39. Aortic Stenosis- Clinical Scenarios

Alexander A. Brescia, MD, MSc, and G. Michael Deeb, MD

Adapted from 1st edition chapter written by Gabriel Loor, MD, and Douglas R. Johnston, MD

Concepts

  • Indications for aortic valve replacement in the setting of aortic stenosis (AS)
  • Diagnostic testing
  • Treatment decisions (TAVR vs. SAVR)
  • Preoperative considerations
  • Options for annular enlargement
  • Valve choices
  • Surgical options and pitfalls

Chief complaint

“A 62-year-old man is referred to you by a primary care physician diagnosed with severe aortic stenosis by echo after presenting with a 3-month history of progressive dyspnea on exertion and chest tightness.”

Differential

The diagnosis of severe AS has been established. Confirmation is important as well as ruling out concomittent pathologies that often coexist.

History and physical

A focused history to elicit symptoms of angina, syncope, or congestive heart failure (CHF) as well as fatigue or decreased exercise tolerance, which often precede more overt symptoms, is essential. Since asymptomatic severe AS is not an indication for intervention, establishing symptoms in a patient suspected of AS is crucial for decision making. A focused physical exam with emphasis on vital signs, heart, lungs, neuro exam, bruits, pulses, and peripheral edema is important. A classic crescendo-decrescendo (diamond shaped) systolic ejection murmur heard best at the 2nd right intercostal space should be appreciated.

Determining comorbidities [end-stage renal disease (ESRD), liver disease, pulmonary failure, bleeding disorders, stroke, peripheral vascular disease, etc.] is important to calculate a STS predicted risk of mortality/morbidity to help establish the most appropriate treatment algorithm.

Tests

  • EKG: arrhythmias, LVH.
  • Echocardiogram. Gradients are determined by continuous wave doppler peak gradient = 4(velocity)2. The peak gradient is the maximum gradient present when simultaneous central aortic pressure is subtracted from LV systolic pressure, while mean gradient is the integral difference over the entire systolic ejection period (e.g. the area under the velocity curve). The aortic valve area (AVA) is determined by the continuity equation: Area = [(LVOT area) x (LVOT velocity)]/continuous wave velocity at the aortic valve. The indexed AVA is the AVA divided by body surface area (BSA). The dimensionless index (DI) is the ratio of the LVOT time-velocity integral to that of the aortic valve jet. Note that velocity is also influenced by cardiac output. Thus, patients may have low gradients because of low cardiac output (low flow).

If low flow/low gradient AS is suspected and the patient has a normal LVEF (≥ 50%), a stroke volume index ≤ 35 mL/min/m2 will confirm the diagnosis. If the LVEF is < 50%, a dobutamine stress echo may be helpful. If the gradient is increased on stress echo and the AVA does not increase, this confirms the diagnosis of AS. However, if the gradient does not change and the AVA increases ≥ 0.3cm2 or to ≥ 1.0cm2, this confirms pseudo-AS. If the patient has a significant subvalvular gradient and asymmetric septal hypertrophy, a septal myectomy and the possibility of intervention on the mitral valve may be required (refer to HOCM chapter). In general, it is imperative to ensure that the echocardiogram is of excellent quality or have it repeated and interpreted by a cardiologist you trust.  

  • Cardiac catheterization. Virtually all patients evaluated for AVR should have evaluation of their coronary arteries for obstructive CAD. If the diagnosis of AS is uncertain by echo, the AV should be crossed for a hemodynamic AV study.
  • Coronary CTA. For patients at low risk for CAD, coronary CTA may be performed to rule out obstructive CAD to avert a cardiac cath.  
  • TAVR protocol CT scan. All patients who are potential TAVR candidates should receive a TAVR CT scan, which will provide important anatomical information including valve morphology (TTE unreliable for morphology), aortic valve annular and LVOT sizing, coronary height and orientation, and sinus height and width sizing.

