Facts and definition of heart disease
- Heart disease develops when a combination of fatty material, calcium, and scar tissue (plaque) builds up in the arteries that supply the heart with blood. Through these arteries, called the coronary arteries, the heart muscle (myocardium) gets the oxygen and other nutrients it needs to pump blood. The plaque often narrows the artery so that the heart does not get enough blood.
- This slowing of blood flow causes signs and symptoms of
chest pain, or
- If plaque completely blocks blood flow, it may cause a
heart attack (myocardial infarction) or a fatal rhythm disturbance (sudden cardiac arrest).
- A major cause of death and disability, coronary
heart disease claims more lives in the United States than the next 7 leading causes of death combined.
- As a child, the inner lining of the coronary arteries is quite smooth, allowing blood to flow easily. As a person ages, the
cholesterol and calcium content in the walls of the coronary arteries increases, making them thicker and less elastic.
- Unhealthy habits, such as a
diet high in cholesterol and other
smoking, and lack of
exercise accelerate the deposit of fat and calcium within the inner lining of coronary arteries.
- This process is known as
atherosclerosis, or hardening of the arteries.
- The deposits, or plaques, eventually obstruct the blood vessel, which begins to restrict blood flow.
- Plaque is like a firm shell with a soft inner core containing cholesterol. As blood hits it during each heartbeat, the plaque may crack open and expose its inner cholesterol core, which promotes blood clotting. Clots may further reduce blood flow, causing severe pain (angina), or even block it all together.
What causes heart disease?
Coronary heart disease is caused by any problem with the coronary arteries that keeps the heart from getting enough oxygen- and nutrient-rich blood. The most common cause by far is atherosclerosis. Lack of sufficient blood is called ischemia, so coronary heart disease is sometimes called ischemic heart disease.
The cause of coronary heart disease is related to multiple risk factors. The following are the most common:
- Heredity: Coronary heart disease runs in the family.
- High cholesterol: Levels of cholesterol in the blood are above healthy levels. This usually involves high levels of low-density lipoprotein (LDL), the bad cholesterol, and low levels of high-density lipoprotein (HDL), the good cholesterol.
- Tobacco abuse: This includes not only smoking any form of tobacco (cigarettes, cigars, pipes), but also chewing tobacco.
- High blood pressure (hypertension)
- Lack of regular exercise
- High-fat diet
- Type A personality (impatient, aggressive, competitive)
What are the symptoms of heart disease?
The most devastating sign of coronary heart disease is abrupt, unexpected cardiac arrest.
- Cardiac arrest commonly occurs in people who have had previous heart attacks, but it may occur as the first symptom of heart disease.
- Most people exhibit some symptom or discomfort.
- Symptoms usually occur during exercise or activity because the heart muscle's increased demand for nutrients and oxygen is not being met by the blocked coronary blood vessel.
More common symptoms of coronary heart disease include the following. No one person usually has all of these symptoms.
- Chest pain on exertion (angina pectoris), which may be relieved by rest
- Shortness of breath on exertion
- Jaw pain, back pain, or arm pain, especially on left side, either during exertion or at rest
- Palpitations (a sensation of rapid or very strong heart beats in your chest)
- Dizziness, light-headedness, or fainting
- Weakness on exertion or at rest
- Irregular heartbeat
Silent ischemia is a condition in which no symptoms occur even though an electrocardiogram (ECG, or heart tracing) and/or other tests show evidence of ischemia. Arteries may be blocked 50% or more without causing any symptoms.
When to seek medical care for heart disease
Call your health-care professional if you notice any of the following symptoms, which suggest angina:
- Chest pain, pressure or feeling of indigestion after physical exertion, which may or may not be relieved by rest
- Shoulder or arm pain involving left, right, or both sides during physical or mentally stressful activity
- Jaw pain, unexplained by another cause, like a sore tooth
- Shortness of breath after exertion or walking uphill
- Fainting spell
- Pain in the upper part of your abdomen
- Unexplained nausea, vomiting, or sweating
- Palpitations or dizziness
Call 911 or have someone take you immediately to a hospital emergency department if you have signs of a heart attack.
- The most crucial factor is time. Each year, thousands of Americans die because they do not seek medical attention quickly.
- Err on the side of caution and go to the hospital.
- This may prove to be the difference between life and death.
