New trials for assessment of left atrial dysfunction by FDG-PET

Abstract

The left atrium (LA) has an important role in modulating left ventricular filling and maintaining cardiac output. In addition, LA has been identified as an important biomarker of cardiovascular disease and adverse cardiovascular outcomes. Therefore, LA function has been focused for precisely and quantitatively analyzed recently. However, most of functional studies of LA have so far been done by echocardiography. Atrial fibrillation (AF) leads to progressive structural and functional changes in LA over time. LA fibrosis is a major determinant of the progression to, and burden ofAF and its substrate, leading to an increase in total atrial activation time. A fibrosis burden demonstrated on late gadolinium contrast-enhanced cardiac magnetic resonance. There is evidence of progressive remodeling of the LA once AF develops with increasing fibrosis alongside lower LA reservoir strain in patients with persistent AF compared with patients with paroxysmal AF (PAF). PET has played an important role for functional and molecular imaging of the heart. FDG-PET has been used for identifying focal tumor lesions in atrial areas. With improvement of image quality, PET has recently been used for assessing atrial tissue function. Of particular, FDG-PET has been used for assessing AF. With maximal use of high-resolution PET, it has a potential for identifying focus of AF as well as for assessing left atrial function quantitatively. FDG is a glucose analog and has been used for tracking glucose metabolism. FDG-PET has two completely different roles for cardiovascular imaging. FDGPET has long been used for assessing tissue viability for patients with coronary artery disease. The heart derives its energy mainly from free fatty acids and glucose. FDG commonly enters cardiomyocytes through the glucose transporters 1 and 4. In ischemic state with the availability of glucose, FDG accumulation in the myocardium is maintained due to the dominant anaerobic glucose metabolism. On the other hand, FDG-PET has recently been used for identifying active inflammatory lesions because glucose is also consumed in the inflammatory process. Depending on the purposes of in vivo functional imaging, patient preparation should be carefully done before the FDG administration. Post-prandial condition, glucose loading, or insulin clamp is applied for myocardial viability assessment, whereas long fasting condition with or without heparin administration is required for identifying active inflammatory lesions with suppressing physiological myocardial FDG uptake. The current paper includes retrospective clinical study to understand the feasibility of FDG-PET/CT under insulin clamp condition in order to relate scar and metabolic parameters identified by this method with structural and electrical remodeling across patients with varying degrees of AF burden in patients with sinus rhythm, PAF, and persistent AF. Ghannam and colleagues suggested that greater AF burden correlates with increased LA metabolism and scar. They have correlated the newly obtained metabolic activity with various structural parameters as well as ECG functional parameters. They suggested that those with AF may have greater LA volumes, increases in the amount and heterogeneity of LA metabolism, and greater amount of LA scar. Reprint requests: Nagara Tamaki, MD, PhD, Department of Radiology, Kyoto Prefectural University of Medicine, Kyoto, Japan; [email protected] J Nucl Cardiol 2020;27:1563–65. 1071-3581/$34.00 Copyright 2019 American Society of Nuclear Cardiology.