The heart is a muscle, not unlike the muscles in your leg or arm. Any of these muscles, including the heart, is composed of millions of small cells which contract, or shorten, under the proper conditions. A muscle cell, (also known as a "myocyte") can physically shorten due to the unique component of proteins contained in that type of cell.
These proteins (called "actin" and "myosin") slide over each other in a unique manner, foreshortening the length of the cell in the process. When millions of such cells act simultaneously, the muscle body shortens, and develops a force of contraction. This is the same mechanism that occurs when you raise your arm, walk, lift, etc.

In the heart, the muscle fibers are aligned in a circular manner to form in a unique conical shaped chamber.
As the heart muscle cells contract in unison, blood is forced out of the chamber into the vascular tree, and from there it flows to every organ and cell in the body.
In essence, the vascular tree is the "highway" bringing "food" or "nutrition" to the body (in the form of chemicals transported in the blood).
In this analogy, the heart is then the "pump or engine" which generates the force needed to move the blood along the vascular highway to the rest of your body.
The task of continuously pumping the blood to the body requires a great deal of energy. The heart must have its own source of blood to bring nutrients to each heart muscle cell. A normal heart in an average sized person will pump 4 to 5 liters of blood per minute. And the average heart will beat almost 4 million times per year. It is estimated that the energy required to continuously pump blood at these rates is almost 5 watts of power per hour. The substrate for this astronomical effort comes exclusively from the chemical byproducts of nutrition which are carried to the heart muscle cells by way of the vascular system.
The main chamber for pumping oxygen-rich red blood to the body is called the left ventricle. After the blood exits the left ventricle, it enters the main channel of the vascular highway, called the aorta. The aorta is a tube of specialized tissue capable of carrying the entire 4 or 5 liters per minute to the rest of the body under a blood pressure of 140 millimetes of mercury (somewhat like the pressure in a garden hose). The very first branches arising from the aorta are small "feeder or nutrient" vessels, called the coronary arteries which double back onto the surface of the heart. There are two main coronary arteries, one to the left ventricle (called the left main coronary artery) and another called the right main coronary artery which supplies mostly the right ventricle but also part of the undersurface of the left ventricle. These main coronary artery give rise to several branches which then dive into the heart muscle, bringing vital nutrients to each muscle cell.
When coronary artery disease occurs, the channel inside these small but vital arteries becomes progressively "plugged" with plaque material. This process is known as atherosclerosis. In this disease, the inner channel of the coronary artery becomes obstructed by progressive buildup of cholesterol and other body fats which invade the lining of the blood vessel wall. Over time, the bodies own inflammatory response to these fatty molecules leads to enlargement and protrusion of the plaque into the flow channel of the artery. If the plaque is large enough, the entire channel can become obstructed to blood flow. The heart muscle cells normally fed by this vessel are no longer able to receive vital nourishment from the blood stream. Under situations where the demand for blood supply is increased, such as during physical exercise and/or emotional stress, the blocked arteries may not be able to deliver enough blood to meet the nutrient needs of the heart muscle cells at that time. This situation is called ischemia, and is best defined as a mismatch between nutrient demand and supply. In that setting, most (but not all) patients will notice chest pain or pressure with futher exercise. This pain is called angina pectoris (or just angina for short). If the obstucted artery closes suddenly, then permanent damage to the muscle cells in that region of the heart can occur. This process is known as a heart attack,or myocardial infarction.
After evaluation of the extent of coronary artery disease, some patients will need intervention to prevent further attacks. With new, modern tools at our disposal, there is not always a need to perform surgery. However, for many patients surgical reconstruction still provides the best long term result. Below, I will briefly discuss the type of diagnostic workup usually performed prior to the decision to operate.
.Diagnostic Workup

Any surgeon intending to reconstruct the circulation to the heart will need a road map of the blood vessels and the location of the blockages. The test most frequently used for this information is called a coronary angiogram. In this test, the small blood vessels feeding the heart are imaged with special x-ray techniques. In summary, the coronary arteries are injected with a special dye solution which shows up on x-ray film. As the dye travels down the branches of the coronary artery itself, moving pictures (or cineangiograms) are taken with the x-ray camera. The entire series of angiographic movies are reviewed by the cardiologist and decisions made about the relative benefits of different treatments.