Diagnosis

The diagnosis of severe AS is defined as the presence of any one of the following:

1.) Mean AV gradient ≥ 40 mmHg

2.) Peak velocity across the AV ≥ 4 meters per second

3.) AVA ≤ 1.0 cm2 or an indexed AVA ≤ 0.6 cm2/m2

4.) Dimensionless index ≤ 0.25  

Confirmation of severe AS after referral is important as well as ruling out simultaneous pathologies such as obstructive CAD, aortic aneurysm, and mitral valve disease.

Index scenario (additional information)

“This patient is a diabetic, without syncope. Echo shows a valve area of 0.8 cm2 and mean gradient of 45 mmHg and LVEF 60%. Cardiac catheterization shows no obstructive CAD. TAVR CT scan shows a tricuspid aortic valve with anatomy amenable to TAVR, no aneurysm, and no ascending calcification. What are his options and how would you proceed?”

Treatment/management

This patient meets AHA Class I indications for an aortic valve replacement (angina, CHF, severe AS). Deciding whether to perform SAVR or TAVR should be determined by 1.) anatomy (including valve morphology and annular size, aortic root dimensions, and vascular access), 2.) patient age and simultaneous medical conditions impacting long-term prognosis, and 3.) patient preference. In light of SAVR vs. TAVR trials, patient surgical risk profile no longer precludes patient eligibility from undergoing TAVR.

An STS risk score should still be calculated to inform shared decision making with patients and determine treatment options. For patients at prohibitive risk (STS score >15%), TAVR has shown survival benefit compared to medical therapy and SAVR should not be offered. For patients at high (STS score 8-15%), TAVR was found to be superior at 3 years in the CoreValve trials and non-inferior at 5 years in both the CoreValve and PARTNER trials. For intermediate (STS score 4-8%) and low (STS score <4%) risk, TAVR has been shown to be non-inferior to SAVR at 2 years in the Evolut and PARTNER trials. Risk of permanent pacemaker implantation is higher after TAVR, while risk of bleeding, atrial fibrillation, and re-hospitalization is higher after SAVR. The current patient is likely low surgical risk. In choosing between TAVR vs. SAVR in a 62-year-old low-risk patient, the surgeon should discuss the likelihood of additional procedures over the patient’s remaining life span, especially if bioprosthetic SAVR or TAVR is performed. As part of this discussion, valve type and durability should be highlighted.

Surgical valve choices include bioprosthetic and mechanical. Patients < 60 years old may benefit from mechanical valves given the lower reintervention rate (up to 98% freedom from reoperation at 25 years) compared with tissue valves. Also, mechanical valves have been associated with superior survival at 15 years follow-up compared to bioprosthetic valves in patients 50 to 70 years old. However, they are associated with a 1-2%/year thromboembolic rate and 1-2%/year bleeding rate from systemic anticoagulation. For older patients (> 70 years old), a bioprosthetic valve offers excellent long-term durability with minimal thromboembolic and bleeding risks (90% freedom from structural valve deterioration [SVD] at 15-25 years). Bioprosthetic valves should be considered in younger patients with a desire to avoid long-term anticoagulation, provided reoperation can be expected with a low mortality rate. If this 62-year old patient chooses a bioprosthetic SAVR, he should be counseled to expect either a redo surgical operation or a transcatheter valve-in-valve (VIV) operation in 8-15 years. Short-term outcomes of transcatheter VIV procedures have been reported with excellent outcomes if the patient does not have patient-prosthesis mismatch from the primary SAVR. Surgical aortic valve bioprosthesis design and structure will influence the degree of technical difficulty for future VIV procedures. Stentless valves and stented wraparound valves pose additional technical challenges to the operator at the time of VIV implantation. This should be taken into consideration at the time of primary SAVR if a future VIV procedure is anticipated.