The most common symptoms of heart attack include the following:
- Unremitting or prolonged chest pain, chest pressure, or a feeling like heartburn
- Shoulder or arm pains (left or right) or upper abdominal pain that won't go away
- Shortness of breath after minimal activity or while resting
- Blackout spells
- Unexplained profuse sweating with or without nausea or vomiting
- Frequent chest pain or discomfort at rest
Heart Attack Warning Symptoms and Signs
Classic symptoms of a heart attack may include:
- Chest pain associated with shortness of breath
- Profuse sweating
The chest pain may be described as tightness, fullness, a pressure, or an ache.
Unfortunately, many people do not have these classic signs. Other signs and symptoms of heart attack may include:
- Jaw ache
- Pain only in the shoulders or arms
- Shortness of breath
How is heart disease diagnosed?
Your first symptom of coronary heart disease may be a heart attack or sudden cardiac arrest. This is why medical professionals use screening tests to detect the presence and severity of coronary disease before it causes problems or sends you to an emergency department with severe symptoms.
The symptoms of coronary heart disease are what medical professionals call nonspecific.
- This means the symptoms could be caused by many different conditions, some not related to the heart at all.
- Upon hearing your symptoms, your health-care professional (whether your primary care provider or a new provider in the emergency department) will begin a process of gathering information.
- The purpose of this is to rule out conditions and pinpoint the correct diagnosis.
- It includes asking questions about your symptoms, your medical and surgical history, your general health and specific medical problems, and the medications you take.
- It will also include a physical examination, an electrocardiogram (ECG), and probably lab tests and imaging tests such as X-ray or CT scan.
Physical exam may reveal evidence of weakened or irritable heart muscle, including sounds called gallops or murmurs. There may be evidence of congestion in the lungs.
The first step will be to rule out a heart attack or other life-threatening condition. The usual tests include blood tests, ECG, and, possibly, chest X-ray.
- Blood tests might check your blood cells, the chemical makeup of your blood, and enzymes leaking out of damaged heart muscle, that suggest that you are having a heart attack. Other tests might be ordered depending on the circumstances.
- ECG is a painless test that measures the electrical activity of the heart. It can reveal several different heart problems, including ischemia, heart attacks, rhythm disorders, long-standing strain on the heart from high blood pressure, and certain valve problems. It gives clues as to the underlying cause of cardiac symptoms. The test takes just a few minutes. You lie on a table with electrodes fastened to the skin of your chest, arms, and legs.
- Chest X-ray can show abnormalities in the size or shape of the heart and can show whether any fluid is building up in the lungs.
If you are having angina symptoms or your health-care professional suspects that you have coronary heart disease, you may have an exercise (treadmill) stress test.
- This test involves measuring ECG tracings before, during, and after stressing the heart by exercise.
- You will walk on a treadmill while connected to an ECG machine.
- This test is 60-70% accurate in showing blockages in blood flow in 1 or more of the 3 coronary arteries.
- Sometimes its readings may be falsely abnormal for people taking certain medications or who have certain medical problems not directly related to coronary heart disease.
Treadmill exercise stress test.
If other tests suggest blockage of the coronary arteries, you may undergo a nuclear (radionuclide) stress test.
- After a tiny dose of a radioactive tracer is injected into a vein, a special camera can identify the quantity of blood flow that reaches different parts of the heart muscle.
- The substance most often used is sestamibi, so this is often called a sestamibi (MIBI) stress test.
- You will have 2 tests, one with stress, or exercise (on a treadmill), and the other at rest.
- If you cannot exercise, you will be given a drug to temporarily stress your heart. The drugs used for this are adenosine (Adenocard), dipyridamole (Persantine), or dobutamine (Dobutrex).
- This test is expensive, but it is noninvasive, and its accuracy is quite good.
Stress nuclear imaging using single photon emission computed tomography (SPECT)
Results of a nuclear stress test from a person with angina. A significant defect in the amount of blood pumped during stress appears to a major blockage (stenosis) in the right coronary artery.
What other exams and tests help diagnose heart disease?
Stress echocardiography is an alternative to the nuclear stress test. Many people prefer this test because it does not use a radioactive agent.
- Echocardiography is a type of sonar that uses sound waves to bounce off walls and valves, creating an image of the heart as it beats.
