Keywords

Epidemiology and Mechanism of Calcific Aortic Stenosis

Senile progressive degenerative calcification leads to thickening of aortic valve (AV) cusps, resulting in aortic valve stenosis (AS). In developed countries, AS is the most prevalent of all valvular heart diseases. The prevalence of severe AS is 1.3% in patients aged 65–75, 2.4% in those aged 75–85, and 4% in those older than 85 years [1]. Risk factors are similar to those of coronary artery disease including age, male sex, hyperlipidemia, and evidence of active inflammation [2]. There is high coincidence of coronary artery disease and AS. Taylor et al., on a large population study of African-American patients, reported that those with AV sclerosis were 4.26 times more likely to have events related to coronary heart disease than those without AV sclerosis [3]. However, the mechanism of the two disease seems to be different. Detailed mechanisms of calcific aortic valve disease are provided in Chap. 4.

Symptoms and Severity of Aortic Stenosis

Patients with AS have a long latent period before symptoms appear. When patients become symptomatic from severe AS, usually after the sixth decade of life, there is a rapid decline in mean survival (Fig. 22.1). Classic symptoms include angina, syncope, and dyspnea [4]. The onsets of dyspnea and heart failure are predictors for worse prognosis in the natural history of AS with 50% mortality in 2 years if left untreated (Fig. 22.2) [4]. Normal aortic valve area (AVA) is 3–4 cm2. When valve area becomes ≤0.8 cm2, the mean gradient across the AV exceeds 40 mmHg, or the velocity across the AV exceeds 4 m/sec, it is considered severe AS. AVA of <0.5 cm2 is considered critical stenosis [5]. Symptomatic severe AS is due to an obstruction to cardiac output. Therefore, effective mechanical relief in the form of surgical or transcatheter aortic valve replacement (TAVR) is indicated according to American Heart Association/American College of Cardiology (AHA/ACC) guidelines [5].

Fig. 22.1
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Survival of patients with aortic stenosis over time. A long latent asymptomatic period with normal survival, followed by rapid decline in survival once symptoms develop. (Modified figure) [4]

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Fig. 22.2
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Mean survival of patients with symptoms of aortic stenosis . (Modified figure) [58]

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Surgical Aortic Valve Replacement

Over the last several decades, surgical aortic valve replacement (SAVR) has been the gold standard for treatment of AS. Two major types of prosthetic AV are available: mechanical and bioprosthetic valves. There are advantages and disadvantages to each. An ideal heart valve prosthesis with the durability of a mechanical prosthesis and low thrombogenicity of a bioprosthetic valves has not yet been manufactured. The technique of SAVR is described in detail elsewhere [6].

Mechanical Valves

Historical background and improvements in hemodynamic design: Dr. Charles Hufnagel, who had worked at Dr. Dwight Harken’s laboratory at the Peter Bent Brigham Hospital, implanted the first in the world aortic “assist” valve in a 30-year-old woman with rheumatic disease in 1952. The Hufnagel valve consisted of a pea-size ball inside a chambered tube placed in descending aorta. More than 200 Hufnagel valves were implanted in patients with aortic insufficiency [7]. Dr. Harken later developed the Harken-Soroff ball valve, a ball valve with a fabricated stainless steel double cage. Several brands and models of ball valves were introduced in the 1960s, namely, the Starr-Edwards (SE) caged-ball valve (Fig. 22.3), Magovern-Cromie valve, Smeloff-Cutter valve, Debakey-Surgitool, and Braunwald-Cutter valve (a silicon rubber ball cage with titanium housing and a ring covered with Dacron fabric).

Fig. 22.3
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Prosthetic heart valves . (a) Bileaflet mechanical valve (St Jude); (b) monoleaflet mechanical valve (Medtronic Hall); (c) caged-ball valve (Starr-Edwards); (d) stented porcine bioprosthesis (Medtronic Mosaic); (e) stented pericardial bioprosthesis (Carpentier-Edwards Magna); (f) stentless porcine bioprosthesis (Medtronic Freestyle) [59]

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Disc valves were introduced in the late 1960s. They allowed blood to flow in a more natural way while reducing damage to red blood cells from destructive, mechanical forces. They had superior hemodynamics compared to ball valves. Three landmark, non-tilting disc valves were the Kay-Shiley, Beall-Surgitool, and Cooley-Cutter biconical disc valves. Five landmark tilting disc valves were the Bjork-Shiley flat, Bjork-Shiley convexo-concave, Lillehei-Kaster, Omniscience, Omnicarbon, and Medtronic Hall tilting disc valves [8]. Unfortunately, the struts of these valves tended to fracture over time due to fatigue and design flaw. Later, silicon was replaced by pyrolytic carbon which helped to reduce wear and tear.

