity of the stenosis, regurgitation, or both. Information available from the echocardiogram includes defini- tion of valve anatomy, assessment of ventricular contractile func- tion, determination of the magnitude of valve regurgitation using color flow Doppler imaging, and determination of the severity of valve stenosis. Transthoracic echocardiography is noninvasive and may provide the necessary information. If more information is needed, transesophageal echocardiography may provide better definition of aortic and mitral valve anatomy; it is also a more sensitive imaging modality for the detection of mitral regurgitation. Although most valve lesions may be accurately diagnosed by echocardiography, cardiac catheterization may be necessary to confirm the diagnosis or to provide additional information pertaining to ventricular function. Before surgery, it may be appropriate to exclude the presence of coronary artery disease. Mitral or aortic valve areas may be determined at cardiac cath- eterization using the Gorlin formula,2 which permits calculation of the valve area, as follows: Valve area flow across the valve/(C [ mean transvalvular gr = × aadient ]) where C is an empirical constant, 44.5 for the aortic valve and 38 for the mitral valve. MITRAL VALVE Surgical Anatomy of the Mitral Valve The normal function of the mitral valve is dependent on coor- dinated interaction of the mitral valve apparatus, which includes the mitral valve annulus, valve leaflets, valve chordae tendineae, and left ventricular papillary muscles. The normal mitral valve has two leaflets, the anterior (or aortic) and poste- rior or (mural) leaflet. Two papillary muscles arise from the left ventricular wall, the posterior (or posteromedial) and anterior (or anterolateral). Each leaflet of the mitral valve is connected to each of the papillary muscles by tendons, the chordae tendineae. The leaflets are suspended from the mitral annulus, a col- lagenous structure that encircles the orifice between the left atrium and ventricle. Although the two leaflets have approxi- mately the same surface area, they have different shapes (Fig. 61-1). The anterior leaflet is rectangular. Its base is attached to the mitral annulus anteriorly and the width of the base is approximately one third the circumference of the mitral annulus. FIGURE 61-1  Anatomy of the mitral valve as it relates to other cardiac  structures.  Important  surgical  landmarks  include  the  relationship   of  the  mitral  valve  to  the  aortic  valve,  circumflex  coronary  artery,   and  atrioventricular  (AV)  node.  (From  Buchanan  SA,  Tribble  CG:   Reo perative mitral replacement. In Kaiser LR, Kron IL, Spray TL [eds]:  Mastery  of  cardiothoracic  surgery.  Philadelphia,  1998,  Lippincott- Raven, p 351.) L. main coronary a. Aorta Pulmonary a. Subaortic curtain Mitral valve Aortic (ant.) l. Mural (post.) l. Circumflex coronary a. R. coronary a. Tricuspid valve AV node Artery to AV node Post. descending coronary a. Coronary sinus ACquIREd HEART dISEASE: VALVuLAR  ChapTEr 61  1681 SECTIO N XI C H EST to chronic obstruction to pulmonary venous drainage (fixed component); and (3) pulmonary arterial vasoconstriction (reac- tive component). Diagnosis Symptoms Dyspnea is the principal symptom of mitral stenosis. Dyspnea is typically brought on with exertion or is associated with the abrupt onset of atrial fibrillation. The increased cardiac output or heart rate with exertion or the loss of atrial kick and tachycardia with atrial fibrillation result in an increased trans- valvular gradient. This in turn increases left atrial pressure and the pulmonary veins and capillaries become engorged, produc- ing the sensation of dyspnea and promoting pulmonary edema. If the left atrium enlargement is sufficient to compress surround- ing structures, the patient may complain of dysphagia or hoarse- ness. Marked elevation in left atrial pressure may produce hemoptysis. physical Examination The left ventricle is typically normal in size and the apex is therefore not displaced. The murmur of mitral stenosis is best heard at the apex. It is a low-pitched, rumbling diastolic murmur that decreases with inspiration and increases during expiration; it may be markedly decreased by the Valsalva maneuver. An opening snap precedes the murmur, is heard at the apex, and represents the completed excursion of the mitral valve leaflets. If the mitral leaflets are stiff or calcified, an opening snap may not be heard. In patients with pulmonary hyperten- sion, signs of elevated right ventricular and central venous pres- sure may dominate the clinical picture. Physical findings, such as distended neck veins, hepatomegaly, ascites, and peripheral edema, combined with a loud pulmonary valve component of the second heart sound (P2) heard on cardiac auscultation, suggest significant pulmonary hypertension. Diagnostic Tests  Chest Radiography Several findings may be noted on the chest radiograph. The cardiac silhouette may be normal in size, but the left atrium is enlarged. The enlarged left atrium may be seen as a double density behind the right atrium on the poster ante- rior projection or it may be seen to displace the left mainstem bronchus superiorly. On the lateral projection, the enlarged left atrium may displace the esophagus posteriorly. Calcification of the mitral leaflets or the mitral annulus may be seen. Pulmonary venous hypertension should be suspected when the pulmonary arteries are enlarged and there is cephalization of pulmonary blood flow. Echocardiography Echocardiography is the principal modality used to confirm the diagnosis. Using the echocardiogram, the mitral valve area may be determined by two mechanisms. First, the mitral valve area may be determined directly from the echo- cardiogram by planimetry. Second, measurement of the velocity