- The movements of the ventricular walls are compared during stress and at rest. Wall motion drops during stress if the coronary artery supplying that part of the heart has significant obstruction.
- Like the other stress tests, the heart is stressed either by exercise on a treadmill or by administration of a drug.
Electron beam (ultrafast) CT scan (EBCT) is a noninvasive but somewhat controversial test. By measuring the amount of calcium deposited in the plaques of coronary arteries, it can detect blockages of only 10-20% of an artery, which may not show up in other tests.
- Generally, such minor blockages are treated medically; lifestyle changes and risk factor modifications are recommended to prevent worsening of the blockage.
- Because elderly people frequently have calcium in their coronary arteries without significant narrowing, EBCT is of limited value in this age group.
- The advantage of EBCT comes in screening young people with one or more heart disease risk factors.
Coronary angiography by cardiac catheterization is the best way to evaluate coronary heart disease.
- You will go to a hospital or an outpatient catheterization lab (for same-day surgery).
- Under guidance of an X-ray camera, a long, thin plastic tube (catheter) is threaded into the opening of your coronary arteries from a blood vessel in either your groin (femoral artery) or your arm (radial artery).
- Once the catheter reaches the coronary artery opening, it injects a small amount of iodine dye, which makes the coronary arteries visible on the X-ray screen.
- Pictures of the coronary arteries are then recorded in a computer for later review. The images show the diameter of the coronary arteries and any blockages narrowing them.
- Coronary angiography is an invasive test. In experienced hands, the risk of complications is less than 1%.
- It is the only test that helps a cardiologist to determine precisely whether to treat you with bypass surgery, a less-invasive technique such as angioplasty or stent placement, or just medications.
Coronary angiography in cardiac catheterization laboratory.
Coronary angiogram from a person with angina and an abnormal stress test showing 90% blockage in the right coronary artery (arrow). In the lower panel, the blockage has been treated with angioplasty (PTCA) and a stent was put in place (double arrow)
How can I prevent my heart disease from getting worse?
If you have coronary heart disease, following the recommendations of your
health-care professional is very important if you wish to improve your condition or prevent it from getting worse. If you notice any change in your condition, you may need further diagnosis or treatment.
The most important ways to reduce the risk of heart disease are in your control, not the control of your
- Lifestyle changes are the most powerful way to prevent heart disease from getting worse or of reducing the risk of getting heart disease in the first place.
- The phenomenal drop in the heart disease death rate over the past 30 years has been due more to reducing risk factors than to advances in treatment.
Everyone should take the following measures to lower the risk of heart disease:
- Eat a heart-healthy diet: This is the most important step you can take in lowering your risk.
- Lower your fat intake: Calories from fat should be less than 30% of your total calorie intake every day. This translates to less than 60 grams of fat per day for an adult.
- Lower your blood cholesterol to the recommended level, especially the LDL cholesterol: This keeps plaque from building up within your coronary arteries.
- Engage in regular exercise: This can reduce your risk of heart disease. Exercise strengthens the heart, makes it more efficient, and lowers your blood pressure and bad cholesterol (LDL), yet raises you good cholesterol (HDL). Check with your
health-care professional before beginning an exercise program. The American Heart Association recommends at least 30 minutes of exercise 3-5 times a week.
- Quit smoking: This also provides a very striking benefit. After only 3 years of not smoking, your risk of heart disease drops to that of a nonsmoker. Your
health-care professional can help you quit smoking by providing guidance on changing your behavior. Certain medications have been shown to help some people quit smoking.
- Control high blood pressure and diabetes: If you have diabetes, keep your blood sugar under control every day. You should know the value of your HbA1c, a measure of how your blood sugar is controlled; it should be less than 7.0.
- Take a low-dose aspirin daily: This can reduce your risk of heart attack. With aspirin, there is some risk of bleeding, so ask your
health-care professional before taking aspirin daily.
- No scientific clinical trial in humans has shown a beneficial effect of vitamins on the heart.
Note that hormone replacement therapy (HRT) was used for many years to prevent coronary heart disease and heart attack in women who had gone through menopause.
- Replacing certain hormones was thought to provide a heart-protective effect enjoyed by women before menopause.
- A research study that ended in 2002 found, however, that women who took HRT actually had higher rates of heart disease and stroke than women who did not take HRT.
- HRT is no longer recommended for prevention of heart disease.