The two major bileaflet mechanical heart valves , the St. Jude Medical (SJM) bileaflet valve (Fig. 22.3) and CarboMedics bileaflet valve, were produced in the late 1970s and are still in use today without major change in design. The hinge mechanism located near the central axis of the housing mimics human physiology and makes these valves superior to previous designs. Discs are made of pyrolytic carbon, and the sewing ring is made of either PTFE or Dacron. SJM mechanical valves have been used with excellent results [9]. The CarboMedics (CM) mechanical valve has similar design to the SJM valve. It has a solid pyrolite carbon housing and flat leaflets made of pyrolite carbon-coated graphite that is impregnated with tungsten. The pyrolite carbon housing is reinforced by an outer ring composed of titanium that eliminates the risk of leaflet escape. Bileaflet valves have been used in both the aortic and mitral position with excellent long-term durability and freedom from reoperation [10]. The standard aortic valve prosthesis has the sewing cuff located at the outflow level of the valve cylinder. Both SJM and CM valves have supra-annular models where the sewing cuff has been transferred to the inflow level of the valve cylinder, allowing the valve to be upsized by one to two sizes. This is very important for optimizing hemodynamics and preventing patient-prosthesis mismatch [11]. The On-X valve is a newer-generation mechanical bileaflet valve [12]. Use of pure pyrolytic carbon (devoid of silicon), and design modifications such as more natural length-to-diameter ratio and leaflet opening angle, has translated into increased strength, improved valve hemodynamics, and reduced hemolysis and thrombogenicity. The 2014 AHA/ACC guidelines for the management of patients with valvular heart disease recommend an international normalized ratio (INR) of 2.5 (range, 2–3) in patients with a mechanical valve in the aortic position. However, based on the results of the Prospective Randomized On-X Anticoagulation Clinical Trial (PROACT) [13], the Food and Drug Administration (FDA) approved use of this valve in April 2015 with a lower INR goal of 1.5–2.0 in the aortic position. This reduction in INR goal led to a statistically significant reduction in the combined endpoint of clots, bleeding events, and stroke rates with 9/patient-years for the lower INR group compared with 12/patient-years in the standard INR group.

Bioprosthetic Valves

Durability and hemodynamic performance are of upmost importance when selecting a bioprosthetic aortic valve for patients. The earlier-generation stented bioprosthetic valves included the Medtronic Hancock II Ultra (Medtronic Minneapolis, MN), which is a porcine bioprosthesis, and the Carpentier-Edwards Perimount (Edwards Lifesciences LLC, Irvine, CA), which is a pericardial bioprosthesis. These two valves have shown very good long-term durability in multiple studies [14,15,16,17,18]. Design of some of these earlier-generation valves intentionally allowed them to be implanted in the supra-annular position, allowing upsizing to achieve maximal hemodynamics and decrease the incidence of patient-prosthesis mismatch. The newer-generation prostheses are processed in a zero- or low-pressure fixation with anti-mineralization. This reduces material fatigue and calcification over time. Stents are thinner, allowing a lower profile to minimize protrusion into the aortic wall and facilitating coronary clearance. The third-generation bovine bioprostheses include the Carpentier-Edwards Magna Ease (Edwards Lifesciences, LLC) (Fig. 22.3) and the Trifecta (Abbott Vascular, Santa Clara, California). The Magna Ease has a narrow sewing cuff and was designed for supra-annular placement. It has demonstrated excellent durability and hydrodynamic performance [19]. The Trifecta is a pericardial valve that utilizes pericardium around the exterior of the stent, allowing a larger opening diameter to maximize flow. These characteristics make it an attractive option for the small aortic annulus. That said, Wendt et al. [20] compared the hemodynamic performance of the Trifecta versus the Perimount Magna and Magna Ease valve prostheses, in a nonrandomized, observational, single-center study, concluding no influence of prosthesis type on mean pressure gradient or aortic valve area.

