Critical Care Medicine

Aortic stenosis

Aortic Stenosis

Synonyms

Aortic stenosis

Aortic sclerosis

Subvalvular aortic stenosis

Supravalvular disease

1. Description of the problem

  • Aortic stenosis (AS) is most common valvular disease. ~2% of people over the age of 65, 3% of people over age 75, and 4% of people over age 85 have the disorder.

  • There are three primary causes of valvular AS: a congenitally abnormal valve with superimposed calcification (unicuspid or bicuspid); calcific disease of a trileaflet valve; or rheumatic valve disease.

  • The pathobiology of calcific aortic valve disease is characterized by three primary processes: lipid accumulation, inflammation, and calcification.

  • In general, symptoms in patients with AS and normal left ventricular systolic function rarely occur until the valve area is <1.0 cm2, the jet velocity is >4.0 m/sec, and/or the mean transvalvular gradient exceeds 40 mmHg.

  • In patients with known AS who are followed prospectively, the most common symptoms are decreased exercise tolerance and dyspnea on exertion. Once symptoms develop, even when mild, prompt surgical intervention is needed because average survival without valve replacement is only 2-3 years, with a high risk of sudden death.

  • Although the physical examination correlates with the severity of AS, no single finding on physical examination or combination of findings has both high sensitivity and high specificity for excluding severe AS, particularly in asymptomatic patients. Echocardiographic data are more reliable.

  • Table I describes the severity of AS in adults. Table II gives information about the causes of left ventricular outflow tract obstruction.

Table I.

Table I. Severity of aortic stenosis in adults
Aortic jet velocity, m/sec Mean gradient, mmHg Valve area, cm2
Normal ≤2.0 <5 3.0-4.0
Mild <3.0 <25 >1.5
Moderate 3.0-4.0 25-40 1.0-1.5
Severe >4.0 >40 <1.0

Table II.

Distinguishing characteristics of the causes of left ventricular outflow tract obstruction
Valvar Supravalvar Discrete subvalvar Hypertrophic obstructive cardiomyopathy
Pulse pressure after VPB Increased Increased Increased Decreased
Valsalva effect on systolic murmur Decreased Decreased Decreased Increased
Murmur of aortic regurgitation Common after age 40 Rare Sometimes No
Fourth heart sound (S4) If severe Uncommon Uncommon Common
Paradoxic splitting Sometimes No No Common
Ejection click Most (unless valve calcified) No No Uncommon or none
Maximal thrill and murmur Second RIS First RISSuprasternal notch Second RIS Fourth LIS
Carotid pulse Normal to anacrotic (parvus et tardus) Unequal Normal to anacrotic Brisk, jerky, systolic rebound
Valve calcification Common after age 40 No No No
Dilated ascending aorta Common after age 40 Rare Rare Rare

There are three classic symptoms associated with AS, which typically occur with exertion:

Dyspnea and Heart Failure (HF)

The most common symptom of AS is dyspnea, usually with exertion, and two factors are responsible for that:

1. Diastolic dysfunction, with an increase in left ventricular filling pressures with exercise, and an inability of the left ventricle to increase the cardiac output during exercise because the stiff aortic valve obstructs flow

2. Systolic left ventricular dysfunction is rare and overt HF is a late, often end-stage finding, usually in patients who have not received regular medical care. Once overt HF occurs, the patient may complain of shortness of breath, easy fatigability, debilitation, and other signs and symptoms of a low-cardiac-output state.

Syncope or Dizziness

There are several proposed explanations for exertional dizziness or syncope, both of which reflect decreased cerebral perfusion:

  • Exercise-induced vasodilation in the presence of an obstruction with fixed cardiac output can result in hypotension.

  • A transient bradyarrhythmia that can occur during or immediately after exertion

  • Abnormalities in the baroreceptor response with an ensuing failure to appropriately increase the blood pressure

  • An arrhythmia, such as atrial fibrillation; ventricular arrhythmias are uncommon.

Angina

Angina with effort occurs in about two thirds of patients with severe AS. ~50% of these patients have underlying coronary artery disease.

Angina in the remaining patients is due to left ventricular hypertrophy, which can cause coronary ischemia by other mechanisms.

