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MY APPROACH

MY APPROACH to selecting cardiac computed tomography vs cardiac magnetic resonance imaging vs echocardiographyn currently the best modality for imaging coronary luminal stenosis noninvasively. In the majority of cardiac patients for whom assessment of cardiac structure and function are indicated, TTE should be the initial imaging test. In up to 15% of TTEs where image quality is compromised because of a poor acoustic window, CMR should be considered as an alternative option. Similarly, for patients who need assessment of the severity of valvular stenosis or regurgitation, TTE with color Doppler imaging

Raymond Y. Kwong, MD, MPH

should be the initial test; however, CMR should be the next option in case of a poor echocardiographic window or if a

For selecting echocardiography, cardiac magnetic resonance imaging (CMR), or cardiac computed tomography (CCT) in the management of cardiac conditions, important determining factors are what specific clinical questions need to be answered and what imaging technique is most appropriate to provide the answers, patient conditions that can lead to suboptimal imaging quality, contraindications to imaging, and healthcare costs of the imaging study.

What questions need to be answered? Echocardiography, CMR, and CCT each has unique technologic capabilities that define what imaging question(s) can be best answered. Echocardiography has the advantages of extensive clinical adaptation, high temporal resolution (ability to freeze rapid cardiac motion), and high portability so that imaging can be performed on the sickest patients. Both transesophageal (TEE) and transthoracic (TTE) echocardiography are suitable for patients who are hemodynamically unstable. CMR and CCT have unlimited imaging fields of view and can measure cardiac chambers volumetrically. Using various pulse sequence methods, CMR can be used to view cardiac structure and function and multiple myocardial physiologic parameters (eg, perfusion, infarction, edema, iron infiltration) in defined scanned planes in a single imaging session. CT coronary angiography (CTA) is n

precise quantitative measurement of cardiac chamber sizes is needed to further understand the severity of pressure/volume loading secondary to the valvular dysfunction. For patients with new-onset heart failure, CMR is playing an increasing and complementary role to TTE. Although TTE remains the most common initial imaging test to assess cardiac structure and function in patients with new-onset heart failure, CMR probes into the specific cause of heart failure noninvasively. CMR can assess perfusion, infiltration, infarction, edema, and iron content of the myocardium in the same study. These CMR methods help the clinician to draw conclusions about whether infarction or ischemia burden from coronary artery disease is responsible for the heart failure, or if nonischemic patterns of heart failure exist. This knowledge has been shown to improve the effectiveness of downstream invasive angiography. In addition, in patients with a nonischemic pattern of heart failure, late gadolinium enhancement imaging may offer a specific diagnosis of heart failure including amyloidosis, sarcoidosis, iron overload, or myocarditis. CTA has high negative predictive value in detecting epicardial coronary stenosis and may also be useful in ruling out coronary artery disease as the cause of heart failure in some patients (eg, young patients with a low coronary-risk profile). For assessment of chest pain syndromes, exercise stress TTE is an effective tool if the patient can achieve an adequate

First published on PracticeUpdate on July 07, 2014. Republished with permission.

http://dx.doi.org/10.1016/j.tcm.2014.07.008 1050-1738/& 2015 Published by Elsevier Inc.

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exercise workload and has no limitation on the echocardiographic window. In patients who cannot perform an adequate exercise stress test or who have a limited echocardiographic window, pharmacologic stress CMR and CCT are reasonable options. Most pharmacologic stress CMR uses vasodilating agents to image for perfusion deficits as a result of coronary stenosis. Stress CMR aptures the extent of both stress perfusion deficits and myocardial infarction. In addition, stress CMR can size the myocardial extent of ischemia and infarction more precisely than stress TTE. This feature may be desirable in selected patients with a moderate to high pretest likelihood of disease when precise estimates of ischemia/infarction can guide decisions toward invasive coronary intervention. CCT seems to be most effective in patients with a low pretest likelihood of disease or when there exists an equivocal result from cardiac nuclear scintigraphy. In a minority of centers, dobutamine infusion has been used during stress CMR to image for wall motion abnormalities developed because of ischemia induced by the inotropic stress. In patients with a limited acoustic echocardiographic window, dobutamine stress CMR has been shown to be more accurate than dobutamine echocardiography. In patients with acute chest pain with dissecting aortic aneurysm suspected, TEE is the preferred bedside tool (vs the next best choice of CCT) because it provides ready access to the patient should acute treatment of hemodynamic compromise become necessary.

Conditions that lead to suboptimal imaging quality Other than patient body habitus affecting the TTE acoustic window, other factors that affect suboptimal imaging quality should be considered. Frequent premature ventricular contractions affect the quality of both CMR and CCT but

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may be controlled by administration of a small dose of intravenous atropine or beta blocker during the study. CMR and CCT imaging of patients who are unable to follow breathholding instructions almost always result in suboptimal quality.

Contraindications to imaging CTA and, in most cases, CCT involve the use of iodinated contrast, which is contraindicated in patients with renal dysfunction. Administration of gadolinium-based contrast in CMR is contraindicated in patients with severe renal dysfunction (eGFR o30 mL/min/1.73 m2) because of development of a life-threatening condition known as nephrogenic systemic fibrosis. Use of gadolinium-based contrast agents is safe in patients with an eGFR o30 mL/min/1.73 m2, although a dose reduction is indicated in patients with mild renal dysfunction (eGFR, 30–60 mL/min/1.73 m2). Since 2008, when surveillance eGFR testing and contrast dose adjustment were implemented, the incidence of nephrogenic systemic fibrosis has been extremely rare worldwide.

Healthcare costs CMR is more costly than CCT, and CCT is more costly than TTE. However, in cases where imaging with multiple tests or an invasive costly procedure could be avoided, the use of CMR and CCT is cost-justified. Harvard Medical School; Director Cardiac Magnetic Resonance Imaging, Brigham and Women's Hospital Boston, Massachusetts E-mail addresses: [email protected] [email protected]

MY APPROACH to selecting cardiac computed tomography vs cardiac magnetic resonance imaging vs echocardiography.

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