48. Aortic Stenosis- Indications and Guidelines

Chi Chi Do-Nguyen DO, S. Sikandar Raza MD, Bo Yang MD PhD
University of Michigan
August 22, 2024

Abbreviations

AAE – aortic annular enlargement, used interchangeably with aortic root enlargement (ARE)
AR – aortic regurgitation
AS – aortic stenosis
AVA – aortic valve area
AVC – aortic valve calcium
AVR – aortic valve replacement
AU – Agatston units
BAV – bicuspid aortic valve
BNP – brain natriuretic peptide
BSA – body surface area
CABG – coronary artery bypass graft
EOA – effective orifice area
GDMT – guideline-directed medical therapy
LVEF – left ventricular ejection fraction
LVOT – left ventricular outflow tract
MR – mitral regurgitation
PPM – patient-prosthetic mismatch
PROM – preoperative risk of mortality
RVOT – right ventricular outflow tract
SAVR – surgical aortic valve replacement
SVD – structural valve deterioration
TAVR – transcatheter aortic valve replacement
TEE – transesophageal echocardiogram
TTE – transthoracic echocardiogram
ViV – valve-in-valve
VKA – vitamin K antagonist

Definitions

Prosthesis-patient mismatch (PPM) is defined as having an effective prosthesis valve area (the opening of the cusps) less than the native human valve area after insertion into the patient.1

Effective orifice area (EOA) is the net flow-passing capacity of a prosthetic valve regarding inflow orifice diameter, valve leaflet design, and opening kinematics.2

Aortic Vmax is the transaortic maximum velocity when the transaortic volume flow rate is normal, which is the best characterization of the hemodynamic severity of AS.3

Aortic valve area (AVA) is the transaortic valve area calculated using the Gorlin formula with a Fick or thermodilution cardiac output measurement.3

Mean ΔP is the mean transaortic pressure gradient calculated using the Bernoulli equation.3 This is a strong predictor of outcome after AVR, with better outcomes seen in patients with higher gradients.

Indications & Guidelines for Management by Grade/Stage of Disease

The key measurements for clinical decision-making in patients with AS are the aortic Vmax, AVA, and mean ΔP. The most common initial symptom of AS is exertional dyspnea or decreased exercise tolerance; syncope and angina are more advanced symptoms of AS. Based on these measurements and the presence of symptoms, the severity and stage of AS can be classified.3

Stage A: At risk for AS (Vmax <2 m/s)

Stage B: Mild/moderate AS (Vmax 2.0–3.9 m/s or mean ΔP <39 mmHg)

Stage C: Asymptomatic severe AS (Vmax2)

Stage D: Symptomatic severe AS (Vmax2)

Class 1 indications for AVR are either symptomatic severe AS (stage D) or asymptomatic severe AS (stage C) with an LVEF <50% or undergoing cardiac surgery for any other indications. Patients with Stage A, B, or C1 AS should be medically managed with standard GDMT and statin therapy as a Class 1 indication. There are varying circumstances for patients with Stage B and C1 AS where AVR may be a Class 2 indication (see Table 1).

When AVR is indicated, the approaches include SAVR and TAVR. Note that mechanical valves are only an option for SAVR, and suitable anatomy should be considered before recommending either approach. Using the STS risk calculator for PROM, if the risk is high or prohibitive for SAVR, decision-making focuses on TAVR if post-intervention survival is >12 months versus palliation if post-intervention survival is <12 months. Otherwise, current recommendations for SAVR vs TAVR are based on age:

Class 1:

Patients <65 years of age or have life expectancy >20 years: SAVR

Patients 65-80: SAVR or transfemoral TAVR

Patients >80 or younger patients with a life expectancy <10 years: transfemoral TAVR

Class 2b:

Critically ill patients with severe AS may be considered for a percutaneous aortic balloon dilation as a bridge to SAVR or TAVR

Shared decision-making about the choice of prosthetic valve type is influenced by several factors, including patient age, values, preferences, expected bioprosthetic valve durability, avoidance of PPM, the potential need for and timing of reintervention, and the risks associated with long-term anticoagulation. In patients where VKA anticoagulation is contraindicated, cannot be managed appropriately, or is not desired by the patient, it is a Class 1 indication for a bioprosthetic valve. Otherwise, current recommendations are based on age:

Class 2a:

Patients <50 years of age: mechanical > bioprosthetic

Patients 50-65: mechanical or bioprosthetic

Patients >65: bioprosthetic > mechanical

Class 2b:

Patients <50 years of age: the Ross procedure may be considered in patients with appropriate anatomy at a Comprehensive Valve Center

Table 1. Summary Table of Indications and Guidelines for Management by Stage of AS

