Functional Valve Assessment: The Emerging Role of Cardiovascular Magnetic Resonance

Introduction

The prevalence of valvular heart disease is increasing along with the life span of the population. In assessing individuals with valve disease, echocardiography is the primary imaging modality used by clinicians both for initial assessment and for longitudinal evaluation. Information regarding valve morphology and function, cardiac chamber size, wall thickness, ventricular function, and estimates of pulmonary artery pressures can be readily obtained and integrated to formulate an assessment of valve disease severity. In some instances, body habitus or the presence of coexisting lung disease may result in suboptimal acoustic windows on echocardiography, which may lead to technically difficult studies. Additionally, in some patients, information from clinical history and physical examination or other diagnostic tests may be discordant with echocardiographic findings. In these instances, there is a significant clinical role for cardiovascular magnetic resonance (CMR).

The diagnostic capabilities of CMR have increased substantially over the past 20 years due to hardware and software advances. Today, CMR has a number of unique advantages over other imaging modalities — primarily, it provides a view of the entire heart without limitations from inadequate imaging windows or body habitus. Furthermore, CMR can obtain imaging data in any imaging plane prescribed by the scan operator, which makes it ideal for accurate investigation of all cardiac valves — aortic, mitral, pulmonic, and tricuspid. In addition, CMR for valve assessment is noninvasive, free of ionizing radiation, and in most instances does not require contrast administration.

Since a comprehensive review of the role of CMR in all valve lesions is beyond the scope of this article, we will focus on the most common valvular indication for performance of clinical CMR studies in our laboratory: mitral insufficiency. The following provides a description of the CMR techniques and an overview of selected validation and reproducibility studies.

The objectives of a comprehensive CMR study for evaluating mitral insufficiency are threefold: 1) to provide insight into the mechanism of mitral insufficiency, 2) to quantify the severity of mitral insufficiency, and 3) to discern the consequences of the lesions including the effects on left ventricular (LV) volume, LV systolic function, and left atrial volumes. In most instances this information can be obtained without the need for intravenous contrast agents (gadolinium). Therefore, CMR can be performed even in patients with severe renal failure.