A Shift in Focus: From a Multi to Single Modality Approach
Since the first A-mode echocardiogram, there have been great revolutional changes and the use of noninvasive cardiac imaging has grown substantially during the past decade. Echocardiography and nuclear modality have been the primary imaging modalities for management in patients with different cardiovascular diseases. The introduction of cardiac magnetic resonance (CMR), computer tomography (CT), and three-dimensional (3D) printing, makes things quite different. Multi-modality imaging plays a role in all cardiovascular diseases that includes ventricular function, coronary artery disease, valvular disease, congenital heart disease, guidance for interventions, and vascular diseases. However, the use of each modality requires knowledge, expertise and forethought about cardiac diagnoses to avoid excess coast, inappropriate testing and to improve outcomes. Unnecessary duplication of investigations must be avoided for cost effective healthcare delivery.
For more than a decade, organizations such as the American College of Radiology and the American College of Cardiology Foundation have published criteria delineating the appropriate use of cardiac imaging. These specialty society guidance documents are designed to provide clinicians with recommendations regarding the use of imaging and are focused on reducing unnecessary and inappropriate testing. In response to rapid and unsustainable growth in the use of cardiac imaging procedures, various professional medical organizations have developed appropriate use criteria (AUC) to guide physicians and payers on effective use of these procedures. The AUC serves as a guide for physicians to incorporate symptoms, risk factors, and clinical history in selecting the patients for whom testing is most appropriate, based on the best available evidence or expert consensus; Furthermore, the AUC can help physicians steer other patients to alternative tests or no testing at all.
The AUC classify the appropriateness of testing across a range of clinical scenarios in 3 categories: “appropriate” (established value), “may be appropriate” (uncertain value), and “rarely appropriate” (no clear value). The AUC are intended to be used as part of a comprehensive disease management plan to maximize the value of care by minimizing unnecessary imaging and resultant downstream invasive procedures. (1). Appropriate use helps to avoid excess costs; enhances the value of imaging in risk stratification and decision making; and reduces radiation risk, particularly in women (2). Moreover, the principle of applying expert consensus criteria to choose the best testing strategy for each patient is widely accepted by payers, physicians, and patient groups.
- The goal of this statement is not to showcase CMR as the exclusive modality for cardiac diagnosis but to highlight this tool as the corner stone of noninvasive cardiac imaging. By using a static and a gradient magnetic field in combination with a radiofrequency field, CMR imaging has evolved from a less commonly used technique into a tool with the potential to find an important clinical role in the near future for the noninvasive assessment of morphological and functional aspects of the heart. Consequently, CMR belongs to the fastest growing new fields of broad MR application. At the same time, CMR uses some of the strongest and fastest switching electromagnetic gradients available in MR imaging. CMR has become the primary imaging tool in many centers in characterizing disease severity and planning of patient management.
- Volumes and Function: CMR measures ventricular volumes and mass using a simple acquisition of a 3D stack of contiguous short-axis cines with full biventricular coverage. CMR is significantly more accurate and reproducible than other techniques which makes it the technique of choice for longitudinal study of patients over time and for reducing sample size for drug studies.
- Great Vessels: Three-dimensional angiography with gadolinium enhancement may show the lesion more clearly in high resolution, but it also shows any associated pathology (collaterals). CMR is fast and accurate for the diagnosis of aortic dissection although local issues relative to availability will determine whether CMR, CT, or echocardiography is used.
- Valvular Heart Disease: CMR has a significant role in valve disease, but it usually acts as a second-line technique to assist when echocardiography with Doppler has proved problematic because of limited acoustic access, highly eccentric jets, or the need for quantification. The quantification of valve regurgitation is a strength of CMR because of its capability of measuring accurate ventricular stroke volumes from multislice ventricular planimetry and comparing this with the measurement of great vessel flow from velocity mapping.
- Congenital Heart Disease: CMR is widely used to assess congenital heart disease, and when used in concert with echocardiography, the need for invasive assessment has been significantly reduced. CMR is particularly useful for the safe, accurate, and reproducible quantification of the left-to-right shunting of blood that occurs frequently in congenital heart defects such as atrial or ventricular septal defects, patent ductus arteriosus, aortopulmonary window, and partial or total anomalous pulmonary venous return.
- Myocardial Ischemia: CMR is a safe and proven modality for detecting ischemic heart disease. Within a single study, CMR is able to assess rest and stress regional contraction, and localize and evaluate regions of myocardial ischemia and viability, of importance given the prognostic impact for the patient. With performance that is comparable to PET/SPECT and at times favorable compared to stress echocardiography, it is now an essential tool for diagnosing ischemia and for determining the likelihood of success following myocardial revascularization.
- Non ischemic cardiomyopathy: CMR with its higher spatial resolution is considered the gold standard for evaluating ventricular mass, volumes, and ejection fraction. CMR can be used for accurate diagnosis of several conditions, especially cardiomyopathies. CMR is an invaluable tool, not only in differentiating nonischemic from ischemic cardiomyopathy, but also in aiding the accurate diagnosis of the subtype of nonischemic cardiomyopathy. CMR should routinely be integrated in the diagnostic workup of various cardiomyopathies.
CMR is a valuable tool for the evaluation of patients with, or at risk for, heart failure and has a growing impact on diagnosis, clinical management, and decision making. Through its ability to characterize the myocardium by using multiple different imaging parameters, it provides insight into the etiology of the underlying heart failure and its prognosis. CMR continues to develop across a broad range of clinical applications, and much can be expected of this technology in the future.
Dr. Fawaz Abdulaziz M Alenezi is a Clinical Imaging Fellow at the Duke University Health Systems. He conducts medical research on the derivation and validation of novel echocardiographic approaches to myocardial deformation and a new echocardiographic technique which assists patients with heart ventricular function.