Balloon-Expandable Transcatheter Aortic Valve Replacement Systems

Cardiac Catheterization and Rapid Ventricular Pacing

Femoral arterial and venous access is obtained with 8-Fr sheaths. Coronary angiography is obtained, and if indicated, coronary intervention is performed in the same setting but usually after the BAV is completed. Right heart catheterization is performed using a Swan-Ganz thermodilution catheter. If the patient is being considered for TAVI, ascending aortic angiography is obtained, followed by abdominal aortic, iliac, and femoral angiography. When using the appropriate technique, the stenotic aortic valve can be crossed within a few minutes in most cases. An Amplatz left coronary catheter 2 (AL-2) is commonly used for this task. A straight tip, fixed core, 0.035-inch guidewire is positioned at the tip of the catheter. In the 40-degree left anterior oblique projection, the catheter tip is positioned at the rim of the valve. The catheter is slowly pulled back while maintaining firm clockwise rotation, to direct the catheter tip toward the center of the valve plane. The guidewire is carefully moved in and out of the catheter tip over a short distance, sequentially mapping the valve surface and exploring for the valve orifice. Once the wire crosses the valve, the catheter is advanced over the wire in the RAO view and positioned in the middle of the left ventricle (LV). The transvalvular gradient is obtained using the sidearm of the femoral sheath or through a dual-lumen catheter to record aortic pressure. Cardiac output can then be measured and the aortic valve area calculated using the Gorlin formula. An extra-stiff Amplatz 0.035-inch, 270-cm length guidewire (Cook, Bjaeverskov, Denmark) is used to perform all catheter exchanges and to assist in stabilizing the valvuloplasty balloon during inflation, deflation, and withdrawal. Prior to inserting the wire, a large pigtail-shaped curve is formed at the distal end of the wire using a dull instrument to prevent ventricular perforation and decrease ectopy. A 6-Fr temporary bipolar pacing lead is positioned in the right ventricle posterior wall and connected to a pulse generator capable of pacing at up to 220 beats per minute (bpm). Pacing and sensing parameters are determined, and then the blood pressure response to pacing at 200 to 220 bpm is evaluated. The rapid ventricular pacing (RVP) causes a precipitous fall of blood pressure to at least 50 mm Hg to be effective. If this is not achieved at a rate of 200 bpm, then the response is checked again at 220 bpm. If 2:1 conduction block is seen, then the rate will need to be reduced to 180 bpm or the lead position modified. The pacer is set on demand mode at 80 bpm, serving as a backup in the event that a vagal episode or interruption of atrioventricular conduction occurs resulting in bradycardia or asystole in response to balloon inflations.

