Aortic stenosis overview

Aortic Stenosis Microchapters
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Patient Information
Overview
Historical Perspective
Classification
Pathophysiology
Causes
Differentiating Aortic Stenosis from other Diseases
Epidemiology and Demographics
Risk Factors
Natural History, Complications and Prognosis
Diagnosis
History and Symptoms
Physical Examination
Cardiac Stress Test
Electrocardiogram
Chest X Ray
CT
MRI
Echocardiography
Cardiac Catheterization
Aortic Valve Area
Aortic Valve Area Calculation
Treatment
General Approach
Medical Therapy
Surgery
Percutaneous Aortic Balloon Valvotomy (PABV) or Aortic Valvuloplasty
Transcatheter Aortic Valve Replacement (TAVR) TAVR vs SAVR Critical Pathway Patient Selection Imaging Evaluation Valve Types TAVR Procedure Post TAVR management AHA/ACC Guideline Recommendations
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Precautions and Prophylaxis
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-In-Chief: Mohammed A. Sbeih, M.D. [2]; Lakshmi Gopalakrishnan, M.B.B.S. [3] Assistant Editor-In-Chief: Kristin Feeney, B.S. [4]

Overview

The aortic valve assures that blood moves forward the from the left ventricle into the aorta and that it does not leak backward during diastole. When functioning appropriately, the aortic valve does not impede the flow of blood between the left ventricle and the aorta and it does not leak. Under some circumstances, the aortic valve becomes narrower than normal, impeding the flow of blood. This is known as aortic valve stenosis, or aortic stenosis, often abbreviated as AS.

Classification

Aortic stenosis can be classified broadly in two main categories: acquired and congenital. Further classification can be applied based on the origin of the stenosis such as acquired rheumatic, congenital bicuspid, congenital subaortic, congenital subvalvular, and congenital supravalvular aortic stenosis.

Pathophysiology

The impedance to antegrade blood flow as a result of aortic stenosis results in chronic pressure overload of the left ventricle. The most common complication of aortic stenosis is left ventricular hypertrophy. The obstruction of flow in aortic stenosis can obviously occur at the level of the aortic valve itself, but can also occur at the subvalvular (below the aortic valve) or supravalvular (above the aortic valve) level as well.

Left Ventricular Hypertrophy

Long-standing aortic stenosis exposes the left ventricle to prolonged pressure overload which leads to concentric hypertrophy. The left ventricular wall increases in thickness (i.e. concentric hypertrophy occurs) as a result of the parallel replication of the sarcomeres.

Diastolic Dysfunction

During the initial period of concentric hypertrophy, the left ventricle is not dilated and there is preservation of left ventricular systolic function. Diastolic function, however, may be reduced due to a reduction in diastolic compliance .

This diastolic dysfunction may in turn lead to a rise in pulmonary capillary wedge pressure and dyspnea. Cardiac output may also be reduced as a result of diastolic dysfunction and impaired filling of the left ventricle. Early in the course of aortic stenosis, there may be a failure to augment cardiac output during exercise resulting in dyspnea on exertion.

Systolic Dysfunction

Later in the course of aortic stenosis, left ventricular dysfunction may develop due to a variety of pathophysiology processes. Systolic dysfunction is associated with a poor prognosis, and often does not partially or fully reverse following operative repair .

Excess Hypertrophy Causes Systolic Dysfunction

Although, this massive concentric hypertrophy characterized by a reduced diastolic radius-to-wall thickness ratio has shown to initially counter balance the increased systolic left ventricular pressure, if this process continues, an inverse relationship has been observed such that ejection fraction eventually goes down as left ventricular mass increases beyond a certain point..

Myocardial Ischemia

The hypertrophied left ventricle and the prolonged ejection time (the time for the heart to eject blood) results in increased myocardial oxygen requirements. The elevated diastolic filling pressure also reduces the gradient between the aorta and the right atrium ("the height of the waterfall") that drives coronary blood flow. There may be a relative reduction in the density of the capillary network. The hypertrophied ventricle may also compress the capillaries. All of the above lead to a reduction in coronary blood flow even in the absence of obstructive epicardial stenoses. This may lead to subendocardial ischemia during stress or exercise..

Myocardial Fibrosis

Myocardial scarring or fibrosis may develop with prolonged aortic stenosis, perhaps due to chronic subendocardial ischemia or increased wall stress.

Dyssynchronous Contraction

Another factor that may contribute to reduced left ventricular systolic function is dyssynchronous contraction subsequent to regional wall motion abnormalities, fibrosis or ischemia.