Stage Criteria Recommendations Evidence
A (At risk of AS – BAV, other congenital valve anomaly, or AV sclerosis) Aortic Vmax <2 m/s with normal leaflet motion Class 1: Treat hypertension with standard GDMT and statin therapy
B (Progressive AS) Mild AS: Aortic Vmax 2.0–2.9 m/s or mean ΔP <20 mmHg Moderate AS: Aortic Vmax 3.0–3.9 m/s or mean ΔP 20–39 mmHg Class 1: Treat hypertension with standard GDMT and statin therapy Class 2b: AVR if undergoing cardiac surgery for other indications
Stage C – Asymptomatic severe AS
C1 (Normal LVEF) Severe AS: Aortic Vmax 2 (or AVAi 0.6 cm2/m2) Very severe AS: Aortic Vmax Class 1: Treat hypertension with standard GDMT and statin therapy AVR if undergoing cardiac surgery for other indications Class 2a: SAVR only if Exercise test demonstrates decreased exercise tolerance of fall in SBP >10 mmHg from baseline Low surgical risk and Very severe AS BNP >3 times normal Serial testing shows an increase in Vmax > 0.3 m/s per year Class 2b: AVR if Progressive decrease in LVEF on 3 serial imaging studies to <60% 52-56 53, 67-69 55, 70-74 11, 75-76 77-78 10, 49-51, 72 0
C2 (Reduced LVEF) Severe or very severe AS AND LVEF <50% Class 1: AVR 10, 49-51
Stage D – Symptomatic severe AS
D1 (High-gradient AS) Severe or very severe AS AND LVEF <50% Symptoms AND Aortic Vmax Class 1: AVR 15, 43-48
D2 (Low-flow, low-gradient AS with reduced LVEF) max <4 m/s or mean ΔP <40 mmHg Dobutamine stress echocardiography shows AVA <1.0 cm2 with Vmax AND LVEF <50% Class 1: AVR 8, 57-63
D3 (Low-gradient AS with normal LVEF or paradoxical low-flow AS) 22/m2) with an aortic Vmax <4 m/s or mean ΔP <40 mmHg AND Stroke volume index <35 mL/m2 (measured when patient is normotensive with SBP <140 mmHg) AND Class 1: AVR if AS is the most likely cause of symptoms 64-66

Supporting Evidence for Current Indications & Guidelines

Medical management: Hypertension and concurrent CAD is common and may be a risk factor in patients with AS, as it adds to the total work overload on the LV in combination with valve obstruction. Hypertension is associated with a 56% higher rate of ischemia cardiovascular events and a 2-fold higher mortality rate.4 Patients on statin therapy saw a 20% reduction in ischemic events,5 but not in the progression of AS.6

Timing of intervention: When severe AS is present, the rate of progression to symptoms is high, with an event-free survival rate of only 30-50% at 2 years.3 Ample evidence demonstrates the benefits of AVR on survival, symptoms, and LV systolic function.7 In patients with asymptomatic severe AS, periodic monitoring is needed because symptoms onset is insidious and may not be recognized by the patient. In patients with low LVEF and severe AS, survival is better in those who undergo AVR compared to those with medical management.8 The depressed LVEF in many patients is caused by excessive afterload, and LV function improves after AVR in such patients.9 Patients with very severe AS or reduced LVEF <60% have a >4-fold higher risk of cardiovascular death, making these patients eligible for consideration for an AVR despite lack of symptoms.10 An elevated serum BNP is a marker of subclinical heart failure and LV decompensation. It is associated with an increased 5-year risk of AS-related events and is predictive of symptom onset during follow-up and persistent symptoms after AVR.11 With at least mild AS, the annual rate of progression is an increase in Vmax of 0.3 m/s, mean ΔP of 7-8 mmHg, and a decrease in AVA of 0.15 cm2. The rate of symptom onset is strongly dependent on AS severity, with an event-free survival rate of 75-80% at 2 years for mild-moderate AS.12

SAVR vs TAVR: SAVR has demonstrated excellent durability and outcomes for both mechanical and bioprosthetic valves, as SVD typically occurs after >10 years. However, there is currently no data on the use of TAVR in patients <65 years of age.13 For patients aged 65-80, multiple factors should be considered in a shared decision-making process for SAVR or TAVR. TAVR has a slightly lower mortality risk and is associated with a shorter hospital length of stay, more rapid return to normal activities, lower risk of transient or permanent atrial fibrillation, less bleeding, and less pain than SAVR. However, it must be noted that the durability of transcatheter valves beyond 5-6 years is not yet known. On the other hand, SAVR is associated with a lower risk of paravalvular leak, less need for valve reintervention, and less need for a permanent pacemaker.14 In a prospective randomized controlled trial of patients with Stage D AS and prohibitive risk, TAVR was compared to standard medical therapy and showed a lowered rate of all-cause death at 2 years (43.3% vs 68%).15 Most of these trials included only older patients with a mean age in the mid-80s.

