What future for the myocardial sympathetic innervation imaging?

Abstract

The myocardial sympathetic innervation plays a pivotal role in the progression of heart failure and in the occurrence of lifethreatening arrhythmias. An impaired function of presynaptic sympathetic nerve terminals is considered to reflect impaired reuptake and thus impaired removal of the neurotransmitter from the synaptic cleft [1], resulting in overexposure of the myocardium to catecholamines and in a pre/post-synaptic signaling imbalance [2]. Consistent with this pathophysiologic model, prospective, large-scale clinical trials confirmed an excellent prognostic value of adrenergic imaging in patients with heart failure, both with single photon emission tomography (SPECT) and with positron emission tomography (PET) [3,4].Although extensively validated and embedded in clinical practice, the study of myocardial sympathetic innervation activity with standard SPECT suffers from evident limitations. In fact, its main prognostic parameters, i.e., the heart-tomediastinum ratio and the cardiac washout rate, are generally derived from planar scans of the chest, thus allowing only for a semiquantitative evaluation of the global activity of sympathetic innervation. But as underlined also by a recent report, the heterogeneity of innervation may be more prognostically relevant than the assessment of the degree of sympathetic denervation [5]. As such, an imaging modality able to allow for a regional assessment of myocardial sympathetic innervation would be highly desirable. In this regard, new heart dedicated camera systems equipped with cadmium-zinc-telluride (CZT) solidstate detectors may constitute a valid alternative. Owing to improved image quality and temporal and spatial resolution over standard SPECT, a regional assessment of sympathetic innervation activity is feasible and accurate [6,7]. Unfortunately, despite its great advantages, this novel, recently available SPECT technology is not widely deployed yet.Hence, PET may be a preferred technique for the assessment of the cardiac sympathetic nervous system, able to yield a significantly higher impact on clinical practice. PET provides superior sensitivity and resolution over conventional nuclear imaging, thus allowing for a precise localization of innervation defects. To date, the main limitation of PET relates in the need of an on-site cyclotron, which is required to produce 11

Does lipid-lowering medication improve cardiac sympathetic nerve integrity?

“…3 Thus, sympathetic neurons appear to be more susceptible to ischemic injury than cardiomyocytes, which may help in identifying (pro-)arrhythmic, denervated but viable areas-at-risk, such as the infarct borderzone. 4,5 Given its incremental value in outcome prediction, studies in recent years have also investigated the complementary benefit of cardioprotective medication on the cardiac sympathetic nervous system (SNS) in combination with the overall ventricular performance among CHF patients. [6][7][8] The prescription of statins (3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors) is endorsed by current guidelines of the American College of Cardiology and American Heart Association.…”