Heart attack

What is a heart attack?

The heart is a muscle that needs a good blood supply to keep it healthy. As we get older, the smooth inner walls of the arteries that supply blood to the heart can become damaged and narrow due to a build up of fatty materials.

A heart attack (also known as a myocardial infarction) is the death of heart muscle from the sudden blockage by a blood clot in a coronary artery that supplies blood to the heart. Blockage of a coronary artery deprives the heart muscle of blood and oxygen resulting in injury to the heart muscle. If blood flow is not restored within 20 to 40 minutes, irreversible death of the heart muscle will begin to occur. Muscle continues to die for 6 to 8 hours by which time the heart attack is usually 'complete'. The dead heart muscle is replaced by scar tissue.

Heart attacks require immediate medical attention. If you're unsure you're having a heart attack, do not delay, call your doctor or dial 911 for an ambulance immediately. The longer you wait, the greater the chance of complications.

Causes

The main blood supply to the heart muscle is via coronary arteries. These arteries are prone to being narrowed due to a build-up of fats within their walls. This is known as atherosclerosis, or cholesterol plaques. If there is widespread or significant atherosclerosis the condition is known as coronary heart disease.

Coronary heart disease increases the risk of developing a heart attack. The plaques can spontaneously rupture, triggering a blood clot to form on its damaged surface. If the blood clot gets big enough, it can completely block coronary arteries, causing a heart attack.

Signs and symptoms

Common symptoms of heart attack include:

• Pain, discomfort or tightness in the chest that may also radiate to the jaw, neck, arms, shoulder or back;
• Shortness of breath;
• Palpitations, which is the sensation of a rapid or irregular heartbeat;
• Excessive sweating;
• Nausea or vomiting, and;
• Feeling dizziness.

Symptoms of a heart attack can vary. Some individuals with a heart attack may report severe chest pain, while others may only experience indigestion. If you have diabetes, are elderly or have high blood pressure (hypertension), you may not even notice any pain. A common sensation is the feeling that "an elephant is sitting on the chest". If you have angina, the symptoms of a heart attack may be similar but more severe, last longer or not respond to treatment.

If you're unsure you're having a heart attack, don't delay, call 911 for an ambulance immediately. The longer you wait, the greater the chance of complications.

Methods for diagnosis

Doctors will run a series of diagnostic tests to confirm the suspicion of a heart attack. While these tests are being performed, you may also be given some treatment to make you more comfortable, such as oxygen, pain-relief medications, and medications to help improve blood flow to the heart muscle.

Common tests that are performed include:

Electrocardiogram

Electrocardiography (ECG) uses electrodes attached to the chest to check heart rhythm. The beat of the heart is caused by coordinated electrical currents through its cells. This test is used to determine if there are any abnormalities in heart rhythm. During a heart attack, certain areas of the heart may be damaged. The ECG can tell the doctor if this is likely to have happened.

Cardiac enzyme test

A cardiac enzyme test is a blood test - the most commonly measured enzyme is troponin. Damage to the heart, such as that caused by a heart attack, releases cardiac enzymes into the bloodstream. Blood may be taken multiple times as it can take several hours for this test to be positive after a heart attack.

Chest X-ray

If you're experiencing chest pain, the doctor is likely to order a chest X-ray. This can exclude other causes of chest pain and is also used to determine if there has been a build-up of fluid on the lungs due to the heart attack.

Echocardiogram

Echocardiography uses ultrasound waves to create an image of the heart. It allows the doctor to see the size of the heart and also how well it's working. It can indicate the level of difficulty being experienced by the heart in pumping blood, whether there's heart valve leakage and highlight areas of damage. An echocardiogram is not usually performed immediately, but in the days and weeks following a heart attack.

Coronary angiogram

A coronary angiogram involves the insertion of a thin catheter into one of the major arteries in the groin or arm, under local anesthetic. Radioactive dye is injected and X-rays taken to highlight any blockages or narrowing in the coronary arteries.

Types of treatment

Prompt diagnosis and treatment is essential to limit heart damage. Treatment begins at the initial suspicion of a heart attack. This may include oxygen, pain-relief medication, aspirin (to thin the blood and prevent further blood clotting), and nitroglycerin (to reduce stress on the heart and improve blood flow through the coronary arteries). You will be closely monitored to recognize any complications at the earliest opportunity.