More recently, Edwards Lifesciences has manufactured a new bioprosthetic valve, the INSPIRIS RESILIA, with the goal to improve durability by reducing prosthesis calcification. This valve was built based on the design of the Carpentier-Edwards Perimount Magna Ease valve. RESILIA tissue is bovine pericardial tissue transformed by novel integrity preservation technology which permanently blocks residual aldehyde groups known to bind to calcium. As a result, the valve may have a longer shelf life and improved durability when implanted. The Inspiris valve has an expandable frame designed to allow for the possibility of valve-in-valve transcatheter aortic valve re-replacement if indicated in the future. This valve has been studied in the COMMENCE trial [21] with reported 2-year outcomes demonstrating early safety and effectiveness and has received FDA approval.

Stentless AV and root replacement using homografts or porcine xenograft (Fig. 22.3) has fallen out of favor in recent years mainly due to the complexity of the technique, limited durability despite excellent hemodynamics, and difficult reoperations. Use of homografts is limited to the treatment of active aortic valve endocarditis, particularly in patients with root abscesses [22].

Choice of Valve Type

Mechanical valves affect quality of life with the need for lifelong anticoagulation. According to AHA/ACC guidelines, the class 1 indications for prosthetic valve choice include the valve type being a shared decision between the patient and physician and bioprosthetic valves being recommended in patients of any age for whom anticoagulant therapy is contraindicated, cannot be managed appropriately, or is not desired. In other cases, the choice of valve is debatable, with no strong preference for one type over the other based on the guidelines. For elderly patients over age 70, the decision is easy, and most physicians and patients agree on biological valves, either via a surgical or transcatheter approach. For patients between the ages of 60 and 70, the decision is more debatable. Patients younger than age 60 tend to favor mechanical valves in order to avoid reoperation in future. However, this trend has changed in favor of bioprosthetic valves in recent years [23]. The primary motive for this is to avoid anticoagulation and subsequent lifestyle change with the added benefit of allowing for transcatheter valve-in-valve options should the bioprosthetic device fail. It is important to implant the largest bioprosthetic valve possible during the initial surgery to optimize the frame to accommodate a large valve in the future should valve-in-valve procedure become necessary.

Life Expectancy with Prosthetic Valves

Bouhout et al. [24], in a study of young, low-risk adults (<65 years) undergoing elective isolated mechanical AVR, demonstrated that survival is lower than expected in the age- and gender-matched general population in Quebec, Canada (actuarial survival at 1, 5, and 10 years was 98% ± 1%, 95% ± 1%, and 87% ± 1%, respectively). Expected survival in the age- and gender-matched general population was 99.6%, 97.6%, and 94.2% at 1, 5, and 10 years, respectively. The risk of a major valve-related event such as endocarditis, major bleeding, valve thrombosis, prosthesis dysfunction such as paravalvular leak, and thromboembolism was 27% within 10 years in these young patients. Zellner et al. [25] looked at competing risks after mechanical valve replacement in both the aortic and mitral positions. Freedom from all complications (death, reoperation, endocarditis, major bleeding, stroke) in 15 years was only 41.5% for the AVR group. The decreased life expectancy compared to the general population after AVR is not inclusive to mechanical valves but also to bioprosthetic valves. A Canadian study of a younger patient population showed reduced life expectancy with bioprosthetic aortic valves compared with an age- and gender-matched Quebec population and was comparable to mechanical valves [26]. A randomized clinical trial from Italy showed no difference in survival between biologic and mechanical valves in the aortic position at 13 years [27]. In addition, a large database study of the STS registry including more than 30, 000 patients aged between 65 and 80 years old showed no survival difference between biologic and mechanical valves [28]. This study showed significantly higher probability of reoperation in those with biologic valves due to structural valve deterioration.

Chikwe et al. [29], using the state of New York database, showed no difference in survival with biologic or mechanical valves implanted either in the aortic or mitral position in patients between 50 and 69 years old. In the same study, incidence of thromboembolism and incidence of major bleeding requiring transfusion were significantly higher in patients with mechanical valves, whereas risk of reoperation for structural valve problems was higher in patients with biologic valves. More recently however, in a large observational study of California State patients, a survival advantage of 4 percent at 15 years was shown in younger patients (45–54 years old) in favor of those who received mechanical aortic valves compared to those who received biologic valves [30]. Patients older than 54 years had similar survival with either valve type in that study.

