narrowing of aortic valve orifice

In patients younger than 65 years old with symptomatic aortic valve stenosis, the most frequent pathologic finding is a bicuspid aortic valve (normally tricuspid), which occurs in 2-3% of the population, being four times as common in men and boys than in women and girls.

20% of cases with bicuspid valve have an associated heart abnormality, like a patent ductus arteriosus or aortic coarctation.

The bicusp valve has a simple fused commissure and eccentrically oriented orifice ( see figures 46a, 46b, 46c, 47 ).

Due to the stresses of pressure, the valve becomes thickened and calcified, leading to reduced motion. Calcific valvular disease represents the end stage of stage of an active disease process. In the early stages, the aortic side of the valve contains focal lesions characterized by thickening of the subendothelium and the adjacent fibrosa. These lesions contain low density-lipoproteins, Lp(a) lipoproteins, macrophages, and T lymphocytes. Areas of microscopic calcification form within regions of lipoprotein accumulation, and some macrophages within lesions produce osteopontin, a protein that modulates tissue calcification.

This stage of the disease process is evident on echocardiography as a mild, irregular leaflet thickening without obstruction of ventricular outflow and is termed aortic sclerosis. As the disease progresses, calcification and fibrosis increase leaflet stiffness and reduce systolic opening, eventually leading to a reduction in the area of the valve and an increase in forward velocity.

Clinically significant obstruction of flow through the valve is present in about 1 to 2 % of adults over the age of 65 years, and it is likely that most of these patients will ultimately have symptoms necessitating valve replacement.

Obstruction of left ventricular outflow results in pressure overload, with compensatory hypertrophy of the left ventricle to maintain normal wall stress, preserving systolic function, which can improve after valve replacement. Clinical outcome is most closely related to the presence or absence of symptoms.

Once symptoms occur, the clinical outcome is extremely poor, with two year survival rates below 50%. It is well established that this dismal prognosis can be reversed by valve replacement with acceptable levels of operative mortality and morbidity and postoperative survival similar to that of age-matched normal adults.

In symptomatic adults with systolic murmurs,echocardiography is essential to identify those likely to benefit from surgery. Surgery should be considered even for elderly persons and those with left ventricular dysfunction, since they often improve with valva replacement.

But adults without symptoms have an excellent prognosis.The simplest measure of the extent of stenosis is the forward velocity across the aortic valve. This velocity is about 1.0 m per sec. in normals and increases to 2.5 to 2.9 m per sec. in mild stenosis,3.0 to 4.0 m per sec. in moderate stenosis, and more than 4.0 m per sec. in severe stenosis.

Measurement of the area of the valve is useful, being above 1.5 cm2 in mild disease, 1.0 to 1.5 cm2 in moderarte, and in severe disease less than 1.0 cm2.

There is a substantial variation in the degree of stenosis associated with the onset of symptoms; as a result, many asymptomatic patients with severe obstruction are now identified by echocardiography. Although some feel that valve replacement should be preformed in patients with severe aortic stenosis before the onset of symptoms, others feel that the optimal time for surgery is when symptoms develop. Periodic echocardiography is appropriate to determine when to operate. Once symptoms supervene, prompt valve replacement surgery is indicated.

Reference:Otto,C.M.,N Engl J Med.Vol.343,No.9,652-654.

Reference:Rosenhek,R. AND OTHERS,N Engl J MED.,vOL.343,N.9,611-624.

Dilatation of the aortic root may occur as a sequelae of the stenosis.

The normal adult aortic valve opening is 3.0-4.0cm2. Aortic stenosis becomes hemodynamically significant when the area is about 1cm2 to 0.8cm2 (as noted above in the above discussion of the area of the valve orifice which can be classified as to severity of stenosis), as the systolic flow is impeded across the valve.