Transcatheter valves have shown similar mid-term outcomes and are anticipated to have similar 10-year durability to bioprosthetic surgical valves, though outcomes beyond 10 years are not yet available. The impact of suitability of future TAV-in-TAV based on patient anatomy and the ability to access the coronary arteries for future treatment is unknown and controversial. This consideration is a particularly important component in determining treatment for this 62-year-old low risk patient, for whom multiple future procedures will be necessary if a bioprosthetic valve is implanted at the index procedure. In addition, mid- and long-term durability of TAV-in-SAV and TAV-in-TAV are currently unknown.

Alternative scenarios/treatment decisions

“Cardiac catheterization in the same patient showed 3-vessel, obstructive CAD including a severe proximal LAD lesion.”

Patients with concomitant CAD should be evaluated as CABG vs. PCI candidates. In this case, the severe proximal LAD lesion and obstructive 3-vessel disease are an indication for CABG. In assessing CAD, a SYNTAX score > 22 in the setting of 3-vessel disease strongly favors surgery over PCI. If the patient has not yet undergone CT, they should have an aortic protocol gated CT scan performed to assess the aorta prior to surgery. This patient should be counseled on receiving a mechanical vs. bioprosthetic SAVR. Patients opting for mechanical valves should not have contraindication to lifelong anticoagulation and must be socioeconomically capable of anticoagulation therapy.

“In the same patient, TAVR CT shows a Sievers Type 1 functional bicuspid aortic valve with right to left fusion.”

In dealing with patients with bicuspid valves, STS risk score is important. For patients with a functional bicuspid valve at low surgical risk, TAVR has not been approved for use. In patients at intermediate surgical risk, it is important to assess for associated ascending aneurysm, which would be a strong indication for surgery if > 4.5 cm. For patients < 65 years of age, patients should be advised there is an approximate 57% of a 2nd procedure, 18% chance for a 3rd procedure, and 2% for a 4th procedure in their lifetime. Therefore, strong consideration should be given for surgery with a mechanical prosthesis or surgical bioprosthetic valve since the outcomes with future TAV-in-SAV are more predictable than TAV-in-TAV. Additionally, future reoperative open surgery will be less complex after a primary SAVR versus TAVR. For patients at high risk without associated aneurysm or CAD and with anatomy suitable for TAVR, shared decision making incorporating patient preference should be prioritized in deciding between TAVR and SAVR. Prohibitive risk patients should undergo TAVR.

“An 82-year-old patient with 2-vessel severe, obstructive CAD (RCA & circumflex), severe symptomatic AS, extremely poor functional status, and a 12% STS risk of mortality.”

With a 12% risk of mortality, this patient is at high-risk for SAVR and the randomized TAVR trials show the patient would benefit from staged PCI and TAVR procedures. A SYNTAX score < 33 in the setting of 2-vessel disease favors PCI over CABG and should be performed in conjunction with TAVR. However, TAVR CT scan and full work-up should be undertaken to assess anatomic suitability for TAVR, followed by shared decision-making with the patient. If the patient requests surgery, a SAVR + 2-vessel CABG could be performed with a bioprosthetic valve.

“Patient is 78-year-old, ESRD, inactive, EF=30%, and the EOAI is 0.8 with a highly calcified root.”

This patient’s age, low EF and ESRD will more than likely calculate an STS-PROM in the high-risk category and TAVR would be more appropriate if the anatomy is suitable. If the STS-PROM falls within the intermediate range of risk, then SAVR with a mechanical valve should be considered due to the poor durability of a bioprosthetic valve in ESRD secondary to early calcification.

The resultant EOAI (cm2/m2) for SAVR is an important component for this patient and can be determined by sizing the valve, checking the EOA for the valve using the manufacturer published (IFU – Information for Use) chart and dividing the resultant EOA by the patients BSA. An EOAI < 0.85 suggests a small aortic root with the risk of moderate patient prosthesis mismatch (PPM) for EOAI 0.65–0.85, and severe PPM for EOAI < 0.65.