Follow these dietary guidelines.
- Soy products help reduce LDL cholesterol.
- Eat a fruit plate or low-fat yogurt for dessert. Cut sweets and sugars to a minimum.
- Cook foods in olive oil or canola oil, which are high in monounsaturated fats. These fats decrease LDL and total cholesterol levels.
- Eat 1 or 2 servings of fish or seafood each week.
- Eat nuts that are rich in monounsaturated fats, such as hazelnuts, almonds, pecans, cashews, walnuts, and macadamia nuts. These nuts are healthful but high in fats. They should be eaten in small amounts.
- Cooking foods with garlic, which may have a slight cholesterol-lowering effect.
Alcohol may be taken in moderation.
- No more than two drinks per day for men and 1 drink per day for women is recommended to raise the good cholesterol (HDL).
- However, some people should not use alcohol. People who have liver or kidney problems, certain other medical problems, problems with alcohol abuse, or who are taking certain medications should not use alcohol.
- If you do not use alcohol, most medical professionals would recommend that you not start just for the benefits to your heart.
- If you have any questions about alcohol's positive and negative effects on your health, ask your
What medications reduce the risk of heart attack, stroke, or angina?
Coronary artery disease decreases blood supply to the heart from the blocked coronary artery. The lower blood flow may fail to meet the heart's demand for oxygen. Treatment aims to balance blood supply to the heart with heart oxygen demand, and prevent worsening of coronary heart disease.
Aspirin: When taken daily or every other day, aspirin reduces the risk of developing angina or heart attack by reducing the tendency of your blood to clot.
- It reduces the chance that a clot will form over a rupturing plaque in the coronary artery, a common underlying phenomenon in heart attack (myocardial infarction).
- Side effects of aspirin include ulcers or bleeding problems.
- Talk to your health-care professional before starting aspirin.
Beta-blockers: Beta-blockers decrease your heart rate and blood pressure, thus reducing your heart's demand for oxygen. Clinical trials have shown prevention of future heart attacks and sudden death.
Nitroglycerin: This medication reduces chest pain both by decreasing your heart's oxygen demand and by dilating the coronary arteries, increasing the oxygen supply.
- Sprays or tablets placed under your tongue are designed to be taken when you need instant relief from angina.
- Long-acting nitroglycerin tablets or skin patches work slowly over many hours.
Calcium channel blockers: Calcium channel blockers dilate the coronary arteries to improve blood flow. They also reduce blood pressure, and slow heart rate.
ACE inhibitors: Angiotensin-converting enzyme (ACE) inhibitors work by dilating blood vessels, increasing blood flow.
- They recently have been shown to reduce the numbers of cardiac events, heart attacks, and deaths in people with coronary heart disease, unrelated to their blood pressure lowering effect. Therefore, additional beneficial tissue effects on blood vessels and heart muscle is thought to occur.
- They are immensely useful in people with diabetes and those with weakened heart muscles.
Statins: Statin drugs work by reducing the amounts of lipids (cholesterol and other fats) in your blood.
- This changes the inner lining of the blood vessels so plaques are less likely to form or get large.
- They slow or stop the progression of coronary heart disease and also deter repeat heart attacks.
- Clinical trials have shown beneficial effects immediately after a heart attack or threatened heart attack, even before the fat lowering effect is maximal, meaning they stabilize the plaque.
- Examples include atorvastatin (Lipitor), pravastatin (Pravachol), simvastatin (Zocor), lovastatin (Mevacor), and rosuvastatin (Crestor).
What invasive medical procedures treat heart disease?
When angina symptoms worsen despite medications, you may need an invasive procedure in the cardiac catheterization lab to clear the blocked artery. These procedures are performed by a cardiologist, not a cardiac surgeon, and have fewer complications.
Coronary angioplasty (PTCA): This procedure is similar to coronary angiography (cardiac catheterization or a dye study to visualize the inside of coronary arteries) but is therapeutic as well as diagnostic.
- A similar but sturdier tube (guide catheter) is inserted into an artery in your groin or arm, and a hair-thin guide wire is threaded through it into your coronary artery.
- A much thinner catheter is threaded over the guide wire into the blocked artery.
- This thinner catheter has a tiny balloon at the end.
- Once the balloon is positioned at the blockage, the balloon is inflated to widen your artery and improve blood flow. The plaque is still there, just flattened against the wall of the artery.