Treatments aimed at removing blockages and restoring blood flow within the coronary arteries include:

Coronary angioplasty and stenting

Coronary angioplasty is a procedure that can be performed at the same time as a coronary angiogram. If a blockage or narrowing is diagnosed on the angiogram, specialized catheters can be used to enter the coronary arteries. These catheters are able to extract blood clots or dilate narrowed arteries to restore blood flow. A self-expanding stent can also be inserted, through a similar catheter, to keep the arteries open.

Coronary artery bypass graft

A coronary artery bypass graft (CABG) is a type of open-heart surgery, designed to bypass narrowed blood vessels and increase blood flow to certain areas of the heart. The operation involves using healthy veins or arteries taken from another region of the body, to replace narrowed, blocked or diseased coronary arteries. This procedure is undertaken with a general anesthetic and can take several hours to perform.

Medications

Thrombolytics

Medications, called thrombolytics, can be given as an injection to break down the blood clots that caused the heart attack. This medication is generally used in hospitals that lack the facilities to perform an angioplasty.

Anticoagulants

Medications, called anticoagulants, such as heparin or low-molecular weight heparin, are given to help prevent the formation of further blood clots. Anticoagulant medication is generally continued for a few days after the initial heart attack, when the risk of further heart attacks is greatest.

Potential complications

Further heart attacks

Having had a heart attack increases the risk of further heart attacks. To reduce risk, it is important to maintain a healthy lifestyle, follow doctor's advice and directives, and take prescribed medications. Medications may include:

• Beta-blockers, which block the sympathetic nervous system on the heart. This reduces the amount of stress on the heart by slowing it down;
• ACE (angiotensin converting enzyme) inhibitors, which block the production of the hormone angiotensin II to lower blood pressure. This in turn lessens the pressure and stress placed on the heart;
• Aspirin, which reduces the likelihood of blood platelets clumping together to form clots, and;
• Statins, which reduce the amount of certain cholesterols in the blood. Cholesterol is linked to atherosclerosis and coronary heart disease, so managing cholesterol levels can help protect against further heart attacks.

Irregular heartbeats

Any damage occurring during a heart attack can result in scar tissue. This scar tissue can cause electrical instability in your heart, leading to irregular heart rhythms, known as arrhythmias. Generally, arrhythmias can be treated with medication and are often short-lived. However, some arrhythmias need to be managed with an implantable cardiac pacemaker and/or defibrillator (ICD), which is a small electrical device surgically placed in the chest. Once implanted, a pacemaker can help maintain a minimum heart rate, and a defibrillator can automatically shock the heart, should there be a dangerous or chaotic arrhythmia.

Heart failure

If the heart is badly damaged during a heart attack, it may mean that the heart can't pump enough blood around the body to prevent fluid build-up. This is called heart failure. Heart failure is treated with certain medications to help the heart pump more effectively and prevent fluid retention.

Cardiogenic shock

Cardiogenic shock is a serious complication following a heart attack. It occurs when the heart muscle has been so badly damaged it cannot provide blood for many of the body's vital functions. Treatment may involve medications to raise blood pressure, surgery to fit an intra-aortic pump, or coronary graft bypass.

Valve damage

If the heart valves are damaged during a heart attack, it can lead to serious leakage by the valve and in severe cases, death. Valve replacement surgery can rectify this situation through the use of animal or artificial valves. This may result in the need for blood-thinning medications, depending on the type of valve used.

Heart rupture

A heart rupture is a serious complication following a severe heart attack. It occurs when the heart walls, valves, or muscles split. Treatment may require surgery.

Prognosis

Many people will continue to live active and fulfilling lives following a heart attack, although chronic health issues will require ongoing medications and medical follow-up. It is perfectly natural to feel anxious about getting fit again, but it is the best way to avoid having a repeat attack.

Cardiac rehabilitation programs are designed specifically around personal health circumstances and will start before leaving hospital. These programs are designed to support fitness levels, while providing advice on good health.

Prevention

Care teams, which usually include your doctor, a dietitian, physiotherapist and exercise specialist, may be available to support people who have experienced a heart attack in healthy lifestyles and may include:

• Eating a healthy diet, with an increased intake of naturally oily fish such as mackerel or salmon each week, eating five portions of fruit or vegetables daily and replacing butter or margarine with olive oil;
• Losing weight;
• Not smoking and limiting alcohol, especially if experiencing high blood pressure;
• Working with a cardiac rehabilitation team to improve exercise, up to 150 minutes each week, and;
• Involving family or friends - suggest leaving the car at home whenever possible and a daily walk.

References

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