of blood flow across the valve by Doppler echocardiography permits calculation of the transvalvular gradient. Because the transvalvular gradient persists longer with greater stenosis of the valve, the time required for the transvalvular gradient to decline may be measured; this is referred to as the pressure half-time. The mitral valve area may then be calculated using the following formula: Mitral valve area /(pressure half-time)= 220 patient’s third or fourth decade of life. Healing of the inflam- mation from rheumatic fever ultimately causes the cusps and commissures of the mitral valve to thicken and fuse, with con- comitant fusion and shortening of the chordae tendineae. The structure of the valve apparatus then calcifies and narrows, becoming funnel-shaped. Such thickening and fusion of the valve not only creates stenosis but also often prevent complete closure of the valve. Of all patients with rheumatic mitral valve disease, approximately 50% have combined mitral stenosis and mitral regurgitation. Other causes of mitral stenosis that are far less common than rheumatic fever include malignant carcinoid, systemic lupus erythematosus, and rheumatoid arthritis. Rarely, congeni- tal malformation of the valve may cause mitral stenosis, and congenital mitral stenosis is almost never an isolated congenital cardiac lesion. Pathophysiology The cross-sectional area of the normal mitral valve is 4 to 6 cm2. A mitral valve area of 2 cm2 is considered moderate mitral ste- nosis and an area of 1 cm2 is considered severe mitral stenosis. Under normal conditions, there is no pressure gradient across the mitral valve and the left atrial pressure is usually less than 15 mm Hg. As the mitral valve becomes more narrowed, an increasing pressure gradient is required to move the blood across the mitral valve from the left atrium into the left ventri- cle during diastole; a transvalvular gradient of 10 mm Hg indi- cates severe mitral stenosis. The significance of the transvalvular gradient is that left atrial pressure progressively increases as the mitral valve becomes more stenotic. In turn, the increased left atrial pressure is transmitted retrograde into the pulmonary veins, pulmonary capillaries, and ultimately pulmonary arteries. A left atrial pressure of approximately 25 mm Hg increases pulmonary capillary pressure enough to produce pulmonary edema. The severity of obstruction across the valve is determined by the transvalvular gradient and flow rate across the valve. The flow rate is a function of cardiac output and heart rate; because flow across the mitral valve occurs during diastole and diastole is shortened as heart rate increases, a faster heart rate at any given cardiac output increases the transvalvular gradient and raises left atrial pressure. The contribution of the atrial contraction (kick) to cardiac output is particularly important in mitral stenosis; it accomplishes as much as 30% of the transvalvular gradient. Thus, the onset of symptoms is generally associated with exer- tional activities or loss of the atrial kick with the onset of atrial fibrillation. To maintain adequate left ventricular filling across a 1-cm2 valve, for example, a pressure gradient of 20 mm Hg is required. A normal left ventricular end-diastolic pressure of 5 mm Hg results in a left atrial pressure of 25 mm Hg. Left atrial pressure rises further if flow rate across the valve increases (increased cardiac output), transit time across the valve is shortened (decreased diastolic time), or atrial kick is lost (atrial fibrillation). Pulmonary hypertension is an important component of the pathophysiology of mitral stenosis and, when severe, may dominate the clinical picture. At least three pathophysiologic mechanisms contribute to the pulmonary hypertension seen in long-standing mitral valvular disease: (1) increased left atrial pressure transmitted retrograde into the arterial circulation; (2) vascular remodeling of the pulmonary vasculature in response 1682  SECTION XI  CHEST Contraindications to this procedure include the presence of moderate mitral regurgitation, thickening and calcification of the mitral leaflets, and scarring and calcification of the subval- vular apparatus.5 Performed in the cardiac catheterization suite under fluoroscopic guidance, the technique entails advancement of one or two balloon catheters across the interatrial septum and inflation of the balloon within the stenotic mitral valve. Balloon mitral valvuloplasty has provided good short-term and intermediate-term results in appropriately selected patients. Balloon inflation should increase the mitral valve area to approx- imately 2 cm2. This increase in mitral valve area is usually associ- ated with a significant decline in left atrial pressure and transvalvular gradient and with at least a 20% increase in cardiac output. The mortality rate associated with balloon mitral valvu- loplasty is 0.5% to 2%. Other risks associated with this proce- dure include systemic embolism, cardiac perforation, and creation of mitral regurgitation; the risk of each of these com- plications is approximately 1% to 2%. Increased pulmonary vascular resistance has been shown to decline after successful balloon valvuloplasty. Approximately 10% of patients are left with a residual interatrial septal defect. Three years after balloon valvuloplasty, at least 66% of patients are free of subsequent intervention. In appropriately selected patients, the results of balloon valvuloplasty compare favorably with those of surgical valvuloplasty.6 Open Mitral Commissurotomy Open surgical valvuloplasty (com- missurotomy) is not commonly performed and has largely been supplanted by balloon mitral valvuloplasty. However, the proce- dure permits careful examination of the mitral valve and chordae tendineae under direct visualization and remova