Illuminating the Hidden: Standardizing Cardiac MIBG Imaging for Sympathetic Dysfunction.

The heart's innervation relies on a delicate balance between the sympathetic and parasympathetic nervous systems, each using distinct neurotransmitters to regulate heart rate, contractility, and vascular tone. The sympathetic division primarily uses norepinephrine, whereas the parasympathetic division operates through acetylcholine. A range of diseases, through intrinsic and extrinsic mechanisms, can disrupt these neural pathways, resulting in autonomic dysfunction. This review highlights intrinsic causes such as dysautonomias, amyloidosis, diabetes mellitus, Parkinsonian syndromes, and Lewy body dementia, as well as extrinsic factors such as heart failure, myocardial ischemia, infarction, and drug-induced cardiotoxicity. This article examines the effects of various conditions on cardiac sympathetic innervation and highlights how 123I-radiolabeled metaiodobenzylguanidine (MIBG), a norepinephrine analog, can target the cardiac sympathetic nervous system for early detection and disease characterization. Currently, variability in cardiac 123I-MIBG imaging protocols across institutions leads to inconsistencies in image acquisition and interpretation, limiting the establishment of universal benchmarks for distinguishing normal from abnormal cardiac sympathetic innervation. To address this, we propose a simple, clinically useful, standardized protocol based on European Association of Nuclear Medicine guidelines and the AdreView Myocardial Imaging for Risk Evaluation in Heart Failure trial, incorporating both qualitative and semiquantitative methods for disease assessment and highlight cutoff values for some pathologies that can assist in visual interpretation. Standardizing these protocols will enhance the consistency, reliability, and diagnostic accuracy of 123I-MIBG imaging, improving clinical decision-making and optimizing patient outcomes.