Aortic Stenosis: What You Need to Understand

2. What It Is

Aortic stenosis (AS) is a progressive narrowing of the aortic valve opening that increases resistance to LV outflow, forcing the left ventricle to generate progressively higher pressure to maintain adequate forward cardiac output.

The valve normally opens to 3-4 cm2. AS is classified by severity:

• Mild AS: Valve area above 1.5 cm2, mean gradient below 20-25 mmHg
• Moderate AS: Valve area 1.0-1.5 cm2, mean gradient 25-40 mmHg
• Severe AS: Valve area below 1.0 cm2, mean gradient above 40 mmHg
• Very severe AS: Mean gradient above 60 mmHg or jet velocity above 5 m/s

These thresholds carry prognostic weight: the RECOVERY trial (NEJM 2020) used an initial valve area of 1 cm2 or below and jet velocity of 4 m/s or above as entry criteria for severe asymptomatic AS. 5 / Solid .

Calcific vs Congenital AS

Calcific (degenerative) AS is the most common form in adults over 65. It follows the same biological pathway as atherosclerosis: lipid infiltration of valve leaflet fibrosa, inflammatory cell infiltration, calcification, and progressive leaflet immobility. Risk factors overlap with atherosclerosis (age, male sex, LDL, smoking, hypertension). The progression rate is approximately 0.1-0.3 cm2/year loss in valve area 5 / Solid 00572-7).

Bicuspid aortic valve (BAV) is a congenital abnormality (two leaflets instead of three) present in 1-2% of the population. BAV accelerates calcification and stenosis, typically presenting 10-20 years earlier than tricuspid calcific AS (in the 40s-60s). BAV is also associated with aortopathy (ascending aortic dilation and risk of aortic dissection), requiring surveillance imaging of the ascending aorta.

Rheumatic AS results from post-streptococcal inflammatory scarring of the valve leaflets; commissural fusion predominates. This is the dominant form globally in low-income countries but uncommon in the United States.

3. The Mechanism

The pressure overload cascade

As the aortic valve narrows, the LV must generate higher pressure to maintain forward flow. The wall stress on the LV rises (law of Laplace: wall stress is proportional to pressure times radius divided by wall thickness). The LV adapts by concentric hypertrophy: myocyte thickening without cavity dilation, which increases wall thickness and reduces wall stress to normal levels. This is the compensated phase. Patients may have severe AS for years with no symptoms during this period.

The compensated phase ends when:

1. The hypertrophied myocardium outgrows its blood supply, causing subendocardial ischemia (explaining angina even without obstructive coronary disease)
2. Diastolic dysfunction from hypertrophy and fibrosis impairs LV filling, raising filling pressures and causing dyspnea on exertion
3. Atrial contribution to LV filling becomes critical; new-onset AF or loss of atrial kick can precipitate acute decompensation
4. The LV can no longer generate the pressure required to maintain forward flow; SBP begins to fall; syncope occurs from inadequate cerebral perfusion during exertion (demand exceeds supply)
5. EF begins to fall (late finding; EF below 40% in AS usually represents decompensated severe AS)

The mortality curve once symptoms begin:

• Angina: median survival 3 years
• Syncope: median survival 2-3 years
• Heart failure: median survival 1-2 years 5 / Solid

This is not a curve where watchful waiting makes sense once symptoms appear.

Low-flow, low-gradient AS

A specific diagnostic challenge: patients with severely reduced EF (below 40%) and “low-gradient” AS (mean gradient below 40 mmHg). Is the valve truly severe (small area, low gradient because the weak LV cannot generate enough flow to produce high gradient)? Or is the area measurement artifactually small because low flow reduces the opening force on a truly non-severe valve? This is “pseudo-severe” AS. Distinguishing true severe from pseudo-severe AS requires a low-dose dobutamine stress echocardiogram: dobutamine increases contractility; if the gradient rises above 40 mmHg with the same (small) valve area, the stenosis is true-severe. If the valve area increases above 1 cm2 with dobutamine, the low area at rest was a flow-dependent artifact.

