eMedicine Specialties > Cardiology > Valvular Heart Disease

Aortic Stenosis: Differential Diagnoses & Workup

Author: John A McPherson, MD, FACC, FSCAI, Assistant Professor of Medicine, Division of Cardiovascular Medicine, Medical Director of Cardiovascular Intensive Care Unit, Vanderbilt Heart and Vascular Institute
Contributor Information and Disclosures

Updated: Aug 25, 2009

Differential Diagnoses

Mitral Regurgitation
Mitral Valve Prolapse

Other Problems to Be Considered

Supravalvular aortic stenosis
Congenital subvalvular aortic stenosis
Hypertrophic obstructive cardiomyopathy

Workup

Laboratory Studies

There is emerging data that B-type natriuretic peptide (BNP) may provide incremental prognostic information in predicting symptom onset in asymptomatic patients with severe aortic stenosis.

Imaging Studies

• Echocardiography
  • Two-dimensional Doppler echocardiography is the imaging modality of choice to diagnose and estimate the severity of aortic stenosis and localize the level of obstruction. American College of Cardiology/American Heart Association (ACC/AHA) recommendations for echocardiography in aortic stenosis are summarized in Table 2. LV size, mass, and function should also be evaluated in each patient.
  • The etiology of aortic stenosis (bicuspid, rheumatic, or senile degenerative) may be assessed from the 2-dimensional echocardiographic parasternal short-axis view. Although the presence of aortic stenosis is readily diagnosed with 2-dimensional echocardiography, the severity of aortic stenosis cannot be judged based on the 2-dimensional echocardiographic images alone.
    
    

    

    Calcific aortic stenosis (parasternal long-axis and short-axis views).

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    Calcific aortic stenosis (parasternal long-axis and short-axis views).

  • Doppler echocardiography is an excellent tool for assessing the severity of aortic stenosis. Using the modified Bernoulli equation, a maximum instantaneous and mean aortic valve gradient can be derived from the continuous-wave Doppler velocity across the aortic valve.
  • In a laboratory with experienced personnel, Doppler-derived aortic valve gradients are accurate and reproducible and correlate well with those obtained during cardiac catheterization.
  • The transvalvular gradient is dependent on the severity of obstruction and the flow across the valve. In patients with low cardiac output, the valvular stenosis may be severe even though the transvalvular gradient is low. To overcome this problem, 2-dimensional Doppler echocardiography can also provide a reliable estimation of aortic valve area (AVA). The echocardiographic criteria for assessment of aortic stenosis severity are outlined in Table 3.
  • The major limitation of Doppler echocardiography in assessing the severity of aortic stenosis is underestimation of the gradient if the beam is not parallel to the aortic stenosis velocity jet. Thus, in a patient with clinical features of severe aortic stenosis but echo/Doppler findings of mild-to-moderate aortic stenosis, further evaluation with repeat Doppler or catheterization is required. Rarely, Doppler may overestimate the mean gradient in cases of severe anemia (hemoglobin <8 g/dL), a small aortic root, or sequential stenoses in parallel (coexistent LVOT and valvular obstruction). Furthermore, echocardiographic calculation of AVA is highly dependent on accurate measurement of the diameter of the LVOT. In patients with poor transthoracic echocardiographic images, transesophageal echocardiography (TEE) may be used to measure the mean and peak gradient and a planimeter may be used to assess the AVA. Table 2. ACC/AHA Recommendations for Echocardiography in Aortic Stenosis
    

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    Table

    Indication	Class
    Diagnosis and assessment of severity of AS	I
    Assessment of LV size, function, and/or hemodynamics	I
    Reevaluation of patients with known AS with changing symptoms or signs	I
    Assessment of changes in hemodynamic severity and ventricular function in patients with known AS during pregnancy	I
    Reevaluation of asymptomatic patients with severe AS	I
    Reevaluation of asymptomatic patients with mild-to-moderate AS and evidence of LV dysfunction or hypertrophy	IIa
    Routine reevaluation of asymptomatic adult patients with mild AS who have stable physical signs and normal LV size and function	III

    Indication	Class
    Diagnosis and assessment of severity of AS	I
    Assessment of LV size, function, and/or hemodynamics	I
    Reevaluation of patients with known AS with changing symptoms or signs	I
    Assessment of changes in hemodynamic severity and ventricular function in patients with known AS during pregnancy	I
    Reevaluation of asymptomatic patients with severe AS	I
    Reevaluation of asymptomatic patients with mild-to-moderate AS and evidence of LV dysfunction or hypertrophy	IIa
    Routine reevaluation of asymptomatic adult patients with mild AS who have stable physical signs and normal LV size and function	III

    Table 3. Criteria for Determining Severity of Aortic Stenosis
    

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    Table

    Severity	Mean gradient (mm Hg)	Aortic valve area (cm2)
    Mild	<25	>1.5
    Moderate	25-50	1-1.5
    Severe	>50	<1 (or <0.5 cm 2/m 2 body surface area)
    Critical	>80	<0.5

    Severity	Mean gradient (mm Hg)	Aortic valve area (cm2)
    Mild	<25	>1.5
    Moderate	25-50	1-1.5
    Severe	>50	<1 (or <0.5 cm 2/m 2 body surface area)
    Critical	>80	<0.5

• Radionuclide ventriculography may provide information on LV function, including LV ejection fraction, ESV, and EDV.
• Multislice computed tomography: Three-dimensional volume quantification of aortic valve calcification demonstrates a close, nonlinear relationship to echocardiographic parameters of severity of aortic stenosis. This method is not yet clinically validated.
• Cardiac magnetic resonance imaging: Comparison of AVA measurements via echocardiography/Doppler and cardiac magnetic resonance imaging has shown excellent correlation. This method is not yet clinically validated.

