Radionuclide imaging in acute coronary syndromes

IntroductionAcute coronary syndrome encompasses acute forms of ischemic heart disease – unstable angina and myocardial infarction with or without ST elevation. Chest pain patients have a wide spectrum of cardiac risk including those with typical symptoms and abnormal electrocardiography who require immediate catheter angiography with a view to intervention; at the other end of the spectrum are those of low risk with atypical symptoms and a normal ECG who can be discharged without investigation. Between these two groups is a large number of patients with diagnostic uncertainty.MethodsRadionuclide imaging can be useful in different phases of the course of atherosclerosis with subsequent myocardial ischemia. Primarily, radionuclide imaging can be used for the identification of subclinical coronary artery atherosclerosis to enhance primary prevention of CAD, acute myocardial infarction, and sudden cardiac death. Secondly it can be used at the emergency department to help to decide whether to admit or discharge a patient presenting with chest pain. And finally it helps to stratify and follow patients who survive ACS for choosing optimal treatment strategy.ResultsRadionuclide imaging is potentially able to detect endothelial dysfunction and early, preclinical atherosclerotic plaques vulnerable to rupture. Rest 99mTc-sestamibi SPECT has been shown to improve medical decision making by decreasing unnecessary hospitalizations. The strength of resting MPI lies with its high negative predictive value, approaching 100%. A possible future approach for risk stratification of patients with suspected ACS involves imaging myocardial fatty acid metabolism. The study of myocardial perfusion and metabolism in the sub-acute phase of STEMI has allowed us to considerably improve our knowledge of its pathophysiology, but its clinical usefulness is limited by the complex interplay between epicardial artery obstruction, coronary microvascular obstruction, and inflammatory cell activation.ConclusionThe optimal imaging strategy in acute coronary syndromes is determined not only by the diagnostic performance of a modality but also by local practice, expertise with imaging techniques, medical facilities, and individual patient characteristics.