Heart Attack Pathology
(Photo Essay)
Medical Author:
Michael C. Fishbein, M.D.
Medical Editor:
Leslie J. Schoenfield, M.D.,
Ph.D.
Medical Reviewing Editor:
Jay W. Marks, MD
What is a Heart Attack?
A heart attack is a layperson's term for a sudden blockage of a coronary
artery. This blockage, which doctors call a coronary artery occlusion, may be
fatal, but most patients survive it. Death can occur when the occlusion leads to
an abnormal heartbeat (severe arrhythmia) or death of heart muscle (extensive
myocardial infarction). In both of these situations, the heart can no longer
pump blood adequately to supply the brain and other organs of the body. Almost
all heart attacks occur in people who have coronary artery disease (coronary
atherosclerosis). So, this photo essay will review the structure (anatomy) of
the normal coronary artery, the structural abnormalities (pathology) of the
coronary artery in atherosclerosis, and the effect of these abnormalities on the
heart.
What are the structures and functions of a normal coronary artery?
The coronary arteries carry blood to the heart to supply oxygen and necessary
nutrients. As seen in Figure 1, the wall of a coronary artery has 3 distinct
layers: the inner (intima), middle (media), and outer (adventitia) layers. The
wall of the artery surrounds the lumen of the artery, which is the channel
through which blood flows.
Figure 1: Normal Coronary Artery
Cross-sectional Microscopic View
In Figure 1, smooth muscle is red, and connective (supporting) tissue is black (elastic) or blue (collagen).
The intima is best seen in the close-up view in Figure 1. It is composed
of a layer of so-called endothelial cells that covers the artery's inner
(lumenal) surface, connective (supporting) tissue (collagen and elastin), and a
layer of compact elastic tissue called the internal elastic lamina (IEL). In the
past, the intima was thought to be simply a passive layer whose major purpose
was to serve as a barrier. Now, however, we know that the endothelial cells
actually keep track of the pressure, flow, and "health" of the artery.
Moreover, endothelial cells secrete chemicals that can adjust the function of
the artery (e.g., vasodilator chemicals to widen and vasoconstrictors to narrow
it) and growth of the artery wall (e.g., growth factors).
The media (M) is a layer made up primarily of smooth muscle cells (SMCs). The
muscle can contract and relax to control the blood pressure and flow in the
artery. Elastic tissue and collagen in the media, along with elastic tissue in
the IEL, increase the elasticity and strength of the wall of the artery, as the
artery contracts and relaxes. The adventitia is a layer of connective tissue and
cells (e.g., SMCs) that produce this connective tissue. The adventitia contains
potent factors, including one called tissue thromboplastin, that promote blood
clotting. The clots are useful when the artery becomes injured because they can
limit excessive bleeding from the injured artery.
Next: What happens to the coronary artery in atherosclerosis? »
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