  • Increased left ventricular oxygen demand as a result of increased left ventricular mass; the myocardial oxygen uptake per gram is normal

  • Compression of intramyocardial coronary arteries from prolonged contraction and impaired myocardial relaxation

  • Reduced diastolic coronary perfusion time during tachycardia

  • Reduced coronary flow reserve

Key management points

  1. Careful history and evaluation of symptoms

  2. Physical examination

  3. Investigations: ECG, echocardiogram, cardiac catheterization, chest x-ray, computed tomography,cardiovascular magnetic resonance

  4. Management of symptomatic and asymptomatic patients, which includes:

    • Medical management - Diuretics, beta blockers, ACE inhibitors and other vasodilators

    • Surgical management (aortic valve replacement [AVR])

    • Valvotomy

    • Trans-catheter aortic valve intervention (TAVI)

  5. Palliative care

2. Emergency Management

Aortic valve replacement is the standard treatment for AS (Table III).

Table III.

Indications for aortic valve replacement in aortic stenosis
Class
Patients with severe AS and any symptoms IB
Patients with severe AS undergoing coronary artery bypass surgery, surgery of the ascending aorta or another valve IC
Asymptomatic patients with severe AS and systolic LV dysfunction (LVEF <50%) unless due to other cause IC
Asymptomatic patients with severe AS and abnormal exercise test showing symptoms on exercise IC
Asymptomatic patients with severe AS and abnormal exercise test showing fall in blood pressure below baseline IIaC
Patients with moderate AS undergoing coronary artery bypass surgery, surgery of the ascending aorta or another valve IIaC
Asymptomatic patients with severe AS and moderate to severe valve calcification, and a rate of peak velocity progression ≥0.3 m/s per year IIaC
AS with low gradient (<40 mmHg) and LV dysfunction with contractile reserve IIaC
Asymptomatic patients with severe AS and abnormal exercise test showing complex ventricular arrhythmias IIbC
Asymptomatic patients with severe AS and excessive LV hypertrophy (≥15 mm) unless this is due to hypertension IIbC
AS with low gradient (<40 mmHg) and LV dysfunction without contractile reserve IIbC

3. Diagnosis

Diagnostic tests and procedures

Electrocardiogram (ECG)

Although AS does not lead to any specific findings on the ECG, it still often leads to a number of ECG abnormalities. ECG manifestations of left ventricular hypertrophy (LVH) are common in AS and arise as a result of the stenosis having placed a chronically high pressure load on the left ventricle (with LVH being the expected response to chronic pressure loads on the left ventricle no matter what the cause). As noted above, the calcification process that occurs in AS can progress to extend beyond the aortic valve and into the electrical conduction system of the heart. Evidence of this phenomenon may include heart block that is apparent on the ECG but otherwise undetectable.

Heart Catheterization

Cardiac catheterization provides a definitive diagnosis, indicating severe stenosis in valve area of <0.8 cm2 (normally 1.5-2 cm2). It can directly measure the pressure on both sides of the aortic valve. The pressure gradient may be used as a decision point for treatment. It is useful in symptomatic patients before surgery.

Echocardiogram

Echocardiogram (heart ultrasound) is the best noninvasive test to evaluate the aortic valve anatomy and function.

The aortic valve area can be calculated noninvasively using echocardiographic flow velocities. Using the velocity of the blood through the valve, the pressure gradient across can be calculated by the modified Bernoulli equation.

Gradient = 4(velocity)2 mmHg

A normal aortic valve has a gradient of only a few mmHg. A decreased valvular area causes an increased pressure gradient, and these parameters are used to classify AS as either mild, moderate or severe. The pressure gradient can be abnormally low in the presence of mitral stenosis, HF or coexistent aortic regurgitation.

The echocardiogram may also show left ventricular hypertrophy, a thickened and immobile aortic valve and a dilated aortic root. However, it may appear deceptively normal in acute cases.

Chest X-ray

Chest x-ray can also assist in the diagnosis, showing a calcific aortic valve and, in longstanding disease, an enlarged left ventricle and atrium.

Computed Tomography

Both electron beam and rapid multislice chest tomography can provide quantitative evaluation of the amount of valve calcification. The degree of calcification correlates both with stenosis severity by echocardiography and with clinical outcomes. However, the role of quantitation of valve calcium in clinical decision-making has not been defined.

Cardiovascular Magnetic Resonance

Cardiovascular magnetic resonance (CMR) imaging can detect the presence of AS and the anatomic valve area can be measured from short-axis views of the valve. In addition, velocity-encoded imaging can accurately measure the antegrade velocity through the stenotic valve with the advantage, compared to echocardiography, that it is not angle-dependent.

Despite these observations, CMR evaluation of AS severity is not yet widely accepted, in part due to limited experience and availability.

