Transcatheter Aortic Valve Replacement
Introduction
Aortic stenosis (AS) affects morbidity and mortality as populations continue to age. Recent studies have estimated the prevalence of calcific AS between 2% and 4% among adults over 65 years of age and, for many years, there were limited or no treatment options for certain subsets of patients. In the absence of intervention, once symptoms develop, severe aortic stenosis is associated with a median survival of 1–2 years.
Surgical aortic valve replacement (SAVR) has been the gold standard therapy for severe symptomatic AS and remains important for selected patients. However, at least 30% of patients do not undergo SAVR because of comorbidities and other risk factors believed to place them at prohibitive surgical risk, such as advanced age, prior cardiac surgeries, severe lung disease, frailty, and other significant medical and anatomic considerations. Balloon aortic valvuloplasty (BAV) can increase valve area and offer short-term symptomatic improvement to inoperable patients, but studies have shown a high rate of restenosis and no improvement in survival without definitive valve replacement. To address the unmet need, transcatheter aortic valve replacement (TAVR) was developed.
Cribier and colleagues performed the first TAVR in a human in 2002. Several trials followed and established the safety and efficacy of TAVR. The US Food and Drug Administration (FDA) approved TAVR for use in inoperable patients in 2011. TAVR quickly became an established treatment option for a variety of subgroups, including those at high and intermediate risk from surgery, and continues to demonstrate excellent safety and outcomes.
This chapter provides an overview of indications, patient selection, identification, and management of important comorbidities, contra-indications, procedural technique and considerations, peri-operative management, and the indication and management of complications of TAVR. We will focus primarily on the transfemoral implantation of two device products currently available in the United States at the time of writing: the balloon-expandable Edwards Sapien XT and S3 valves (Edwards Life Sciences Inc., Irvine, California) and the self-expanding Medtronic CoreValve and Evolute-R valves (Medtronic Inc., Minneapolis, Minnesota).
Indications and Patient Selection
The cornerstone of avoiding complications is appropriate patient selection. This is done with collaborative multidisciplinary evaluation using a “heart team” approach. Each patient is assessed by cardiac surgeons and interventional cardiologists. In some programs, cardiac imaging specialists analyze multimodality imaging to determine anatomic feasibility and valve sizing, while others involve vascular surgeons in screening to determine access options. The key is that each program must critically self-evaluate to ensure that all needs are met to provide appropriate clinical and anatomic evaluation. It is important to understand and to account for specific preferences, goals, expectations, or limitations each individual may have to determine the best treatment strategy.
The diagnosis of severe aortic stenosis can be ascertained by following multidisciplinary consensus guidelines for valvular heart disease. Patients should be symptomatic from their valve disease with at least New York Heart Association (NYHA) Functional Class II symptoms or greater. For high-risk patients with severe aortic stenosis or insufficiency resulting from bioprosthetic valve degeneration, “valve-in-valve” TAVR is approved.
Surgical risk should be assessed by cardiac surgeons and include review of cardiovascular and noncardiovascular comorbid conditions. Clinical decision aids, including the Society of Thoracic Surgeons predicted risk of mortality (STS-PROM) calculator and the European System for Cardiac Operative Risk Evaluation (Logistic EuroSCORE) assist with quantitative risk assessment. It is widely recognized that not all important conditions are included in the risk calculators and that these factors must be considered on a patient-by-patient basis. Factors known to increase substantially the risk of SAVR and/or limit rehabilitation potential following traditional surgery include prior cardiac surgeries/sternotomies, chest wall deformities, prior chest wall radiation, porcelain aorta, prior coronary artery bypass grafting with anatomy lying in unsafe proximity to the chest wall, severe lung disease, cirrhosis, or significant frailty.
The PARTNER IA trial demonstrated an absolute 20% relative risk reduction in mortality with TAVR in comparison with medical therapy. Patients at low surgical risk in the PARTNER-3 and CoreValve low-risk trials were recently demonstrated to have better outcomes with TAVR than surgical AVR when anatomically appropriate.