Balloon Preparation and Balloon Aortic Valvuloplasty

The diagnostic catheter is removed from the LV over the extra-stiff wire while carefully maintaining the looped flexible segment of wire in the LV cavity. The 8-Fr sheath is replaced by a 10-Fr sheath over the extra-stiff wire . In our center, all procedures are performed using a 10-Fr sheath (Cook, Bjaeverskov, Denmark). The evolution of the technique has seen a reduction in the profile of the devices, reducing local complications at the femoral artery puncture site; this was previously the most common complication reported. At the end of the procedure, hemostasis is obtained by using an 8-Fr Angioseal device (Angioseal Vascular Closure Device, St. Jude Medical, Zaventem, Belgium). The majority of our experience was obtained with specifically designed balloon catheters for BAV, the double-sized Cribier-Letac catheters. When the production of those catheters was discontinued, we chose the Z-Med II balloon catheter (Numed Inc., Hopkinton, NY), compatible with a 12- or 14-Fr sheath. Currently we use the lower-profile Cristal balloons (Balt Extrusion, Montmorency, France) which are compatible with a 10-Fr sheath. The 20- and 23-mm diameter balloons are 45 mm in length, and the 25-mm diameter balloon is 50 mm in length. In general, we start with a 23-mm balloon. A 20-mm balloon is used if the valve is densely calcified or the aortic annulus is small (<19 mm by echo). In up to 25% of the cases, the 25-mm diameter balloon size can be used if the aortic annulus diameter is larger than 24 mm. Other catheters have recently become available, such as the TRUE balloon (Bard, New Providence, NJ) or the V8 (Intervalve, Inc, Minnetonka, MN) that minimize balloon migration and facilitate valve expansion. The Trueflow balloon (Bard, NJ) can be used without the need of rapid pacing in patients with a precarious hemodynamic condition. A short extension tubing with a three-way stopcock attached is connected to a handheld 30-mL Luer-Lok syringe filled with diluted contrast. The contrast is diluted 15%:85% contrast to saline to reduce viscosity and facilitate the inflation/deflation cycles. After flushing the distal lumen, the balloon is partially inflated and then completely deflated one or more times to completely purge it of air bubbles. The balloon catheter is advanced across the aortic valve, centering the valve between the two markers. Before using RVP, it was always challenging to maintain the balloon in optimal position during balloon inflation. There must be clear communication between the operators manipulating the balloon catheter and the pacing device. RVP is turned on, and balloon inflation is started quickly and with enough pressure to rapidly inflate the balloon as soon as the blood pressure falls. RVP is continued for a few seconds after the balloon reaches maximal inflation. The balloon is rapidly deflated, the pacer is turned off, and the balloon is withdrawn from the valve. This step requires coordination of the two operators to quickly allow restoration of antegrade flow while maintaining safe wire position in the LV. Rapid balloon deflation and restoration of blood flow is important to minimize the time of hypotension and hypoperfusion. Time must be allowed for the heart rate and blood pressure to return to preinflation values before deciding to inflate the balloon again. Because the pressure gradient cannot be measured through the current generation of balloon catheters, it is important to assess the effects of the balloon dilation and the hemodynamic consequences by observing the waveform of the aortic pressure tracing, as well as the heart rate response, rhythm, and blood pressure recovery. A sudden change in waveform with loss of the dicrotic notch or falling diastolic blood pressure could indicate the presence of severe aortic regurgitation. An improvement in the pressure slope is suggestive of a successful procedure. If the balloon does not appear to be fully expanded or there is no hemodynamic improvement, then repeat inflations are usually carried out before remeasuring the transaortic gradient. The residual gradient is obtained by simultaneous measurement of the pressure in the LV and aorta. If there is a significant gradient, the next larger size balloon may be chosen, and the sequence is repeated. A pullback gradient is also obtained after the final balloon inflation. For the final results, the pacemaker is removed, the cardiac output measured, and the final aortic valve area is calculated. An optimal result is considered to be doubling of the valve area or decreasing the gradient by 50% compared with the baseline value. Supravalvular angiography to determine the presence and/or severity of aortic regurgitation may be performed . If contrast cannot be used, assessment of the presence of aortic insufficiency (AI) and its severity may be performed by transthoracic echocardiography (TTE).

Immediate Management After Balloon Aortic Valvuloplasty

Manual compression is used for hemostasis at the venous entry site. Arterial hemostasis is achieved with the closure device as specified earlier. If a technical failure occurs, a pneumatic pressure device is used (FemoStop II Plus, Radi Medical Systems AB, Uppsala, Sweden). When the case is uncomplicated, the patient is usually discharged within 2 days. However, when BAV is performed in patients with severely impaired LV function or when rescuing a patient from cardiogenic shock, hemodynamic monitoring with inotropic support is usually required in the intensive care unit (ICU). Vagal reactions are the most common cause of hypotension associated with BAV. There must be a low threshold for ruling out the occurrence of pericardial tamponade or retroperitoneal bleed when evaluating the hypotensive patient after BAV.

