Coronary Artery Disease

Description

The heart is a muscle and like all muscles it needs blood to function. Blood comes to the heart from two major arteries – the left and the right coronary artery. The left coronary artery splits in two to form the left anterior descending artery (LAD) and the circumflex artery. Each of these major arteries has branches and the number of branches varies from person to person.

Coronary artery disease (CAD), arteriosclerosis, atherosclerosis and hardening of the arteries all refer to the build up of calcium and cholesterol in the walls of these blood vessels that bring blood to the heart. The build up of these materials (plaques) causes the blood vessels to narrow and as a result less blood is delivered to the heart.
If the artery is blocked completely it will cause a heart attack (or myocardial infarction). When this happens the heart muscle that was getting blood from the blocked artery dies. Sometimes the blockage limits blood flow but does not completely close off the artery. When this happens the patient will experience chest pain (or angina).

History

The Egyptian princess Ahmose-Meryet-Amon, who lived in 1580 BC, is the oldest example of a person with coronary artery disease. It is surprising that she developed blockages without many of the modern risk factors for coronary artery disease. Today we know that there are two major components to coronary artery disease: genetics and environment.

Genetics is the component of heart disease that we do not control. But a family history of heart disease is an indication that the patient has a higher risk of developing coronary artery disease.

On the other hand many of the environmental contributors to heart disease are within our control. Three of the best-known risk factors are diet, smoking, and lack of exercise.

Anatomy

The two major arteries to the heart are the left and right coronary arteries. The left coronary artery splits into the left anterior descending artery (LAD) and the circumflex artery. Each of these arteries has branches too. How many other major branches there are varies from person to person, and in 15% of people the right coronary artery is small and almost all the blood supply to the heart comes from the left coronary.

Often when doctors refer to 2 and 3 vessel disease they are not referring to the number of branches that are narrowed but to the number blockages in the major arteries of the heart – LAD, circumflex and right coronary arteries.

Symptoms

The best-known symptom of coronary artery disease is angina – chest pain. Unfortunately many people think that this is the only symptom and assume that since they did not have “chest pain” they don’t have a problem with their heart.

It is important to know that some people with coronary artery disease don’t have any symptoms and many others have symptoms that they would not describe as chest pain. Symptoms like: chest pressure, chest tightening, difficulty catching your breath, jaw pain, jaw numbness, left arm numbness or tingling, shoulder pain, and the list goes on. Women are less likely to have the traditional typical “chest pain”.

The key is to remember if you have risk factors for coronary artery disease – like a family history of heart disease or a personal history of smoking or obesity- and you develop symptoms that occur with activity you should see your doctor.

Treatment Options

Prevention:
The best treatment is prevention. We know that communities who live in the Mediterranean have a lower incidence of heart disease because of their diet. A lifestyle that incorporates a heart healthy diet, exercise and avoidance of tobacco products is the best treatment to prevent heart disease and prevent further progression of the blockages that have already developed in the arteries to the heart. So it is never too late to change you lifestyle. You can still see benefits even after you have developed coronary artery disease.

However it is important to realize that once you develop coronary artery disease you might need more than just a change in lifestyle to treat the blockages that have developed.

Medical Management
There are a number of medicines that help relieve symptoms of coronary artery disease (like nitroglycerin) and others that reduce the workload of the heart (like beta-blockers). The choice of medications is selected based on each individual patient. Although an attempt is made in most patients to put them on aspirin, a medication to lower cholesterol (statin), a beta-blocker and a class of drugs called ACE inhibitors.

Angioplasty & Stents
Sometimes narrowed arteries can be opened by inflating a balloon in the artery and squishing the plaque (calcium and cholesterol deposits) against the wall and in this way opening up the artery so it can bring more blood to the heart. Often to prevent the plaque from reclosing the artery after a balloon angioplasty, a stent is placed to hold the artery open. A simple way to think of the stent is as a strut or brace that hold the artery open. In order to reduce the rebuild up of plaque and clot patients must take medications that reduce the body’s ability to make clot.

Angioplasty and stenting are done by inserting a needle into the leg artery in the groin, or in the artery at the wrist. A wire is passed through the needle and fed back to the arteries that bring blood to the heart. This wire is used a guide to pass and position the balloon and wire stents.

Coronary Artery Bypass Surgery
For some patients with narrowed or blocked arteries to the heart the best option is coronary artery bypass surgery (CABG –pronounced cabbage). CABG is using a second blood vessel (conduit) from somewhere else in the body to bring blood around the narrowed coronary artery. Essentially one end of the second blood vessel (conduit) is attached to the coronary artery above the blockage and the other end is connected to the coronary artery below the blockage – hence a bypass. It is not a replacement of the blocked arteries.

Indications for Surgery

Coronary artery bypass surgery is one of the best-studied operations in the history of medicine; and because it is so well studied we are able to predict who would benefit the most from surgery as opposed to medical treatment or angioplasty.

There are only two reasons to operate: 1. An operation will make the patient live longer or 2. It will improve the quality of the patient’s life.

Whether bypass surgery will make a patient live longer or improve the quality of their life is determined by a number of factors: location of the artery narrowing, heart function, all the patient’s other medical problems, etc. Needless to say because of all these many variables there is no one formula and so the decision to operate is made patient by patient. Therefore we recommend that all patients review their coronary artery disease with their primary care doctor, their cardiologist and their surgeon before assuming that medical therapy, angioplasty or surgery is the best option for them.

Surgery

Anesthesia
Coronary artery bypass surgery is performed under general anesthesia. The level of anesthetic is deep enough that it suppresses the body’s breathing center; therefore the patient is placed on a breathing machine (ventilator) for the duration of the operation. Once the patient is asleep their skin is cleansed with an antiseptic solution and covered with sterile barriers.