The preferred approach for TAVR is the common femoral artery (transfemoral [TF]). As device profiles and equipment have continued to improve, approximately 90% of patients are able to undergo TF TAVR safely. In patients with acceptable renal function, iliofemoral anatomy and aortic valve annular sizing can both be quickly and reliably assessed using contrast-enhanced computed tomography (CT) scan. Important factors to consider when evaluating patients for iliofemoral suitability of TF TAVR include the minimal luminal diameter (MLD), amount and distribution of calcification, and tortuosity of the iliofemoral vessels, because these can identify patients at high risk of peripheral vascular complications. While the iliofemoral dimensions required are dependent on the type and size of valve chosen, most patients with an iliofemoral MLD of 5.5–6.0 mm are able to accommodate the necessary sheath(s) for TF TAVR. In patients with significant iliofemoral calcification or tortuosity, a larger MLD may be necessary and care should be taken with sheath insertion, valve advancement, and post-TAVR sheath withdrawal, because these patients may be at risk of iliac artery avulsion. For patients whose renal function does not allow contrast CT assessment, other strategies for assessment include noncontrast CT, angiography using minimal contrast dye, or intravascular ultrasound (IVUS) assessment in the catheterization laboratory.
Chest CT images should be gated to cardiac cycle to allow the most accurate sizing of the aortic annulus. The annulus is assessed either manually or using software packages that facilitate semi-automated three-dimensional (3D) reconstruction of CT images. Sizing performed by CT has been shown to be more precise and accurate than measurements using standard echocardiography. Careful assessment of the coronary sinus and aortic root dimensions, calcium distribution in the left ventricular outflow tract, and the height of the coronary ostia from the annular plane are important in selecting the optimal valve size and type. Other strategies for annular assessment include cardiac MRI or echocardiographic modalities (e.g., 3D TEE). It is important to understand the differences in measurements produced by these different modalities, as valve undersizing is an important risk factor for TAVR complications, such as paravalvular regurgitation.
Management of Important Comorbidities Prior to TAVR
It is essential that patients being considered for AVR undergo coronary angiography to assess for obstructive disease. During SAVR, patients with CAD can undergo surgical revascularization (CABG) at the time of their valve replacement. For patients undergoing TAVR, the timing and approach to percutaneous coronary intervention (PCI) for revascularization remains an area of active clinical investigation.
Carotid artery disease is also prevalent in patients with severe AS and must be considered and assessed.
Contra-Indications for TAVR
TAVR is not appropriate for patients with severely limited life expectancy as a result of factors outside their AS, clear medical futility, or severe/incapacitating dementia. TAVR is not currently approved for isolated native-valve aortic regurgitation (AR), although this is under investigation. Cardiac surgery can often provide more complete and definitive treatment for patients with other concurrent valve disease not amenable to current transcatheter therapies, patients with concomitant aortopathy, or severe coronary artery disease not amenable to percutaneous coronary intervention (PCI). Additionally, patients whose valve annulus is either too small or too large for currently available transcatheter devices may not be candidates for TAVR.
Procedural Considerations, Equipment, and Technique for TAVR
Optimal TAVR outcomes are obtained from a multidisciplinary approach with interventional cardiologists, cardiac surgeons, anesthesiologists, nurses, and other support staff working collaboratively. There may be institutional variability in personnel, equipment, and facilities used. In our institution, TF TAVR is most often performed in a minimally invasive fashion, using a fully percutaneous approach with local anesthetic and conscious sedation in a “hybrid” suite. Although rarely required, full surgical preparation of every patient is performed in the event that conversion to an open surgical procedure is necessary.
Preparation and attention to detail when obtaining access is of the highest importance in TF TAVR to mitigate the risk of access site complications ( Chapter 1 ). The common femoral artery should be accessed just above the bifurcation of the profunda and superficial femoral arteries and below the inferior epigastric artery with a micropuncture system under imaging, with verification of location by angiography prior to upsizing. Prior to the insertion of the delivery sheath for the TAVR valve, preclosure of the site can be performed using a variety of devices, such as the Perclose Proglide or ProStar XL devices (Abbott Vascular, Santa Clara, California).
