Mechanisms of ischemic cardiac pain and silent myocardial ischemia.

The mechanisms of cardiac ischemic pain remain obscure. It is unknown whether ischemia causes cardiac pain by the release of chemical substances or by mechanical stretching. It is also unknown whether ischemia activates specific nociceptors and pain fibers or mechanoreceptors and chemoreceptors. In patients who have both painful and painless ischemic episodes, a certain minimal duration and severity of ischemia are necessary but insufficient to explain the presence of pain, since very severe ischemia of long duration can be silent. Thus, central transmission of painful stimuli and the pain perception threshold appear to play major roles in determining the presence or absence of pain. The emotional state and psychologic expectations of patients may affect their perception and threshold of pain considerably.