Establishing the diagnosis

The classic symptoms of AS are heart failure, angina, and syncope; however, the most common symptoms of AS are decreased exercise tolerance and dyspnea on exertion.

On physical examination, among many findings, the most useful findings for ruling in AS are slow rate of rise of the carotid pulse, ejection systolic murmur, and decreased intensity of the second heart sound. No single finding on physical examination or combination of findings has both high sensitivity and high specificity for diagnosing AS, particularly in asymptomatic patients. Echocardiographic data to diagnose AS are more reliable. Cardiac catheterization is reserved for patients in whom echocardiography is nondiagnostic or when clinical and echocardiographic data are discrepant.

Subvalvular Disease

Subvalvular AS can result from a variety of fixed lesions. These include a thin membrane (the most common lesion), thick fibromuscular ridge, diffuse tunnel-like obstruction, abnormal mitral valve attachments, and occasionally, accessory endocardial cushion tissue.

Supravalvular Disease

There are at least two anatomic forms of supravalvar AS. The majority of patients (60-75%) have an hourglass deformity, consisting of a discrete constriction of a thickened ascending aorta at the superior aspect of the sinuses of Valsalva. More diffuse narrowing for a variable distance along the ascending aorta is seen in the remaining patients.

There is a high frequency of supravalvular AS in patients with Williams syndrome, which is due to a mutation in the elastin gene. Supravalvular AS is also common in patients with homozygous familial hypercholesterolemia and occurs infrequently in heterozygotes.

AS can be accurately assessed with echocardiography. Cardiac catheterization is reserved for patients in whom echocardiography is nondiagnostic or when clinical and echocardiographic data are discrepant.

4. Specific Treatment

Management of Asymptomatic AS

  • The primary goal in treating patients with asymptomatic AS is monitoring of disease and early detection of symptom onset.

  • Among patients with asymptomatic AS, there are no medical therapies that have been proven to delay progression of the leaflet disease.

  • In patients with mild AS, echocardiography is recommended every 3-5 years. In patients with moderate AS, echocardiography is recommended every 1-2 years. In patients with severe asymptomatic AS, echocardiography is recommended every 6 months. Clinical decisions should not be based solely on echocardiographic data, but echocardiograms are a useful component of the clinical assessment of AS.

  • In patients with asymptomatic AS and hypertension, the ventricle is exposed to a "double load" of increased systemic blood pressure and valve stenosis. Treatment of hypertension in these patients is appropriate, although therapy should be cautious given concerns about potential adverse hemodynamic effects.

  • In patients with valvular heart disease, conventional coronary risk factors should be evaluated and treated based upon accepted guidelines for adults.

Management of Symptomatic AS

AVR

Symptomatic AS is an indication for AVR, and medical therapy has limited utility in treating symptoms. However, medical management may be required in patients who are not candidates for surgery (either due to comorbid conditions or patient refusal to undergo valve replacement).

ACC/AHA Guideline Summary: Indications for AVR in AS

Class I

• Symptomatic severe AS

• Severe AS in patients undergoing coronary artery bypass graft surgery or surgery on the aorta or other heart valves

• Severe AS with a left ventricular ejection fraction <50%

Class IIa

• Moderate AS in patients undergoing coronary artery bypass graft surgery or surgery on the aorta or other heart valves

Class IIb

• Severe AS in asymptomatic patients who have an abnormal response to exercise such as the development of symptoms or hypotension

• Severe AS in asymptomatic patients with a high likelihood of rapid progression (as determined by age, valve calcification, and coronary heart disease)

• Severe AS in asymptomatic patients in whom surgery might be delayed at the time of symptom onset

• Mild AS in patients undergoing coronary artery bypass graft surgery in whom there is evidence, such as moderate to severe valve calcification, that progression may be rapid

• Extremely severe AS (aortic valve area <0.6 cm2, mean gradient >60 mmHg, and aortic jet velocity >5.0 m/sec) in asymptomatic patients in whom the expected operative mortality is 1% or less

Class III

• For the prevention of sudden cardiac death in asymptomatic patients who have none of the class IIa or IIb findings

TAVI

TAVI is considered in inoperable and high-risk surgical patients.

AORTIC VALVOTOMY

In percutaneous aortic balloon valvotomy the aim is to relieve the stenosis, presumably by fracturing calcific deposits within the valve leaflets. Stretching of the annulus and separation of the calcified commissures also may contribute. Early changes after successful valvotomy include a moderate reduction in the transvalvular pressure gradient and an often dramatic improvement in symptoms; however, the postprocedure valve area rarely exceeds 1.0 cm2.

