Circulation. 2007;116:e340-e341
doi: 10.1161/CIRCULATIONAHA.107.719930
(Circulation. 2007;116:e340-e341.)
© 2007 American Heart Association, Inc.
Natural Bypasses Can Save Lives
Steffen Gloekler, MD;
Christian Seiler, MD
From the Department of Cardiology, University Hospital Bern, Switzerland.
Correspondence to C. Seiler, MD, Professor and Cochairman of Cardiology, University Hospital Bern, Bern, Switzerland. E-mail christian.seiler{at}insel.ch
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Introduction
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Blood to the heart muscle is provided by the left and right
coronary arteries, which arise from the aorta and then branch
into increasingly tinier vessels. Each coronary artery supplies
blood to its own area of muscle (
Figure 1). In humans, very
small, hairlike vessels (capillaries) are often the only interconnections
between the coronary arteries and their service areas. Sometimes,
however, larger vessels interconnect the supplied areas. These
vessels are called "collateral vessels" or "natural bypasses."
Only these collaterals, not the capillary network, are capable
of delivering an adequate amount of blood to the heart muscle.
The extent of these natural bypasses varies from person to person
and depends on individual conditions, such as hereditary factors,
the degree of physical activity, and the existence of constrictions
in the main coronary arteries, called "coronary artery disease."
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Figure 1. Influence of collateral supply on infarct size. A, Occlusion of a coronary artery with subsequent myocardial infarction. Before the occlusion occurred, the area of infarction (depicted in gray) was not supplied sufficiently by collateral vessels; thus, the size of the infarct comprises a large area (that is, the entire area at risk). B, Occlusion of the same coronary artery at the same site, but in this case, the area at risk was well supplied by collateral vessels (arrows). Therefore, this patient will have no infarction at all.
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Myocardial Infarction Is a Major Cause of Death
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In industrialized countries, coronary artery disease is a major
killer. The disease is characterized by a general inflammatory
process of the entire coronary artery system, with development
of local deposits (called "plaques") of lipids, cells of inflammation,
connective tissue, and calcium. This can lead either to progressively
slow narrowing of the affected artery (which is typically sensed
as angina pectoris) or a sudden rupture of a plaque (
Figure 1)
caused by its instability. In the latter situation, the downstream
blood flow is abruptly blocked (which is the classic "heart
attack" or myocardial infarction;
Figure 1).
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Factors That Determine the Size of an Infarct
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As a consequence of such a blockage, the section of heart muscle
normally supplied by the vessel lacks "fuel," that is, oxygen
and nutrients, and it finally dies. If the patient survives,
the final stage is a loss of cardiac pumping strength and a
scar that replaces the former muscle. The size of an infarction
is not the same in every case: It is mainly influenced by the
size of the blocked artery (that is, a larger artery supplies
a larger area of muscle, the so-called area at risk), the duration
of the blockage (that is, the damage is smaller when rapid reopening
of the artery occurs), and importantly, the extent of blood
flow through collaterals from neighboring vessels (that is,
the more that collaterals can "step into the breach" to supply
the starving muscle tissue in need, the smaller is the size
of the infarction;
Figure 2). In the ideal case, a very good
collateral supply to the area at risk can make the infarct size
shrink to zero when there is a sudden blockage of an artery.
In the worst case, when no or a very low collateral flow to
the starving area of infarction is available, the infarct involves
the entire area at risk of the supplying vessel, which is blocked.
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Figure 2. Coronary angiography with an example of the muscle- and life-saving impact of collaterals. In this patient, the right coronary artery (RCA) is filled with contrast agent. By a natural bypass, that is, the collateral channel (arrows), the left coronary artery (LAD), which is blocked at its origin (ring), is filled with blood. Without the collateral vessel providing blood to the large territory of the left coronary artery, this area would have died off; that is, the patient would have suffered a potentially deadly infarction.
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Established Treatments for Coronary Artery Disease
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Besides treatment with drugs, constricted vessels can be widened
by inflating a balloon on a catheter (angioplasty) and, in most
cases, also placing a wire tube (stent) to keep the vessel open.
In an infarction, this is the superior therapy, because blood
flow to the heart muscle is restored as quickly as possible,
and damage can be limited. Coronary artery bypass grafting (CABG;
pronounced "cabbage") operation is needed if numerous severe
constrictions near the outlets of the coronary arteries are
present. Altogether, these technologies have led to enormous
progress in the treatment of the disease in the last 30 years.
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Treatment Limitations
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As in every catheter-based intervention or surgical operation,
there are risks related to the procedures. Apart from that,
approximately one fourth of all patients are not suitable for
these revascularization procedures at all. These procedures
do indeed repair the local problem of narrowings, but they do
not alter the natural progression of the disease. Alternative
treatment practices are therefore required to alter the course
of coronary artery disease, alleviate angina pectoris, and thereby
decrease the number of deaths due to infarction.
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How to Turn the Capillary Network Into Collaterals
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When there is increasing traffic volume on a highway, it may
make sense to make the highway into a larger freeway to allow
a higher traffic volume. In short, the same happens to the coronary
arteries: When blood flow is increased, the inner layer of vessel
cells (endothelial cells) sense this necessity and start the
process of enlarging from capillaries into genuine collateral
vessels. In response to endurance exercise training (such as
running, bicycling, swimming, and hiking), blood flow is increased,
which leads to a conversion from capillaries into collaterals.
This is a very elegant treatment everybody can accomplish. It
reduces the chances of the occurrence of angina pectoris, myocardial
infarctions, and death. Beyond the interventional, surgical,
and medical treatments against coronary artery disease, this
collateral training is a natural and valuable therapy that many
patients can apply by themselves, for themselves, if only they
are aware of it.
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Key Points
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- As a pump, the heart muscle is critically dependent on the coronary arteries for sufficient blood supply.
- Narrowing of the coronary arteries by deposits (plaques) can starve the heart muscle of oxygen and nutrients. This results in chest pain (angina pectoris).
- A heart attack results when a diseased coronary artery is blocked completely. As a consequence, the portion of the heart muscle normally supplied by this artery dies (myocardial infarction).
- After a myocardial infarction, a certain mass of muscle is lost forever. Depending on infarct size, quality of life and life expectancy can be shortened.
- Collateral training results in a better blood supply of the heart and thus demonstrably fewer heart attacks, less severe loss of valuable heart muscle, better quality of life, and higher survival rates.
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Footnotes
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The information contained in this
Circulation Cardiology Patient
Page is not a substitute for medical advice, and the American
Heart Association recommends consultation with your doctor or
healthcare professional.
Related Article:
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Issue Highlights
Circulation 2007 116: 1213.
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Introduction
Myocardial Infarction Is a...