In this patient who is elderly with a poor EF and calcified root, a moderate amount of PPM through SAVR would be preferred over the longer cross-clamp time and technically more challenging aortic root procedure. However, if anatomically acceptable, a TAVR should be favored, since the randomized trials show PPM occurs significantly less for TAVR than SAVR and would minimize the concerns for PPM and the morbidity of SAVR. Patient education and shared decision making is critical for this patient.

“A 70-year-old female undergoing workup for 3V CABG is found to have moderate AS on echo – would you replace the aortic valve at the time of the CABG?”

This scenario represents a Class IIa indication (i.e., weight of evidence is in favor of usefulness). The decision to replace the valve hinges on the risks involved with the added procedure and the benefits of a longer interval free from reintervention. In general, it is prudent to replace moderate AS at the time of CABG for reasonable candidates with minimal comorbidities especially in the setting of a highly calcified valve, fast progression, or patients younger than 70 years of age.

“Patient is 75-year-old asymptomatic with severe aortic stenosis on echo. How would you determine the timing of surgery?”

The prognosis for patients without symptoms is excellent but it falls significantly once symptoms develop. Watchful waiting with medical management including risk factor modification and statin therapy is appropriate for most patients. However, some require surgery based on specific indications and others require additional testing to elicit symptoms. Patient with severe AS unintentionally limit their activity to minimize or eliminate symptoms and it is important to perform a monitored stress test to determine the status of the patients claim of asymptomatic. Patients with atypical or vague symptoms may undergo a stress echo. Inappropriate hemodynamic response, dizziness, or chest discomfort signifies a positive test and provides grounds for AVR.

Immediate indications for surgery in this patient would include: a low gradient (< 40 mmHg) severe AS with LV dysfunction (< 50%) and contractile reserve; critical AS, a velocity of > 5 m/sec or a MVG > 50 mm/Hg; evidence of severe LVH (LV thickness > 1.6 mm); and patients undergoing another open heart procedure (i.e., CABG, mitral valve surgery).

SAVR operative steps

Goals: relieve obstruction, replace the valve, protect the heart and coronaries, and prevent embolization.

  • Large bore IV, arterial line, general endotracheal anesthesia (GETA), pulmonary artery catheter (optional), Foley catheter – watch for v-fib on induction.
  • Intraoperative TEE to confirm/re-evaluate valve or other unexpected pathology.
  • Minimally invasive approach via partial sternotomy or mini thoracotomy as well as full median sternotomy are acceptable approaches. Pericardial stay sutures palpate the aorta or use epiaortic ultrasound to evaluate for calcifications to determine aortic cannulation site.
  • Heparin (400 u/kg), aortic cannulation, 2-stage venous cannula, retrograde cardioplegia cannula (not mandatory), once ACT is 400 initiate CPB, dissect aorta from PA, insert antegrade cardioplegia cannula.
  • De-air antegrade line, clamp, and run antegrade induction, follow with retrograde. Intermittent doses of retrograde with occasional doses directly down the right coronary (depending on duration and whether good retrograde flow is noted coming from the RCA).
  • Venting strategies:
  • LV vent through right superior pulmonary vein
  • LA vent
  • Floppy-tipped pump sucker dropped through the valve into the LV
  • PA vent
  • Aortotomy – define the RCA, small transverse aortotomy anterior midline 1 cm above the RCA. Extend laterally towards and superior to the LCA ostium, then medially in an oblique fashion towards the middle of the noncoronary sinus. Place stay sutures as needed.
  • Inspect and resect the valve along the annulus.
  • Completely debride the calcium from the annulus, patch or primary closure of any defects with autologous pericardium, irrigate copiously and size the valve. When sizing the valve, check the EOA for the specific chosen valve type using the manufacturer published IFU chart and dividing the resultant EOA by the patients BSA to evaluate for PPM.
  • Place horizontal mattress sutures along the annulus (2-0 braided pledgeted (infra-annular), unpledgeted mattress, or figure-of-eight stitches).
  • Pass them through the valve ring, seat the valve.
  • Check the pledgets, LCA ostium, RCA ostium.
  • Tie the valve down under the left coronary ostium, then the right ostium, and make sure both coronary ostia are patent prior to completion of tying.
  • Irrigate, check LCA and RCA ostium again, and close the aortotomy with a running prolene suture.
  • De-air by valsalva and compressing the heart prior to closing the aortotomy, assess rhythm, pacing wires, wean from CPB, assess the valve by TEE.

