123I-meta-Iodobenzylguanidine Imaging in Patients with Cardiac Resynchronization Therapy: Results are Intriguing, but Unknowns Remain

Abstract

See related article, pp. 283-290 Excess sympathetic activation and subsequent decrease in neuronal reuptake of norepinephrine due to receptor downregulation are important in the pathogenesis of congestive heart failure. 123 I-meta-iodobenzylguanidine (mIBG) scintigraphy has emerged as a method to measure cardiac sympathetic activity because 123 I-mIBG shares the same biological properties as norepinephrine, but is not metabolized by the body. Impaired sympathetic integrity is manifested by low cardiac 123 I-mIBG uptake relative to the mediastinal background, resulting in a low heart-to-mediastinal ratio (HMR). The comparison between early and delayed HMR is quantified by the washout rate, with high rates corresponding to increased sympathetic activity. 1,2