The current Edwards and Medtronic valve series have different sheath sizes. The Edwards SAPIEN-3 is inserted via a 14-French expandable sheath (the 29-mm valve is placed via a 16-French sheath). The Medtronic CoreValve Evolut-R can either be placed using the “in-line” 14-French sheath or through a separate 18-French sheath. The Evolut-Pro utilizes either the in-line 16-French sheath or a separate 20-French sheath. Iliofemoral sizing/access requirements for the SAPIEN-3 and Evolut-R are similar and valve choice is often based on operator preference and aortic root characteristics. The Evolut-Pro requires a larger iliofemoral system.
Additional access is required for placement of a temporary transvenous pacemaker and pigtail catheter to be placed in the noncoronary cusp, to perform aortic root angiography, and to assist in valve positioning. These sheaths can either be placed ipsilateral or contralateral to the delivery sheath. The pigtail catheter can be inserted from a radial artery site; however, it is more difficult to complete endovascular interventions rapidly in the event of an iliofemoral vascular complication and may occupy the access site needed for a cerebrovascular embolic protection device. Some sites routinely place pacemaker wire via the internal jugular (IJ) approach. For patients who already have a permanent pacemaker, the venous sheath can be omitted and rapid pacing for valve deployment performed using a device programmer and the patient’s own pacemaker. For patients at high risk of requiring a permanent pacemaker after the procedure (i.e., using a self-expanding valve), we prefer to place an active fixation lead from the right IJ, which can more easily be left in place after the TAVR procedure.
Because cerebrovascular events are one of the most feared complications, we routinely perform our TAVR procedures using cerebral embolic protection (CEP). Currently, the Sentinel device (Claret Medical, Santa Rosa, California) is the only FDA-approved CEP system available in the United States. It consists of one basket in the innominate artery and one basket in the left common carotid artery to capture debris embolized during valvuloplasty and/or valve deployment that are later collapsed and removed at the conclusion of the procedure. The pivotal trial demonstrated a strong trend toward reduced periprocedural cerebrovascular events, and a recent meta-analysis demonstrated that cerebral embolic protection during TAVR was associated with a statistically significant reduction in the primary endpoint of death or stroke. Importantly, there were no device-related complications in this trial. It is important that operators are experienced in radial access, radial catheterization, and atraumatic entry to the great vessels when attempting to use this device.
Once vascular access has been obtained and the temporary pacemaker secured, intravenous heparin is given for an activating clotting time (ACT) of 250–300 seconds. The TAVR delivery sheath is inserted over a stiff wire, such as the Lunderquist (Cook Medical, Bloomington, Indiana). Next, the aortic valve is crossed using a catheter and guidewire. In our practice, this is most commonly performed using an Amplatz Left-1 (AL-1) catheter and a 0.035″ straight-tip guidewire; however, other preformed catheters (e.g., Judkins Right) or specialty wires (e.g., Glidewire [Terumo Medical, Somerset, New Jersey]) can be utilized. It is important to avoid crossing through the mitral subvalvular apparatus, and pass catheters and stiff guidewires slowly into the ventricle to avoid perforation.
Once access to the left ventricle is secured, hemodynamic assessment is performed to assess simultaneous LV and aortic pressure measurements for valve gradient as well as end-diastolic pressures. The catheter can then be used to exchange for a preformed stiff guidewire. For balloon-expandable valves, we prefer the 0.035″ Amplatz Extra-stiff (Cook Medical, Bloomington, Indiana) with a curve at the end of the wire for placement in the LV apex. For self-expanding valves, we routinely utilize the Confida wire (Medtronic, Minneapolis, Minnesota).
An important consideration for optimal valve positioning is to align correctly the inferior margins of the left, right, and noncoronary aortic cusps in a coplanar view. A number of methodologies have been described to aid in finding the best fluoroscopic projections to visualize the annular plane, and the preprocedural CT images can assist; however, we find that a right anterior oblique (RAO) caudal angulation optimized for valve co-axiality is helpful in the majority of patients, to understand the positioning of the valve at the level of the noncoronary sinus (the “lowest” of the three). In current practice, balloon aortic valvuloplasty (BAV) is performed with decreasing frequency prior to balloon-expandable valve placement and rarely for self-expanding valve placement.