Results Using Contemporary Balloon Aortic Valvuloplasty Techniques

Over the past 20 years, the results of BAV have been reported in innumerable series and multicenter registries showing clashing results depending on various experiences and techniques used. Our most recent series including 323 consecutive patients with severe AS who underwent BAV (with the exception of patients undergoing percutaneous heart valve implantation) between January 2005 and December 2008 has been reported. In this group of patients, the average age was 80.5 ± 10 years, 42% were women, and the mean logistic EuroSCORE (European System for Cardiac Operative Risk Evaluation) was 28.7 ± 12.5. New York Heart Association (NYHA) functional class III or IV was observed in 82% of patients, and the procedure was done emergently for patients in cardiogenic shock in 15% of cases. BAV was done using the retrograde approach in 100% of cases. Procedural success was achieved in 80.8% of the procedures. In-hospital mortality rate was 2.5%. Discharge from the hospital was at 5.6 ± 3 days. Over a mean follow-up of 20.7 ± 20.0 months, 26.3% of patients were bridged to SAVR or TAVI and 8.7% had repeat BAV. The other patients were left with medical treatment alone. Patients bridged to SAVR had the most favorable outcomes. Patients bridged to TAVR had better outcomes compared with those treated by single BAV. Finally, our study confirmed that survival was poor in patients treated by a single BAV (56% mortality at 1 year). In our series, the frequency of clinically apparent neurologic events was less than 2%. This compares favorably with the reported incidence of cerebrovascular events in a series of retrograde catheterizations of the aortic valve without intervention. Minimizing the duration of RVP and balloon inflation are important technical issues, and maintaining optimal heart rate and blood pressure during the procedure are crucial. Improvements in the procedure such as RVP and vascular closure devices, as well as continued experience, have resulted in decreased complications despite an increasingly aged and sicker population of patients ( Table 53.1 ).

Background and Development of Transcatheter Aortic Valve Implantation

Percutaneous catheter-based systems for the treatment of patients with valvular disease have been an exciting area for research since the mid-1960s. The initial animal investigations were performed by Davies in 1965, followed by Moulopoulos in 1971, Phillips in 1976, and Matsubara in 1992. These investigators reported various catheter-based systems for temporary relief of AI, but no further human application was possible due to unsolved major limitations. A new era of investigations started with the development of endovascular stents, raising the concept of balloon-expandable valvular prosthesis. In 1992, Andersen et al. reported their work in a porcine model in which they evaluated a transluminal stented heart valve. Here again, despite encouraging experimental results, there was no development of human application. Subsequently in 2000, Bonhoeffer and coworkers, using a valve from a bovine jugular vein mounted within an expandable stent, reported the feasibility of delivering such a device inside the native pulmonary valve of lambs and thereafter were able to perform the first successful human percutaneous replacement of a pulmonary valve in a right ventricle to pulmonary artery prosthetic conduit with valve dysfunction. Our team in Rouen has been working since the early 1990s on the development of a catheter-based treatment for nonsurgical patients with severe calcific AS that could overcome the high restenosis rate seen after BAV. Early cadaver work in 1994 provided early information on the ability to deploy a Palmaz stent in the aortic position and contributed to appropriate stent dimensions. In 1999, under the auspices of Percutaneous Valve Technologies (PVT; Fort Lee, NJ, USA), an original catheter valve was developed and tested in the sheep model. In vitro testing confirmed the valve hemodynamic profile and durability. An original animal model of chronic aortic regurgitation which allows for the long-term evaluation of the catheter valve in the systemic circulation was developed for in vivo testing. The first TAVI in a human was performed by our group in April 2002 followed by an initial series of human implantations for compassionate use that were serially reported. Following the acquisition of PVT by Edwards LifeSciences (Irvine, CA) in 2003, further modifications of the Cribier-Edwards device were achieved with the development of the Edwards SAPIEN Heart Valve that preceded multicenter clinical trials and the pivotal randomized PARTNER study in the United States. The first series of patients with severe AS treated with the self-expanding CoreValve Revalving System (Medtronic Inc, Minneapolis, MN) was reported by Grube et al. afterwards. Since the first implantation of this device in 2004, several technological improvements were obtained and the efficacy of the CoreValve demonstrated in multiple registries and in the U.S. CoreValve Pivotal trials. Over the past years, Edwards Lifescience and Medtronic have been developing new models of transcatheter valves and delivery systems, leading to a clear-cut improvement of the results with decreased rate of complications, whereas a number of other models of transcatheter valves were launched by several companies, some of them being already approved in Europe.

This section will provide a review of the patient selection, procedural techniques, results, and future strategies with balloon-expandable valves.