To repeat the movie click the coronary angiogram of the heart.

History

Surgical reconstruction of the blocked arteries began in the late 1960's and has proven to be remarkably successful. The operation we call Coronary Artery Bypass Grafting (CABG or "cabbage") is the foundation of surgical management. The goal of this operation is to restore the blood supply to the heart muscle by creating a new route (aka bypass) for the blood to flow around the blockages. CABG is not only the most common operation performed on the human heart, it is currently the most common procedure of any kind in the USA. Last year, over 200,000 CABGs were performed nationwide.
The first surgeon to attempt a direct hookup to the coronary artery was the famous experimental vascular surgeon, Alexis Carrel. In the early 1900's Dr. Carrel developed most of the suturing techniques for small vessels hookups that are still used today, In 1910, Dr. Carrel reported to the American Surgical Association his first attempt to suture a carotid artery graft to the left coronary system in an experimental animal. Although the animal did not survive, the principle of directly grafting into the coronary artery branches was demonstrated. Although this particular contribution went largely unnoticed for over 50 years, Alexis Carrel was eventually honored for his lifetime accomplishments in developing the techniques of vascular surgery with the Nobel Prize in Medicine.
During the 1930's and 1940's, there were several attempts to bring new blood supply to the heart, most notably the Beck procedure and the Vineberg procedure. However, these procedures did not directly connect a new source of blood to the heart arteries, and the success rates were not very high. In 1940s and early 1950s, the innovative Canadian surgeon Gordon Murray made two major advances. The first was the introduction of the powerful anticoagulant (blood thinner) heparin into the field of vascular surgery. Secondly, Murray reported initial success with direct suturing of a graft to the coronary artery in dogs. However, widespread clinical usage of Murrays discoveries was delayed due to the primitive and largely unavailable angiogragraphy techniques present at that time. In 1956, Thal and Demikhov bot reported similar success in connecting the internal mammary artery to the coronary artery in experimental animals.
The development of modern surgical techniques awaited major developments in x-ray diagnostic techniques. It was Dr. Mason Sones at the Cleveland Clinic who accidently injected angiography dye into the mouth of the coronary arteries for the first time in a living patient. Aware of the significance of this observation, Dr. Sones went about designing catheters and techniques to routinely x-ray the various coronary arteries in human patients. The utility of the Sones (and later) techniques for safely documenting coronary artery blockages in humans was readily appearant and the procedure gained immediately popularity throughout the world.
Meanwhile, other researchers were pursuing a means of supporting the circulation while the heart beat was temporarily stopped. Using mechanical devices to pump the blood and restore the oxygen content of the blood, the artificial heart-lung machine was gradually designed and modified in the 1950's and early 1960's. At first, the heart-lung machine was used by surgeons to correct congenital anomalies of the heart, such as the birth defects seen in "blue babies". However, as improvements were made in heart-lung technology, its use spread to other types of heart operations. Although most of the initial cases of coronary artery surgery took place on the beating heart without the benefit of the heart-lung machine, surgeons quickly saw the advantages offered by performing these reconstructions when the heart was motionless.
The first courageous attempt to directly suture a saphenous vein bypass graft into the coronary circulation in humans is credited to Dr. David Sabiston at Duke University in 1962. His first vein bypass patient died from a stroke, and Dr. Sabiston did not officially report his technique until 1974. In 1963, Dr. Lester Sauvage was the first investigator to report the results of a whole series of direct coronary artery vein bypass grafts in an animal model. In 1966, Kolessov in Leningrad, USSR reported the use of the internal mammary artery (from the inside of the chest wall) to create a bypass to the coronary artery in 6 patients, with 5 survivors. In May 1967, Dr. Renee Favalaro, an Argentinian working at the Cleveland Clinic, reported initial results in a small series of patients where coronary bypass was performed in human patients with the saphenous vein from the leg. Following these important milestones, many investigators began to expand on the concept of reconstructing the blood supply to the heart with bypass grafts. The results of these pioneering efforts were immediately obvious to the medical community. Surgical reconstruction of the blood supply to the heart was highly effective in relieving angina. Soon, the primary treatment of unrelenting angina was through surgical bypass procedures. Now there are many other treatment options, but surgery remains the mainstay for a large group of patients for which other options are not effective.
How It Works

