Aortic valve disease

Overview

The aortic valve has two basic pathologies: stenotic or inadequate valve function (regurgitant). When the valve leaflets stiffen, the orifice narrows and the pressure gradient across the valve increases, sometimes resulting in decreased anterograde flow during systole.

 This can have a number of clinical consequences, starting with left ventricular hypertrophy and progressing to dilation, decreased cardiac output, arrhythmias, ischemia, and other complications. Aortic insufficiency occurs when the aortic valve fails to close properly during diastole, allowing retrograde blood flow from the aorta into the left ventricle.

Etiology

Causes of aortic stenosis (AS)

There are two common causes of aortic stenosis (AS):

• Calcified (age-related) aortic stenosis and 
• Congenital bicuspid aortic valves.

Rarely, rheumatic heart disease can cause aortic stenosis and/or aortic regurgitation, albeit this is more typically a mitral valve condition observed in underdeveloped nations. The most prevalent cause is calcified aortic stenosis, which is thought to develop over time as a result of increasing endothelial damage.

Causes of aortic regurgitation

Aortic regurgitation can develop in both chronic and acute conditions. Aortic dissection spreading to the valve or leaflet injury from viral or noninfectious endocarditis are two causes of acute aortic regurgitation. Chronic aortic regurgitation is most typically caused by the same diseases that cause aortic stenosis, calcific disease, congenital bicuspid valve problems, and Marfan syndrome in developing nations.

Other less common causes include problems from percutaneous aortic balloon valvuloplasty and transcatheter aortic valve replacements (TAVR), as well as a variety of inflammatory illnesses such as systemic lupus erythematosus, rheumatoid arthritis, and Takayasu arteritis. Rheumatic heart disease is the most common cause of persistent aortic regurgitation in developing countries.

Epidemiology

Aortic stenosis is a disease that is more common among the elderly (fifth through eighth decades). A prospective population-based study found that the incidence of aortic stenosis was 0.2 percent in the fifth decade, 1.3 percent in the sixth, 3.9 percent in the seventh, and 9.8 percent in the eighth.

When a sample of individuals with congenital anatomic anomalies of the aortic valve was compared to those with normal anatomy in those who underwent surgery for isolated aortic stenosis, the proportion of aberrant valves reduced with age. Two-thirds of post-surgery individuals under the age of 50 were found to have a bicuspid valve.

In contrast, one-third of patients were unicuspid, two-thirds were bicuspid, and one-third had typical tricuspid anatomy. In individuals above the age of 70, 60% had a tricuspid valve and 40% had a bicuspid valve.

The estimated prevalence of aortic regurgitation is 4.9 percent, with incidence increasing with age until the sixth decade, when it begins to decline. This figure, however, may be artificially low because up to 75% of aortic stenosis patients may have some degree of regurgitation that goes undetected.

Pathophysiology

Aortic stenosis causes the valve to narrow due to fusion of the leaflets or calcifications that cause the valve to be less mobile and block the orifice. Calcified aortic stenosis develops as a result of increasing endothelial damage, which causes inflammation and the infiltration of macrophages and other inflammatory cells at first. This inflammation and damage cause profibrotic factors to build a collagen matrix, which, like bone growth, eventually becomes calcified.

The most typical outcomes of aortic stenosis include a reduction in anterograde flow from the left ventricle into the aorta, which results in a blood backup in the left ventricle and elevated left ventricular pressures. This backflow can produce heart failure symptoms such as left atrial dilatation and mitral regurgitation, which can progress to pulmonary edema and right-sided heart failure.

A healthy aortic valve measures 3 to 4 cm in diameter; symptoms usually do not appear until the valve area is less than 1.0 cm. The more stenotic the valve, the more difficult it is to maintain appropriate cardiac output. The left ventricle experiences hypertrophy and remodeling, which can result in increased left ventricular oxygen demand, which, when combined with lower cardiac output, can result in ischemia, arrhythmias, and decreased brain perfusion.

Aortic regurgitation causes retrograde blood flow from the aorta into the left ventricle, an increase in left ventricular volume, and chamber dilatation. This causes a rise in cardiac output at first and can be sustained for a long time.

