Up to 40% of patients being considered for aortic valve replacement might have an aortic valve area ≤1 cm2 (indicating severe AS) but with only a moderate gradient: >20 and <40 mmHg (typical of moderate stenosis). Nevertheless, this would also be considered severe aortic stenosis and is known as low-gradient AS.
Cardiology
InShort
by Warren Rosenblum, M.D.
Aortic Valve Gradient
The aortic valve gradient is the difference in pressure between the left ventricle and the aortic root just distal to the aortic valve.
Diagnostic Evaluation
The aortic valve gradient can be obtained invasively during cardiac catheterization by measuring pressures directly from the left ventricle and the ascending aorta or estimated noninvasively using echocardiography.
Staging
An elevated aortic valve gradient suggests aortic stenosis. If the elevated gradient is found via echocardiography, correlation with aortic valve morphology is readily available. If the elevated aortic valve gradient is obtained at cardiac catheterization, echocardiography is appropriate to evaluate the aortic valve morphology. A mildly elevated gradient is < 20 mmHg, a moderately elevated gradient is 20-40 mmHg, and a severely elevated gradient is > 40 mmHg.1
Reference
1Classification of valve stenosis and regurgitation. ECHOpedia Web site. http://www.echopedia.org/wiki/Classification_of_valve_stenosis_and_regurgitation. Updated December 11, 2016. Accessed May 15, 2017.
Critical Aortic Stenosis
Critical aortic stenosis involves severe narrowing of the aortic valve orifice secondary to calcific aortic valve sclerosis, rheumatic heart disease, or congenital malformation. The mean gradient > 40 mmHg, and the valve area < 1.0 cm2.
Causes and Risk Factors
Critical aortic stenosis is related to congenital-unicuspid or bicuspid valve, aortic valve calcification, and rheumatic fever.
Signs and Symptoms
Symptoms of critical aortic stenosis include shortness of breath, decreased exercise tolerance, chest pain/pressure, near syncope, and, occasionally, congestive heart failure. Symptoms are often subtle as patients reduce physical activity with disease progression.
Diagnostic Evaluation
Transthoracic echocardiographic diagnosis of critical aortic stenosis is based on American College of Cardiology/American Heart Association guidelines for severe stenosis, including jet velocity > 4.0 m/sec, mean gradient > 40 mmHg, valve area < 1.0 cm2, valve area index < 0.6 cm/m2, and confirmation during cardiac catheterization with direct pressure measurements and calculated aortic valve area using Gorlin formula.
Pearl
Exercise testing may be warranted in "asymptomatic patients" to elicit left ventricular dysfunction or ischemia.
Low-Gradient Aortic Stenosis
Up to 40% of patients being considered for aortic valve replacement might have an aortic valve area ≤ 1 cm2 (indicating severe AS) but with only a moderate gradient: >20 and <40 mmHg (typical of moderate stenosis). Nevertheless, this would also be considered severe aortic stenosis and is known as low-gradient AS. The prognostic implications of low-gradient AS are mixed. However, the low-flow low-gradient AS with reduced left ventricular ejection fraction would have the worst prognosis and thus would also be considered critical AS.
Treatment
Surgical aortic valve replacement (bioprosthesis vs mechanical) or transcatheter aortic valve replacement (TAVR) may be indicated.
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References
Nishimura RA, Otto CM, Bonow RO, et al. 2014 AHA/ACC guideline 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. Circulation. 2014;129:2440-2492.
Roberts WC. Anatomically isolated aortic valvular disease: the case against its being of rheumatic etiology. Am J Med. 1970;49:151–159.
Lewin MB, Otto CM. The bicuspid aortic valve: adverse outcomes from infancy to old age. Circulation. 2005;111:832-834.
Rizzello V. Moderate gradient severe aortic stenosis: diagnosis, prognosis and therapy. Eur Heart J Suppl. 2021 Oct 8;23(Suppl E):E133-E137. doi: 10.1093/eurheartj/suab108. PMID: 34650372; PMCID: PMC8503314.