Diagnosis is suggested by the detection of an ejection high pitched click, a harsh diamond-shaped crescendo, decrescendo, basal systolic heart murmur transmitted into the neck, a soft or absent aortic component of the second heart sound by auscultation, a palpable apical thrust reflecting enlargement of the left side of the heart confirmed by electrocardiography (increased amplitude of the QRS complex with ST and T wave changes, increased amplitude of S waves in the right precordial leads, increased amplitude of the R wave in the left precordial leads, depression of the ST segment and inversion of the the T wave, (see figure 24 )

Doppler echocardiography and echocardiography can determine the severity of the stenosis including degree of thickening, calcification,and reduced mobility of the aortic leaflets and assess the left ventricle contraction function and wall thickness regarding the presence of left ventricular hypertrophy. A bicuspid valve aortic valve can be recognized by the asymmetry of the two leaflets ( figure 47 ).

The doppler tecnique allows measurement of the velocity across the aortic valve, which provides good estimates of the systolic gradient ( figure 46f ), and using the continuity equation the aortic valve area can be calculated ( figure 46e ).

Heart catherterization can be used to judge severity of the valve stenosis (if undeterminable non-invasively) by recording the gradient across the valve, estimating the stenotic area ( figure 46d ), evaluating the left ventricular function and to determine if coronary artery disease is concurrently present.

Symptoms include chest pain (exertional, angina pectoris), fainting, and heart failure (exertional shortness of breath, nocturnal cough, orthopnea, paroysmal nocturnal dyspnea, hemoptysis). The syncope may related to decreased left ventricular cardiac output due to myocardial ischemia both during and separate from exertion or to cardiac arrhythmias (which may also account for episodes of sudden death).

Adults with asymptomatic stenosis have a normal life expectancy, but should receive antibiotic prevention against infection of the aortic valve(see above discussion).

If symptoms develop, survival is limited. Hence, valve replacement should be performed promptly. In asymptomatic younger individuals, however, the documentation of severe aortic stenosis is, in itself, an indication for intervention. Mild aortic stenosis in asymptomatic patients with gradients below 50mm warrants careful surveilance.The management of patients in the intermediate group (gradients 50-75mm Hg) is more controversal, but evidence argues in favor of elective intervention.

Surgery in the young adult with congenital aortic stenosis must be considered as palliative. In the absence of calcification, aortic valvotomy is the procedure of choice. Perioperative mortality in adolescents and adults is extremely low and late survival is excellent. As surgical valvotomy is palliative, catheter balloon valvotomy has obvious attractions as the initial procedure or as treatment for restenosis.

Valve replacement is the only option for valves unsuitable for valvotomy, including those with significant calcification and regurgitation.

Late Results of Aortic Valve Replacement

Late morbidity and mortality in patients after aortic valve replacement are generally quite satisfactory. Actuarial survival at 5 years with various types valve prostheses is about 80% (See Figure 203 Immediately Below).

The degree of left ventricular dysfunction, as well as concomitant coronary disease and coexiting morbid conditions are significant determinants of late mortality. Late deaths are most often due to chronic congestive heart failure, thromboembolic stroke, myocardial infarction in those with coronary disease, and cardiac arrhythmias leading to sudden death, erspecially in those with an enlarged dilated heart.

Sudden death after aortic valve replacement is most commonly thought to due to ventricular arrhythmias, but it may also result from thromboemboli. The risk of thromboembolism is much less after aortic valve replacement than after mitral valve replacement because most patients are in sinus rhythm ( figure 180 ). The thromboembolic risk is lowest after a homograft or pulmonary autograft valve replacement, following which it is virtually zero. Patientswith porcine or pericardial valves have a risk of about 1.5 events per 100 patient years, and in patients with prosthetic valves the risk is 1.5 and 2.5 events per 100 patient years. Thrombosis of prosthetic valves was a more frequent complication with previous prosthetic valves, but it now occurs rarely and only when anticoagulation is stopped for a long period of time. With newer, low-profile, more hemodynamically efficient valves, this morbidity has decreased, and warfarin anticoagulation provides excellent protection from thromboembolism for most patients. It is recommended that patients with mechanical prosthetic valves be maintained on levels of wararin that prolong the INR to 2.5 to 3.5.