Risk Stratification

According to the guidelines, TAVI is currently being offered to patients who are at high risk or intermediate risk due to their age or comorbidities. Surgical risk is most commonly estimated by the Society of Thoracic Surgeons Predicted Risk of Mortality (STS-PROM) and the EuroSCORE. The EuroSCORE II has been validated in patients undergoing valvular surgery. Previous versions of the EuroSCORE had shown to overestimate surgical mortality in high-risk patients, and as a result the logistic EuroSCORE II was developed. The STS-PROM score is derived from the STS database, a voluntary registry of practice outcomes, and estimates the risk of mortality, morbidity, renal failure, and length of stay after valvular and nonvalvular cardiac surgery. This score has been shown to underestimate the true mortality rate after cardiac surgery, but it more closely reflects the operative and 30-day mortality for the highest-risk patients having aortic valve replacement.

The STS-PROM and the EuroSCORE provide an objective way to quantify risk. Although thorough, these risk scores do not include certain characteristics that would complicate surgery and increase the operative mortality such as: previous mediastinal irradiation, chest wall deformity, presence of a severe calcification in the thoracic aorta (porcelain aorta), history of mediastinitis, liver cirrhosis, previous bypass graft preventing safe reentry to the chest, or patient’s frailty. In addition, the algorithms were calculated from patients who underwent surgery, thus limiting their applicability to patients who were not considered surgical candidates. Clinical judgment and the patient’s level of independent function are subjective parameters that influence outcomes after cardiac surgery but are difficult to measure. A dedicated in-hospital mortality calculator for patients undergoing TAVR has been created with improved accuracy. More accurate risk calculators that will more precisely estimate the risk of patients selected for TAVI are currently being investigated.

Patient Selection for Transcatheter Aortic Valve Implantation

Over the past decade, heart valve teams have transitioned from being able to perform TAVI to become more proficient in performing TAVI while minimizing complications and obtaining perfect outcomes. Not every high-risk patient with symptomatic severe AS needs to be treated with TAVI. Special emphasis should be placed on performing this procedure in patients who will benefit consistently from this procedure. Certain patient characteristics have been associated with poor prognosis after TAVI. Of inoperable patients, those who were inoperable for technical reasons had a better prognosis that those who were considered inoperable for medical reasons. Preprocedural risk assessment is performed using the EuroSCORE or the STS score as described previously. Patients are usually classified as high risk for surgery when the logistic EuroSCORE and the STS score are greater than 20% and 8%, respectively. However, further expansion of TAVI to intermediate-risk patients has been recently validated by the FDA and appears in the European and U.S. recommendations after the positive results of two randomized studies with the Edwards SAPIEN XT valve (PARTNER 2 trial with a STS Score between 3% and 8%) and the Medtronic CoreValve (SURTAVI trial, with a STS Score between 3% and 15%). These studies showed comparable benefit of TAVI and SAVR on the primary end point of death and disabling stroke at 2 years.

Patient frailty, which has been shown to have a significant impact on clinical outcome after SAVR and TAVI, has become another inclusion criterion. Severe lung disease, oxygen dependence, low body mass index (BMI), worsening renal function, and low transvalvular gradients are also factors associated with poor prognosis. Until a dedicated TAVR risk score is created, patient selection should be based on objective evidence associated with elevated surgical mortality and a multidisciplinary approach. The indication of TAVI and the benefit/risk profile must be discussed in detail by a multidisciplinary team (heart valve team) of primary cardiologists, interventional cardiologists, cardiac surgeons, echocardiographers, radiologists, anesthesiologists, and geriatricians. Inclusion requires patients to have severe symptomatic AS, be considered high risk for surgical complications, have a greater than 1-year survival from their comorbidities, and likely benefit from valve replacement ( Table 53.2 ).

Meticulous preprocedure planning with multimodality imaging assessment must be obtained for each patient to determine the feasibility and safety of TAVI and select the best approach. Current prosthesis can be placed via a transfemoral (TF), transapical, transaortic, axillary, transcaval, or carotid approach. The minimum femoral artery diameters according to the different generation of Edwards valves are shown in Table 53.3 .