Valve choice: Patients <50 years of age at the time of AVR incur a higher and earlier risk of bioprosthetic valve deterioration, with a predicted 15-year risk of reoperation due to SVD of 22% for patients 50 years of age.16-18 Similarly, at least half of pulmonic homograft valves require reintervention within 10-20 years.19-20 In patients aged 50 to 65 years, large retrospective studies have shown similar long-term survival rates in patients who undergo mechanical versus bioprosthetic valve replacement.16-18, 21 In general, patients with mechanical valves experience a higher risk of bleeding caused by anticoagulation, whereas individuals who receive bioprosthetic valves experience a higher rate of reoperation because of SVD.21 In patients >65 years of age at the time of bioprosthetic AVR, the likelihood of primary SVD at 15 to 20 years is only about 10%.22-23 Older patients are also at higher risk of bleeding complications related to VKA therapy.

There has been a global trend towards the increased use of biological over mechanical valves for all age groups (75.2% before 2007 vs. 87.8% after 2007) since the introduction of TAVR in 2002, and valve-in-valve (ViV) TAVR in 2007.24 The cut-off age at which the number of mechanical valves outnumbered biological valves implanted shifted from 68 to 61 years of age in 2014.24 Data suggest there are serious clinical implications to performing biological SAVR in patients <55 years of age, with an accelerated risk for SVD and need for reoperation.24 Note that performing a ViV TAVR in a previously small bioprosthesis (<21 mm) is associated with a doubling in mortality and highlights the importance of understanding clinical practice trends in the selection of valve types and size.24 Therefore, patients <60 were more likely to receive a larger labeled valve size than those >70.

Ongoing Trials/Recent Publications

There are several ongoing trials assessing treatment modalities for AS that may change the future landscape of intervention, especially concerning the transcatheter space. The PARTNER, Evolut Low Risk, and NOTION trials assess the ideal valve choice (TAVR vs SAVR) for patients who are at low-moderate risk of undergoing SAVR for severe AS. These studies will direct the future of the type of treatment modality for AS; however, their study design and clinical implications will be discussed in the following chapter of TAVR. Herein, we will discuss the current trends and long-term outcomes as these two modalities relate to each other.

As TAVR has emerged as a less invasive therapeutic alternative, demonstrated promising outcomes for high surgical risk, and emphasized non-inferiority with low-intermediate risk patients in recent trials, the incidence of TAVR has increased in all age ranges over the last decade.25 In contrast to the current guidelines that recommend SAVR over TAVR for <65 years of age, TAVR has had a notable increase in this cohort.26 In 2021 National Trends by JACC, TAVR doubled in utilization from 2015 to 2021; however, in patients aged <65 years, TAVR utilization increased 2.7-fold, reaching nearly equal volumes as SAVR by 2021.25 Increasing utilization of TAVR in younger patients, life expectancy post-valvular surgery, and preference for bioprosthetic valve choices have all led to an increasing number of surgical patients requiring redo valve replacements.27-28 Assessing long-term outcomes and the need for re-interventions is important to guide clinical decision-making in which approach to initially offer patients. The overall trends in the last decade signify that the number of patients requiring redo SAVR has mostly stayed consistent and is projected to not dramatically change in the next 5 years; however, both AVR and non-AVR (CABG, mitral) surgeries have increased in the last decade and are projected to increase in the coming years.29-30 Several studies have demonstrated that redo cardiac surgery (SAVR, CABG, mitral repair/replacement) after TAVR is independently associated with an increased risk of mortality, as compared to SAVR-after-SAVR.29-31 These recent studies advise that a “TAVR first approach” in those that will have a longer life expectancy than valve longevity could limit future interventions and long-term mortality, compared to a “SAVR first approach.”

2, and AVC <1200 AU in women or <2000 AU in men) who received TAVR had significantly lower 2-year all-cause and cardiovascular mortality rates, compared with those on medical management.32 This suggests some utility in resolving afterload in patients with a reduced LVEF and can confer survival advantage via AVR. This data likely foreshadows the study findings of the TAVR UNLOAD trial; however, further studies will be needed to elucidate the most appropriate intervention approach in this patient population.

Expert Commentary – Aortic annulus/root enlargement (AAE/ARE)

The introduction of TAVR for use in patients who are at high risk for conventional SAVR has changed the lifetime management of aortic valve disease. All prospective randomized controlled trials thus far comparing TAVR and SAVR have shown that in patients with annuli <26 mm, SAVR had negative hemodynamic and clinical outcomes.33 However, SAVR remains the most durable treatment option for patients, especially younger patients and those requiring concomitant cardiac surgery for other pathologies. How can we improve our SAVR outcomes?

