ABSTRACT
Every year, approximately 800,000 people in the United States experience acute myocardial infarction (MI). Early recognition and treatment can improve mortality, reduce the size of myocardial injury, and preserve left ventricular (LV) function. Management of patients after acute MI also has long-term implications, including the possibility of ventricular aneurysm, reduced (frequently and severely reduced) ventricular function, heart failure, atrial and ventricular arrhythmia, and ‘‘sudden death.’’ The amount of remaining viable myocardium provides a determinant of prognosis. Conversely, the amount of myocardial scar also provides a determinant of outcomes. Several imaging approaches provide a means to assess whether dysfunctional myocardium is alive (viable) or dead/scarred (nonviable). One of the first imaging approaches that allows assessment of myocardial viability was the radionuclide method. The two approaches include single photon methods (using thallium-201 and technetium-99m) as the radionuclides and positron emission tomography (PET) [using 18F fluorodeoxyglucose (FDG) to detect the viable myocardium coupled with 13NH3 or
82Rb to
evaluate myocardial perfusion]. It is most useful to assess myocardial perfusion or ventricular function, which is reduced in both viable ischemic myocardium and nonviable myocardium. Single photon emission computed tomography (SPECT) has been widely used for detection of myocardial ischemia and MI, since the early 1980s. SPECT has limited spatial resolution, making it difficult to determine the transmural extent and the presence of small territories of infarction. SPECT is also unable to provide high quality images of ventricular structure and function. Furthermore, imaging with SPECT to determine viability in segments with myocardial dysfunction requires follow-up imaging hours (up to 48 hours) after thallium administration. PET had been considered the ‘‘gold standard’’ imaging approach for the assessment of myocardial viability. However positron-emitting tracers are very expensive and technically difficult to produce, requiring a cyclotron or with the perfusion imaging agent 82Rb, and an expensive generator. Also, the distribution of FDG is variably affected by the presence of diabetes. Finally, echocardiography has been a widely used approach for evaluating viability in asynergic myocardial segments by demonstrating improvement in wall motion during the infusion of low dose dobutamine. Cardiovascular magnetic resonance (CMR) imaging has become an important tool for identifying myocardial scar. This technique also is able to provide high-resolution images of cardiac morphology, function, and perfusion. The present chapter will describe the application of CMR imaging in acute and chronic MI.
