Myocardial Ischemia, Fluorodeoxyglucose, and Severity of Coronary Artery Stenosis: The Complexities of Metabolic Remodeling in Hibernating Myocardium

Medication and ECG Patterns That May Hinder SPECT Myocardial Perfusion Scans

Coronary artery disease (CAD) is the leading cause of death followed by cancer, in men and women. With risk factors being endemic and the increasing costs of healthcare for management and treatment, myocardial perfusion imaging (MPI) finds a central role in risk stratification and prognosis for CAD patients, but it comes with its limitations in that the referring clinician and managing team must be aware of and use at their advantage. This narrative review examines the utility of myocardial perfusion scans in the diagnosis and management of patients with ECG alterations such as atrioventricular block (AVB), and medications including calcium channel blockers (CCB), beta blockers (BB), and nitroglycerin which may impact the interpretation of the exam. The review analyzes the current evidence and provides insights into the limitations, delving into the reasons behind some of the contraindications to MPI.

Likely Common Role of Hypoxia in Driving 18F-FDG Uptake in Cancer, Myocardial Ischemia, Inflammation and Infection

First introduced in 1976, ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography (PET) has become an indispensable tool for diagnosis and prognostic evaluation of tumors, heart disease, as well as other conditions, including inflammation and infection. Because ¹⁸F-FDG can accurately reflect the glucose metabolism level of organs and tissues, it is known as a "century molecule" and is currently the main agent for PET imaging. The degree of ¹⁸F-FDG uptake by cells is related to both the rate of glucose metabolism and glucose transporter expression. These, in turn, are strongly influenced by hypoxia, in which cells meet their energy needs through glycolysis, and ¹⁸F-FDG uptake increased due to hypoxia. ¹⁸F-FDG uptake is a complex process, and hypoxia may be one of the fundamental driving forces. The correct interpretation of ¹⁸F-FDG uptake in PET imaging can help clinics make treatment decisions more accurately and effectively. In this article, we review the application of ¹⁸F-FDG PET in tumors, myocardium, and inflammation. We discuss the relationship between ¹⁸F-FDG uptake and hypoxia, the possible mechanism of ¹⁸F-FDG uptake caused by hypoxia, and the associated clinical implications.

Dual-time-point myocardial 18F-FDG imaging in the detection of coronary artery disease

Background

Myocardial ¹⁸F-deoxyglucose (¹⁸F-FDG) uptake has been observed to be enhanced in patients with coronary artery disease (CAD) under fasting conditions. However, whether the increased ¹⁸F-FDG is induced by myocardial ischemia and how to discriminate ischemic from physiological ¹⁸F-FDG uptake have rarely been investigated.

Methods

Under fasting conditions, ¹⁸F-FDG PET imaging was performed in 52 patients with suspected CAD. Two ¹⁸F-FDG imaging sessions were conducted within two hours after a single administration of ¹⁸F-FDG (dual-time-point imaging), and with an intervention of an exercise test after the first imaging. Abnormal ¹⁸F-FDG uptake was determined by the classification of the ¹⁸F-FDG distribution pattern, and the changes of the ¹⁸F-FDG distribution between the two PET imaging sessions were analyzed. ^99mTc-sestamibi was injected at peak exercise and myocardial perfusion imaging (MPI) was conducted after ¹⁸F-FDG imaging. Coronary angiography was considered the reference for diagnosing CAD.

Results

Overall, 54.8% (17/31) of CAD patients and 36.2% (21/58) of stenotic coronaries showed exercise-induced abnormal uptake of ¹⁸F-FDG. Based on the classification of the ¹⁸F-FDG distribution pattern, the sensitivity and specificity of exercise ¹⁸F-FDG imaging to diagnose CAD was 80.6% and 95.2% by patient analysis, 56.9% and 98.0% by vascular analysis, respectively. Compared with MPI, ¹⁸F-FDG imaging had a tendency to have higher sensitivity (80.6% vs 64.5%, P = 0.06) on the patient level.

Conclusion

Myocardial ischemia can induce ¹⁸F-FDG uptake. With the classification of the ¹⁸F-FDG distribution pattern, dual-time-point ¹⁸F-FDG imaging under fasting conditions is efficient in diagnosing CAD.

Direct myocardial ischemia imaging: a new cardiovascular nuclear imaging paradigm

Myocardial perfusion imaging (MPI), using radiotracers, has been in routine clinical use for over 40 years. This modality is used for the detection of coronary artery disease (CAD), risk stratification, optimizing therapy, and follow-up of patients with CAD. Molecular cardiovascular imaging using targeted radiotracers provides a unique opportunity for imaging biochemical and metabolic processes, and cell membrane transporter and receptor functions at a cellular and molecular level in experimental animal models as well as in humans. Cardiac imaging using radiolabeled free fatty acid analogues and glucose analogues enable us to image myocardial ischemia directly as an alternative to stress-rest MPI. Direct ischemia imaging techniques can avoid and overcome some of the limitations of standard stress-rest MPI. This article describes recent studies using (18) F-fluorodeoxyglucose ((18) FDG) for myocardial ischemia imaging.