Show notes
CardioNerd Amit Goyal is joined by Dr. Erika Hutt (Cleveland Clinic general cardiology fellow), Dr. Aldo Schenone (Brigham and Women’s advanced cardiovascular imaging fellow), and Dr. Wael Jaber (Cleveland Clinic cardiovascular imaging staff and co-founder of Cardiac Imaging Agora) to discuss nuclear and complimentary multimodality cardiovascular imaging for the evaluation of cardiac sarcoidosis. Show notes created by Dr. Hussain Khalid (University of Florida general cardiology fellow and CardioNerds Academy fellow in House Thomas). To learn more about multimodality cardiovascular imaging, check out Cardiac Imaging Agora!
Cardiac sarcoidosis is a leading cause of morbidity and mortality for patients with sarcoidosis. A high index of suspicion is needed for the diagnosis as it is often recognized late or unrecognized. It is difficult to diagnose given the focal nature of the cardiac involvement limiting the utility of biopsy and the available clinical criteria have limited diagnostic accuracy. Multimodality imaging plays a large role in the diagnosis and management of patients with cardiac sarcoidosis with the different imaging modalities offering complimentary information and functions.
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Quoatables
“It’s not important for you to love the Soviet Union. It’s important for the Soviet Union to love you back [Stalin regarding the famous dissonant Russian poet Anna Akhmatova]. When we talk about PET, you love PET, but the PET has to love you back, and it has to love you back in a way where you have to know how to approach this test. With, first, some humility about its limitations: 1) inflammation is universal...and 2) the prep is extremely important.” -- 11:25
“A test without a good preparation is a preparation to fail.” --15:30
“Sarcoidosis is kind of the tuberculosis that we have in medicine—it can present as anything.” --36:40
Pearls
Cardiac Magnetic Resonance Imaging (Cardiac MRI) and/or 18-Fluorodeoxyglucose Positron Emission Tomography (FDG-PET) are complimentary tests in the evaluation of cardiac sarcoidosis. Both tests look for scarring and inflammation. Cardiac MRI is a good initial test due to its high negative predictive value (i.e. absence of LGE makes cardiac sarcoidosis less likely) but not great for following a cardiac sarcoidosis patient’s response to therapy. Cardiac FDG-PET is great to follow a patient's response to therapy especially in patients with intracardiac devices such as a pacemaker.
18-fluorodeoxyglucose (FDG) is a glucose analog and just like glucose, is transported into the cell by transporters. Once in the cell, it is phosphorylated, like glucose is, by hexokinase in preparation for use in glycolysis. Unlike glucose, however, it does not proceed to be metabolized any further in the glycolysis pathway and remains trapped in the cell. In the inflammatory cells within sarcoid granulomas, glycolysis is significantly increased to fuel the large energy requirement. Thus, these inflammatory cells (i.e. macrophages) can take up large amounts of FDG.
When planning to obtain a cardiac FDG-PET for evaluation of cardiac sarcoidosis, patient preparation is key! There are several available dietary protocols to accomplish the goal of switching the patient’s metabolism to be reliant on fatty acids instead of glucose as an energy source. One such protocol used by the discussants in the episode is prolonged fasting (10-12 hours) prior to the study preceded by two meals that are high in fat and proteins and low in carbohydrates—a ketogenic diet. By having the patient eat this diet, we are trying to switch the metabolism because there is no ability or no offer of glucose for the body to use as an energy source! After we have switched the body’s metabolism to purely fat, when we inject the patient with FDG, hopefully most of the myocardium not affected by inflammatory cells within a granuloma will not have any uptake!
Why do we start with resting perfusion images in the imaging portion of the cardiac FDG-PET protocol for cardiac sarcoidosis? Resting perfusion images allow us to identify any perfusion defects at baseline. These images can be compared to the FDG images to see if there is match or mismatch in areas of abnormalities. Resting perfusion images also allow us to assess LV and RV function. Resting perfusion images in conjunction with FDG images can also allow us to monitor the patient’s response to treatment by demonstrating return to normal myocardium from active sarcoid granuloma after treatment or by showing the progression to development of scar.
