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Does the Brain Know When the Heart Is Ischemic?
- Carl J. Pepine, MD
- University of Florida Gainesville, FL 32610-0277 Requests for Reprints: Carl J. Pepine, MD, Division of Cardiovascular Medicine, University of Florida, Box 100277, Gainesville, FL 32610-0277.
Chest pain has traditionally been accepted as the principal warning of ischemic heart disease, but doubts were raised long ago about whether severe ischemia is always signaled by chest pain [1]. With better ambulatory and in-hospital monitoring, it has become apparent over the years that patients who have angina, have had infarction, or are elderly have most of their ischemic episodes without chest pain [2-6]. It follows that the objective signals of cardiac ischemia (such as transient electrocardiographic ST-segment depression, perfusion, or wall motion abnormalities) are more closely linked with adverse outcomes than either the presence or severity of chest pain itself [3-11]. Nevertheless, because symptoms are still the principal reason patients present after a long latent phase of asymptomatic coronary artery disease, considerable attention has been focused on the variability in perception of chest pain during ischemia.
The classic theory was that stretching of the ventricular wall caused angina through the mechanical stimulation of pain-sensitive fibers in the myocardium [12]. This theory was elaborated with the suggestion that mechanical dysfunction caused local release of chemical substances, which stimulated pain receptors [13]. Several problems were associated with these theories. First, biochemical phenomena are the initial derangements during ischemia; regional mechanical impairment is also an early finding. Yet pain, if it occurs, occurs late in the temporal sequence of an ischemic episode. Second, substantial myocardial pathology, sometimes associated with mechanical dysfunction, may occur in the complete absence of pain. Specifically, myocarditis, endocarditis, and even endomyocardial biopsy are painless. These facts and others have led to questions about the presence of a specific myocardial nociceptor [14]: Some argue that either the stimulus that conveys cardiac nociception must be subthreshold or that a neuropathy must exist in patients who have …
