Section V VALVULAR HEART T DISEASE. Chapter 27 Aortic Stenosis Chapter 28 Aortic Insufficiency Chapter 29 Mitral Valve Disease...

Transcription

1 Section V VALVULAR HEART T DISEASE Chapter 27 Aortic Stenosis Chapter 28 Aortic Insufficiency Chapter 29 Mitral Valve Disease Chapter 30 Mitral Valve Prolapse Chapter 31 Tricuspid and Pulmonic Valve Disease Chapter 32 Infective Endocarditis Chapter 33 Percutaneous Balloon Valvuloplasty Chapter 34 Surgical Treatment for Valvular Heart Disease

2 Chapter 27 Aortic Stenosis Timothy A. Mixon and Gregory J. Dehmer The leaflets of the aortic valve form three pocketlike cusps of approximately equal size that separate the left ventricle from the aorta. The normal aortic valve opens completely during systole, allowing unimpaired ejection of blood from the left ventricle. Closure of the aortic valve prevents retrograde blood flow from the aorta into the left ventricle and allows the left ventricle to fill solely from the left atrium in preparation for the next beat. The outflow of blood from the left ventricle can become obstructed at several levels. The most common cause of aortic stenosis is an abnormality within the valve apparatus that obstructs flow by impairing valve mobility and opening. Nonvalvular obstruction of left ventricular (LV) outflow usually results from a congenital narrowing and may occur above or below the valve. Hypertrophic cardiomyopathy, which produces a dynamic subaortic obstruction is also an important cause and is the focus of chapter 13. ETIOLOGY AND PATHOGENESIS The etiology of valvular aortic stenosis varies with the patient s age at presentation. In childhood, valvular congenital abnormalities are the usual cause of stenosis. The aortic valve may be unicuspid, bicuspid, tricuspid, or, rarely, even quadricuspid (Fig. 27-1). Unicuspid valves usually are severely narrowed at birth and produce symptoms in infancy. Bicuspid and malformed tricuspid valves rarely cause symptoms during childhood. More frequently, the abnormal architecture of bicuspid and malformed tricuspid valves alters flow patterns across the valve, slowly traumatizing the leaflets, leading to progressive fibrosis, calcification, and stenosis between age 50 and 70 years. Acquired abnormalities from senile, calcific degeneration of a previously normal valve predominate in patients diagnosed after age 70 years (Fig. 27-2). Rheumatic involvement of the aortic valve, less prevalent now than a generation ago, usually results in a combination of stenosis and regurgitation, often with mitral valve disease. Less common causes of aortic valve stenosis include obstructive vegetations from endocarditis, prior radiation therapy, and rheumatoid involvement with severe nodular thickening of the valve leaflets. Aortic stenosis may also be associated with systemic diseases including Paget s, Fabry s, ochronosis, and end-stage renal disease. Aortic stenosis is more common in older patients (>70 years) and men, but there is no apparent racial predilection. An association has been noted between aortic stenosis and some risk factors for coronary artery disease, including diabetes and hypercholesterolemia, supporting a concept that degenerative, calcific aortic stenosis is a proliferative, inflammatory disease. CLINICAL PRESENTATION Aortic stenosis is often asymptomatic for years. Prolonged, severe pressure overload imposed by outflow tract obstruction results in concentric LV hypertrophy (LVH), a compensatory adaptation that lowers wall stress and maintains forward flow but also has detrimental effects, including an abnormal diastolic filling pattern and subendocardial ischemia. The principal symptoms of aortic stenosis are angina, syncope, and overt congestive heart failure. The average survival period without valve replacement is 5 and 3 years in patients who present with angina or syncope, respectively. The most concerning symptom is CHF. In patients with aortic stenosis presenting with CHF, the average survival without valve replacement is 2 years. Angina occurs in two thirds of patients with severe aortic stenosis, and approximately half of these have concomitant coronary artery disease. In the absence of coronary artery disease, angina is caused by subendocardial ischemia induced by increased wall thickness 256