Computed Tomography

Computed tomography (CT) with three-dimensional reconstruction is invaluable to assess the valvular (calcium distribution, leaflet length) and aortic root anatomy (diameters, angulation, calcification, sinus of Valsalva), the distance coronary ostia/annulus (to assess the risk of coronary occlusion during TAVI), and the aortobifemoral anatomy. CT is currently considered the best tool to accurately evaluate the dimensions of the ovoid-shaped aortic annulus (diameters, circumference, and area) and select the appropriate prosthesis size to prevent valve embolization and paravalvular regurgitation (too small device) or annulus rupture (too large device). This information will be adapted to the model of prosthesis used ( Fig. 53.2 ).

CT has a key role for evaluating the peripheral arteries and preventing complication of the TF approach using large introducers and delivery systems. The prosthesis may be delivered by various approaches, the TF approach being considered the default approach by most teams because it is less invasive than alternative routes. Recent decrease in sheath size allows the TF approach to be used in more than 80% of cases, whereas it was limited to 50% of cases with the first-generation devices. Selection depends on tortuosity, calcification, and internal diameter of the femoral, external iliac, and common iliac arteries. The presence of abdominal aortic aneurysms or history of their repair would favor the use of alternative approaches. Vascular complications have been associated with significant mortality and may be prevented with appropriate screening. Safety should not be sacrificed if other approaches than the TF approach are available and patients are considered good candidates. If chronic renal insufficiency precludes the use of a fully contrasted study, then intraarterial administration of a small contrast bolus or a noncontrasted CT may provide appropriate images for the necessary measurements.

Edwards SAPIEN Valve

The Edwards SAPIEN prosthesis is the first generation of balloon-expandable valve developed by Edwards Lifescience in 2005 (Edwards LifeSciences, Irvine, CA), after the acquisition of PVT. This device is a modified version of the percutaneous valve used in the first-in-human implantations and subsequent feasibility studies performed between 2002 and 2005 by our group, then by other investigators. This model of valve has been used in all feasibility studies in Europe and Canada, later on in the U.S. PARTNER trial, and in many Outside United States (OUS) registries, including the SOURCE (Edwards SAPIEN Aortic Bioprosthesis European Outcome Registry) registry. This model of balloon expandable was the first one approved in the United States. The device consists of a bioprosthetic valve, a balloon catheter on which it is mounted, and a crimping tool.

The Edwards SAPIEN prosthesis is a trileaflet bioprosthesis made of bovine pericardium that is mounted in a balloon-expandable stainless steel stent ( Fig. 53.3A ). It has been pretreated to decrease calcification and functional deterioration. The stent has a fabric cuff placed in the ventricular side that covers one-half of the frame, limiting stent expansion and decreasing perivalvular insufficiency. Due to the lack of a sowing ring, the valve is oversized to the aortic annulus to ensure postdeployment stability and is available in several sizes selected based on the CT measurement of aortic annular dimensions In benchtop testing, its durability is greater than 10 years. The SAPIEN valve provides a larger effective orifice area and lower hemodynamic profile than corresponding surgically implanted valves but has a higher incidence of perivalvular insufficiency. The valve is mounted on a custom-made balloon with balloon diameters that correspond to the prosthesis size and ends in a nose cone that facilitates crossing the native valve ( Fig. 53.4 ). An original crimping tool is used to manually and symmetrically compress the overall diameter of the prosthesis from its expanded size to its minimal delivery profile. A cylindrical gauge is used to confirm the collapsed profile of the delivery system to ensure that it will move smoothly through the introducer sheath. A measuring ring is used to calibrate the balloon inflation to its desired size and to determine the amount of saline/contrast mixture in the syringe necessary for the proper inflation at the time of deployment. The Retroflex catheter (see Fig. 53.4 ), an innovation to facilitate the passage of the mounted valve across the aortic arch from the retrograde approach, was initially evaluated by Webb. This catheter has a deflectable tip that changes direction when activated by the rotation of an actuator incorporated in the handle. The catheter is then used to direct the valve delivery system through the arterial system, around the aortic arch, and across the aortic valve providing a less traumatic passage. The Retroflex catheter assists in centering and supporting the valve as it crosses the calcified and stenotic native valve. This system also provides precise positioning at the aortic annulus. The SAPIEN valve and deflecting guiding catheter are introduced through a hydrophilic coated sheath that extends into the abdominal aorta to decrease vascular complications.