Prognostic Value of Myocardial Perfusion Heterogeneity in Normal SPECT Studies

Overview

Myocardial perfusion imaging is an efficient tool to assess the risk of major cardiac events for patients with known or suspected coronary artery disease. If the test is normal, or if the abnormalities of perfusion represent less than 10% of the left ventricle myocardium, the patient is considered at low risk and should be managed with optimal medical treatment only. Recently, new gamma cameras using semi-conductor detectors have been developed. Their diagnostic performances have been demonstrated and confronted with various anatomical and functional reference techniques, such as coronary angiography and FFR. The prognostic value of a normal SPECT MPI has not been specifically assessed yet. Coronary microvascular dysfunction (CMVD) has been demonstrated to be an early marker of coronary artery disease (CAD). Preliminary data suggest that myocardial perfusion heterogeneity (a potential surrogate marker of endothelial dysfunction) can be assessed on conventional MP-SPECT, but its additive and independent prognostic value over the presence of myocardial ischemia remain unknown. Accordingly, the purpose of this study is : * To assess the prognostic value of a normal myocardial perfusion stress imaging using a semiconductor gamma camera with a dual isotope high speed protocol, * To evaluate the prognostic value of myocardial perfusion heterogeneity assessed by a new automatized image processing method, in normal SPECT MPIs. The main hypothesis is that the presence of myocardial perfusion heterogeneity is predictive of cardiovascular events in patients referred to the Nuclear Cardiology Department for routine evaluation of known or suspected CAD.

SPECT imaging protocol and analysis Stress tests and SPECTs are performed according to the routine protocols in use in our center. Briefly, at peak stress, patients were injected with thallium-201. Five to 10 minutes after stress, a 5-minutes supine acquisition was performed followed by a 5-minutes prone acquisition. Subsequently, technetium-99m-sestamibi was injected, and 2 minutes later a single 5-minutes rest acquisition was performed. During stress acquisition, patients were imaged in supine and prone positions with their arms positioned over their head. The rest acquisition was only acquired in supine position. The gated SPECT studies were performed at each acquisition. Injected activity (IA) was adjusted for patient weight. For weights of \<80 kg/ 80-100 kg/\>100 kg, thallium-201 IAs were 74/92/111 MBq and technetium-99m-sestamibi IAs were 300/370/450 MBq, respectively. A uniform imaging pre-treatment for the reconstruction of raw myocardial perfusion imaging data was applied, and images were reconstructed and reoriented to obtain transaxial sections of the left ventricle according to the three standard cardiac planes. In this study, we use a new mathematic technique from entropy analysis to provide precise, objective, automated quantification of perfusion heterogeneity at stress with camera SPECT. This method may be a non-invasive imaging to assess coronary microvascular dysfunction.