3 Figure 27-1 Anomalies of the Left Ventricular Outflow Tract Right pulmonary artery Ductus arteriosus Left pulmonary artery Hypoplastic ascending aorta Pulmonary valve Left ventricle Right ventricle Congenital aortic atresia Congenital bicuspid aortic valve Congenital aortic valvular stenosis 257

4 Figure 27-2 Rheumatic and Nonrheumatic Causes of Aortic Stenosis Moderate stenosis (beginning fusion of other commissures) Stenosis and insufficiency (fusion of all commissures) Acquired bicuspid aortic valve(rheumatic) Calcific stenosis Congenital bicuspid aortic valve Great hypertrophy of left ventricle in aortic stenosis Elongation of left ventricle with tension on chordae tendineae which may prevent full closure of mitral valve 258

5 with relatively decreased capillary density, prolonged ejection time, and increased LV end-diastolic pressure, which reduces the diastolic transmyocardial perfusion gradient. The causes of syncope include exertion, LVH, and arrhythmias. Exertion lowers the systemic vascular resistance while an increase in cardiac output is limited by the fixed outflow tract obstruction; this combination leads to cerebral and cardiac hypoperfusion. LVH from the development of aortic stenosis may cause an exaggerated vasodepressor response when activity increases the already elevated LV systolic pressure. Arrhythmias, including atrial fibrillation, ventricular tachycardia, ventricular fibrillation, and atrioventricular conduction abnormalities, may cause syncope at rest or on exertion. Congestive heart failure is often caused by diastolic dysfunction, related to the development of LVH-related abnormal ventricular relaxation and decreased compliance. Systolic dysfunction with progressive ventricular dilation may occur late in the disease course. To compensate for the LV pressure load, the left atrium hypertrophies and develops vigorous contractions that allow adequate filling of the left ventricle despite increased LV end-diastolic pressure. However, as the disease progresses or with physical activity, left atrial pressure increases further, leading to higher pulmonary venous pressures and eventually to pulmonary congestion and edema. Pulmonary edema may develop abruptly during activity or with the loss of atrial function, as in atrial fibrillation. Other manifestations of aortic stenosis may include gastrointestinal bleeding from angiodysplasia, the development of infective endocarditis, embolic phenomenon from an infective vegetation or detachment of small calcium deposits, and sudden cardiac death from serious ventricular arrhythmias. Physical Examination One of the most reliable findings in severe aortic stenosis is decreased pulsation of the carotid arteries, slowed arterial upstroke (pulsus parvus et tardus), with the maximum carotid upstroke noticeably delayed after the apical impulse (Fig. 27-3). A marked vibration may be felt in the carotid artery. The jugular venous pressure is not elevated unless heart failure is present. In mild aortic stenosis, the jugular venous pulsation may show a prominent a wave, whereas late in the disease a prominent v wave may occur from tricuspid insufficiency caused by pulmonary hypertension and bulging of the hypertrophied septum into the right ventricle. The LV apical impulse is usually displaced inferiorly and laterally, with a palpable presystolic pulsation ( palpable S 4 ). If the apical impulse is hyperdynamic, concomitant aortic or mitral insufficiency should be considered. The first heart sound is usually normal; the second heart sound may be single because of the absence of the aortic component from immobile aortic leaflets, or it may be paradoxically split from a marked delay of LV ejection. The murmur may be preceded by an early systolic ejection click, heard more frequently with a bicuspid valve or a congenital aortic stenosis in which the leaflets have preserved pliability. The murmur is characteristically described as crescendodecrescendo and harsh in quality, most prominent at the right upper sternal border, with transmission to the carotids. High-frequency resonations may be heard at the apex ( Gallavardin murmur ) and can be misinterpreted as mitral regurgitation. As aortic stenosis worsens, the murmur can continue into mid systole and late systole with progressively later peaking. The murmur of aortic sclerosis is similar to that heard in aortic stenosis, but tends to be an earlypeaking murmur, and carotid pulsations are normal. The murmur of mitral regurgitation is usually easily distinguished from aortic stenosis. It is pansystolic, with a more musical quality and constant intensity despite variable cardiac cycle length. The murmur of aortic stenosis is accentuated after pauses such as those associated with post-extrasystolic beats or long cycles in atrial fibrillation. The LV outflow tract murmur associated with hypertrophic obstructive cardiomyopathy can be similar in character, but responds to provocative maneuvers in a very characteristic manner (see chapters 1 and 13). The murmur of valvular aortic stenosis increases with increased flow across the valve resulting from squatting or maneuvers to increase preload and decreases in intensity with a Valsalva maneuver. The murmur of hypertrophic cardiomyopathy with obstruction becomes more 259

