IJCS | Volume 33, Nº4, July and August 2020

393 Figure 2 – Suggested algorithm for the investigation of patients with biopsy-proven extracardiac sarcoidosis; *palpitations were defined as prominent patient complaint lasting > two weeks ** abnormal electrocardiogram (ECG) defined as complete left or right bundle branch block and/or presence of unexplained pathological Q waves in two or more leads and/or sustained second or third degree atrioventricular block and/or sustained or non- sustained ventricular tachycardia *** abnormal echocardiogram defined as regional wall motion abnormality and/or wall aneurysm and/or basal septum thinning and/ or left ventricular ejection fraction < 40% CMR: cardiovascular magnetic resonance; ECG: electrocardiogram; FDG-PET: 18F-fluorodeoxyglucose-positron emission tomography;  reproduced with permission from Birnie et al . 25 CMR has some benefits compared with PET imaging, as there is no exposure to ionizing radiation and no need for patient preparation such as specific diet before the image acquisition. CMR is useful when the diagnosis is complex in order to rule out other types of cardiomyopathies and/or infiltrative diseases. However, CMR imaging is limited in patients with recently implanted pacemakers or other metallic devices and gadolinium is contra-indicated in patients with advanced renal disease (estimated glomerular filtration rate [eGFR] < 30 mL/min/1.73 m 2 ). 39 PET for CS 18F-FDG is a glucose analog used in PET imaging to evaluate myocardial inflammation. 40,41 Myocardial cells use a mixture of free fatty acids and glucose for energy production under normal resting conditions. When preferentially switched to free fatty acid substrate, the presence of 18F-FDG uptake can indicate an inflammatory lesion. Inflammatory cells such as macrophages and lymphocytes utilize glucose as their primary energy source. 42,43 18F-FDG follows the Wiefels et al. 18F-FDG PET/CT and cardiac sarcoidosis Int J Cardiovasc Sci. 2020; 33(4):389-400 Review Article