Patients with biologic aortic valves, of course, have the risk of late structural valve degeneration. The probablity of freedom from valve reoperation at 10 years in patients witha cryopreserved homograft is about 90%; this is somewhat better than the porcine bioprostheses, where the freedom from structural valve degeneration is about 90% at 8 years and 40% at 15 years. In the aortic position, a bioprosthetic valve is the valve of choice in most elderly patients because the rate of valve tissue degeneration is considerably lower than in younger age groups and the probability of valve tissue failure in patients over 70 is 20% at 10 years. The use of tissue valves in the elderly obviates the use of anticoagulation, which is very advantageous. In the younger age group, mechanical prosthetic valves tend to be used because most patients wish to minimize the probability of reoperation due to valve dysfunction and because of the accelerated fibrosis-calcification in biologic prosthetic valves in children and young adults. An exception is the child-bearing-age female, who should not anticoagulation during pregnancy because of the teratogenic potential of warfarin in the first trimester, and who should receive a biologic valve if replacement is indicated.

Reference:Rapaport,E. and Others,Aortic Valve Disease,Hurst's,Heart,8th Edition,PP1457-1466

It is debatable whether or not any patient who has had significant obstruction should be allowed to participate in competitive sports. A residual gradient greater than 20 mmHg or persistent left ventricular hypertrophy are considered to be contraindications to vigorous physical activity.

Reference:Deanfield,J.E. and others,Adult Congental Heart Disease,Hurst's THE HEART,8TH edition, 1829-1853.

Pathophysiology Of Aortic Stenosis

The AVA has to be reduced by about 50% of normal before a measurable
gradient can be demonstrated in humans.In most patients with AS ,cardiac
output is in the normal range and initially increases normally with
exercise. Later, as the severity of AS increases progessively,the cardiac
output remains within the normal range at rest,but,on exercise, it no
longer increases in proportion to the amount of exercise undertaken or
does not increase at all (fixed cardiac output). With the development of
heart failure,there is a reduction in the resting cardiac output and a
tachycardia.As a result,stroke volume may be so lowered that it results
in a small gradient across the left ventricular outflow tract in spite
of severe AS.
Echo/Doppler, when properly applied , is extremely useful for estimating
the valve gradient and AVA noninvasively.When compared with results
obtained at cardiac catheterization,the standard error of the mean
gradient in the best laboratories is 10mmHg.Thus,the mean gradient by
Doppler can be expected to be within +- 20mmHg (95% confidence level) of
that obtained at catheterization.

Table 1 Suggested Conservative Guidelines for Relating Severity of Aortic Stenosis to Doppler Gradients in Adults with Normal Cardiac Output and Normal Average Heart Rate

Peak Gradient---------- MeanGradient

--------------------------------------------------------Severe AS
mmHg ---------------------mmHg

Approx.80------------------70 --------------------------Highly likely

60-79----------------------50-69----------------------- Probable

<60----------------------- <50---------------------------Uncertain

Rahimtoola,S.H.,Aortic Valve Disease,Hurst's Diseases of The Heart,10th Edition,Vol.2,Pp.1682-1695.

Cardiac cathetrization remains the standard technique to assess the
severity of AS "accurately".

As indicated in the table below, AS can be considered severe when the valve area is 1.0 cm2 or less or the AVA index is 0.6 per square meter or less.

TABLE 2 A Suggested Grading of the Degree of Aortic Stenosis

Aortic Stenosis , AVA, cm2 , AVA Index, cm2/m2

Mild------------ >1.5 ,------------->0.9

Moderate-------->1.0-1.5, -------->0.6-0.9

Severe------------0.8-1.0 ,--------- 0.4--0.6

Rahimtoola,S.H.,Aortic Valve Disease,Hurst's Diseases of The Heart,10th Edition,Vol.2,Pp.1682-1695.