6 Figure 27-3 Aortic Stenosis Small, slow radial pulse Low blood pressure and low pulse pressure; auscultatory gap Cerebral insufficiency: dizziness, fainting spells, syncope Pallor Dyspnea Pulmonary congestion Edema Systolic thrill: 2nd and 3rd right interspaces and R. side of neck R. heart failure IV I Ejection sound Gradient Aortic pressure L. ventricular pressure II I P A IV Poststenotic dilatation Coronary insufficiency (precordial pain) Obstruction to L. ventricular outflow L. ventricle dilated Hypertrophy Harsh, loud systolic, crescendo decrescendo murmur in aortic area 4th sound; paradoxical splitting of 2nd Failure Fibrillation Death Peripheral vasoconstriction helps maintain blood pressure I avr V 1 Apex shift to left; visible sustained thrust V 2 V 3 II avl V 4 V 5 V 6 III avf Left ventricular enlargement and moderate dilatation of ascending aorta (poststenotic) Evidence of left ventricular hypertrophy (large S in V 2, large R in V 5 ) and strain (inverted T and depressed S T in I, II, avl, V 5, V 6 ) 260

7 prominent with decreasing preload, such as the straining phase of the Valsalva maneuver or standing upright. Further, the carotid upstroke in hypertrophic cardiomyopathy with obstruction is rapid and has a bisferious quality. DIFFERENTIAL DIAGNOSIS Differentiation of valvular aortic stenosis from other causes of LV outflow tract obstruction is important because the treatment and prognosis differs depending on the precise disease etiology. Subvalvular outflow tract obstruction may be due to a discrete subaortic membrane, a fibromuscular deformity (tunnel defect), or disproportionate muscular hypertrophy of the intraventricular septum with dynamic obstruction of the outflow tract (previously called idiopathic hypertrophic subaortic stenosis). Supravalvular outflow tract obstruction is much less common than the other varieties. It occurs in three forms: a circumferential hourglass narrowing of the aorta above the valve, a discrete fibromembranous ring, or a hypoplastic variety with diffuse narrowing of the ascending aorta. DIAGNOSTIC APPROACH In patients with an aortic stenosis, the ECG most commonly shows sinus rhythm until late in the disease course. The most common findings are LVH (>80%) (Fig. 27-4) and left atrial abnormality manifested by a negative terminal deflection of P waves in lead V 1 corresponding to left atrial hypertrophy. Less common findings include ST-segment depression in leads V 4 through V 6 (the left ventricular strain pattern ) and conduction system disease from calcification of the specialized conduction tissue, manifested as atrioventricular block, left anterior fascicular block, or a nonspecific intraventricular conduction delay. A chest x-ray usually shows a normal-sized cardiac silhouette, as the ventricles may be hypertrophied but usually not grossly dilated. Left atrial enlargement and signs of pulmonary venous congestion may be present. It is uncommon to see calcification of the aortic valve leaflets on standard chest x-ray examination, but some calcium near the aortic and mitral valve annuli is common and poststenotic dilatation of the ascending aorta may be present. Calcified aortic valve leaflets can often be visualized by careful cardiac fluoroscopy. Two-dimensional echocardiography with Doppler is useful for evaluating suspected aortic stenosis. A complete echocardiogram can reveal the location of the aortic outflow obstruction, estimate the severity of valvular obstruction, and provide supplemental information such as the function of the left ventricle, the degree of LVH, the size of the left atrium, and the presence or absence of associated valvular abnormalities (most notably, mitral regurgitation or aortic insufficiency) (Fig. 27-5). Doppler interrogation of the flow across the aortic valve can be used to estimate the transvalvular aortic pressure gradient, using a modification of the Bernoulli equation. The measured pressure decrease across the valve depends on the severity of the stenosis and the flow volume across the valve. With valvular aortic stenosis, the valve area is fixed, but flow across the valve, and hence the pressure gradient, varies depending on a number of factors, including exercise, anxiety, anemia, or concomitant aortic insufficiency and LV systolic dysfunction, sedation, or hypovolemia. Transvalvular gradients are reported as a mean value or as a peak instantaneous gradient. Although these measures are linearly related, neither corresponds exactly to the peak-to-peak gradient frequently reported from simultaneous measurements made with catheters. In general, a peak transvalvular gradient of greater than 100 mm Hg or a mean transvalvular gradient of greater than 50 mm Hg is consistent with severe aortic stenosis. Aortic valve areas can be calculated via the continuity equation or estimated directly by planimetry. Because the pressure gradient can vary considerably under different conditions, the calculated aortic valve area is generally thought to be a more reliable measure of severity. A calculated aortic valve area of less than 1.0 cm 2 or 0.5 cm 2 /m 2 is consistent with severe aortic stenosis. Because of the relationship of flow and pressure across the valve, some patients with low cardiac output secondary to left-sided heart failure have a low transvalvular pressure gradient (<30 mm Hg) despite the presence of significant aortic stenosis. Valve area calculations in this circumstance may be misleading; it is often helpful to increase the cardiac output with intravenous inotropic drugs and to use the new data to recalculate the valve area. If the increase in cardiac output causes a sub- 261