Coronary Artery Bypass Grafting doesn't remove the obstructing blockages in the arteries. The procedure "reroutes" the flow of blood by using a "detour" pathway. Typically, the blockages occur in the first centimeter or two of the major branches feeding the heart. The smaller branches are usually not involved until very late life. Thus, it is possible to hook a new source of blood into the artery just beyond the last major blockage. Blood flows into the artery through a different path (such as a vein bypass graft) and reaches the heart muscle tissue where it is needed. The heart doesn't care how the blood gets there, as long as it gets what it needs during times of peak demand. Once the volume and pressure of blood flow is restored, the symptoms of exertional chest discomfort are relieved . The most common material used to build this new pathway is a vein from the lower extremity. In each of us, there is a long straight vein called the Greater Saphenous Vein (or GSV) running from just inside the ankle bone up to the groin. This vein is just one of a large series of veins in the lower extremity. However, the GSV is the right size, shape, and length for use as a bypass conduit. The other major vessel used as a bypass graft is the Left Internal Mammary Artery (LIMA). Recent studies have shown that the LIMA is more resistant to atherosclerotic deposition than even the native coronary arteries. This vessel courses alongside the undersurface of the breastbone (aka sternum). By detaching the lower end of the LIMA, the vessel can be transplanted to the surface of the heart.

Regardless of which conduit is used for the bypass, the main advantage offered by this surgical approach is the restoration of blood supply to the heart. The vein or mammary artery provide a new and unobstructed route for blood flow. When the surgeon connects the bypass to the native coronary artery beyound the obstruction, blood has a new path in which to flow into the blood vessel beyound the blockage. Then when the heart demands more blood flow, the situation can be met by the new source of blood flowing through the bypass graft. It is important for the surgeon to provide a bypass for each major branch that is obstructed. In that way, the whole heart will have more blood supply, and the anginal (chest) pains will be relieved.

Technical Aspects

Although possible, it is difficult to sew tiny arteries and veins together when the heart is still beating. Many of the initial CABG operations in the 1960s were done without stopping the heart beat. However, the invention and improvement of the heart-lung machine permitted surgeons to temporarily stop the heart from beating while these delicate hookups were created. The heart-lung machine is connected to the patient before the actual bypass grafts are created. During the operation, the patients vital functions become fully supported by this "artificial circulation" while the heart is rested and the bypass grafts are created. After completion of the grafting, the heart contractions are restored and the circulation transfered back to the native heart and lungs. The pump equipment is removed from the patients vascular system, the anticoagulant is reversed, and the operation is finished.

A typical CABG operation begins with a vertical opening into the front of the chest. The breast bone (aka "sternum") is divided with a specialized (reciprocating) saw, similar to a "jig" saw used in woodworking (only designed just for this incision). The split sternum is spread open with a device that functions like a winch. The soft tissues in front of the heart are parted, and the membrane surrounding the heart (the pericardium) is incised. Next, the surgeon removes the Internal Mammary Artery from the chest wall to provide a donor artery for grafting.

