When to Use CT Calcium Scoring in Aortic Stenosis
Use CT calcium scoring when echocardiography shows conflicting measurements—specifically when you have a small aortic valve area (<1.0 cm²) suggesting severe AS but low gradients (<40 mmHg) suggesting non-severe AS, particularly in low-flow, low-gradient AS with preserved LVEF (paradoxical LF-LG AS) and normal-flow, low-gradient AS. 1, 2
Primary Clinical Scenarios Requiring CT Calcium Scoring
Low-Flow, Low-Gradient AS with Preserved LVEF (Paradoxical LF-LG)
- This is the most important indication for CT calcium scoring 1
- Defined by: AVA <1.0 cm², mean gradient <40 mmHg, LVEF ≥50%, and stroke volume index <35 mL/m² 1
- Dobutamine stress echo is less helpful in these patients with small, hypertrophied ventricles and normal EF 1
- CT calcium scoring becomes the primary tool to distinguish true-severe from pseudo-severe AS 1, 3
Normal-Flow, Low-Gradient AS
- Characterized by AVA <1.0 cm², mean gradient <40 mmHg, but stroke volume index ≥35 mL/m² 1
- Severe AS is very unlikely with normal flow, but CT calcium scoring helps confirm when clinical suspicion remains high 1
- Particularly useful when peak velocity is <3.0 m/s and mean gradient <20 mmHg 1
Low-Flow, Low-Gradient AS with Reduced LVEF (Classical LF-LG)
- Use CT calcium scoring when dobutamine stress echo is not feasible, not conclusive, or shows no contractile reserve 1, 3
- Patients without contractile reserve (failure to increase stroke volume by ≥20%) cannot be distinguished by dobutamine echo alone 1
Sex-Specific Diagnostic Thresholds
Men: 1
- Severe AS likely: ≥2000 Agatston units
- Severe AS very likely: ≥3000 Agatston units
- Severe AS unlikely: <1600 Agatston units
Women: 1
- Severe AS likely: ≥1200 Agatston units
- Severe AS very likely: ≥1600 Agatston units
- Severe AS unlikely: <800 Agatston units
The sex difference exists because women have relatively more valvular fibrosis than men, which contributes to stenosis but is not detected by CT 1
Critical Diagnostic Algorithm
Step 1: Confirm measurement accuracy 1
- Exclude underestimation of LVOT area (most common error)
- Verify all components of AVA calculation
- Ensure proper Doppler alignment
Step 2: Determine flow status 1
- Calculate stroke volume index (SVi)
- Low flow: SVi <35 mL/m²
- Normal flow: SVi ≥35 mL/m²
Step 3: Assess LVEF 1
- Preserved: ≥50%
- Reduced: <50%
Step 4: Apply appropriate imaging strategy 1
- Paradoxical LF-LG (preserved LVEF): CT calcium scoring is primary tool
- Classical LF-LG (reduced LVEF): Dobutamine stress echo first; if inconclusive or no contractile reserve, use CT calcium scoring
- Normal-flow, LG: CT calcium scoring when clinical suspicion remains despite normal flow
Important Caveats and Pitfalls
The "Grey Zone" Problem
- Only high calcium scores confirm severe AS, and only low scores exclude it 1
- Intermediate scores (men 1600-2000 AU, women 800-1200 AU) remain diagnostically uncertain 1
- In the grey zone, integrate calcium scoring with clinical data, symptoms, valve morphology, and LV function 1
When NOT to Use CT Calcium Scoring
- Do not use for screening when no stenosis exists 2
- Not indicated when echocardiography shows concordant high-gradient severe AS (velocity ≥4 m/s, mean gradient ≥40 mmHg) 1
- Not the first-line test in classical LF-LG with reduced LVEF—dobutamine stress echo should be attempted first 1, 3
Bicuspid Aortic Valve Consideration
- BAV men with severe AS have significantly higher calcium scores than TAV men 4
- Optimal thresholds for BAV men may be higher (2916 AU by one study) than guideline recommendations 4
- BAV women show similar calcium scores to TAV women 4
- This represents an emerging diagnostic challenge requiring clinical judgment 4