The mean aortic annulus in the United States is 23.1 ± 2.0 mm for men and 21.0 ± 1.8 mm for women, making the normal aortic annular area 3-4 cm2.1, 34 This is why the most used prosthetic aortic valve is size 21–23 in all the clinical trials and large series of SAVR. However, the labeling of the size of the prosthetic valve is based on the inner diameter of the metal frame, which is deceiving. The inner diameter of the actual prosthetic valve orifice is 5–7 mm smaller than the labeled valve size after implantation.35-36 This discrepancy between valve branding and actual orifice diameter creates a mismatch in sizing between a patient’s native annulus/left ventricular outflow tract (LVOT) and the EOA of implanted valves. Because of the discrepancy, the surgically implanted prosthesis based on the patient’s normal aortic annulus (19 – 25 mm) reduces the valve area by at least 36-56% compared to a normal native aortic annulus.36-37 Surgeons have been unintentionally implanting prosthetic valves that are too small in patients undergoing an AVR! 1, 33

AAE could not only improve the hemodynamics and longevity of prosthetic valves in the interim but it can also successfully prime patients for potential future valve-in-valve transcatheter interventions.38 Patients with AVR + AAE have a significantly better survival of 98% at 6 years compared to patients with AVR alone (74%, p = 0.016).38 AAE is an independent protective factor, with similar operative mortality and immediate postoperative morbidity between the groups.38 To implant a prosthetic valve that matches the patient’s native EOA, AAE should be performed for every patient undergoing SAVR unless the largest size bioprosthetic valve (size 29) or mechanical valve (size 27) can be placed in the native surgical annulus since the valve based on the size of native annulus size has a reduced area by 50%. TAVR minimizes downsizing valves due to the use of CT-derived annular dimensions for sizing.33 Therefore, surgeons should carefully assess all patients’ native surgical annulus, root anatomy, and EOA in preoperative CT planning studies and match these dimensions with the surgeon’s commercial valve of choice to identify the appropriate valve size to prevent PPM and prolong the survival of the patient and the bioprosthetic valve.33 Further, surgeons should recognize a small aortic annulus or the presence of PPM and recommend AAE + SAVR to accommodate an upsized valve.33

Several techniques have been cited over the years, with the Nicks and Manouguian being the most popular among current cardiac surgeons. Nicks first described a posterior approach to AAE in 1970 that involved an aortotomy in the midline of the noncoronary cusp, which extends as far inferior as the origin of the mitral valve. A similar posterior approach was described by Manouguian in 1979, in which the aortotomy is extended by a vertical incision through the left- and non-commissure and extended onto the aortomitral continuity, down onto the initial portion of the anterior mitral leaflet and to its origin with about 1 cm. The Manouguian technique is critiqued for its risk of MR occurring up to 14%. Both are relatively less complex than the more extensive aortoventriculoplasty of the anterior aspect of the root, originally described by Konno in 1975, which aimed to relieve subvalvular, valvular, and supravalvular stenosis through the enlargement of both the RVOT and LVOT. This procedure carries the risk of injury to the septal arteries (especially the first septal branch of the left anterior descending coronary artery), conduction system, and pulmonary valve when done without precision. Many patients develop RV dysfunction in the initial postoperative period, making appropriate patient selection crucial. The Ross modification to this technique in the congenital arena involves AVR with a pulmonary autograft and has allowed for the growth of the valve with the patient.

A more novel technique introduced in early 2020 by Yang can increase the aortic annulus size by three to five valve sizes.39 Compared to traditional techniques for AAE described by Nicks, Konno, and Manouguian, the Y-incision AAE importantly does not violate any outside structure surrounding the aortic root, such as the mitral valve annulus, anterior leaflet, or ventricular septum. Early data comparing these techniques indicate favorable outcomes of the Y-incision AAE, including lower risk of bleeding, MR, complete heart block, or aortic root to right ventricular outflow fistula while also being more effective at upsizing the valve size.37, 40 Compared with patients treated with a Nicks or Manougian, the hemodynamics in patients treated with Y-AAE are significantly better, including mean gradient, AVA, indexed EOA, and incidence of moderate and severe PPM.41 Further, the mean gradient, AVA, and left ventricular mass index regression in patients with severe AS treated with AVR and Y-AAE are better than those treated with TAVR for up to 24 months.42 No patients who underwent SAVR + Y-AAE had PPM, compared to 32 patients who underwent TAVR (18 moderate and 14 severe).42

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