Ischaemic vs non-ischaemic dilated cardiomyopathy: The value of nuclear cardiology techniques

Abstract

The left ventricular (LV) dysfunction exhibited by the patient is of equivocal origin. Nuclear imaging provides a very well-validated, versatile series of tests for proper diagnosis of disease pathophysiology, with the added, equally well established benefit of incremental information on patient prognosis and guidance towards optimal therapy (Table 1). In this case, the patient should first undergo a perfusion test, to identify or rule out an ischemic origin of LV dysfunction, and to distinguish between ischemia and myocardial infarction. If a fixed perfusion defect is present, a subsequent viability study using metabolic tracers can assist in selecting the appropriate treatment course. In addition, independent of ischemic or nonischemic origin, complementary assessment of absolute myocardial blood flow can identify severity of global microcirculatory dysfunction as a prognostic marker, and imaging of myocardial sympathetic innervation may be employed to determine individual risk of arrhythmia or heart failure progression. Myocardial perfusion imaging (MPI) using SinglePhoton Emission Computed Tomography (SPECT) or Positron Emission Tomography (PET) is routinely applied to detect underlying ischemia. SPECT MPI using Tc-labelled tracers (tetrofosmin or sestamibi) is a cornerstone of clinical evaluation to detect coronary artery disease (CAD) with established diagnostic and prognostic value. A recent meta-analysis reported sensitivity of 88% and specificity of 76%. The application of CT-based attenuation correction (AC) and scatter correction substantially improves specificity, up to 90%. Furthermore, MPI-defined ischemia has emerged as a powerful prognostic tool to predict adverse outcome and to guide interventional therapeutic decisions. Specifically, whereas a normal study identifies patients at low-risk of developing cardiac events, the presence and extent of perfusion abnormalities are directly proportional to the likelihood that a given patient will benefit from revascularization. PET with Rb or N-ammonia also exhibits excellent diagnostic performance in the setting of coronary artery disease. Compared to SPECT, PET displays higher diagnostic accuracy for the detection of coronary disease (85% sensitivity and 90% specificity), relating to improved spatial and temporal resolution, and superior tracer kinetic properties which are more proportional to flow over a wide range of values. Moreover, PET perfusion imaging allows absolute flow quantification, which enables noninvasive calculation of global coronary flow reserve. This is of value in detecting balanced reduction of myocardial perfusion in multiple vascular territories (e.g. triple vessel disease), and in detecting microvascular disease which may be present in diabetes and hypertension as in the discussed case. While reduced global flow reserve indicates an elevated risk in subjects with nonischemic cardiomyopathy, it also provides incremental prognostic value in ischemic heart disease where it may be used to guide therapeutic decision towards bypass surgery, targeted coronary intervention or medical therapy. Of note, in order to potentially expand the availability of absolute quantification, the field is moving towards implementation of quantitative SPECT by implementing principles established for PET imaging on novel, sensitive solid-state detector SPECT cameras. For both SPECTand PET-based perfusion imaging, electrocardiogram-gated acquisition is a routine procedure which enables the complementary evaluation of LV geometry and function at rest and stress, including ejection fraction (EF), ventricular volumes, transient ischemic dilation and dyssynchrony. These measurements Reprint requests: Frank M. Bengel, MD, FAHA, Department of Nuclear Medicine, Hannover Medical School, Carl Neuberg Strase, 1, 30625, Hannover, Germany; bengel.frank@mh-hannover.de J Nucl Cardiol 2015;22:971–4. 1071-3581/$34.00 Copyright 2015 American Society of Nuclear Cardiology.