This increase in cardiac output, however, causes distention and higher pressure in the peripheral arteries, resulting in increased peripheral systolic pressure. This eventually worsens the regurgitation, causing a fast drop in peripheral systolic pressure and, in severe cases, cardiovascular collapse.

Symptoms of Aortic valve disease

An in-depth history and comprehensive physical exam are required, and are frequently used to make the first diagnosis of aortic valvulopathy. Symptoms of aortic stenosis or regurgitation are frequently absent or too mild for the patient to recognize until the disease has progressed to a severe level. As a result, a thorough cardiac physical exam is required for early detection.

A systolic ejection murmur may typically be heard better above the right sternal border at the second intercostal space with aortic stenosis. When the condition is moderate, this murmur will peak early during systole, and as severity grows, it will peak later. It also tends to radiate to the carotid arteries, coupled with a slowly increasing carotid upstroke. Auscultation frequently indicates a persistent apical impulse.

A thrill can occasionally be felt across the carotid arteries and aortic region in severe disease conditions. Other physical exam findings linked with aortic stenosis problems and sequelae include those associated with heart failure and left ventricle remodeling, such as third and fourth heart sounds, pulmonary crackles, jugular venous distention, and pedal edema.

Chronic aortic regurgitation can cause a blown diastolic decrescendo murmur, which has a positive link with the severity of the condition. A laterally and inferiorly displaced apical impulse is frequently present and maintained. The occurrence of Corrigan pulse (water hammer) occurs often. This is a bounding and strong pulse that swiftly increases and collapses.

Consider aortic dissection as a cause if a patient appears with very significant chest pain and physical exam abnormalities such as a difference in blood pressure between the right and left extremities. If the patient had a history of streptococcal infection, fevers, swollen and sore joints, skin nodules, and a new onset of rash, rheumatic heart disease would be high on the differential.

Chronic aortic regurgitation and late-stage aortic stenosis symptoms are classified into two groups: heart failure and impaired coronary and systemic perfusion. Patients may have pedal edema, shortness of breath, orthopnea, paroxysmal nocturnal dyspnea, and exertional dyspnea as a result of elevated pressures in the left ventricle.

Patients may claim that they need extra pillows to sleep because laying flat causes them to be out of breath. Furthermore, patients may claim that their exercise tolerance has reduced, with the number of city blocks they can walk before becoming short of breath or lightheaded decreasing. In severe disease conditions, patients may have syncope or complain of anginal symptoms.

How Aortic valve diseases is diagnosed?

Diagnosis is initially assumed based on either the patient's subjective history or an accidental discovery on physical examination. A 2D echocardiography with Doppler studies would be the gold standard test if there is a suspicion of valvular disease. During an echocardiography, three key parameters are assessed to assess the competence of the aortic valve: aortic jet velocity, mean aortic valve pressure gradient, and aortic valve area.

Chest Radiography 

In individuals with AS, cardiac size is generally normal, with rounding of the LV border and apex due to LV hypertrophy. On fluoroscopy, aortic valve and aortic root calcification are best seen in the lateral projections. Anteroposterior and posteroanterior projections seldom reveal them.

In individuals with bicuspid valves, the proximal ascending aorta may be dilated. Cardiomegaly is a late characteristic in AS patients. The heart is enlarged in individuals with heart failure, and the pulmonary vasculature is congested. The right atrium and right ventricle may also be enlarged in severe heart failure.

Electrocardiography

The most common sign on electrocardiography (ECG) in individuals with AS is LV hypertrophy, which is frequently associated with secondary repolarization abnormalities. This is present in 85 percent of severe AS patients. However, the absence of AS does not rule it out.

Left atrial hypertrophy and conduction problems, including left and right bundle branch block, are also prevalent. This might be owing to the calcification spreading into the surrounding conduction system. The axis can be moved to the left or right. Atrial fibrillation can also occur, especially in older people and those with high blood pressure.

Echocardiography

To help diagnose and determine the severity of AS, echocardiography is the imaging modality of choice. Two-dimensional echocardiography shows the shape of the aortic valve and can frequently determine whether it is trileaflet or bicuspid. The severity of calcific aortic valve disease varies from aortic sclerosis without ventricular outflow blockage to severe AS.

