Percutaneous Transcatheter Valve-in-Valve Implantation

Background

The surgical replacement of heart valves is now routine, with over 275,000 valves implanted worldwide each year. Mechanical prosthetic valves constructed from nonbiologic materials have the advantage of excellent durability but require lifelong anticoagulation. Biologic prosthetic valves, fashioned from animal or human tissue, do not require long-term anticoagulation and have thus been increasingly chosen by implanting cardiac surgeons and patients. In the United States, bioprostheses accounted for 79% of all surgical aortic implants between 2002 and 2010, with the highest rates in older, higher-risk patients. Rates continue to increase, likely in part due to the availability of a valve-in-valve (ViV) option when these valves fail.

All bioprosthetic valves will fail eventually. However, most valves last long enough, given the limited life expectancy of patients receiving them. The reported incidence of aortic or mitral valve deterioration requiring reintervention is high: 20% to 30% at 10 years and over 50% at 15 years. The actual incidence of structural valve deterioration is likely higher. The mean age of surgical valves treated in the Valve-in-Valve International Data (VIVID) registry was only 8 years. The limited durability of these valves, the significant increase in the proportion of bioprosthetic valves implanted, and improved life expectancy have led to an increasing incidence of surgical valve failure. These patients are often at elevated risk for redo open-heart surgery due to advanced age, comorbidities, and postsurgical adhesions. Although the outcomes associated with redo surgery continue to improve, surgical mortality remains between 3% and 23% in various series, and morbidity remains substantial.

Transcatheter aortic valve replacement (TAVR) is an emerging standard of care for many patients with severe native aortic stenosis. The rapid evolution of transcatheter heart valve technology has transformed aortic valve replacement into a minimally invasive percutaneous procedure that is often performed under local anesthesia and with minimal morbidity. The success of TAVR and the clinical needs of high-risk patients with degenerative surgical prostheses has driven the introduction of ViV procedures; as a result, the transcatheter deployment of heart valves within previously implanted surgical bioprosthetic valves in the aortic, mitral, tricuspid and pulmonary positions is becoming increasingly common.

Surgical Bioprosthetic Heart Valves

Tissue heart valves were first utilized as transplanted cadaveric valves (allografts) in the early 1960s; subsequently, in the late 1960s, Carpentier introduced “bioprosthetic” valves made of porcine or bovine tissue (xenografts) and metallic frames. Modern tissue valves are usually made of bovine pericardial tissue or porcine valve leaflets, although some allografts are still used.

Stented surgical heart valves consist of (1) a stent frame composed of metal alloys or polymers; (2) a sewing ring allowing fixation within the valve annulus or above it (supra-annular); and (3) three valve leaflets, which are sewn to the stent frame (either internally or externally). Stented “sutureless” surgical heart valves, modeled on transcatheter valve platforms, have recently been introduced.

Stentless valves eliminate the reduction in the annular area caused by a stent frame, thus increasing the effective orifice area. Most stentless valves utilize porcine root tissue, although homografts as well as pericardial tissue may be used. Stentless valves represent a challenge for ViV implantation as the lack of a rigid frame presents a problem for the fixation and fluoroscopic visualization of a transcatheter heart valve (THV).

Sizing

The size of an implanted bioprosthetic valve has significant implications for hemodynamic performance, likely mode of failure, and options for surgical or transcatheter therapy at the point of failure. Unfortunately the labeling of surgical heart valves lacks standardization across manufacturers ; frequently valves labeled as being of the same size will have different internal and external dimensions. Generally labeled valve sizes refer to the external dimension of the valve frame and/or sewing ring, whereas internal dimensions are 1 to 4 mm smaller.

In-depth knowledge of a surgical heart valve’s characteristics is required to perform ViV procedures. Tables of valve dimensions published by manufacturers are useful but may not represent the true internal dimensions, which is vital for selection of an appropriately sized THV. A ViV smartphone application will list a large range of commonly used surgical and transcatheter valves—with descriptions, images, dimensions, photographic and fluoroscopic images—along with guidance on sizing and positioning. For each valve, stent’s internal diameter as reported by the manufacturer is listed, along with a “true ID,” which takes into account the reduction in internal diameter due to the leaflet tissue. This easy-to-use application is vital for the planning of ViV procedures and reduces much of the confusion associated with the sizing of surgical valves.

The model and its labeled size should routinely be obtained from an operative report. When these are unavailable, measurements from transesophageal echocardiography (TEE) or computed tomography (CT) imaging may be helpful. In addition, pannus formation or leaflet calcification may help guide the choice of THV and procedural strategies.

History

Transcatheter native aortic valve implantation was initially performed via a transvenous transseptal approach in 2002. However, retrograde transfemoral arterial access quickly became the preferred delivery approach, with alternative access routes (apical, subclavian, carotid, caval, and aortic) currently being reserved primarily for patients with iliofemoral arterial disease.

ViV proof of concept was demonstrated in animal models via a transatrial approach by Boudjemline et al. in 2005, followed by others in 2007. Reports of the first human ViV procedures were published in 2007 by Wenaweser et al. and by Webb. Subsequently large case series and reviews documented procedural advances and the reproducibility of the procedure. Simultaneously, ViV implants were shown to be feasible and reproducible in the aortic, mitral, tricuspid, and pulmonary positions via a variety of delivery approaches.

Subsequently the ViV International Data Registry investigators documented the rapidly growing international clinical experience. This work added tremendously to the understanding of the possibilities and limitations of the procedure. Most recently, two large prospective clinical trials have documented excellent clinical, hemodynamic, and quality-of-life outcomes out to 1 year with both the balloon- and self-expandable SAPIEN XT and CoreValve THV systems.

Aortic Valve-in-Valve Procedure