Paradoxical low-flow, low-gradient AS: patients with preserved EF but low stroke volume index (below 35 mL/m2) and low gradient despite severe valve area. Seen in elderly women with small, concentrically hypertrophied LVs. These patients have worse outcomes than their “preserved EF” label suggests and benefit from valve replacement 5 / Solid .

4. How We Diagnose

Auscultation

Classic findings: harsh crescendo-decrescendo (diamond-shaped) systolic ejection murmur, loudest at right upper sternal border, radiation to carotids and apex. The murmur peaks later in systole as AS worsens. S2 becomes single (the aortic component is delayed and the pulmonary component is inaudible in severe AS due to LV pressure overload). The carotid pulse is pulsus parvus et tardus (small volume, delayed upstroke) in severe AS.

Echocardiography

TTE is the primary diagnostic and surveillance tool. Key measurements:

• Peak aortic velocity (m/s)
• Mean aortic pressure gradient (mmHg)
• Aortic valve area (cm2) by continuity equation
• LVEF and LV mass
• Left atrial size
• Pulmonary artery systolic pressure estimate
• Concomitant aortic regurgitation severity

The continuity equation calculates valve area using the principle of conservation of flow: AVA = (LVOT diameter^2 × 0.785 × LVOT VTI) / AV VTI. It requires accurate LVOT diameter measurement, a common source of error.

CT calcium scoring of the aortic valve is increasingly used when echocardiographic gradients and valve area are discordant. CT Agatston score above 2,000 (men) or 1,200 (women) is highly specific for true severe AS 5 / Solid .

Cardiac CT for TAVR planning

Pre-procedural CT angiography is mandatory for TAVR planning: femoral artery access sizing, annular dimensions (for prosthesis sizing), coronary artery height (risk of coronary obstruction during TAVR), landing zone anatomy, and aortic root morphology. Femoral artery calcification and minimal diameter are the primary determinants of percutaneous access feasibility.

5. The Evidence

PARTNER 3: TAVR vs SAVR in low-risk patients (2019)

TAVR (transcatheter aortic valve replacement) was initially developed for high-risk and inoperable patients who could not survive open-heart surgery. The evidence base has systematically expanded to lower-risk populations.

PARTNER 3 enrolled 1,000 low-surgical-risk patients (mean STS score 1.9%, a very low operative mortality prediction) with severe AS and randomized them to TAVR with the Edwards Sapien 3 balloon-expandable valve versus SAVR (surgical aortic valve replacement) 5 / Solid . At one year, TAVR had lower rates of the composite of death, stroke, or rehospitalization (8.5% vs 15.1%, HR 0.54, p < 0.001). At five years (five-year data available), clinical outcomes remained similar between groups, with TAVR having fewer pacemaker requirements in the SAVR group and similar mortality.

EVOLUT Low Risk: TAVR in low-risk patients with self-expanding valve (2019)

The Medtronic EVOLUT Pro/R self-expanding valve was tested in the EVOLUT Low Risk trial in similar low-surgical-risk patients. At two years, TAVR was non-inferior to SAVR for the composite of death or disabling stroke 5 / Solid . The non-inferiority threshold was met; TAVR did not cause more harm.

Together, PARTNER 3 and EVOLUT Low Risk established TAVR as an acceptable alternative to SAVR in low-risk patients. Current ACC/AHA guidelines give TAVR a Class 1 recommendation for patients 65 years and above with severe symptomatic AS and anatomy suitable for transfemoral TAVR, alongside SAVR, with shared decision-making about durability and valve-in-valve procedures determining the final choice 5 / Solid .

The durability question

For younger patients (below 65 years), the critical unresolved issue is TAVR valve durability. TAVR valves are bioprosthetic; they degenerate. The durability data for surgical bioprosthetic valves is 15-20 years. For TAVR valves, the 10-year data is now emerging from PARTNER 1 (the original inoperable cohort): hemodynamic deterioration of TAVR valves at 10 years is present in approximately 14-20% of surviving patients 4 / Promising . The question of whether a 55-year-old patient who receives TAVR today will need a second procedure (TAVR-in-TAVR) at age 65-70 is not fully answered.