The hallmark for detecting cardiac sarcoidosis with cardiac MRI is late gadolinium enhancement (LGE) in the mid-wall and subepicardial regions. Gadolinium is an extracellular contrast agent that washes out slowly from areas of inflammation or scar (both processes with result in an expansion of the extracellular space). Because of this it is important to look at the distribution pattern of the LGE (i.e. a subendocardial enhancement in a coronary distribution is more suggestive of scar from a prior myocardial infarction in this area). Some features of LGE that favor the diagnosis of cardiac sarcoidosis include: 1) multifocal involvement and 2) involvement of the basal anteroseptum and inferoseptum with contiguous spread into the right ventricle.
Show Notes
1. What is the typical patient population with cardiac sarcoidosis and how does it present?
Sarcoidosis is a multisystem disorder of unclear etiology characterized by the formation of noncaseating granulomas in multiple organs with an annual incidence of 5 to 40 cases per 100 000 persons in the USA and Europe. It has a 3-fold higher risk in blacks than in whites and it is more common in females. In the USA most disease occurs between ages 25-45, however in Europe and Japan there is a second peak in women older than 70 years old.
Around 5% of patients with pulmonary/systemic sarcoidosis have symptomatic cardiac involvement and autopsy studies have shown that there is cardiac involvement in 25% of patients. More recent advanced cardiac imaging studies in patients with known extracardiac sarcoidosis suggests asymptomatic cardiac involvement may be present in ~40% of patients. It is difficult to detect given its patchy focal distribution in the heart such that cardiac biopsy has a sensitivity of only 20-30% (this yield may improve with image guidance from cardiac MRI or FDG PET or guidance from electroanatomic voltage mapping).
We may suspect cardiac sarcoidosis in patients presenting with new and unexplained atrioventricular (AV) block, atrial or ventricular arrhythmias, or left ventricular dysfunction—especially in patients with a history of prior non-cardiac sarcoidosis. Palpitations, presyncope, syncope or other nonspecific symptoms may also be the initial presentation.As with our patient in the episode, we should suspect cardiac sarcoidosis and infra-hisian disease in a young previously healthy and active patient who is presenting with evidence of cardiac conduction system disease (i.e. AV block, bundle branch block [BBB], etc.)!
2. Using the patient from the episode as an example (previously healthy presenting with syncope, BBB, frequent non-sustained tachycardia on telemetry monitoring, and intermittent complete heart block, with bilateral hilar fullness on chest x-ray), how should we proceed with evaluation for patients with suspected cardiac sarcoidosis?
To continue our evaluation, we could obtain an echocardiogram to look for wall motion abnormalities and myocardial thinning in the basal areas—findings that can be seen with cardiac sarcoidosis. Even if this is evident, we should still rule out coronary artery disease (CAD) in these patients. In a patient with low risk factors for CAD, we can pursue a coronary computed tomography angiogram (CCTA) and if there is no evidence of obstructive CAD, then we start thinking about an inflammatory process with resultant scar causing the patient’s echocardiography findings. If we have an elderly patient or a patient with significant risk factors for obstructive CAD, then we can obtain a coronary angiogram for evaluation. The bottom line is: common things being common—we don’t want to miss obstructive CAD!Abnormal findings on echocardiography in patients with cardiac sarcoidosis include wall motion abnormalities, diastolic dysfunction, and changes in the left ventricular geometry including: 1) abnormal myocardial wall thickness in a noncoronary distribution (possibly caused by sarcoid granulomas), 2) myocardial wall thinning as a result of a later stage of the same process, 3) left ventricular dilation, and 4) left ventricular systolic dysfunction.Sensitivity, specificity, and negative predictive value of echocardiography for diagnosis of cardiac sarcoidosis are low.There are recent studies that have been published about the value of strain imaging with echocardiography in the diagnosis and assessment of response to therapy of patients with cardiac sarcoidosis, however this is still an evolving area or research.After ruling out obstructive CAD we can proceed to Advanced Cardiac Imaging modalities for further evaluation: Cardiac Magnetic Resonance Imaging (Cardiac MRI) and/or 18-Fluorodeoxyglucose Positron Emission Tomography (FDG-PET). These are complimentary tests. Both tests look for scarring and inflammation. Cardiac MRI is a good initial test but not great for following a cardiac sarcoidosis patient’s response to therapy. Cardiac FDG-PET is great to follow a patient's response to therapy especially in patients with intracardiac devices such as pacemaker or ICD.