Cardiac
Pain
Pain originating in the heart as the result of acute
myocardial ischemia is assumed to be caused by oxygen deficiency and the accumulation
of metabolites, which stimulate the sensory nerve endings in the myocardium.
The afferent nerve fibers ascend to the central nervous system through the
cardiac branches of the sympathetic trunk and enter the spinal cord through the
posterior roots of the upper four thoracic nerves. The nature of the pain
varies considerably, from a severe crushing pain to nothing more than a mild
discomfort
The pain is not felt in the heart, but is referred to the skin areas supplied by the corresponding spinal nerves. The skin areas supplied by the upper four intercostal nerves and by the intercostobrachial nerve (T2) are therefore affected. The intercostobrachial nerve communicates with the medial cutaneous nerve of the arm and is distributed to skin on the medial side of the upper part of the arm. A certain amount of spread of nervous information must occur within the central nervous system, for the pain is sometimes felt in the neck and the jaw.
Myocardial infarction involving the inferior wall or
diaphragmatic surface of the heart often gives rise to discomfort in the epigastrium.
One must assume that the afferent pain fibers from the heart ascend in the
sympathetic nerves and enter the spinal cord in the posterior roots of the
seventh, eighth, and ninth thoracic spinal nerves and give rise to referred
pain in the T7, T8, and T9 thoracic dermatomes in the epigastrium. Because the
heart and the thoracic part of the esophagus probably have similar afferent
pain pathways, it is not surprising that painful acute esophagitis can mimic
the pain of myocardial infarction.
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