Getting to the Heart
The heart, like the brain, is a protected organ. The heart is protected by the chest wall – ribs, breastbone (sternum) and backbone (spine). In order to work on the heart it is necessary to go through one of these protective barriers. Obviously because the spine houses the spinal column it is not a suitable approach. The usual approach is to divide the breastbone (sternum) since this gives the best access to the heart and all the major blood vessels.

Minimally Invasive Approaches
Other approaches include opening the chest between the ribs but this gives limited access to all the coronary arteries and is therefore not suitable for all patients. Many of these other approaches to the heart, other than through the breastbone, are called “minimally invasive”. The operation is the same whichever approach is taken; the only difference is the way the surgeon gets to the heart. We encourage patients to discuss the various approaches to the heart with their surgeon.

The next step, after the chest is opened is to get the second vessel that will be used to bypass the narrowed coronary artery. This second vessel can be: the artery that runs along the inside of the chest (the internal mammary artery or IMA); vein from the legs (saphenous vein); or one of the arteries that brings blood to the hand (the radial artery). Each of these has different advantages and disadvantages.

Internal Mammary Artery
The internal mammary artery (IMA) or internal thoracic artery (ITA) refers to the small arteries that run along the underside of the breastbone. There is one each side. Whenever possible we like to use this vessel (IMA) to perform the bypass because it is more likely to stay open over time, and when it is used to bypass the left anterior descending artery (LAD) it improves patient survival. In general, we like to use both internal mammary arteries (IMA) if we can. But there is a slight increase in wound and bone infection if both arteries are used so we are more selective when we decide to use the second IMA.

Saphenous Vein
The saphenous vein is the large vein that brings blood back from the leg to the heart. The leg has two main vein systems to bring blood back to the heart, the superficial system (which includes the saphenous vein) and the deep system. Fortunately we can take the saphenous vein from the leg and use it to bypass the blocked arteries in the heart without significantly affecting the legs.

In the past these veins were taken out of the leg by making an incision from the ankle to the groin. Today we remove the vein using an endoscope – a lighted tube, that allows us to remove the entire vein through a small 1 inch incision near the knee. Veins, partly because they are designed to handle blood at a lower pressure than arteries, do not stay open as long when used as a bypass graft (conduit). A rule of thumb about vein grafts is that at 10 years: 1/3 will be open without disease, 1/3 will be open with some disease and 1/3 will be closed.

Radial Artery
In most patients, the blood supply to the hand comes from two arteries: the radial and the ulnar artery. We test the circulation of the hand before taking the radial artery, because in a small portion of patients the hand needs both arteries. In these patients the radial artery cannot be safely used. Sometimes there is mild hand numbness; therefore we prefer to take the artery from the patient’s non-dominant hand (the one they don’t use to write with).

Other Bypass Conduit
There are a number of other blood vessels that can be used, like the artery along the stomach wall, the vein behind the calf muscle, and even man made grafts. Unfortunately these do no stay open very long and so we do not use them unless we have a shortage of usable conduit.

Cardiopulmonary Bypass
Once the second vessel (conduit) to be used for the bypass has been taken out the patient is connected to the heart-lung bypass machine (cardiopulmonary bypass). Although the name for this system sounds like the operation (coronary artery bypass) they are not the same. The heart-lung bypass system is a machine that performs the function of the heart and the lungs allowing the surgeon to stop the patient’s heart to work on it, without affecting the rest of the body, which still needs to get blood and oxygen while the operation is being performed.

First the surgeon gives a drug called heparin. This prevents the blood from clotting. Next a tube is connected to the main blood vessel that distributes blood to the body (the aorta), and a second tube is connected to the chamber where blood without oxygen collects when it returns from the body to the heart (the right atrium). The patient’s blood is taken from the right atrium, run though an oxygenator (that allows the blood to get oxygen and get rid of carbon dioxide) and then the blood rich in oxygen is pumped back into the aorta. This is done in a continuous flow, and takes blood around the heart and the lungs, hence heart–lung bypass machine.

Coronary Artery Bypass Grafting
Once the patient is on the heart-lung bypass machine the heart can be stopped for a short time by giving the heart a high potassium solution. This allows the surgeon to work on the heart while it is not beating.

The surgeon then sews one end of the vein (or IMA) to the side of the narrowed coronary artery. The other end of the vein is then sewn to the aorta. Now when the heart beats, blood will flow out the aorta and into the vein graft going around the narrowing in the coronary artery and bring blood to the heart muscle beyond the narrowing.

Off-Pump Coronary Artery Bypass (OP-CAB)
Another technique is to do the operation while the heart is beating and the lungs are breathing. This technique, called off-pump coronary artery bypass (OP-CAB), avoids using the heart-lung machine. While the surgeon is sewing the bypass graft, a small footplate, like the one on a sewing machine is used to stabilize the artery.

The entire operation is done with magnifying loops, because the coronary artery is about the size of a piece of spaghetti and the stiches used to sew the vein to the artery are about the size of a human hair.

Closing the Chest
Once the bypasses have all been completed the surgeon allows the potassium to wash out of the heart and it will start to beat on its own. Sometimes the heart will need a low voltage shock to get it into a regular rhythm. Once the heart has resumed the work of pumping blood to the lungs and the body, the heart-lung machine is switched off and the tubes that connected it to the patient are removed.

Protamine, a medication that reverses the effects of heparin, is given. This will make the blood start to clot again. Because there can still be some oozing that can cause blood to collect around the heart and push on it, a number of tubes (chest-tubes) are left in the space around the heart and lungs. Once there is no sign of bleeding they are removed one or two days after the surgery.

The breastbone it then brought back together and wrapped with wire to hold it in place until it heals. The muscle and skin are then closed. The body will absorb all the stitches.