Aortic sclerosis is a frequent condition that affects persons over the age of 65. It is distinguished on echocardiography by localized foci of valve thickening, often in the leaflet center, with commissural sparing and normal leaflet motion.

Computed Tomography

Both electron beam and multislice cardiac computed tomography (CT) have been demonstrated to correlate with echocardiographic evaluation and clinical outcome. Although the function of CT in clinical therapy is not well defined, it is well established in assessing the existence and severity of aortic root and ascending aortic dilatation in patients with concomitant aortic aneurysms.

Cardiac Magnetic Resonance Imaging

Cardiac magnetic resonance imaging (CMR) can identify and accurately measure the anatomic valve area. The use of velocity-encoded CMR to evaluate velocity across stenotic aortic valves is currently being studied. As with cardiac CT, the role of this modality in the therapy of AS is not clearly defined at the moment, but it has a well-established role in examining aortic root and ascending aorta architecture.

Cardiac Catheterization

 Because echocardiographic evaluation of the severity of AS is so accurate, cardiac catheterization is now more commonly utilized to determine the existence of concomitant coronary artery disease (CAD) rather than to characterize hemodynamic abnormalities. Invasive hemodynamic assessments, on the other hand, are useful in individuals in whom noninvasive diagnostics are ambiguous or offer contradictory data on the severity of AS.

Exercise Testing

Many individuals with AS are oblivious to symptoms that appear gradually and are unable to distinguish tiredness and dyspnea from age and physical deconditioning. Other patients alter their lifestyle to avoid the onset of symptoms. Activity testing may have a role in generating symptoms or an aberrant blood pressure response to exercise in seemingly asymptomatic people with severe AS. Such testing should be done under the guidance of a physician and should not be done on people who are experiencing symptoms.

Staging

Chronic aortic disease is staged A to D. 

• A patient in Stage A (at risk) has no change in hemodynamics of the valve and no symptoms, but has at least one risk factor, such as a bicuspid valve, a sclerotic valve, a history of rheumatic fever, etc.
• Stage B (progressive) involves moderate hemodynamic abnormalities with or without early left ventricular diastolic dysfunction and the presence of established risk factors, but the patient remains asymptomatic.
• Stage C1 (asymptomatic severe) is defined by severe hemodynamic alterations on echocardiography, the existence of left ventricular diastolic dysfunction, no reduction in left ventricular function, and no symptoms in everyday life (however, symptoms may be precipitated with exercise stress testing).
• C2 has the same hemodynamic characteristics as C1 but for a lower left ventricular ejection percent (under 50 percent).
• Stage D1 (symptomatic severe) is characterized by a high gradient (Vmax less than 4m/s), left diastolic dysfunction, left ventricular hypertrophy, and perhaps pulmonary hypertension, as well as angina or heart failure symptoms on exercise.
• D2 (symptomatic severe) has a low flow/gradient, a low left ventricular ejection fraction (Vmax more than 4m/s), a low left ventricular ejection fraction (less than 50%), and symptoms at rest.
• D3 (severely symptomatic) is the final stage and is distinguished by a low gradient with normal left ventricular ejection fraction (aka paradoxical low flow), where ejection fraction is less than 50% but stroke volume is less than 35mL/min, resulting in a small left ventricular chamber and restrictive diastolic filling. Stage D3 aortic stenosis also has symptoms at rest. 

Management

There is no medical treatment that can prevent asymptomatic aortic valve disease from progressing. Management consists of a two-pronged approach that focuses on optimizing other cardiac comorbidities such as hypertension, coronary artery disease, left ventricular dysfunction, atrial fibrillation, and other arrhythmias, as well as vigilante serial evaluation to monitor disease progression and early detection of symptoms.

Patients with Stage B mild aortic valve disease should have echocardiograms every 3 to 5 years, whereas those with Moderate aortic valve disease should have them every 1 to 2 years. Echocardiography is required every 6 to 12 months for individuals with stage C1 severe asymptomatic illness. Regardless of stage, the emergence of new symptoms always necessitates rapid assessment.

Valve replacement for aortic stenosis is advised for asymptomatic individuals with high-grade disease (evidenced by history and/or stress tests) or asymptomatic patients with severe AS (C2) and a left ventricular ejection fraction less than 50%. Patients with significant stenosis (C or D) who are undergoing other cardiac surgery are candidates for valve replacement. 