Atrial Fibrillation

The stiff, non-compliant left ventricle can become increasingly dependent upon the left atrium for filling. The development of atrial fibrillation and the loss of atrial contractility can result in reduced left ventricular filling and reduced cardiac output.

Epidemiology and Demographics

Aortic stenosis primarily affects older adults and the majority of cases are due to calcific degeneration. Aortic stenosis tends to affect approximately 2% of patients over the age of 65, 3% the age of 75, and 4% over the age 85.

Risk Factors

The most common risk factor for the subsequent development of aortic stenosis arises is a congenital bicuspid aortic valve. Rheumatic fever is a risk factor for the subsequent development of aortic stenosis (rheumatic heart disease). Risk factors that may speed up the progression of degenerative calcific aortic stenosis include:

• Hypertension
• Diabetes mellitus
• Hyperlipoproteinemia
• Uremia
• Smoking

Causes

Aortic stenosis can be categorized under two methods of causation: acquired and congenital.

Valvular Aortic Stenosis:

Acquired

• Calcific degeneration
• Rheumatic fever
• Infective endocarditis
• Systemic lupus erythromatosis
• Fabry's disease
• Aortic sclerosis

Congenital

• Bicuspid aortic valve
• Hypoplastic annulus
• Three cuspid valve with commissural fusion

Subvalvular Aortic Stenosis:

• Membranous diaphragm
• Hypertrophic cardiomyopathy

Supravalvular Aortic Stenosis:

• Hypoplasia of aorta
• Hourglass constriction of aorta
• Fibromembranous aortic lesion

A complete list of causes in alphabetic order includes the following:

• Age-induced calcification of normal tricuspid aortic valve with degenerative 'wear and tear'.
• Congenital bicuspid aortic valve
• Endocarditis
• Fabry disease
• Homozygous type II hypercholesterolemia
• Ochronosis
• Paget disease
• Prosthetic aortic valve
• Radiation treatment to the chest
• Rheumatic fever (slowly progressive stenosis)
• Subvalvular aortic stenosis
• Supravalvular aortic stenosis
• Williams syndrome, autosomal dominant trait is associated with supravalvular aortic stenosis

Differential Diagnosis

Aortic stenosis must be differentiated from other cardiac or pulmonary causes of dyspnea, weakness, and dizziness. Furthermore, if there is left ventricular outflow tract obstruction, it is critical to identify if the obstruction is subvalvular, valvular or supravalvular or due to Hypertrophic Cardiomyopathy (HOCM).

Natural History, Complications & Prognosis

Left untreated, aortic valve stenosis can lead to angina, syncope, congestive heart failure, atrial fibrillation, endocarditis, and sudden cardiac death.

Complications

Surgical treatment of aortic stenosis also carries risks and potential complications including vascular complications and mitral valve injury.

Prognosis

30% reduction in gradient is expected as the immediate result of surgical intervention. Patient survival after treatment is higher than that of untreated patients.

Diagnosis

History and Symptoms

The main symptoms of aortic stenosis include angina, syncope and congestive heart failure. Left untreated, the average survival is 5 years after the onset of angina, 3 years after the onset of syncope, and 1 year after the onset of congestive heart failure . Other symptoms include dyspnea on exertion, orthopnea and paroxysmal nocturnal dyspnea.

Physical Examination

Aortic stenosis is most often diagnosed when it is asymptomatic and can sometimes be detected during routine examination of the heart and circulatory system. The major signs include pulsus parvus et tardus (a slow-rising, small volume carotid pulse), a lag time between apical and carotid impulses, and a distinct systolic ejection murmur.

Electrocardiogram

The electrocardiogram in the patient with moderate to severe aortic stenosis may reveal left ventricular hypertrophy and heart block.

Chest X-ray

Chest x ray may be used as a diagnostic tool in the evaluation of aortic stenosis. Findings associated with aortic stenosis include left ventricular hypertrophy and calcification of the aortic valve.

MRI

Magnetic resonance imaging is rarely used in the diagnosis of aortic stenosis, except in rare cases where the echocardiographic findings are inconclusive. There is a signal void where the high velocity jet exits the aortic valve.

CT

Computed tomography can be helpful as a diagnostic tool in conditions where the echocardiographic findings are inconclusive.

Echocardiography

Echocardiography is the best non-invasive test to evaluate the aortic valve anatomy and function. Echocardiography can be used to estimate the gradient across the aortic valve using the modified Bernoulli equation (gradient = 4 X velocity²). The flow must be constant, so as the velocity increases, the valve area decreases proportionally. Echocardiography can also be used to assess the severity of left ventricular hypertrophy.