Current guidance: below 65 years, shared decision-making. SAVR with a mechanical valve provides the longest durability (25-30+ years) but requires lifelong anticoagulation. SAVR with bioprosthetic valve requires reintervention at 15-20 years. TAVR in patients below 65 provides faster recovery but uncertain long-term durability.

RECOVERY trial: early surgery vs watchful waiting in asymptomatic severe AS (2020)

The RECOVERY trial enrolled 145 patients with asymptomatic severe AS and randomized them to early surgery versus watchful waiting with surgery triggered by symptoms or hemodynamic deterioration 5 / Solid . The trial was stopped early: at 6 years, the early surgery group had lower cardiovascular mortality (1 vs 5 deaths, HR 0.33, p = 0.003) and fewer strokes. This was the first RCT showing benefit from early surgery in asymptomatic AS, challenging the traditional “wait for symptoms” approach for severe AS.

The AVATAR trial (asymptomatic severe AS, Czech Republic) showed similar results: early surgery improved event-free survival 4 / Promising . Both trials used surgical populations; RECOVERY-2 (testing TAVR in asymptomatic severe AS) is ongoing.

Sex differences in aortic stenosis

Women with AS have a different biology than men. Key differences 5 / Solid :

• Women develop more fibrotic, less calcific valve disease. The CT calcium score threshold for severe AS is lower for women (1,200 versus 2,000 for men) because women develop hemodynamic severity with less calcium.
• Women have smaller aortic annuli, making prosthesis sizing more critical and patient-prosthesis mismatch (PPM) more common after SAVR.
• Women have worse outcomes after SAVR historically, possibly due to smaller vessel sizing and more anatomically challenging procedures.
• Women benefit at least equivalently from TAVR, with some data suggesting greater relative benefit than men.

6. The Patient Experience

The patient with newly diagnosed severe symptomatic AS faces a decision that feels like it came out of nowhere, because it did. AS is silent for decades. The symptoms arrive, often all three simultaneously, over months. The echocardiogram delivers a diagnosis that feels disproportionate to the symptoms: “severe” valve disease when the patient was walking a mile a week ago.

The two procedures at the center of the decision (TAVR vs SAVR) require understanding at the level that the patient can use to participate meaningfully in the decision. TAVR requires general anesthesia or deep sedation; a catheter is advanced from the femoral artery up through the aorta to the heart, and the prosthetic valve is crimped onto a delivery system and deployed across the diseased native valve (which is pushed aside). The average hospital stay is 1-2 days. Recovery is approximately 1-2 weeks before return to light activity.

SAVR requires general anesthesia, sternotomy (opening the chest through the breastbone), and cardiopulmonary bypass. The surgeon removes the diseased valve and sews in the prosthesis. Hospital stay is 4-7 days. Recovery is 6-8 weeks.

For a 79-year-old retired nurse from Evanston who is otherwise fit, TAVR at Northwestern Memorial Hospital (Chicago) or NorthShore University HealthSystem (Evanston) is the appropriate first choice. Median age at TAVR in the United States is 79 years. For a 58-year-old with BAV AS, the durability conversation strongly influences whether SAVR with a mechanical valve is the better long-term option.

The post-TAVR complications requiring awareness:

• Stroke: 2-4% at 30 days with SAPIEN 3; cerebral embolic protection (Sentinel device) reduces silent MRI lesions but has not definitively reduced clinical stroke in powered trials 4 / Promising .
• Pacemaker requirement: 5-8% with balloon-expandable SAPIEN 3; 15-25% with self-expanding EVOLUT valves, due to proximity of the prosthesis to the AV node and bundle of His.
• Valve regurgitation (paravalvular leak): More common with TAVR than SAVR; trace to mild paravalvular leak is present in 15-30% of TAVR patients but is usually clinically insignificant.
• Vascular access complications: Hematoma, pseudoaneurysm, or arteriovenous fistula at the femoral access site.

Post-procedure: dual antiplatelet therapy (aspirin plus clopidogrel) for 3-6 months is standard post-TAVR for patients without AF. Lifelong aspirin thereafter. Echo at 30 days, 1 year, and every 5 years for valve surveillance.