Other Tests

• Electrocardiogram
  • Although the ECG findings may be entirely normal, the principal finding is left ventricular hypertrophy (LVH), which is found in 85% of patients with severe aortic stenosis; however, its absence does not preclude critical aortic stenosis. The correlation between absolute voltages in precordial leads and the severity of obstruction, unlike in children with congenital aortic stenosis, is poor in adults.
  • T-wave inversion and ST-segment depression in leads with predominantly positive QRS complexes are common. ST depression exceeding 0.3 mV in patients with aortic stenosis indicates LV strain and suggests that severe LVH is present. Occasionally, a septal pseudoinfarct pattern can be seen. Left atrial enlargement with a preterminal negative p wave in lead V₁ is noted in 80% of severe isolated cases of aortic stenosis.
  • The rhythm usually is normal sinus. Atrial fibrillation and can be seen at late stages or as a consequence of coexistent MV disease or hyperthyroidism.
  • Extension of calcification into the conduction system can cause atrioventricular or intraventricular block in 5% of cases of aortic stenosis. Approximately 10% of all cases of left anterior fascicular block are secondary to calcified aortic valve disease. Ambulatory ECG monitoring frequently shows complex ventricular arrhythmias, particularly in cases with myocardial dysfunction.
• Chest roentgenogram
  • The cardiac size often is normal, with rounding of the LV border and apex despite significant aortic stenosis. Poststenotic dilatation of the ascending aorta is common.
  • On lateral view, aortic valve calcification is found in almost all adults with hemodynamically significant aortic stenosis. Although its absence on fluoroscopy in individuals older than 35 years rules out severe valvular aortic stenosis, its presence does not prove severe obstruction in individuals older than 60 years.
  • The left atrium may be slightly enhanced, and pulmonary venous hypertension may be seen.
• Stress testing: Exercise stress testing is usually not needed in patients with severe aortic stenosis to rule out coronary artery disease. However, closely monitored exercise stress testing may be of value to assess exercise capacity in asymptomatic patients. Abnormal results may prove greater disability than the patient would admit. In addition to watching for symptoms on the treadmill, one should also look for hemodynamic abnormalities, such as blood pressure decreases or failure to increase blood pressure normally, which can occur in the absence of symptoms. The test here is not used to screen for coronary disease.
• Provocative stress testing: This is used in cases when the severity of the aortic stenosis is uncertain because of a small stroke volume and a small mean aortic valve gradient (low-gradient aortic stenosis).
  • Infusion of an inotropic agent such as dobutamine, which results in an increase in stroke volume and heart rate, is usually helpful in establishing the correct diagnosis.
  • Cardiac output and LV and aortic pressures are measured simultaneously and AVA is calculated both before and during dobutamine infusion.
  • In patients with an initially low-pressure gradient but severe aortic stenosis, the measured AVA does not change and the mean-pressure gradient increases significantly with an intravenous dobutamine infusion in. In contrast, in patients who have a low cardiac output due to concomitant myocardial dysfunction rather than due to severe aortic stenosis alone, a minimal increase in aortic valve gradient and the measured AVA usually occurs with dobutamine infusion.

Procedures

Cardiac catheterization

In general, if clinical findings are not consistent with Doppler echocardiogram results, cardiac catheterization is recommended for further hemodynamic assessment. ACC/AHA recommendations for cardiac catheterization in aortic stenosis are summarized in Table 4.

Measurement of simultaneous LV and aortic pressures should be used to assess the transvalvular pressure gradient and cardiac output should be measured for the calculation of AVA.

Exclusion of coronary artery disease by coronary angiography is needed in all patients older than 35 years who are being considered for valve surgery. It also should be performed in patients younger than 35 years if they have LV systolic dysfunction, symptoms/signs suggestive of coronary artery disease, or 2 or more risk factors for premature coronary artery disease, excluding sex. Generally, the incidence of associated coronary artery disease has been reported to be 50% in individuals older than 50 years.

Measuring the left ventricular end-diastolic and systolic volume and calculating the ejection fraction (EF) can quantitate the status of LV systolic pump function. However, EF may underestimate LV performance in the presence of the increased afterload associated with severe aortic stenosis. Since bolus administration of contrast may provoke hemodynamic compromise and assessment of LV function can usually be obtained via echocardiography, contrast ventriculography is rarely indicated.

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