Anticoagulation

Implantation of a mechanical heart valve mandates lifelong anticoagulation with warfarin. Unfortunately, this may dictate lifestyle change for some patients. A limitation with use of warfarin is difficulty controlling the international normalized ratio (INR) within the therapeutic level, described by using the term “time within therapeutic range” (TTR). One study showed that in the first 6 months of initiating warfarin, TTR was only 32% [31]. Patients who are not in TTR are exposed to bleeding risk if the INR is higher or thromboembolism if the INR is lower. A randomized control trial showed weekly self-testing of INR has no superiority over monthly clinic testing in reducing the risk of stroke, major bleeding episodes, and death among patients who are taking warfarin because of mechanical heart valves or atrial fibrillation [32]. Unlike warfarin, novel oral anticoagulants (NOACs) , including direct thrombin and factor Xa inhibitors, do not need to be monitored with regular labs, but these new anticoagulants are not approved for prosthetic heart valves. A randomized clinical trial comparing dabigatran, an oral direct thrombin inhibitor, with warfarin was terminated prematurely because of an excess of thromboembolic and bleeding events among patients in the dabigatran group [33].

Prosthetic valve thrombosis (PVT) is a rare but devastating complication affecting primarily mechanical valves. The occurrence of PVT depends to some extent on valve model, as well as patient compliance with oral anticoagulation, and is more common in the mitral position than the aortic. Two early RCTs [34, 35] showed statistically significant increase in bleeding with mechanical valves. However, Stassano et al. [27] in a RCT showed, at mean follow-up of 106 ± 28 months, there were no differences in linearized rate of thromboembolism, bleeding, endocarditis, and valve thrombosis between those who received mechanical and bioprosthetic aortic valves (1.47%/patient-year vs. 0.72%/patient-year). A statistical trend (p = 0.08) for increased bleeding in the mechanical group was noted however. Of note, 21% of patients in the bioprosthetic group in that study was receiving warfarin at the time of follow-up for other reasons. The bleeding rate in patients with bioprosthetic valves who were not receiving warfarin was less than those with mechanical valves on warfarin. Emergent reoperation for thrombectomy and valve replacement is necessary once PVT is diagnosed. A study from Montreal Heart Institute [36] showed high hospital and operative mortality in addition to poor long-term survival after redo valve replacement for thrombosis with 10-year actuarial survival rate of 46% ±10%.

Trends in Choice of Prosthetic Aortic Valves

Despite excellent long-term results with implantation of mechanical valves, the recent trend in their use has declined compared to bioprosthetic valves, even in younger patients, particularly those who pursue an active lifestyle without anticoagulation. Brown et al. [23] reported on 108,687 isolated AVRs over a 10-year period from the Society of Thoracic Surgeons (STS) database showing increase in bioprosthetic use from 43.6% in 1997 to 78.4% in 2006. Similar trends were seen at our institution with an increased use of bioprosthetic valves from 20% to more than 60% in patients aged less than 60 years during past several years. Nowadays, younger patients are leaning more toward tissue valves in order to participate in an active lifestyle by avoiding anticoagulation. Awareness of the advantages and disadvantages of the two valve types has increased in the online information era. As such, patients have usually already made up their mind prior to pre-operative clinic visits with their surgeon. The operative mortality of repeat AVR is acceptable but higher than first-time AVR at 4.6% according to the STS database [37]. On the other hand, the advent of transcatheter aortic valve-in-valve replacement option has changed the landscape in the patient decision-making process despite uncertainty with regard to valve durability and valve thrombosis after valve-in-valve replacement. Candidacy for transcatheter options at time of need for reintervention is not guaranteed [37]. Patients in need of concomitant procedures such as coronary artery revascularization or concomitant aortic surgery for aneurysm replacement may not be candidates for transcatheter valve-in-valve intervention when their bioprosthetic valves fail over time. Patients must be informed of these potential situations prior to deciding on their valve type.

Transcatheter Aortic Valve Replacement

Transcatheter aortic valve replacement (TAVR) is a minimally invasive percutaneous approach to treat patients with symptomatic AS without sternotomy or cardiopulmonary bypass. In less than 8 years since FDA approval of this technology for extreme- and high-risk patients for surgery, TAVR has progressed from a procedure of last resort to a viable alternative to surgery in most patients with native (non-bicuspid) AS as well as those with bioprosthetic aortic valve failure.