Serious complications (stroke, aortic regurgitation, myocardial infarction) occur in approximately 10-20% of patients. Furthermore, restenosis and clinical deterioration occur in most cases within 6-12 months and the long-term outcome resembles the natural history of untreated AS. Repeat balloon valvotomy can be performed, but most patients fail within 6 months.

Based upon these observations, the 2006 ACC/AHA guidelines concluded that balloon valvotomy is NOT a substitute for valve replacement in adults, although selected young adults without valve calcification may represent an exception. In addition, balloon valvotomy is frequently used in children with valvar AS.

In the following settings in adults, balloon valvotomy might be reasonable:

  • As a bridge to surgery in hemodynamically unstable patients who are at high risk for AVR. However, mortality remains high in these patients.

  • Use for palliation in patients with serious comorbid conditions that prevent performance of AVR

  • As a bridge to delivery in symptomatic pregnant women

  • In patients who require urgent noncardiac surgery

    Recent improvements in both balloon technology and procedural technique may lead to a resurgence in the clinical application of balloon valvotomy.

Palliative Care

Palliative care for severe symptomatic inoperable AS includes the following:

  • Treatment of concurrent cardiovascular conditions such as atrial fibrillation and coronary artery disease

  • Management of loading conditions and symptoms. Careful treatment of hypertension is appropriate.

  • For patients with HF, a combination of a diuretic and an ACE inhibitor can be used. These should be started at low doses with gradual titration.

Drugs and dosages

Combination of a diuretic and an ACE inhibitor can be used. These should be started at low doses with gradual titration.

  • Diuretics reduce preload, on which the patient may depend for maintenance of cardiac output. Therefore, diuretics should be used with caution.

  • Beta blockers reduce contractility, which may pose a risk for the overloaded left ventricle. While low-dose beta blockers may be considered in patients with asymptomatic hypertension (particularly in the setting of atrial fibrillation), beta blockers should be avoided in patients with symptomatic AS and HF.

  • Vasodilators (such as hydralazine, nitroglycerin, and nifedipine) in the presence of a fixed valvular stenosis may reduce systemic blood pressure and reduce coronary artery perfusion pressure. These agents should be avoided or used with caution.

Refractory cases

  • In patients with serious comorbid conditions that prevent performance of AVR, aortic balloon valvotomy can be done.

  • TAVI is considered in inoperable and high-risk surgical patients.

  • Treatment of concurrent cardiovascular conditions such as atrial fibrillation and coronary artery disease.

  • Management of loading conditions and symptoms. Careful treatment of hypertension is appropriate.

  • For patients with heart failure, a combination of a diuretic and an ACE inhibitor can be used. These should be started at low doses with gradual titration.

  • Prevention and treatment of concurrent conditions

  • End-of-life discussions and counseling

5. Disease monitoring, follow-up and disposition

  • AVR is the mainstay of treatment of symptomatic AS. It offers substantial improvements in symptoms and life expectancy. Medical therapy may not prolong life in patients with AS and has limited utility in treating symptoms.

  • In patients who are candidates for surgical intervention and are awaiting surgery, medical therapy to optimize hemodynamics in the preoperative setting may be needed. However, when severe symptoms are present, it may be prudent to admit the patient to the hospital and perform surgery urgently as there is a high risk of cardiac death once severe symptoms are present.

  • Longer-term palliative medical management of symptomatic AS is appropriate for patients who are not candidates for aortic valve surgery due to coexisting medical conditions and in patients who have refused AVR.

Follow-up

Treatment is generally not necessary in asymptomatic patients. In moderate cases, echocardiography is performed every 1–2 years to monitor the progression, possibly complemented with a stress test. In severe cases, echocardiography is performed every 3–6 months. In both moderate and mild cases, the patient should immediately make a revisit or be admitted if any new related symptoms appear.

In adults, symptomatic AS usually requires AVR, which decreases the risk of death.

Pathophysiology

  • There are three primary causes of valvular AS: a congenitally abnormal valve with superimposed calcification (unicuspid or bicuspid), calcific disease of a trileaflet valve, or rheumatic valve disease.

  • The pathobiology of calcific aortic valve disease is characterized by three primary processes: lipid accumulation, inflammation, and calcification.

  • In general, symptoms in patients with AS and normal left ventricular systolic function rarely occur until the valve area is <1.0 cm2, the jet velocity is >4.0 m/sec, and/or the mean transvalvular gradient exceeds 40 mmHg.

