Circulatory system

What is heart attack?

Heart attack, also known as myocardial infarction, occurs when there is a blockage in one of the coronary arteries and blood supply to a part of the heart is impeded. This lack of blood flow may damage the heart and lead to death of heart muscle, or myocardium. Depending how much heart muscle is damaged, disability, or death can result.

What causes heart attack?

In nearly all cases, heart attack is the result of coronary artery disease, or artherosclerosis. Coronary artery disease occurs when the accumulation of cholesterol plaque causes thickening and hardening of arteries. As plaque continues to accumulate over time, coronary arteries become increasingly narrowed and hard, thereby restricting blood flow to the heart. As artherosclerosis (or coronary artery disease) progresses, platelets — cells in blood that aid in clotting—can adhere to the roughened walls of arteries. This can lead to the formation of small blood clots. Heart attack occurs when a blood clot on a cholesterol plaque located on the inner wall of a coronary artery restricts blood flow to the heart, causing death of the heart muscle.

To summarize, heart attack may be caused by:¹

• an accumulation of plaque which severely narrows or blocks a coronary artery
• a blood clot which blocks an artery already narrowed by plaque
• a clot that forms on "soft plaque" (also known as vulnerable plaque) may cause the vulnerable plaque to crack, bleed or rupture, causing a clot to form and block blood flow to the heart
• a condition known as coronary artery spasm or vasospasm. This can cause the coronary artery to narrow and go into spasm. Because of this narrowing, blood flow to the heart muscle is decreased or stopped.

What are the signs and symptoms of heart attack?

The most common feature of heart attack is pain, often described as a tightness or heaviness in the chest. Typically, this pain is located in the center of the chest, but it may also radiate from the left arm or jaw. Pain may move to the arm, jaw, shoulder, back, or neck.

Typical symptoms	Atypical symptoms
Anxiety and fear of impending death Breathlessness Sweating Pallor Nausea and vomiting Rapid pulse Light-headedness or fainting	Acute confusion Stroke Syncope (a brief loss of consciousness caused by a temporary lack of oxygen in the brain) Giddiness Abdominal pain Fatigue and exhaustion

Symptoms as described above that last longer than 30 minutes or uncomfortable pressure, fullness, squeezing or pain in the center of the chest lasting more than a few minutes usually indicate a person is having a heart attack. Seek immediate emergency medical attention.

Not everyone will experience the above symptoms. For some people, pain may be confined to only a small area of the chest and it may feel like a burning sensation, similar to indigestion or heartburn.

Women should take particular note, however, since symptoms of heart attack are different in women than they are in men, and heart attacks also tend to be more severe in women than in men. In the first year following heart attack, mortality is 50 percent higher among women. In other words, women are 50 percent more likely than men to die from heart attack. In the first six years following heart attack, women are more than twice as likely then men to suffer a second heart attack.² (See Women and heart disease for more information.)

Because they do not experience the typical pain in the left half of their chest, many women may experience a heart attack and not know it. Symptoms of heart attack in women may include a burning sensation in the upper abdomen, lightheadedness, upset stomach, and sweating.³

Silent heart attack
Some heart attacks may pass unnoticed because victims do not experience any pain or other symptoms. Victims often do not realize they have had a heart attack. Also known as "silent infarctions", such attacks are common in diabetics, women, and the elderly. In the elderly in particular, nerves may tend to be weak and ineffective, making the victim less sensitive to the pain of heart attack. Diabetic neuropathy may cause a similar effect. Elderly people who suffer from other physical conditions and who have grown accustomed to pain and discomfort may dismiss the pain of heart attack.⁴

How is heart attack diagnosed?

If you experience any of the symptoms described above, you may be having a heart attack and should seek immediate emergency medical attention.

Emergency room personnel will talk with you and monitor your heart rate and blood pressure. They will also recommend a combination of chest x-ray, electrocardiogram (ECG or EKG) and blood tests.

A chest x-ray will help determine whether your heart is enlarged. It will also determine whether there is any fluid in your lungs.