Aortic valve replacement is indicated for symptomatic patients with severe AR regardless of LV systolic function (D), asymptomatic patients with chronic severe AR and evidence of LV systolic dysfunction (EF less than 50%), and patients with severe AR (C or D) while undergoing cardiac surgery for any other indication.

Patients whose projected life expectancy following valve replacement is shorter than one year and/or whose quality of life is not predicted to improve are not candidates for valve replacement. However, if the patient's life expectancy exceeds one year and the projections include an increase in quality of life, there are two options for aortic valve replacement: surgical or transcatheter. Transcatheter aortic valve replacement is only used to treat aortic stenosis, not aortic regurgitation.

Differential Diagnosis

The differential diagnosis for individuals with aortic valve disease symptoms includes, but is not limited to, the following:

• Hypertrophic obstructive cardiomyopathy
• Restrictive cardiomyopathy
• Constrictive cardiomyopathy
• Congestive heart failure with reduced ejection fraction (HFrEF)
• Coronary artery disease
• Atrial fibrillation
• Atrial flutter
• Ischemic heart disease
• Pericardial effusion
• Pulmonary hypertension
• Chronic obstructive pulmonary disease
• Restrictive lung diseases
• Symptomatic anemia

Prognosis

The time of development of symptoms has a substantial impact on prognosis. Patients who are asymptomatic but do not become symptomatic have a higher life expectancy. Patients with severe symptomatic aortic valve disease who do not have valve replacement have a very poor prognosis, with survival at 3 years ranging from 40 to 60 percent, whereas those who had valve replacement had a survival rate of 80 to 90 percent.

Valvular Heart Diseases During Pregnancy

During pregnancy, significant hemodynamic changes occur. During the first trimester, plasma volume rises and can reach up to 50% over baseline by the second trimester. The plasma volume then reaches a plateau for the remainder of the pregnancy. The heart rate rises by 10 to 20 beats per minute over the baseline. Endogenous hormones and uterine contraction cause a decrease in peripheral vascular resistance and a broadening of the pulse pressure. The gravid uterus can occlude the inferior vena cava, causing peripheral edema, weakness, and hypotension.

In women with reduced LV function or low cardiac reserve, the increased volume load may cause dyspnea and heart failure. Stenotic valvular lesions are more difficult to tolerate than regurgitant ones. The higher heart rate associated with pregnancy shortens the time for diastolic filling, which can be quite difficult for many individuals, particularly those with MS. It is fairly unusual for women with MS to seek medical assistance for the first time while pregnant.

During birth, uterine contractions result in the discharge of up to 500 mL of blood into the circulation. The lady loses roughly 400 mL of blood during a typical vaginal birth. The risk of blood loss during a cesarean section is much higher, with an average of 800 mL.

Because of autotransfusion from the uterus and because the baby no longer compresses the inferior vena cava, there is an abrupt rise in venous return following birth. Furthermore, autotransfusion of blood continues for 24 to 72 hours following birth. As a result, the danger of pulmonary edema persists for several days after birth.

Patients with moderate to severe valve lesions should be referred to a cardiovascular specialist for assistance with pregnancy and birth care. The dangers of surgery should ideally be communicated with the patient prior to conception.

Conclusion

Aortic valve illness is characterized by both regurgitation, or retrograde flow through the aortic valve, and stenosis, or constriction of the orifice, which limits anterograde flow through the valve. While the pathology may take several years to develop, symptoms may not arise until the illness is severe; at this time, the morbidity and mortality of aortic valvular disease are quite high. Early indications and symptoms of aortic valve dysfunction must be identified by medical specialists.

The difficulty in detecting and treating aortic stenosis stems from the patient's wide range of nonspecific symptoms, which creates a significant disparity. When there are no cardiac comorbidities and the patient does not see a cardiologist on a regular basis, it is frequently the primary care physician's responsibility to undertake a comprehensive physical exam that includes auscultation of the heart as the first step in detecting silent aortic valve disease.

If the patient's symptoms or physical exam results raise suspicion, an echocardiography and consultation with a cardiologist are required for correct staging.

Comorbidity treatment by primary care physicians, nurses, and other experts is critical to ensure the patient is ready for surgery if necessary.