Potential intraoperative scenarios

“The patient has v-fib on induction.”

Secure the airway and ventilation, initiate CPR immediately, assistant preps while you scrub. Drape, give heparin, and perform an emergent median sternotomy. Aortic and venous cannulation. Initiate cardiopulmonary bypass (CPB), assess flows and drainage, and proceed with AVR. Alternatively, you can initiate immediate percutaneous femoral CPB to immediately perfuse all organs, assess flows and drainage, and proceed with AVR.

“You are unable to arrest the heart.”

A slow arrest is not uncommon in a hypertrophied heart. Go systematically down your algorithm for persistent activity – check the cross clamp to ensure you are completely across, check your drainage (distention, elevated pulmonary artery pressures) and improve it if necessary (a pre-clamp LV vent through the right superior pulmonary vein is advantageous in avoiding this issue). AI may be underestimated by echo. When in doubt or if AI is suspected open the aorta and give direct ostial cardioplegia. Add topical ice, consider systemic cooling to mild-mod hypothermia (30° C).

“The intraoperative TEE shows a moderate perivalvular leak.”

Define the anatomy on TEE carefully, clamp, arrest, open the aorta and reassess the valve, if you identify an obvious gap you can place a horizontal pledgeted suture or be prepared to remove and replace the valve. Be certain that complete decalcification of the annulus is achieved prior to inserting the valve since retained calcium can lead to not properly seating the valve causing para-valvular leak. Consider the patient’s condition. A trivial leak in an 85-year-oldpatient should probably be left alone.

“When you release the cross clamp, the heart distends.”

Most often this occurs in the setting of paravalvular leak. With a mechanical valve the washing jet AI may be enough to distend the heart if it fibrillates. Turn flow down, compress the heart, defibrillate, or place a vent and defibrillate. If the heart remains asystolic and distended after defibrillation, place epicardial pacing wires and begin pacing. This issue can usually be avoided by placing an LV vent prior to the initial cross-clamp. If unable to obtain a rhythm the possibilities include electrolyte abnormality such as hyperkalemia or poor protection. If unable to restore rhythm with the heart empty, clamp and re-arrest the heart (see chapter on CPB pitfalls).

“You determine that only a 19 mm St Jude Biocor will fit into this patient. The EOAI assuming a BSA of 2.2 m2 is 0.59. What are your options?”

Options include upsizing with a stentless root (if familiar with this technique), root enlargement, total root replacement, or acceptance of PPM with a valve that yields the greatest EOA. In this patient with relatively good quality tissue and few comorbidities the longer clamp time is likely worth the added EOA.

  • Root enlargement procedure – Nick’s procedure: Extend the aortotomy into the nadir of the noncoronary sinus and base of the anterior mitral leaflet with the goal of obtaining a size that is 1 or 2 increments larger than the original. Use autologous pericardium (or other commercially available products i.e. CorMatrix, Perigaurd) to patch and enlarge the opening. Place sutures along the left and right coronary sinuses as usual. Seat the valve. Pass non-pledgeted sutures outside in through the patch and into the sewing ring for the non-coronary portion and tie. Complete the aortic closure with the patch.
  • Root enlargement procedure – Manouguian procedure: Another enlargement alternative whereby the aortotomy is extended posteriorly through the commissure between the left and non-coronary cusps into the interleaflet triangle and carried into the anterior leaflet of the mitral valve. The left atrium is opened in this process and must be closed as well.
  • Total root replacement: Root replacement with a homograft or a stentless bioprosthesis with upsizing and coronary reimplantation. You can usually place a larger homograft/stentless root than a standard bioprosthetic/mechanical valve and the hemodynamics are better. However, a mechanical valve total root may be favorable in a younger patient. If anticoagulation is contraindicated or not preferred, then perform a stentless or a homemade stented bioprosthetic root replacement, which may be more amenable to future VIV procedures.