Natural History and Prognosis

Valvular AS is frequently a progressive disease, the severity increasing over time. The factors that control this progression and the time it takes for severe outflow obstruction to develop are unknown; however, it appears that in the older patient, AS may progress at about twice the rate that it does in the younger patient. In a study of 142 patients with "mild" stenosis (catheterization-proven AVA >1.5 cm2), the rate of progression to severe stenosis was 8 percent in 10 years, 22 percent in 20 years, and 38 percent in 25 years. At 25 years, 3 percent still had mild AS. The duration of the asymptomatic period after the development of severe AS is also unknown; some recent data suggest that it maybe less than 2 years. The outcome of the asymptomatic patient with severe AS is not known. In the study of 123 asymptomatic patients aged 63 ± 16 years, the actuarial probability of death or aortic valve surgery was 7 ± 5 percent at 1 year, 38 ± 8 percent at 3 years, and 74 ± 10 percent at 5 years. The event rate at 2 years for peak aortic jet velocity by Doppler ultrasound of >4 m/s was 79 ± 18 percent, for 3 to 4 m/s was 66 ± 13 percent and for <3 m/s was 16 ± 16 percent. However, the limitations of gradients and of aortic peak velocity obtained by Doppler ultrasound should be kept in mind. The overwhelming majority of adults with severe AS who are seen by cardiologists have symptoms.
Severe disease in adults is lethal, particularly if the patient is symptomatic, with a prognosis that is worse than for most forms of neoplastic disease. The 3-year mortality is approximately 36 to 52 percent, the 5-year mortality is about 52 to percent, and the 10-year mortality is 80 to 90 percent. A recent study of elderly patients (average age 77 years) showed 1-year and 3-year mortalities were 44 and 75 percent, respectively. With the onset of severe symptoms (angina, syncope, or heart failure),the average life expectancy is 2 to 3 years.Almost all patients with heart failure are dead in 1 to 2 years.A combination of symptoms is much more ominous, a sign of a greatly reduced survival.Sudden death, like syncope, occurs in the presence of severe AS.Its wexact incidence is difficult to determine but may be about 5%.

TABLE 3 Natural History of Mild Aortic Stenosis (n=142), AVA>1.5cm2

----- --10 Years------- 20 Years------- 25 Years

Mild------88%----------- 63%------------3 8%
Moderate-- 4%--- -------15%------------ 25%
Severe -----8%------ ----22% ------------38%

Rahimtoola,S.H.,Aortic Valve Disease,Hurst's Diseases of The Heart,10th Edition,Vol.2,Pp.1682-1695

Natural History and Prognosis of Bicuspid Aortic Valves

The majority of congenitally bicuspid aortic valves are nonobstructive at birth,but with the passage of time, a few of these valves become fibrotic, stiffer,and more obstructive and eventually become the site of calcium deposition, primarily among individuals between ages 15 and 65.Important calcium is unusual before the age of 30, whereas grossly visible deposits of calcium are present in the valves of virtually all patients with severe stenosis beyond that age.A much smaller number of individuals born with a bicusp aortic valve develop isolated aortic regurgitation.

Freed,M.D.,The Pathology,Pathophysiology,Recognition,and Treatment of Congenital Heart Disease,Hurst's Diseases of The Heart,10th edition,Vol.2,Pp.1837-1905.

Aortic dissection is most common in the fifth through the seventh decades of life, but has been reported in children as well as the very old. Men are affected twice as often as women. Certainl congenital lesions (e.g., coarctation and bicuspid aortic valve) are associated with increased frequency of dissection. A greater-than-expected incidence is encountered in patients with aortic stenosis even after aortic valve replacement. The same is true with certain heritable disorders such as Marfan's and Turner's syndromes.predisposes to dissection, especially with stenosis of the valve.
Pregnancy either because of its effects on the aortic wall or because of the attendant hemodynamic stress, has been reported to predispose to medial dissection.This conclusion has been based om the fact that half or more of the reports of aortic dissection in women younger than 40 years have occurred during pregnancy.Since the total nuimber reported is relatively small(certainly in relation to the frequency of pregnancy), and since most reports concern one or few cases, it is possible that selective reporting accounts for this association.
Lindsay Jr,J.,Diagnosis and Treatment of diseases of the Aorta,Hurst's Diseases of theHeart,10thedition,vol.2,p.2387.