Cardiac Catheterization

Left and right heart catheterization as well as angiography may be useful in the assessment of the patient prior to aortic valve replacement surgery.

Aortic Valve Area

The aortic valve area is the size of the orifice for blood to flow from the left ventricle to the aorta. The aortic valve area is reduced in aortic stenosis, and the aortic valve area is the metric that is used to gauge the need for aortic valve replacement surgery. The pressure gradient across a narrowed aortic valve cannot be used to gauge the need for valve replacement as the gradient may be low in patients with impaired left ventricular function.

Aortic Valve Area Calculation

Aortic valve area calculation is an indirect method of determining the area of the aortic valve. The calculated aortic valve orifice area is currently one of the measures for evaluating the severity of aortic stenosis. A valve area of less than 0.8 cm² is considered to be severe aortic stenosis.

There are many ways to calculate the valve area of aortic stenosis. The most commonly used methods involve measurements taken during echocardiography. For interpretation of these values, the area is generally divided by the body surface area, to arrive at the patient's optimal aortic valve orifice area.

Treatment

Once a patient becomes symptomatic with aortic stenosis, aortic valve replacement should be performed. Medical therapy reduces symptoms but does not prolong life. If a patient has extensive co-morbidities, transcatheter aortic valve implantation can be considered. Aortic valvuloplasty can be considered in those patients who are too sick for surgery or transcatheter aortic valve implantation.

• Aortic stenosis surgery via aortic valve replacement
• Transcatheter aortic valve implantation
• Percutaneous aortic balloon valvotomy (PABV) or aortic valvuloplasty

Medical Therapy

While medical therapy may improve the symptoms of patients with aortic stenosis, medical therapy does not prolong life expectancy. Aortic valve replacement remains the definitive treatment of symptomatic aortic stenosis and it improves both the symptoms and life expectancy of patients with aortic stenosis. When pharmacological therapies are used, extreme caution must be exercised in the administration of vasodilators as excess vasodilation may lead to hypotension, a reduction in perfusion pressure to the heart, a further decline in cardiac output and further hypotension. This downward spiral can be fatal and must be avoided at all costs.

Percutaneous Aortic Balloon Valvotomy (PABV) or Aortic Valvuloplasty

Although surgical aortic valve replacement is the mainstay of treatment of aortic stenosis as it improves both symptoms and life expectancy, some patients may not be surgical candidates due to comorbidities, and minimally invasive treatment such as percutaneous aortic balloon valvotomy (PABV) maybe an alternative to surgery as a palliative strategy. PABV is a procedure in which 1 or more balloons are placed across a stenotic valve and inflated to decrease the severity of aortic stenosis. This is to be distinguished from transcatheter aortic valve implantation (TAVI) which is a different method that involves replacement of the valve percutaneously.

Transcatheter aortic valve implantation

Untill recently, aortic valve replacement (AVR) was the only effective treatment for severe symptomatic aortic stenosis. However, over the past decade percutaneous treatment of aortic valve disease with implantation of a stent-based valve prosthesis has been introduced as a new treatment in patients considered inoperable because of severe co-morbidities. In Transcatheter Aortic Valve Implantation (TAVI) also known as Percutaneous Aortic Valve Replacement (PAVR), a synthetic valve is advanced to the heart through a small hole made in groin. This procedure is similar in its mechanism to the insertion of a stent, or performing balloon angioplasty albeit with much larger equipment. Traditional aortic valve replacement is an invasive surgical procedure, with considerable mortality and morbidity, especially in more fragile patients. In the newly developed TAVI procedure, the dysfunctional aortic valve is replaced percutaneously, which obviates the need for open heart surgery.

Surgery

Aortic stenosis requires aortic valve replacement if medical management does not successfully control symptoms.

Prevention

Aortic stenosis associated with rheumatic heart disease can be minimized with antibiotic therapy in patients with documented streptococcal pharyngitis (strep throat). Bicuspid aortic valve disease is a congenital variant and cannot be prevented. Calcific degeneration of the valve can potentially be minimized by rosouvistatin and other measures targeting atherosclerosis prevention.

Precautions and Prophylaxis

People with aortic stenosis of any etiology are at risk for the development of infection of their stenosed valve, i.e. infective endocarditis and antibiotic prophylaxis should be considered. Patients with severe aortic stenosis should avoid strenuous exercise and any exercise that greatly increases afterload such as weight lifting.