8 Figure 27-4 Left Ventricular Hypertrophy I avr V 1 V 4 II avl V 2 V 5 III avf V 3 V 6 Causes Systemic arterial hypertension High voltage in limb leads (R I + S III 25 mm) or precordial leads (S V 1 + R V 5 or R V 6 35mm). Often, left atrial enlargement. ST T abnormalities. Aortic stenosis or insufficiency Mitral insufficiency stantial increase in the calculated valve area, the primary problem is likely to be a primary cardiomyopathy, rather than aortic stenosis. If the increase in cardiac output results in a substantial increase in the gradient (and decrease in the calculated valve area), the primary problem is likely to be a stenotic valve. Patients with severe aortic stenosis and impaired LV systolic function generally benefit from aortic valve replacement, although the immediate risk of surgery is higher than that in individuals with aortic stenosis and normal LV systolic function before surgery. After valve replacement, LV systolic function returns to normal in many patients with impaired LV systolic function as a result of aortic stenosis. In the past, the degree of stenosis was commonly confirmed with invasive hemodynamic measurements; it is now acceptable to forgo invasive hemodynamic evaluation unless the historic, physical, and echocardiographic findings are discordant. In this circumstance, rightand left-sided heart catheterization is indicated to directly obtain pressure gradients and measure of cardiac output. Valve resistance can also be calculated and is less dependent on flow across the stenotic valve orifice. Before replacement of the aortic valve, coronary angiography is indicated for all patients who are older than 35 years or who have two or more risk factors for coronary artery disease. 262