An EKG a is a recording of the electrical activity of the heart. Characteristic electrocardiogram changes may indicate changes in heart rhythm and may also indicate which coronary artery is blocked.⁵

Blood tests are used to determine the extent of damage to the heart muscle by measuring levels of certain enzymes. Doctors look for creatine kinase myocardial band, myoglobin, cardiac troponin T and I, and creatinine phosphokinase (CPK). All of these are enzymes released into the blood by dying heart muscles whose surrounding membranes have dissolved. High levels will confirm diagnosis of a heart attack.⁶

Treatment following heart attack

If it is four hours or less since the onset of symptoms, your doctor may prescribe thrombolytics such as streptokinase, urokinase, or tissue plasminogen activator, drugs to dissolve the clot in the coronary artery and reduce or prevent damage to the heart muscle. When given as soon as possible after a heart attack, such "clot busters" have increased survival rates for heart attack patients.⁷

You will very likely be hospitalized and managed in a dedicated cardiac unit. You will need plenty of bed rest and will be given⁸:

• high flow oxygen, to increase the amount of oxygen in the blood still flowing through your heart
• aspirin and other anticoagulants (blood-thinning medications) to stop clots from forming or growing in size
• intravenous analgesic with or without morphine to relieve pain

You will also be continuously monitored through routine electrocardiograms.

You may also be given other intravenous drugs such as tissue plasminogen-activator (t-PA) and streptokinase. These drugs are designed to dissolve clots and restore blood flow to the heart muscle, a process known as reperfusion. Early reperfusion minimizes the extent of heart muscle damage and preserves the function of the heart.⁹

When your condition has stabilized, doctors may want to conduct further tests to determine the extent of damage to your heart. They may recommend:¹⁰

Echocardiogram

An echocardiogram uses sound waves to create a picture of the heart. More detailed than an x-ray, the echocardiogram shows how well the heart chambers fill with blood and pump it to the rest of the body. An echocardiogram can also help identify areas of poor blood flow to the heart, areas of the heart muscle that are not contracting normally, and any prior injury to the heart caused by poor blood flow. In the case of heart attack, doctors using echocardiography are particularly interested in determining how much damage has been done to the heart muscle by watching the motion of the left ventricle.

Coronary angiography

Conducted in a cardiac catheterization laboratory under mild sedation, coronary angiography involves the injection of dye into the bloodstream. Dye in the coronary arteries allows the doctor to see flow of blood through the heart and to determine where there are blockages and how serious these may be.

Nuclear heart scan (Thallium stress test)

A nuclear heart scan shows blood flow to the heart and also reveals any damage to the heart muscle. Radioactive dye such as thallium is injected into the bloodstream. A specialized camera can see the dye and identify areas of low blood flow as well as serious narrowing in an artery.

Once you are discharged from hospital, your doctor may recommend a cardiac rehabilitation program to help you learn how to prevent further heart disease. Exercise training will help you learn to exercise safely while strengthening muscles and improving daily stamina. Education, counseling and training will help you understand your condition and learn ways to reduce your risk of future heart problems. Working with doctors, nurses, exercise specialists, physical and occupational therapists, dietitians and a psychologist, you will learn not only to cope with the stress of adjusting to a new lifestyle, but also to deal with fears about the future.¹¹

What are common outcomes of heart attack?

If you believe you are having a heart attack, seek immediate emergency medical attention. In most cases, receiving medical attention within an hour of onset of symptoms reduces the amount of heart muscle lost.¹²

The outome of a heart attack depends where the coronary blockage occurred. Generally, blockages that occur on the left side of the heart are more serious. In addition, if the blockage causes an irregular heartbeat known as an arrhythmia, it may cause sudden death. Either tachycardia (rapid heartbeat) or ventricular fibrillation (uncoordinated contractions) may occur. Ventricular fibrillation prevents blood flow and requires CPR (cardiopulmonary resuscitation) or defibrillation (electrical therapy).¹³

The outcome of heart attack is generally better when the heart is supplied by another blood source. In some instances, a person's body responds to a gradual blocking of an artery through what is known as collateral blood source. By widening another vessel that supplies blood to a similar part of the heart, you will suffer less severe damage from the major blockage.¹⁴

Recovery from heart attack

Recovery from heart attack may take from a few weeks to a few months. Your recovery will depend on how active you were before your heart attack, the severity of the attack, and how your body responded to the attack. You can speed your recovery if you avoid stress, extremes in temperature, and conditions that place an added load on your heart.¹⁵

Your doctor may recommend a program of cardiac rehabilitation. As mentioned above, cardiac rehabilitation will help educate you about diet, exercise and lifestyle. You may also need to take aspirin and beta-blockers such as Tenormin.

How can I prevent a second heart attack?

You can significantly reduce your risk of a second heart attack by:

• quitting smoking
• controlling blood pressure
• controlling diabetes
• lowering blood cholesterol

Following heart attack, there is still the issue of the narrowed artery that caused the heart attack. Heart surgery, transcatheter interventions, or medications may be needed to reduce the risk of a second heart attack.¹⁶

To ensure not only a full recovery but also to prevent future heart attacks it's important that you follow the advice of your doctor, including making long-term changes to your lifestyle and diet and taking heart medications as directed.

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