Cath Lab Digest

Ibrahim Akin, MD, Stephan Kische, MD, Henrik Schneider, MD, Tim C. Rehders, MD, Jasmin Ortak, MD, Andreas Liebold, MD*, Christoph A. Nienaber, MD, Hüseyin Ince, MD

Introduction

Rising life expectancy results in an increase in degenerative and neoplastic diseases. Population-based observational studies revealed that 1–2% of patients > 65 years of age have moderate-to-severe aortic stenosis (AS).¹ Surgical aortic valve replacement (AVR) dates back to 1960 and is currently the only treatment option for severe AS. It has been shown to improve survival, regardless of age.² In the ideal candidate, surgical AVR has an estimated operative mortality rate of 4%. Unfortunately, up to one-third of patients with severe AS are ineligible for corrective valve surgery either because of advanced age or the presence of multiple comorbidities.³ Current treatment options for those patients not offered surgery include medical treatment or percutaneous balloon aortic valvuloplasty, though neither has been shown to reduce mortality. Medically treated patients with symptomatic AS have a 1- and 5-year survival rate of 60% and 32%, respectively.⁴ With the introduction of transcatheter aortic valve implantation (TAVI) in 2002, there seems to be an alternative for these patients.

Selection of Patients

Due to the existence of the tried-and-tested surgical valve replacement with good long-term results, the selection of patients for TAVI — which should be performed in a multidisciplinary consultation between cardiologists, surgeons, imaging specialists, and anesthesiologists — involves several critical steps.⁵ Candidates considered for TAVI must have severe symptomatic AS in addition to a formal contraindication to surgery or other characteristics that would limit their surgical candidacy because of excessive mortality or morbidity risks (Figure 1). The procedure should be offered to patients who have a potential for functional improvement after valve replacement. It is not recommended for patients who simply refuse surgery on the basis of personal preference.

Confirming the Severity of Aortic Stenosis

Different imaging modalities can assist in the selection process by providing important information about the aortic valve, coronary arteries, and vascular structures. First, the severity of AS should be assessed. Both transthoracic echocardiography (TTE) and transesophageal echocardiography (TEE) are the preferred tools to assess the severity of AS. In addition, the exact anatomy of the aortic valve should be assessed. Echocardiography, multislice computed tomography (MSCT), and magnetic resonance imaging (MRI) can all help to distinguish between a bicuspid and a tricuspid aortic valve. It is important to point out that the implantation of available percutaneous prostheses is contraindicated in the case of a unicuspid valve, and is not recommended in the case of a bicuspid aortic valve because of the risk of incomplete deployment, significant paravalvular regurgitation, and displacement of the prosthesis.^5,6 Furthermore, the exact location and severity of aortic valve calcifications and the presence of bulky aortic valve leaflets should be assessed. Before the implantation procedure, MSCT may be the preferred tool to identify aortic valve calcifications. A severely calcified aortic valve may result in the inability to cross the native valve with the catheter. Bulky leaflets and calcifications on the free edge of the leaflets may increase the risk of occlusion of the coronary ostia during aortic valve implantation. Thus,the extent and exact location of calcifications should be carefully assessed before the implantation procedure. The assessment of coronary anatomy is also important in the selection process. Conventional coronary angiography, which remains the “gold standard,” should be performed to exclude the presence of significant coronary artery disease.

Analysis of Surgery Risk and Evaluation of Life Expectancy and Quality of Life

The precise evaluation of surgical risk in a specific patient is not easy and involves an attempt at individualization based on statistical data from databases containing a large number of procedures. The most accepted and validated algorithms that are widely available today are the EuroSCORE, the STS score and the Parsonnet score. These algorithms predict the surgical risk by assigning weight to various factors that affect the clinical result, but it is clear that they can underestimate or overestimate it in certain groups of patients who are not represented satisfactorily in the population used to generate the algorithm.⁷ There is some evidence in the literature of the incorrect prediction of aortic valve replacement outcome using the EuroSCORE model.⁸ Osswald et al report on the real risk of overestimation of death by EuroSCORE for patients undergoing isolated AVR, pointing to a possible incorrect assignment of high-risk patients to PAVI procedure.⁹ The key element to establishing whether patients are at high risk for surgery is multidisciplinary clinical judgement, which should be used in association with a more quantitative assessment based on the combination of several scores (for example, expected mortality > 20% with the EuroECORE and > 10% with the STS score). This approach allows the team to take into account risk factors that are not covered in scores, but often seen in practice such as chest radiation, previous aorto-coronary bypass with patent grafts, porcelain aorta or liver cirrhosis.