Percutaneous mitral valve-in-valve and valve-in-ring

Introduction

Mitral valve disease is the most common cardiac valve condition, with the prevalence of significant regurgitation or stenosis increasing with age and estimated to be 9.5% in the general population above the age of 75. The most common treatments for severe mitral valve disease include surgical mitral valve repair (usually including an annuloplasty ring) or replacement with either a tissue or mechanical prosthesis. Patients receiving mitral bioprosthetic valves are often older compared with those receiving mechanical valves due to age and comorbidities that make lifelong anticoagulation unattractive. However, with the estimated bioprosthetic median life span of as little as 12 years in one cohort, this population may require repeat intervention. Mechanisms of prosthesis failure may include degeneration of leaflet tissue, thrombosis, pannus formation, and endocarditis. Repeat mitral valve replacement is associated with increased morbidity and mortality, with initial mortality ranging from 5.4% to 15.1%, with highest risk in those over 75 or having multiple repeat replacements.

Because of the risks in this population, percutaneous mitral valve-in-valve implantation has become an attractive option for patients at prohibitive surgical risk with prosthetic valve or annuloplasty dysfunction. Initial case reports and case series have shown the early feasibility, and international registries have been created for further assessment. ^, Multiple transcatheter valves have been evaluated in the mitral position, including the Melody valve (Medtronic, Minneapolis, MN) designed for percutaneous implantation in the pulmonary position ( Fig. 16.1 ). However, given the design of this valve and the high hemodynamic stresses placed on the mitral valve position, there have been concerns over the long-term durability of the valve in the mitral position. The balloon-expandable SAPIEN valves (Edwards Lifesciences, Irvine, CA) are the transcatheter prosthesis of choice, with improved ease of deployment and expectations of improved durability ( Fig. 16.2 ). Large case series of mitral valve-in-valve with the SAPIEN valve have shown early feasibility and safety, leading to Food and Drug Administration (FDA) approval of the SAPIEN valve for treatment of bioprosthetic mitral valve failure in 2017. Mitral valve-in-ring remains a more investigational procedure involving off-label use of transcatheter valves and will be included in this chapter due to similar procedural techniques.

Evaluation and procedural planning

Procedural planning is crucial to successful percutaneous mitral valve replacement. Evaluation by a structural interventionalist with expertise in the procedure and a cardiac surgeon is recommended to ensure optimal patient selection. Previous surgical records for valve specifications of the failing prosthesis or type and size of annuloplasty ring are vital for sizing of the new prosthetic valve. Beyond this, the mainstay of planning relies on multimodality imaging consisting of transthoracic and transesophageal echocardiography (TEE) and, in selected cases, computed tomography (CT). In conjunction with prior surgical records, annular size and prosthesis internal dimensions can be confirmed by TEE or computed tomography angiography (CTA). Once known, the dimensions can be used in the Valve-in-Valve Mitral application to select the new prosthesis size. Occasionally measurements will be on the margin of two prosthesis sizes. In these cases, it is usually preferred to use the smaller prosthesis size, with the use of additional volume to ensure optimal prosthesis anchoring. Additional volume is added to the deployment balloon to ensure adequate prosthesis flaring on the ventricular side and a “conical” deployment during the procedure. Evidence of irregular or elliptical-shaped annuli (rigid annuloplasty ring or incomplete annuloplasty ring) can predispose to paravalvular leak (PVL) or can cause inadequate anchoring in the case of the latter. In patients undergoing valve-in-valve, this risk is reduced due to a complete and circular annulus on which to anchor.

Echocardiography

The initial evaluation of prosthetic valve dysfunction typically involves transthoracic echocardiography (TTE) ( Fig. 16.3 ). TTE is often useful in identifying the etiology of the patient’s symptoms, assessing right and left ventricular function, and measuring septal thickness and screening for left ventricular outflow tract (LVOT) gradients, which could compromise the LVOT after valve replacement. However, due to shadowing from the valve prosthesis or surgical sewing ring, TTE has decreased sensitivity and is often inadequate to fully evaluate the failing metallic mitral prosthesis. Therefore TEE ( Fig. 16.4 ) should be performed in preparation for the procedure and is superior for the evaluation of mitral regurgitation, the mechanism of prosthesis failure, and the presence of PVL. TEE is also useful to rule out the presence of left atrial appendage thrombus and can be used in evaluation of prosthesis/annular dimensions.

Computed tomography angiography

Although not necessary for the majority of valve-in-valve procedures, gated CTA provides superior anatomic definition for procedural planning ( Fig. 16.5 ) and is critical for planning of mitral valve-in-ring and for valve-in-valve procedures where a high risk of LVOT obstruction has been identified, typically due to a highly angulated mitral prosthesis position. CTA provides precise fluoroscopic angles and high special resolution measurements to guide the intervention. For patients with mitral rings, CTA provides an accurate annular area measured in diastole to determine optimal prosthesis size, and also delineates the circumferential extent of the annular ring. In general, patients with incomplete rings are not considered candidates for valve-in-ring due to inadequate anchoring and risk of prosthesis embolism. CTA provides precise fluoroscopic angles with high spatial resolution to guide the intervention. For patients with mitral rings, CTA provides an accurate annular area measured in diastole to determine optimal prosthesis size and also delineates the circumferential extent of the annular ring. In general, patients with incomplete rings are not considered candidates for valve-in-ring due to inadequate anchoring and risk of prosthesis embolism. Based on the angles of the mitral annulus or existing valve, the ideal fluoroscopy angles for valve deployment can be estimated. Another benefit is identifying the optimal location of atrial septal puncture as well as significant septal thickening or scarring that poses a challenge. The septal puncture should be positioned so that there is adequate room in the left atria and to ensure appropriate angles for valve positioning and stability during deployment. A critical consideration for procedural planning is assessment of LVOT obstruction risk. Because of the intimate relationship of the mitral annulus with the aortic valve annulus and LVOT, any valve that protrudes past the annulus and into the LVOT can potentially create a clinically significant systolic gradient. Therefore it is important to consider the aortomitral angle and the LVOT size during systole. In patients undergoing valve-in-valve, the prior prosthetic valve can provide landmarks for deployment, with the goal of the ventricular strut edges being at the level of the prior valve struts or even to cover just the prosthesis leaflets. In these patients the anterior leaflet has usually been removed or is already immobilized and therefore unlikely to cause obstruction. In the case of valve-in-ring, the presence of the native anterior leaflet poses a potential risk, as it will be displaced anteriorly toward the LVOT, potentially obstructing blood flow. Therefore the length of the anterior leaflet in conjunction with aortomitral angle and LVOT size in systole should be evaluated to ensure adequate area once the anterior leaflet is permanently displaced. CTA computer-assisted detection software is available, which can help in planning by placing various-sized virtual valves based on the patient anatomy to evaluate the “neo-LVOT” after valve deployment. Ideally the anticipated neo-LVOT should be larger than 250 mm ² after valve deployment, though current limited data suggest an area as low as 190 mm ² may be sufficient. In patients in whom the LVOT area will be prohibitive to replacement, two options can be considered. First, alcohol septal ablation 4 to 6 weeks before the procedure can be attempted to maximize LVOT diameter. Second, a novel percutaneous laceration of the anterior mitral leaflet, or “Lampoon” procedure, can be performed at the time of the procedure to minimize the risk of the anterior leaflet causing obstruction.