Silent Myocardial Ischemia

Abstract

Silent myocardial ischemia is defined as objective documentation of myocardial ischemia in the absence of angina or anginal equivalents. Since its original description in the 1970s, it has undergone intensive investigation, and its clinical significance is now well established. This review will serve as an update on the pathophysiology, detection, prevalence, prognosis, and treatment of silent ischemia in both asymptomatic patients and those with angina, whether stable or unstable. ### Pain Studies No discussion of silent ischemia is complete without consideration of the cardiac pain mechanism. Although much has been learned about this subject, much is still uncertain. The afferent fibers that run in the cardiac sympathetic nerves are usually thought of as the essential pathway for the transmission of cardiac pain (Figure 1). The atria and ventricles are abundantly supplied with sympathetic sensory innervation; from the heart, the sensory nerve endings connect to afferent fibers in cardiac nerve bundles, which in turn connect to the upper 5 thoracic sympathetic ganglia and the upper 5 thoracic dorsal roots of the spinal cord. Within the spinal cord, impulses mediated by this sympathetic afferent route probably converge with impulses from somatic thoracic structures onto the same ascending spinal neurons. This would be the basis for cardiac pain referred to the chest, wall, arm, back etc. In addition to this “convergence-projection theory,” the contribution of vagal afferent fibers must be acknowledged for an explanation of cardiac pain referred to the jaw and neck. How these vagal fibers are activated remains unclear. Furthermore, somatic localization of ischemic pain cannot predict the site of myocardial ischemia (anterior, inferior, or lateral) from one patient to the next. Figure 1. Mechanisms of cardiac pain. From Droste and Roskamm (used with permission).4 The actual “trigger” that stimulates the sensory nerve endings remains elusive. If a chemical pain stimulus is involved, …