Simultaneously, an assistant surgeon proceeds with harvesting additional conduit, usually the Greater Saphenous Vein (GSV) from the inside of the calf or thigh. This vein is long, straight, and the proper caliber for use as a donor graft to the heart. In the average patient, there is ample length to reach all the potential target vessels on the heart. In addition, the leg contains many redundant veins, so removal of the GSV does not impair the return of blue blood from the extremity.

After all the donor vessels are harvested, the patients blood is thinned with a large dose of the potent anticoagulant heparin. This renders the blood incapable of clotting when exposed to the plastic tubing and surfaces of the heart-lung machine. As described above, the patients circulation is connected to the heart-lung bypass circuit, and the body placed onto the support machinery. Then the body temperature is lowered (by refrigerating the blood as it circulates through the machine). In addition, blood flow to the heart is separated from that going to the rest of the body by a vascular clamp applied to the aorta just below the insertion of the arterial return cannula. The coronary arteries are then perfused with a cold potassium solution. The heart is immediately rendered motionless, cold, and relaxed. The body is preserved by the nutrient flow provided by the heart-lung circuit, while the heart is preserved by the low temperature and other conditions managed by the surgeon.

Next, each target vessel is identified as it runs across the surface of the heart. For each intended bypass, the surgeon makes a tiny opening into the front wall of the target coronary artery with a very fine knife. The opening is expanded with specialized scissors. A donor vessel, either vein or IMA is stitched to this opening with delicate fine suture material. Currently, the best suture material is made from polypropylene and is finer in diameter than a human hair. After all the grafts are sutured to the heart arteries, the vascular clamp is released, allowing blood to flow into the native heart arteries again. For the IMA, it is already connected to the native circulation proximally, so it can immediately begin its job of perfusing the heart.

Internal Mammary Artery grafts are already attached at their origin from the main artery to the arm (the subclavian artery). Blood flowing through the IMA directly comes from the subclavian artery. However, GSV grafts are detached at both ends. After connecting one end of the vein to the coronary artery, the other end must then be connected to a source of red blood. This is done by partially occluding a segment of the ascending aorta with a specialized, curved vascular clamp. Holes are created in the front wall of the aorta, and the veins are anchored to these openings with fine suture. After releasing this partially occluding clamp, the veins fill with red blood from the aorta and deliver this blood to the coronary arteries downstream.

After the heart has had a chance to recover from the temporary arrest period, the heart-lung circuit can be gradually withdrawn. When the heart is beating strongly again, then the heart-lung machine is stopped, and the equipment removed. The anticoagulant (heparin) is chemically reversed (with a drug called protamine). The surgeon then inspects and controls any remaining bleeding. Finally, the wounds are closed and the patient sent to intensive care for recovery.

Discussion

The average patient, without any major post-operative problems, can leave the hospital in about 6 days from surgery. It will take about another 2 to 3 weeks for most patients to feel stronger and regain normal body habits, such as appetite, sleep patterns, bowel patterns, etc. For patients who work in non-physical jobs, many can return to employment within 4 to 6 weeks of surgery. Some patients return to work even earlier, depending on their level of energy. Usually, antianginal medications are no longer needed. However, high blood pressure and diabetic medications will often continue as they did pre-operatively. After full recovery, the vast majority of patients (over 90%) can return to full and active lifestyle, including exercise, travel, and employment.
Over 200,000 CABG operations are performed annually in the USA. Many of you will surely know relatives, friends, or neighbors who have undergone this operation. Millions are now living longer and healthier as a result of the surgical treatment of their blocked coronary arteries. Coronary Artery Bypass Surgery continues to provide a safe and effective treatment for a large number of people for whom medications and other treatments are not satisfactory. With overall improvements in technique and peri-operative care, the vast majority of patients can undergo this complex operation with a high margin of safety and an excellent chance for full recovery.

this literature is referenced from HEART SURGERY FORUM WEB PAGE.
Authored by:M Levinson md.