Evolution of TAVR Indications

The rationale for the invention of TAVR was to offer a treatment for patients with symptomatic severe AS who presented with prohibitive risk for SAVR. Two clinical trials, including the PARTNER IB [38] (completed, FDA approval 11/2011) with the Edwards Sapien valve and the CoreValve US Pivotal Trial [39] (completed, FDA approval 1/2014), showed significant improvement in mortality with TAVR for patients with extreme surgical risk or those deemed inoperable (STS risk score of >15–50) when compared to medical therapy or balloon valvuloplasty alone. For high-risk patients, the PARTNER IA trial [40] (completed, FDA approval 5/2012) demonstrated non-inferiority of TAVR compared to surgery, and the CoreValve US Pivotal Trial (completed, FDA approval 6/2014) showed that all-cause mortality and major adverse cardiovascular and cerebrovascular event (MACCE) rates after TAVR were significantly better compared to SAVR, including better valve hemodynamics for high-risk patients. These satisfactory results led to the expansion of TAVR studies to include intermediate risk patients (4% < STS score < 8%) with severe AS. The PARTNER 2A (with Edwards Sapien valve) [41] (completed, FDA approval 8/2016) and SURTAVI trials (with CoreValve) [41] showed that TAVR was non-inferior to surgery in terms of mortality, with lower mean gradients and larger aortic-valve areas compared to surgery. Patterns of adverse events in this intermediate risk cohort were different with each procedure. Surgery was associated with higher rates of acute kidney injury, atrial fibrillation, and blood transfusions, whereas TAVR had higher rates of permanent pacemaker implantation and residual aortic regurgitation [42] (Table 22.1).

Table 22.1 Summary of 30-day outcomes in trials of TAVR versus SAVR in patients at intermediate or low surgical risk [42]
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Following the favorable results of these trials, a clinical trial was conducted for low-risk patients with STS mortality risk <4% to compare transfemoral TAVR using a balloon-expandable valve with SAVR. This trial, published in May 2019, showed the rate of composite of death, stroke, and rehospitalization at 1 year was significantly lower with TAVR compared to surgery [43]. This result led to FDA approval for TAVR for low-risk patients. These studies have shown that TAVR reduces composite endpoint of all-cause mortality, cardiovascular mortality, and repeat hospitalization with improvement in mean aortic valve gradient, valve area, NYHA functional class, 6-minute walk test, and quality of life.

Use of TAVR has rapidly increased over the past several years. According to STS/ACC/TVT registry public reporting, more than 600 institutions perform TAVR in the United States as of March 2019. In other words, 1 TAVR site exists for every 80,000 people over the age of 65 with a steady growth in number each year. The number of TAVR procedures surpassed the number of isolated SAVR in 2016 and continues to rise, with more than 51,000 commercial TAVR procedures performed in the year 2018. The proportion of patients with intermediate STS risk of mortality who are receiving TAVR has steeply increased from 5% of all TAVRs in 2014 to more than 43% in 2018. With FDA approval of the procedure for low-risk patients, it is predictable that this technology will be applied to low-risk, and perhaps younger, patients, more frequently in coming years. However, adoption of TAVR to this extent must be taken with caution until several concerns regarding this procedure resolve.

Conduction system abnormalities and high-rate of 30-day new permanent pacemaker (PPM) implantation after TAVR remain an ongoing concern without improvement over the last several years, despite the development of new generations of valves (Fig. 22.4). According to a TVT registry study, the rate of 30-day PPM implantation is 6.7% and varies among those receiving self-expanding valves (25.1%) versus balloon-expanding valves (4.3%) [44]. The study showed early PPM implantation is associated with a higher mortality and a composite of mortality and heart failure at 1 year, adverse outcomes that are not acceptable for a lower-risk, younger patient population.

Fig. 22.4
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Latest-generation transcatheter heart valves . (a) Self-expanding valve , CoreValve Evolut PRO (Medtronic, USA); (b) self-expanding valve, ACURATE neo TF (Boston Scientific, USA); (c) mechanically expandable valve, LOTUS Edge (Boston Scientific, USA); (d) self-expanding valve, Portico (Abbott, USA); (e) balloon-expanding valve, SAPIEN 3 (Edwards Lifesciences, USA) [42]

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Stroke remains a potentially devastating complication after TAVR as well, ranging from 3.5% to 5.5% in different studies [41, 45]. Few embolic protection devices are under further investigation with the goal to decrease stroke rates with TAVR [46,47,48]. Another concern is the high rate of unplanned 30-day hospital readmission after TAVR with no improvement over the past few years according to a report from the National Cardiovascular Data Registry (NCDR). The 30-day readmission rate was 9.2% in a TVT registry study with the rate being higher for high-risk patients compared to low-risk patients [49].

Long-term durability of TAVR valves remains an unanswered question as most clinical trials in the field are only few years old compared with the excellent benchmark for long-term durability of surgical valves shown in multiple studies as mentioned earlier in this chapter. Daubert et al., in a longitudinal assessment of the PARTNER I trial, demonstrated that valve performance and cardiac hemodynamics are stable in both TAVR and SAVR patients alive at 5 years [50]. A 5-year report of the PARTNER I trial did show higher rates of moderate to severe aortic insufficiency in TAVR patients (14% versus 1%, p <0.0001), which was associated with increased 5-year risk of mortality in that study [51]. When counseling younger patients, it is critical to inform them about the uncertainty in long-term durability at this time as well as the higher rate of paravalvular leak, especially with the earlier generation of TAVR valves. The lifelong treatment strategy of aortic valve stenosis in younger low-risk patients is yet to be defined. Whether surgical aortic valve replacement with biological valves (to avoid anticoagulation) should be the first treatment step followed by subsequent transcatheter valve-in-valve implantation for failed bioprosthesis or TAVR as the first-line therapy followed by SAVR and subsequent TAVR for failed bioprosthesis is still being debated. Leaving calcium and/or degenerated bioprosthetic valves behind in TAVR and valve-in-valve procedures may add to the complexity of future reoperations or expose patients to patient-prosthesis mismatch if an appropriate-size valve cannot fit.

Pre-procedural Evaluation

Patients who are considered for TAVR procedure undergo extensive pre-procedural evaluation by the “heart team” that includes an interventional cardiologist and a cardiac surgeon. A full Heart Team assessment is mandatory before any decision can be made to determine whether TAVR or SAVR is the best choice for that individual patient. The work-up includes echocardiograms; computed tomography angiography of the chest, abdomen, and pelvis; cardiac catheterization; pulmonary function testing; and carotid Doppler studies. Despite the development of a risk model specifically for TAVR [52], the Society of Thoracic Surgeons (STS) risk model is still used by most centers to calculate the predicted risk of mortality and morbidity for TAVR, categorizing patients into low, intermediate, and high risk. Aside from the STS risk score, other factors play an important role in decision-making. For example, porcelain aortas and prior mediastinal radiation are both associated with worse outcomes in SAVR but are not included in the STS risk model. These factors may deem a patient technically inoperable, qualifying them for TAVR instead [53]. In contrary, patients who in addition to severe AS have other cardiac diseases such as coronary artery disease, other valvular disease, atrial fibrillation, or ascending aortic aneurysm that can be addressed with concomitant surgery may benefit more from a surgical approach instead of TAVR.

Procedure and Recovery

As experience with transcatheter aortic valve replacement (TAVR) has increased, some centers have performed transfemoral (TF) TAVR in a standard cardiac catheterization laboratory without general anesthesia or transesophageal echocardiography (TEE), the so-called minimalist approach as opposed to a standard approach (SA) performed in a hybrid operating room [54]. In the minimalist approach to TAVR, the patient is sedated with midazolam and fentanyl. Femoral access is obtained with micro-puncture technique under fluoroscopic guidance. Two pre-closure sutures are placed with Perclose devices (Abbott Vascular, Abbott Park, Illinois) after entry into the femoral artery and will be tied down to close the artery once sheaths were removed at the conclusion of the procedure. For patients with severely calcified, limited size, or tortuous iliofemoral arteries, alternative peripheral access options are subclavian and carotid artery. Alternative central access options are trans-aortic and trans-apical approaches. However, trends in using central access have significantly decreased in favor of femoral and peripheral alternative approaches [55]. Caval-aortic access is another alternative approach used in some centers [56]. Once access is obtained, the operator delivers the TAVR valve to the stenotic aortic valve through a series of wire and catheter techniques and the designed delivery system for deployment under rapid ventricular pacing. Valve position and hemodynamics are confirmed using echocardiography and angiography, with special care taken to ensure the absence of significant paravalvular leak. Post-procedurally, patients are monitored in the perioperative recovery unit for a few hours with special attention paid to vascular access sites and vital signs. Then, most patients are transferred to the floor and discharged on post-operative day one. Dual antiplatelet therapy (DAPT) with aspirin and clopidogrel is common practice after TAVR. If patients are on an anticoagulation regimen for other reasons, a single antiplatelet therapy (SAPT) regimen with aspirin or no antiplatelet therapy at all is chosen by most physicians. The best antithrombotic therapy after TAVR is yet to be determined despite ongoing clinical trials [57].