- The balloon catheter is then withdrawn.
- This procedure is sometimes referred to as PTCA, which stands for its full formal name: percutaneous (through the skin) transluminal (through the hollow center of the blood vessel) coronary angioplasty.
Stent: A stent is a small, sieved, coil-like metallic tube or scaffold mounted over a balloon.
- The balloon is inflated at the blockage, which expands the stent.
- The balloon is then withdrawn, but the stent stays in place, keeping the artery from narrowing again.
- Like arteries treated with angioplasty alone, arteries treated with a stent can eventually close up again.
- The stent is a longer lasting solution for many people.
What about surgery for heart disease?
Surgery in coronary heart disease is reserved for people whose disease is either severe or is not improved or stabilized by medication and other less invasive therapies.
Coronary artery bypass grafting (CABG): This is the standard operation for blockages of coronary arteries.
- If multiple coronary arteries are blocked, or if the left main artery shows significant blockage, bypass surgery is usually the best treatment choice.
- The blocked parts of the arteries are detoured or bypassed with blood vessels "harvested" from your chest (internal mammary), arm (radial artery), or a leg (saphenous vein).
- During the surgery, the heart is stopped temporarily and you are connected to a machine called a bypass pump that takes over the functions of the heart.
- These operations are very successful and have a low rate of complications.
Off-pump bypass surgery: Sometimes surgeons can perform open heart surgery without using a bypass pump and while the heart is beating. The procedure causes fewer side effects than the standard procedure, but it is not feasible in all situations.
Minimally invasive coronary bypass (MINI-CABS): If just your front or right coronary arteries need bypass, a surgeon may replace the blocked artery with an artery from the
Should I follow-up with my doctor after being diagnosed with heart disease?
Regular follow-up visits with your health-care professional are essential. Coronary heart disease is a chronic (long-term, ongoing), relentlessly progressive disease.
- Reducing risk factors may only slow its pace.
- Even angioplasty or bypass surgery only reduces the severity of the symptoms. It does not cure the disease.
- It often comes back and gets worse, requiring further treatment for people with previous heart attacks or bypass, especially if the patient has not corrected the abnormal risk factors.
Your health-care professional will usually monitor you for the following conditions:
- New symptoms or signs of disease progression (periodic physical exams and ECGs or stress tests)
- Silent ischemia (periodic treadmill or radionuclide stress tests or stress echocardiography)
Your health-care professional will also monitor your progress in risk reduction and how well treatment is working. Keep track of your own numbers. This is your life.
- Checking weight and activity levels
- Checking blood lipid levels, including the bad LDL, the good HDL, and triglycerides, another fat frequently elevated in overweight patients, especially if diabetic - LDL should be less than 100
- Checking blood pressure, which should be less than 130/80 mm Hg
- If diabetic, checking blood sugar and A1C (should be less than 7.0%)
- Checking progress with quitting smoking
He or she will monitor how well your medications, making adjustments as necessary. Side effects of medications will also be monitored and treated if necessary.
How can heart disease be prevented?
Risk refers to the odds that something will occur, but there are no guarantees.
- Having one or more risk factors does not mean heart disease is inevitable.
- Similarly, absence of risk factors does not guarantee you will not have heart disease.
Monitoring and modifying certain risk factors is the best way to prevent coronary heart disease.
- If possible, adopt a healthy lifestyle early in life.
- Because risk factors are interrelated, many are present together in the same person.
- Thus, moderate changes in one area of your life often reduce other risk factors at the same time.
You can't change some risk factors.
- Age: Men older than 45 years and women older than 55 years are at increased risk for coronary heart disease.
- Family history: If someone in your immediate family has had coronary heart disease, angina, or heart attack by age 55 years, your risk of developing heart disease is increased. If heart disease runs in the family, seek medical attention. Your
health-care professional may recommend screening tests and preventive measures.
You can change the following risk factors:
- High blood fats, the bad LDL, good HDL, and triglycerides
- High blood pressure
- Emotional stress
What do your cholesterol numbers mean?
