TAVI for failing surgical aortic bioprostheses (valve-in-valve)

Among elderly subjects undergoing surgical aortic valve replacement (SAVR), implantation of bioprosthetic heart valves is considered to be the standard of care. These prostheses are recommended for patients ≥60 years of age or in those at high risk of bleeding with systemic anticoagulation. Consequently, the use of bioprosthetic heart valves now greatly outweighs their mechanical equivalents. Despite advances in prosthetic design, valve durability remains the Achilles’ heel; current iterations are expected to degenerate within 12 to 20 years and in some cases even sooner. Redo SAVR is recommended for stenotic or regurgitant bioprosthesis, through surgery is often denied due to elevated operative risk in these elderly patients with comorbid medical conditions. In such patients, implantation of a transcatheter aortic valve (TAV) within the degenerated bioprosthetic surgical aortic valve (SAV) has proven to be feasible, safe, and effective. Nevertheless, limitations of TAV-in-SAV implantation include a relatively higher rate of malposition and coronary occlusion, device underexpansion, and residual aortic stenosis, compared to TAVI for native aortic valve stenosis. This section aims to describe the pre-procedural planning, implantation techniques, and evidence for TAV-in-SAV procedures.

By Darren Mylotte, Vinayak Bapat, Danny Dvir, Ran Kornowski, Rüdiger Lange and Nicolo Piazza.

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Fluoroscopic identification of stented bioprostheses

Surgical aortic valve replacement remains the therapy of choice in the majority of patients with aortic stenosis. This section includes the device design along with its radiological/fluoroscopic appearance focussing on how this correlates with the implanted valve, as transcatheter aortic valve implantation is performed under fluoroscopic guidance.

Recognising the fluoroscopic appearance of a specific valve design, whether in providing a more complete understanding of the failing valve or in the choice and implantation for the valve-in-valve intervention itself, is a critical step in the overall success of the procedure.

Failure modes of surgical bioprostheses

With the increased use of surgical bioprosthetic valves and an ageing population, today’s clinician will inevitably be confronted with cases of bioprosthesis failure. While newer devices have much improved durability, being able to identify the nature and conditions that might lead to failure in these newer, as well as older devices, is critical. Knowledge of the basic construction and dimensions, radiographic identification, and potential failure modes of SAV bioprostheses is fundamental in understanding key principles involved in TAV-in-SAV implantation.

Bioprosthetic surgical aortic valve (SAV) construction

Two types of prosthetic valves are used for heart valve replacement surgery - mechanical or bioprosthetic. Mechanical valves have long-term durability, but require lifelong anticoagulation, with the risk of thrombosis, thromboembolism, or spontaneous bleeding and are therefore less than ideal, particularly in younger patients, pregnant patients, or patients in the developing world where close monitoring is difficult to ensure.

Bioprosthetic heart valves (BHVs) are constructed from porcine heart valves or bovine pericardium preserved with glutaraldehyde. Patients with BHVs do not require anticoagulation, but structural valve deterioration may occur, particularly in younger patients, necessitating replacement, where it is associated with a higher risk of mortality.

Stented bioprostheses

Stented valves are primarily constructed using a rigid radiopaque or radiolucent base ring from which a stent or frame is positioned as support for the valve leaflets. This ring is covered by a synthetic fabric or pericardium that protects the frame. A sewing ring is attached here and the three stent posts rise at a right angle to support the valve leaflets which then serve as markers for positioning the transcatheter valves.

Biological stented prostheses are currently the main type of prosthetic valve used for aortic valve replacement with the ratio of bioprostheses to mechanical prostheses reversing itself over the last 15 years. Moreover, the total number of implanted stented bioprostheses has remained stable over the last few years despite competing procedures like stentless prostheses or transcatheter aortic valve implantation.

Size labelling of surgical bioprostheses: implications for TAV-in-SAV

When novel techniques are considered in the treatment of high risk patients who already underwent surgical aortic valve replacement (SAVR) and are facing a bioprosthetic valve failure a detailed imaging approach is crucial. Recognising bioprosthetic valve design and relevant anatomical details, along with the evaluation of coexisting risk factors for adverse effects during TAV-in-SAV procedure, are the main goals of this chapter as we explore what “Heart Team” needs to know.

Transcatheter aortic valve (TAV) sizing

While oversizing a transcatheter heart valve (THV) is a critical step in TAVI, it remains a complex question in TAV-in-SAV procedures. Apps exist to help in sizing transcatheter aortic valves (TAV), as well as industry guidance on valve dimensions and aortic annuli measurements. A consensus has emerged behind the choice of CT evaluation as the most appropriate method for measuring the “true diameter” of a degenerated bioprosthesis and correctly sizing the prostheses.  Insufficient sizing of either self-expanding or balloon expandable transcatheter valves has been associated with more paravalvular leak (PVL), valve migration and patient-prosthesis mismatch.

Procedural complications: post implantation gradients

Transcatheter heart valve (THV) implantation for native valve aortic stenosis has evolved as a viable, less invasive alternative to open-heart surgery in selected patients. In these cases, mean transvalvular gradients average 5 to 15 mmHg. In contrast, mean transvalvular gradients following TAV-in-SAV are frequently higher in the range of 10 – 25 mmHg. Initially, for this reason, TAV-in-SAV cases did not meet the Valve Academic Research Consortium (VARC) definition for acute procedural success. Recently, with the development of a newer generation of devices, THV implantation within failed surgically implanted bioprostheses has proven to be feasible. In this section we look at the This section focuses our evolving knowledge concerning this issue.

Procedural complications: Transcatheter heart valves (THV) malposition

Correct positioning of transcatheter heart valves (THV) is always critical and the incidence of malposition in valve-in-valve interventions has been cited as being greater than 15%. Increased experience, more in-depth knowledge of the modalities of failure including considerations of the size of the failed valve and higher post-implantation gradients have helped to achieve better results. Today, developments in the THVs, the choice of the valve, the nature of its radiopacity, all are equally involved in the complexity leading to the success of the intervention. This section examines the different parameters involved in meeting the challenge of malposition.

Procedural complications: stroke

Rates of stroke are low today in transcatheter aortic valve implantation (TAVI) and despite the inherent challenges of dealing with degenerate surgical bioprostheses, recent registries have shown that the rate of stroke in TAV-in-SAV procedures is similar to that seen in TAVI performed in native valves. This section explores this situation in detail, looking specifically at the TAV-in-SAV procedure and examines what needs to be done to ensure that the risks for this complication remain low.

TAV-in-SAV procedural tips and tricks: patient selection

Patient selection plays a crucial role in the success of any procedure and has an equally important role in TAV-in-SAV. It requires meticulous attention to the smallest of details and needs to be performed in a systematic manner for every patient. In essence, the patient must be assessed from access to implantation site. Becoming over “complacent” and “routine” may lead to failure and impact patient safety.

What are the different steps in patient selection specifically for this procedure? Learn about the role of CT analysis in THV sizing and access route selection and why CT analysis is now recommended for all patients being considered for a TAV-in-SAV procedure. How does the routine use of transoesphageal echocardiography (TOE) in cases with predominant regurgitation exclude paravalvular leak? Learn more about these and other points in patient selection in this section.