9 Figure 27-5 Two-Dimensional Echocardiography and Doppler Analysis in a Patient With Aortic Stenosis A B (A) Parasternal long axis two-dimensional echocardiogram showing an immobile, heavily calcified aortic valve (arrow). (B) continuous wave Doppler echocardiography shows the velocity profile across the aortic valve. Standard on-line software assists in determining the peak velocity and time + velocity integral, which are used to determine the valve area based on the continuity equation. It is essential to intergrate the jet from multiple transducer positions to obtain the true maximal jet, which is found when the transducer is parallel to the direction of flow. MANAGEMENT AND THERAPY Medical therapy for valvular aortic stenosis is usually limited to the treatment of complications, such as heart failure, rhythm disturbances, and infective endocarditis. Heart failure is treated with digoxin and the judicious use of diuretics. Volume depletion must be avoided, because aggressive diuresis may lead to severe hypotension. Elevated blood pressure may be controlled with medications, but excessive afterload reduction is not helpful and should be avoided. Because the ability of cardiac output to increase is limited in severe aortic stenosis, lowering the systemic pressure can increase the transvalvular gradient and worsen symptoms. Atrial fibrillation may occur late in the disease course of patients with aortic stenosis, raising the question of concomitant mitral valve disease. Atrial fibrillation is treated in the usual manner, with emphasis on the maintenance of sinus rhythm and appropriate anticoagulation. In patients with aortic stenosis, loss of atrial contraction can result in a marked decrease in cardiac output. Rarely, the onset of atrial fibrillation may be catastrophic in terms of hemodynamic decompensation due to loss of effective ventricular filling; urgent electrical cardioversion may be necessary in this circumstance. Infective endocarditis occurs more frequently with congenital valvular abnormalities and is less common with senile, calcific aortic stenosis. Patients with moderate to severe degrees of outflow tract obstruction should not engage in vigorous, unsupervised exercise. Aortic valve replacement is indicated for the treatment of symptomatic aortic stenosis. In fact, replacement is frequently delayed until symptoms develop. Prosthetic, bioprosthetic, and homograft valves all provide excellent symptom relief and improve the mortality rate, with the expected survival rate approaching that of the unaffected population. Asymptomatic patients with a severe aortic stenosis generally have an excellent prognosis without valve replacement, but 1 to 2% die suddenly or have rapid progression, with syncope and sudden cardiac death. Nevertheless, valve replacement is not recommended for most asymptomatic individuals because the rate of mortality for the operation is similar to the rate without the operation and placement of a prosthetic valve exposes the patient to associated risks (valve dysfunction, prosthetic valve endocarditis, bleeding from anticoagulant therapy). Surgery may be considered for asymptomatic patients who have LV dysfunction, exercise-induced hypotension, ventricular tachycardia, very severe valvular aortic stenosis, or extreme LVH. Balloon valvotomy is useful in the palliation of congenital aortic stenosis (in young patients) but 263

10 late restenosis and a need for valve replacement often occur. In older patients with calcific aortic stenosis, balloon valvotomy is indicated only as a bridge to surgery in critically ill patients, in patients who require urgent noncardiac surgery, or as palliation for terminal patients with a limited life expectancy. FUTURE DIRECTIONS Minimally invasive aortic valve replacement surgery via a right parasternal incision is gradually replacing the traditional approach of a median sternotomy. Percutaneous alternatives to surgical valve replacement are also being developed and tested in patients. Although valve replacement surgery has been considered the only treatment option, there is now preliminary evidence that therapy with statin drugs reduces the rate of progression of aortic stenosis by about half compared to the rate in patients not receiving statin drugs. REFERENCES Carabello BA. Aortic stenosis. N Engl J Med 2002;346: Ford LE, Feldman T, Chiu C, Carroll JD. Hemodynamic resistance as a measure of functional impairment in aortic valvular stenosis. Circ Res 1990;66:1 7. Lester SJ, Heilbron B, Gin K, Dodek A, Jue J. The natural history and rate of progression of aortic stenosis. Chest 1998;113: Lombard JT, Selzer A. Valvular aortic stenosis: A clinical and hemodynamic profile of patients Ann Intern Med 1987;106: Marcus ML, Doty DB, Hiratzka LF, Wright CB, Eastman CL. Decreased coronary reserve: A mechanism for angina pectoris in patients with aortic stenosis and normal coronary arteries. N Engl J Med 1982;307: Perloff JK. Clinical recognition of aortic stenosis: The physical signs and differential diagnosis of the various forms of obstruction to left ventricular outflow. Prog Cardiovasc Dis 1968;10:323. Roberts WC. Valvular, subvalvular, and supravalvular aortic stenosis: Morphological features. Cardiovasc Clin 1973;5: