**5. Pre-procedural work-up**

Appropriate patient selection via individual risk stratification, optimal valve sizing, and determining feasibility of different access routes are all factors that are

#### **Figure 3.**

*A schematic for management of AS adopted from the 2020 AHA guidelines (image obtained from Ref. [16]).*

carefully and meticulously worked up prior to TAVR. This pre-screening is an everchanging multifaceted selection process that utilizes a multidisciplinary approach. A Heart Team consisting of an interventional cardiologist, cardiac surgeon, clinical

cardiologist, and anesthetist are responsible for actively performing the preprocedural screening and work-up. However, because these patients are generally elder with many comorbidities, physicians from even other specialties often participate in pre-procedural optimization.

The confirmation of severe AS is done with echocardiography demonstrating a valve area of <1.0 cm<sup>2</sup> mean pressure gradient of 40 mmHg or greater or a maximum aortic velocity of 4.0 m/s or greater. This step is heavily operator dependent as any misalignment of the probe can result in underestimation of the pressure gradient and jet velocity. The measured valve area should be indexed to the patient's body surface area ≤ 0.6 cm<sup>2</sup> /m<sup>2</sup> in patients with normal left ventricular ejection fraction. Note that patients with low-flow, low gradient severe AS may have aortic velocities and valve gradients that are falsely lower. If these patients demonstrate a reduced ejection fraction, then we use low-dose dobutamine echocardiography (maximum dose 20 μg/ kg/min) to mimic normal physiological flow and obtain accurate values. If valve area remains ≤1.0 cm2 and peak velocity exceeds 4.0 m/s, then a diagnosis of true severe AS is made regardless of the flow rate. If the aortic valve area increases to greater than 1.0 cm<sup>2</sup> during dobutamine echocardiography, then a diagnosis of pseudo-severe AS or moderate AS can be assumed, and the patient should undergo heart failure therapy and close clinical follow-up.

Transesophageal echocardiography tends to underestimate the severity of AS when compared to transthoracic echocardiography [21]. In the majority of patients, transthoracic echocardiography is adequate enough to confidently establish a diagnosis of severe AS. However, when there are discordant findings, we look for other tests to help guide our decision-making. Thus, in addition to echocardiography, we utilize computed tomography to confirm the severity of AS. Similar to that of coronary calcium scoring, computed tomography allows us to use the Agatston algorithm to quantitate the severity of aortic valve calcifications. We utilize calcium score cutoffs of 2065 in males and 1275 in females for severe AS [22]. Recent studies have revealed that an elevated pre-TAVR calcium score from computed tomography is an independent risk factor for acute stroke, thus providing prognostication capabilities as well [23]. Computed tomography also provides the added benefit of a three-dimensional visualization of the valve and left ventricular outflow tract as two-dimensional imaging often results in underestimation of the severity of stenosis. This is largely due to the fact that the continuity equation which we use to calculate valve area from stroke volume states that flow passing through the outflow tract equals the flow through the aortic valve and assumes a circular outflow tract though in reality, the tract is frequently oval. Computed tomography angiography of the chest, abdomen, and pelvis is generally also done to help confirm valve size but more importantly, to visualize the patient's vasculature and determine the optimal entry point for access, if any.

Because the association of coronary artery disease and AS is strong, conventional guidelines recommended left heart catheterization prior to TAVR in order to assess presence of unstable coronary disease and determine if revascularization or bypass grafting should be performed prior to AVR. Depending on heart catheterization findings, the Heart Team may elect to proceed with SAVR versus TAVR. However, recent studies published by AHA revealed that revascularization TAVR did not result in improved clinical outcomes and in fact, was associated with an increased risk of major vascular complications and 30-day mortality [24].

Other conventional preprocedural testing includes carotid duplex ultrasonography, pulmonary function testing, and assessing baseline ambulatory function status, complete blood counts, and renal function. Carotid ultrasonography allows clinicians to screen for internal carotid artery stenosis which is believed by many to correlate with risk of periprocedural stroke. However, some studies have since emerged showing no statistically significant benefit in performing carotid ultrasonography [25, 26]. For now however, it remains a part of preprocedural workup at many centers. Pulmonary function testing remains a routine part of the risk stratification and STS scoring of patients undergoing valve replacement as the severity of the patient's lung disease continue to show direct correlation to peri-procedural mortality [27].

We universally assess for baseline functional status with a simple outpatient sixminute walk test during which we assess both speed, gait, and ability to complete the test. It is a simple and cheap test that helps us further risk stratify patients and to monitor functional status pre and post procedurally. Among high-risk adults undergoing TAVR, the six-minute walk test does not predict post-procedural outcomes but does however predict long-term mortality [28].

Renal function is also important to assess as both acute and chronic kidney disease are associated with adverse events in patients undergoing valve replacement [29]. In patients who develop acute kidney injuries, studies have shown a four-fold increase in postoperative mortality [30, 31]. A baseline complete blood count allows to assess platelet counts and for any anemia. Finally, a preprocedural international normalized ratio and type and screen are also obtained as part of preprocedural blood work.

#### **6. Contemporary devices**

Contemporary TAVR devices consist of balloon-expandable valves, self-expanding valves, mechanically expanding valves, and delivery systems/sheaths. In the last two decades, technological advancements have significantly improved devices by incorporating and enhancing features that allow for recapture, easier deployment, repositioning, all while reducing associated complications such as perivalvular leaks and stroke [32]. As TAVR continues to undergo procedural modifications and indications, these devices are expected to continue to evolve. As of 2023, there are three newer-generation valves that are FDA-approved for commercial TAVR in the US: the SAPIEN 3 Ultra (Edwards Lifesciences), Evolut PRO+ (Medtronic), and Portico (Abbott Laboratories). Other valves such as the ACURATE Neo/Neo2 (Boston Scientific), JenaValve (JenaValve Technology), Myval THV (Meril Life Sciences), Allegra (New Valve Technologies) have Conformite Europeenne (CE) markings by the European Union and actively undergoing review for potential US FDA-approval in the near future.

Balloon-expandable valves are intra-annular valves that include the Sapien system and the Myval system. They require transient rapid ventricular pacing with concomitant valve-balloon inflation. Close monitoring of the pacer lead is imperative in order to avoid risk of pacing lead perforation. The cons of these valves are that they are not able to be repositioned. Additionally, sicker patients may not be able to tolerate rapid ventricular pacing, thus hemodynamics must be very closely monitored. One major advantage of these valves is that they have a lower frame height thus allowing for easier coronary access [33, 34]. They have delivery sheaths that typically allow for better controllable flexibility and steerability, and thus are preferred in patients with difficult vascular anatomy.

Self-expanding valves are typically supra-annular but newer prototypes that are intra-annular are now being manufactured. These valves do not require rapid ventricular pacing. They offer the advantage of being able to be repositioned and

*Catheter-Based Therapies: Current Practices and Considerations DOI: http://dx.doi.org/10.5772/intechopen.113334*

**Figure 4.** *Various types of contemporary transcatheter aortic valves.*

retrievable. The cons of these valves include limited maneuverability. They also tend to create a greater challenge for coronary access due to their larger frame sizes. Selfexpanding valves tend to have higher rates of pacemaker implantations and paravalvular leaks (**Figure 4**) [35].
