Differences Between Unstable Angina and Acute Myocardial Infarction: Pathophysiological and Clinical Spectrum

INTRODUCTION The acute coronary syndromes (ACS) belong to a diagnostic and pathophysiological continuum of acute myocardial ischemia, with or without evidence of myonecrosis, and encompass unstable angina, non-ST-segment elevation myocardial infarction (NSTEMI), and ST-segment elevation myocardial infarction (STEMI) (Figure 1). At the interface between unstable angina and myocardial infarction (MI), these entities become nearly indistinct as most features are shared. Indeed, the phrase “unstable angina” was first used by Conti [1] and Fowler [2] in the early 1970s to specifically describe symptom complexes intermediate in severity between stable angina pectoris and MI. Other terms used to describe unstable angina also show its close apposition to MI: intermediate coronary syndrome and preinfarction angina [2-5]. On the other hand, a number of features distinguish unstable angina from acute MI. These differences are seen in the pathophysiologic as well as the clinical spectrum of ACS, and they affect the diagnosis, treatment, and outcome. This chapter will review the shared features and distinguishing characteristics of unstable angina and acute MI regarding etiology, pathology, and clinical course.