“You take your Nick’s annular enlargement too far into the anterior leaflet of the mitral valve and the patient has moderate MR on TEE after coming off pump”

Examine the mitral carefully on TEE, clamp, re-arrest the heart, expose the mitral valve through either the left atrium or right atrium and transseptal approach, and make every effort to repair the mitral valve. While the Nick’s annular enlargement allows an increase by more than one valve size, its main risk is extending too far on the anterior mitral leaflet. For surgeons not comfortable with the Nick’s or Manouguian annulus enlargement procedures or for very small EOAIs, a total root replacement may be a safer option.

Pearls/pitfalls

  • Replace symptomatic severe AS (velocity ≥ 4 m/s, mean ≥ 40 mmHg, AVA ≤ 1.0 cm2, indexed AVA ≤ 0.6 cm2/m2, dimensionless index < 0.25).
  • Replace asymptomatic severe AS only IF low gradient with < 50% EF, critical AS (velocity ≥ 5 m/sec or MPG ≥ 50 mm/Hg), severe LVH, concomitant cardiac operation, fast progression, severely calcified.
  • Determination of SAVR vs. TAVR by anatomy, concomitant pathology, patient age, and patient preference
  • Patients > 70-year-old– generally bioprosthetic SAVR or TAVR rather than mechanical SAVR
  • Assess the aorta intraoperatively for calcifications that may change clamp/CPB strategy.
  • Irrigate debris and check the LCA and RCA ostia after seating the valve.
  • Patient-prosthesis mismatch (PPM) – EOAI < 0.85 → consider root enlargement procedure or total aortic root replacement.

Suggested readings

  • Brzezinski A, Koprivanac M, Gillinov A, Mihaljevic T. Pathophysiology of Aortic Valve Disease. In: Cohn LH, Adams DH, editors. Cardiac Surgery in the Adult, 5e New York, NY: McGraw-Hill; 2018. Chapter 26.
  • Al-Atassi T, El Khoury G, Boodhwani M. Surgical Treatment of Aortic Valve Disease. In: Selke FW, del Nido PJ, and Swanson SJ, editors. Sabiston and Spencer Surgery of the Chest, 9e Philadelphia, PA: Elsevier; 2016. p. 1334-1349.
  • Diaz R, Hernandez-Vaquero D, Alvarez-Cabo R, Avanzas P, et al. Long-term outcomes of mechanical versus biological aortic valve prosthesis: Systematic review and meta-analysis. J Thorac Cardiovasc Surg 2019 Sep;158(3):706-714.
  • Duncan A, Moat N, Simonato M, de Weger A, et al. Outcomes Following Transcatheter Aortic Valve Replacement for Degenerative Stentless Versus Stented Bioprostheses. JACC Cardiovasc Interv 2019 Jul 8;12(13):1256-1263.
  • Ranganath NK, Koeckert MS, Smith DE, Hisamoto K, et al. Aggressive tissue aortic valve replacement in younger patients and the risk of re-replacement: Implications from microsimulation analysis. J Thorac Cardiovasc Surg 2019 Jul;158(1):39-45.
  • Rahhab Z, El Faquir N, Tchetche D, Delgado V, et al. Expanding the indications for transcatheter aortic valve implantation. Nat Rev Cardiol 2019 Sep 16. [Epub ahead of print]
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