Know your total cholesterol level and take measures to control it with diet and exercise if your levels are high. Your
health-care professional will check your levels and compare them with guidelines from the National Cholesterol Education Program (NCEP). Your total cholesterol levels are measured in your blood after a 9- to 12-hour fast. The following subtypes of cholesterol are important:
- Less than 100 - Optimal
- 100-129 - Near optimal/above optimal
- 130-159 - Borderline high
- 160-189 - High
- 190 or higher - Very high
- Less than 200 - Desirable
- 201-239 - Borderline high
- 240 or higher - High
HDL cholesterol (the good cholesterol)
- Less than 40 - Low
- 60 or higher - High (desirable)
What about diet and heart disease prevention?
A balanced, low-fat diet is good not just for people with high cholesterol but for everyone.
- The American Heart Association recommends that maximum calories from fat be less than 30% of total calories in any meal.
- Each day, try to eat 6-8 servings of bread, cereal, or rice; 2-4 servings of fresh fruit; 3-5 servings of fresh or frozen vegetables; 2-3 servings of nonfat milk, yogurt, or cheese; and 2-3 servings of lean meat, poultry, fish, or dry beans.
- Use olive or canola oils for cooking. These oils contain monounsaturated fats known to lower cholesterol.
- Eat 2 servings of fish each week. Eat fish such as salmon, mackerel, lake trout, herring, sardines, and albacore tuna. All of these fish are high in omega-3 fatty acids, which lower levels of certain fats in the blood and help prevent irregular heartbeats and blood clots that cause heart attacks.
- Research suggests that alcohol can help protect against coronary heart disease, but limit your intake to 1-2 drinks per day. Higher amounts can increase blood pressure, cause heart rhythm disorders (arrhythmias), and damage your heart muscle and liver directly.
- Avoiding fast food may not be pleasant or convenient, but it may provide significant benefit in the long run.
What about other lifestyle changes to prevent heart disease?
Smoking: Quitting smoking is the single best change you can make.
- Quitting can be difficult, so seek your health-care professional's help.
- Passive smoking (breathing in tobacco smoke), smoking cigars, or chewing tobacco are equally dangerous to your health.
Physical inactivity: Exercise helps to lower your blood pressure, increase your level of good cholesterol (HDL), and control your weight.
- Try to complete an endurance exercise of at least 30 minutes, 3-5 times a week. But just brisk walking alone will improve cardiovascular survival.
- Exercise can include walking, swimming, biking, or aerobics.
- Before beginning an exercise program, talk to your health-care professional.
Obesity: Excess weight puts extra strain on your heart and blood vessels by increasing blood pressure, plus frequently associated with diabetes, high cholesterol and triglycerides, and low HDL.
- A high-fiber, low-fat diet and regular exercise can help you lose weight and keep it off.
- Fad diet programs may be unsafe. Seek your health-care professional's advice before starting any weight loss program.
- Don't rely on drugs to lose weight. Certain medicines used for weight loss-for example, Fen-Phen-have been associated with dangerous heart valve damage and other serious medical conditions in some users.
High blood pressure: If you have high blood pressure, your
health-care professional should treat it aggressively.
- Proper diet, low salt intake, regular exercise, reduction in alcohol intake, and weight reduction are of paramount importance.
- If your health-care professional prescribes medications, take them faithfully.
Diabetes: Diabetes causes blockage and hardening (atherosclerosis) of blood vessels everywhere in the body, including coronary arteries. Controlling diabetes significantly reduces coronary risk.
Viagra and coronary heart disease: If you intend to use sildenafil (Viagra) for erectile dysfunction, contact your doctor to make sure it is safe for you.
- If you have a significant coronary blockage, angina or heart attack may occur with use of Viagra.
- Also, you must avoid taking nitroglycerin in any form-pill, patch, or spray-within 48 hours of taking Viagra. Using Viagra with nitroglycerin may cause dangerously low blood pressure.
What is the outlook for someone with heart disease?
Recovery from coronary heart disease depends on many factors.
- Extent of coronary artery disease and number of coronary arteries involved
- History of previous heart attacks or bypass surgery
- Capacity for exercise or exertion
- Heart function - How well the heart contracts
- Acuteness of symptoms - The need to visit an emergency department with angina, unstable angina, or heart attack
Reviewed on 7/25/2016
Medically reviewed by Robert J. Bryg, MD; Board Certified Internal Medicine with subspecialty in Cardiovascular Disease
"Revascularization in patients with stable coronary artery disease: Coronary artery bypass graft surgery versus percutaneous coronary intervention"