7. Decisions and Trade-Offs

TAVR vs SAVR: the age-centered framework

The 2021 ACC/AHA Valve Guidelines provide a practical framework:

• Below 65 years: Prefer SAVR with a mechanical valve or bioprosthetic SAVR, given TAVR durability uncertainty and the need for a second intervention lifetime.
• 65-80 years: Either TAVR or SAVR is reasonable based on anatomy, patient preference, surgical risk, and informed discussion of durability. Many patients in this range, particularly those over 75 with transfemoral anatomy, are best served by TAVR.
• Above 80 years: TAVR is the preferred approach for most patients with suitable anatomy, given faster recovery and equivalent or better 1-2 year outcomes compared to SAVR.

Frailty assessment matters beyond age. A 72-year-old with a grip strength of 14 kg, slow gait, and multiple comorbidities may be better served by TAVR than the surgical pathway. A 72-year-old triathlete with a STS score of 1.5% may be better served by SAVR for durability.

The asymptomatic severe AS dilemma

RECOVERY trial data shifted the conversation toward earlier intervention for truly severe asymptomatic AS. The 2021 valve guidelines moved the Class 2b recommendation for AVR in asymptomatic severe AS to a 2a recommendation when it is performed at experienced centers with anticipated operative mortality below 1% (2a for very severe AS: AVA below 0.6 cm2 or mean gradient above 60 mmHg, or rapidly progressing).

In practice: asymptomatic severe AS patients should be followed every 6-12 months with echocardiography and assessed for symptoms at each visit. Exercise stress testing to unmask symptoms or hemodynamic deterioration is appropriate for patients who deny symptoms; an inability to complete a standard Bruce protocol without symptoms or BP fall indicates “functionally symptomatic” disease warranting intervention.

Bicuspid aortic valve considerations

BAV-associated AS has specific TAVR technical challenges: the elliptical annulus of a bicuspid valve is harder to seal with a circular stent frame, resulting in higher rates of paravalvular regurgitation with TAVR compared to tricuspid AS. SAVR is often preferred for BAV AS in younger patients, particularly if concurrent aortopathy requires aortic root repair. In older BAV patients with higher surgical risk, TAVR is performed at experienced centers with favorable results in registries 4 / Promising .

8. The SDE Synthesis

Aortic stenosis is a condition where two things are simultaneously true: it is highly treatable once identified, and it is frequently identified too late. The three to five years between the development of severe calcific AS and symptom onset are a window in which echocardiographic surveillance can catch the progression from moderate to severe, allowing timely referral before decompensation occurs.

The SDE Audit for patients over 60, particularly those with known risk factors for calcific AS (hypertension, dyslipidemia, prior mild AS on a previous echo), includes aortic valve surveillance as a component of the standard imaging protocol. Detecting the progression from moderate (mean gradient 30-35 mmHg) to severe (mean gradient above 40 mmHg) on serial echocardiography allows the intervention discussion to begin before syncope, heart failure, or hemodynamic deterioration.

The SDE Cohort for patients with moderate AS: the standard of care is surveillance echocardiography every 1-2 years for moderate AS and every 6-12 months for severe asymptomatic AS. Many patients lose track of this schedule without a proactive reminder system. The Cohort provides that system.

For patients diagnosed with severe symptomatic AS requiring valve replacement, the SDE Executive tier facilitates referral to the valve programs at Northwestern Memorial (Bluhm Cardiovascular Institute, Chicago), NorthShore University HealthSystem (Evanston), Rush University Medical Center (Chicago), and University of Chicago Medical Center, all of which offer both TAVR and SAVR with experienced multidisciplinary Heart Team processes.

The nurse from Evanston received TAVR at Northwestern Memorial. She was home on post-procedure day 2, walking her dog on day 9, and back to full nursing consultant work at week three. She knows the mean gradient on her new valve is 8 mmHg. She knows what that number means. She also knows she should have had her echocardiogram followed more carefully four years ago when it first showed moderate AS.

She is advocating for the follow-up. Now she understands why.