From the Guidelines
Severe aortic stenosis (AS) is diagnosed when the aortic valve area is less than 1.0 cm², the mean aortic valve gradient is ≥ 40 mm Hg, or the peak aortic valve velocity is ≥ 4.0 m/s, as defined by the 2024 AHA/ACC/ACS/ASNC/HRS/SCA/SCCT/SCMR/SVM guideline 1.
Key Measurements for Severe AS
The key measurements that define severe AS include:
- A valve area less than 1.0 cm²
- A mean pressure gradient across the valve greater than 40 mmHg
- A peak jet velocity exceeding 4.0 m/s In low-flow, low-gradient situations, dobutamine stress echocardiography may be necessary to distinguish true severe AS from pseudo-severe AS, as recommended by the 2021 ACC/AHA guideline for the management of patients with valvular heart disease 1.
Additional Parameters
Additional parameters that support a diagnosis of severe AS include:
- A dimensionless velocity index less than 0.25
- A valve area index (indexed to body surface area) less than 0.6 cm²/m² These measurements are crucial for clinical decision-making, as severe AS typically requires intervention, either through surgical aortic valve replacement or transcatheter aortic valve implantation, particularly when patients become symptomatic with angina, syncope, or heart failure.
Clinical Decision-Making
The pathophysiology behind these measurements reflects the progressive narrowing of the valve opening due to calcification and fibrosis, which increases resistance to blood flow from the left ventricle to the aorta, creating higher pressure gradients and reduced cardiac output. The 2017 ACC/AATS/AHA/ASE/EACTS/HVS/SCA/SCAI/SCCT/SCMR/STS appropriate use criteria for the treatment of patients with severe aortic stenosis also emphasize the importance of these measurements in clinical decision-making 1.
Diagnosis and Management
The 2024 AHA/ACC/ACS/ASNC/HRS/SCA/SCCT/SCMR/SVM guideline recommends that patients with severe AS who meet criteria for intervention should undergo transcatheter or surgical aortic valve replacement (AVR) before elective noncardiac surgery to reduce perioperative risk 1. In patients with severe AS who require urgent elevated-risk noncardiac surgery, balloon aortic valvuloplasty may be considered as a bridging strategy. Patients with asymptomatic severe AS and normal LV function can safely undergo elective low-risk noncardiac surgery, especially in the absence of severe CAD, but patients should be monitored closely to avoid hypotension, excessive hypertension, and tachycardia.
From the Research
Aortic Valve Measurements of Severe AS
- The aortic valve area (AVA) is a key measurement in diagnosing severe aortic stenosis (AS), with an AVA of <1 cm2 indicating severe AS 2, 3, 4.
- The indexed AVA, which takes into account the patient's body surface area (BSA), is also used to diagnose severe AS, with an indexed AVA of <0.6 cm2/m2 indicating severe AS 2, 4.
- However, some studies suggest that indexing AVA to height (H) may be more accurate than indexing to BSA, with an AVA/H of <0.6 cm2/m indicating severe AS 4.
- Other measurements, such as maximum jet-velocity (Vmax) and mean transvalvular gradient, are also used to diagnose severe AS, with a Vmax of >4 m/s and a mean gradient of >40 mm Hg indicating severe AS 2.
- The classification of severe AS can be further subdivided into different subtypes, including high-gradient severe AS, classic low-flow, low gradient (LF-LG) AS, and paradoxical LF-LG AS, which can have different outcomes after aortic valve replacement 5.
Diagnostic Criteria
- The diagnostic criteria for severe AS include an AVA of <1 cm2, an indexed AVA of <0.6 cm2/m2, a Vmax of >4 m/s, and a mean gradient of >40 mm Hg 2, 3, 4.
- Exercise testing and dobutamine echocardiography can also be used to diagnose severe AS, particularly in patients who are asymptomatic or have low-flow, low gradient AS 6.
- Aortic valve calcification can also be used to diagnose severe AS, with a higher amount of calcification indicating more severe disease 6.
Outcomes
- The outcomes of patients with severe AS can vary depending on the subtype of AS and the presence of other comorbidities 5.
- Patients with classic LF-LG AS may have a higher risk of major adverse cardiac and cerebrovascular events (MACCE) after surgical aortic valve replacement compared to those with high-gradient severe AS 5.
- Older age, high B-type natriuretic peptide (BNP), preoperative atrial fibrillation, and small aortic annulus on CT are also independent predictors of MACCE after surgical AVR 5.