What characterizes very severe Aortic Stenosis (AS)?

Definition of Very Severe Aortic Stenosis

Very severe aortic stenosis (AS) is defined by a peak aortic jet velocity ≥5 m/s or mean gradient ≥60 mmHg, usually accompanied by an aortic valve area ≤1.0 cm².

Diagnostic Criteria

Very severe AS represents the extreme end of the AS severity spectrum and has specific hemodynamic parameters that distinguish it from severe AS:

Primary Hemodynamic Parameters

• Peak aortic jet velocity: ≥5 m/s (compared to ≥4 m/s for severe AS) 1
• Mean pressure gradient: ≥60 mmHg (compared to ≥40 mmHg for severe AS) 1
• Aortic valve area: Typically ≤1.0 cm² (similar to severe AS) 1

Additional Echocardiographic Findings

• Severe leaflet calcification with severely reduced leaflet opening
• Indexed aortic valve area ≤0.6 cm²/m²
• Velocity ratio <0.25

Clinical Significance

The distinction between severe and very severe AS is clinically important for several reasons:

1. Poorer Prognosis: Patients with very severe AS (peak velocity ≥5 m/s) have significantly worse outcomes compared to those with severe AS (4-5 m/s), even when asymptomatic 2, 3.

2. Management Implications: According to the 2023 ESC/EACTS guidelines, intervention should be considered in asymptomatic patients with very severe AS (mean gradient ≥60 mmHg or peak velocity >5 m/s) if procedural risk is low, even with normal exercise test and preserved LVEF >55% (Class IIa recommendation) 1.

3. Risk of Rapid Deterioration: Research shows that asymptomatic patients with very severe AS have a high event rate and risk of rapid functional deterioration 2:

   • Event-free survival at 1,2,3, and 4 years was only 64%, 36%, 25%, and 12%, respectively
   • Patients with peak velocity ≥5.5 m/s had even worse outcomes, with event-free survival of 44%, 25%, 11%, and 4% at 1,2,3, and 4 years

Subgroups of Very Severe AS

Very severe AS can be further stratified based on peak velocity:

• 5.0-5.5 m/s: Higher risk than severe AS (4-5 m/s) but better prognosis than the most severe form
• ≥5.5 m/s: Highest risk subgroup with poorest outcomes and highest likelihood (52%) of developing severe symptoms (NYHA or CCS class >II) 2

Management Implications

The 2023 ACC/AHA guidelines recommend that in asymptomatic patients with very severe AS (defined as aortic velocity ≥5 m/s) and low surgical risk, aortic valve replacement is reasonable (Class 2a, Level of Evidence B-R) 1.

This recommendation differs slightly from the ESC/EACTS guidelines, which use a similar threshold but specifically mention a mean gradient ≥60 mmHg as an alternative criterion.

Clinical Pitfalls

1. Underestimation of Velocity: Multiple imaging windows (apical, right parasternal, suprasternal notch) should be used to avoid angle-related errors that could underestimate the peak velocity.

2. Misclassification: Some patients with very severe AS may be misclassified as having merely severe AS if proper technique is not used to obtain the highest velocity.

3. Symptom Assessment: Patients with very severe AS may unconsciously limit their activities to avoid symptoms, making clinical assessment challenging. Exercise testing may be valuable in these cases.

Very severe AS represents a high-risk condition that warrants close monitoring and consideration for early intervention, even in asymptomatic patients, due to its malignant natural history and high risk of rapid deterioration.