  • In patients with known AS who are followed prospectively, the most common symptoms are decreased exercise tolerance and dyspnea on exertion. Once symptoms develop, even when mild, prompt surgical intervention is needed because average survival without valve replacement is only 2-3 years, with a high risk of sudden death.

  • Although the physical examination correlates with the severity of AS, no single finding on physical examination or combination of findings has both high sensitivity and high specificity for excluding severe AS, particularly in asymptomatic patients. Echocardiographic data are more reliable.

Epidemiology

AS is a common problem. ~2% of people over the age of 65, 3% of people over age 75, and 4% of people over age 85 have the disorder. In North America and Europe, at least, the population is aging. Hence, the prevalence of AS is increasing. Since the disease carries with it considerable morbidity and mortality, both with large personal and economic impact, AS is a major health problem.

Prognosis

The classic symptoms of AS are heart failure, angina, and syncope. However, the most common symptoms in patients who are followed prospectively are nonspecific (eg, decreased exercise tolerance and dyspnea on exertion), so it is necessary to determine whether the symptoms are due to heart failure.

Mortality dramatically increases after the development of the classic symptoms. As a result, prompt valve replacement is recommended in such patients. This guideline is widely accepted, although as many as one third of such patients do not yet have critical AS (valve area <0.75 cm2). The mortality rate is very high in symptomatic patients who do not undergo valve replacement, which may be due in part to comorbidities that preclude surgery.

A substantial number of patients with severe AS are not yet symptomatic, although these patients have low event-free survival rates (56-63% at 2 years and 25-33% at 4-5 years). In comparison, patients with mild disease (ie, aortic jet velocity <3.0 m/sec) are unlikely to develop symptoms due to AS over the ensuing 5 years.

Serial hemodynamic measurements alone have not been proven clinically useful in asymptomatic patients since the absolute valve area or transvalvular pressure gradient does not determine the optimal time for valve replacement. However, serial echocardiography, which also provides information about left ventricular function and associated lesions, can be an important part of an integrated approach that includes a detailed history, a careful physical examination, and evaluation of exercise tolerance. Guidelines for serial monitoring are discussed separately.

Some, including the Working Group on Valvular Heart Disease of the European Society of Cardiology, have attempted to identify asymptomatic patients with severe AS who might be at high risk without surgery. This includes patients with an abnormal response to exercise, a decline in left ventricular ejection fraction <50%, a rapid increase in aortic jet velocity of ≥0.3 m/sec in combination with moderate to severe valvular calcification, a hyperdynamic ventricle with marked left ventricular hypertrophy, and serious ventricular arrhythmias. The threshold for surgery may be lower in such "high-risk" patients with critical valve areas of <0.75 cm2 than in those with valve areas of <1.0 but ≥0.75 cm2.

Special considerations for nursing and allied health professionals.

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What's the evidence?

Agabegi, ED, Agabegi, SS. "Valvular heart disease". Diseases of the Cardiovascular System. Step-Up to Medicine (Step-Up Series). Lippincott Williams & Wilkins. 2008.

Bach, DS, Siao, D, Girard, SE. "Evaluation of patients with severesymptomatic aortic stenosis who do not undergo aortic valve replacement: the potential role of subjectively overestimated operative risk". CircCardiovasc Qual Outcomes. vol. 2. 2009. pp. 533.

Bonow, RO, Carabello, BA, Chatterjee, K. "2008 Focused update incorporated into the ACC/AHA 2006 guidelines for the management of patients with valvular heart disease: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Writing Committee to Revise the 1998 Guidelines for the Management of Patients With Valvular Heart Disease): endorsed by the Society of Cardiovascular Anesthesiologists, Society for Cardiovascular Angiography and Interventions, and Society of Thoracic Surgeons". Circulation. vol. 118. 2008. pp. e523.

Gorlin, R, Gorlin, SG. "Hydraulic formula for calculation of the area of the stenotic mitral valve, other cardiac valves, and central circulatory shunts". I. Am Heart J. vol. 41. 1951. pp. 1.

Otto, CM. "Valvular aortic stenosis: disease severity and timing of intervention". J Am Coll Cardiol. vol. 47. 2006. pp. 2141.

Vahanian, A, Baumgartner, H, Bax, J. "Guidelines on the management of valvular heart disease: The Task Force on the Management of Valvular Heart Disease of the European Society of Cardiology". Eur Heart J. vol. 28. 2007. pp. 230.

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