The valve is then advanced into position coaxial to the aortic annulus, confirmed using angiography via the pigtail catheter in the noncoronary cusp. Self-expanding valves are placed by unsheathing the device, beginning in the LV outflow tract and continuing until it is completely deployed with the top of the scaffold in the ascending aorta. Rapid right ventricular (RV) pacing is not always required when placing a self-expanding valve, but temporary pacing at a rate of 100–120 beats per minute (bpm) can be used to reduce cardiac output and minimize migration while the valve is unsheathed. For balloon-expandable valves, rapid RV pacing at a rate of 180–220 bpm is required prior to inflation of the device. This temporarily arrests the heart and allows precise placement. Rapid pacing is continued until the valve balloon is completely deflated to prevent the balloon from being ejected from the annulus and inadvertently dislodging the valve. While balloon-expandable valves cannot be repositioned once deployed, current self-expanding valves have the ability to be recaptured/retrieved and repositioned prior to full deployment and release.
Following valve deployment, attention is turned to evaluating the positioning and function of the valve through a combination of aortic root angiography, hemodynamic assessment, and echocardiographic evaluation. Even when not well visualized by echocardiogram, the presence of aortic regurgitation (AR) is suggested by the absence of a dicrotic notch, wide pulse pressure, low aortic diastolic pressures, and elevated LV end-diastolic pressures. The presence of moderate or severe AR has been correlated with poor outcomes after TAVR and interventions to address this (e.g., postdilation of the valve, placement of a second valve in a “valve-in-valve” fashion, percutaneous paravalvular leak closure, etc.) should be considered.
Once the valve has been successfully deployed and no further interventions are anticipated, equipment is removed and hemostasis achieved. The TAVR delivery sheath should always be removed over a wire to maintain vascular access in the event of failure of the predeployed sutures and/or vascular injury. The other arterial access site can be used to perform completion angiography and to exclude occult bleeding stenosis or dissections. Protamine can be given in the absence of contra-indications.
Alternatives to Transfemoral Access
For patients who do not have adequate iliofemoral anatomy, alternative approaches have been developed. Transcatheter valves have been implanted safely following direct surgical access to the thoracic cavity through either a mini-thoracotomy exposing the left ventricular apex (transapical) or direct access to the aorta via a mini-sternotomy (transaortic). In contrast to SAVR, neither of these approaches requires placing the patient on full cardiopulmonary bypass. In more recent years, access has been obtained in the subclavian artery, axillary artery, carotid artery, or via antegrade transseptal or retrograde transcaval–transaortic approach via the femoral veins.
Perioperative Management and Adjunctive Therapies
Standard practice at our institution is to monitor patients in the postanesthesia recovery unit overnight. Hospital management is focused on early mobilization and monitoring for vascular and conduction system complications.
Routine antibiotic prophylaxis is recommended for all patients undergoing TAVR to reduce the risk of wound infection and endocarditis. The optimal antithrombotic regimen following TAVR remains unknown. Current guidelines and FDA labeling reflect the protocols used in the initial randomized clinical trials, lifelong low-dose aspirin and 3–6 months of dual antiplatelet therapy (DAPT) with clopidogrel. For patients with a separate indication for therapeutic anticoagulation (e.g., atrial fibrillation, hypercoagulable disorders, etc.), practice varies and may include a short period of “triple therapy” with aspirin, clopidogrel, and anticoagulation or may omit clopidogrel and treat with just low-dose aspirin and anticoagulant. Trials are currently underway to determine whether empiric anticoagulation may be beneficial for valve and clinical outcomes after TAVR.
Complications of TAVR
The incidence of major complications associated with TAVR continues to decrease. The Valve Academic Research Consortium (VARC-2) has standardized the definitions for important peri- and postprocedural complications and has allowed greater consistency of use. A summary of the notable periprocedural complications after TAVR, their risk factors, and management are summarized in Table 25.1 .
