What is a heart attack?
A heart attack, also known as a myocardial infarction (usually abbreviated to MI) or ‘coronary thrombosis’ occurs when part of the heart muscle is prevented from getting its blood supply, usually by a blood clot blocking off the artery. As a result of this, part of the heart muscle becomes permanently damaged.
Typically, a heart attack is associated with severe chest pain lasting for more than 15 minutes. This can spread to the:
- Arms or
- Through to the upper back
It usually (but not always) is accompanied by:
- Nausea and / or vomiting
- Burping or a feeling of indigestion
When part of the heart muscle becomes deprived of its blood supply the muscle can become irritable. This can lead to a disturbance in heart rhythm associated with palpitations, lightheadedness and sometimes blackouts.
Occasionally heart attacks are ‘silent’, producing no symptoms and are discovered only when other investigations are performed at routine medicals or when patients present with other symptoms.
Angina is different to a heart attack. Angina is caused by insufficient blood and oxygen getting to the heart muscle and is usually due to narrowings rather than complete blockage of the coronary arteries. The supply of oxygen is usually sufficient at rest but inadequate to meet the needs during exertion. The pain associated with angina is often less severe than the pain from a heart attack and does not last as long. GTN tablets or spray will usually relieve the symptoms of angina but will not relieve the pain associated with a heart attack.
- Occurs during exertion or stress.
- Presents as chest tightness which may spread to the arms, neck, jaw or upper back.
- The duration of symptoms is usually less than 10 to 15 minutes.
- Symptoms relieved by rest or GTN.
- No permanent damage occurs.
- Unpredictable onset, often at rest.
- Similar discomfort to angina but more severe and usually associated with nausea, vomiting, shortness of breath and sweating profusely.
- Symptoms usually last more than 15 minutes.
- Symptoms are not relieved by rest or GTN.
- Results in some permanent damage to the heart muscle.
What causes a heart attack?
A heart attack or myocardial infarction means that there is death of some of the heart muscle. This is caused by a blood clot blocking an artery and resulting in a lack of blood supply.
As we get older the smooth, inner lining of the heart arteries becomes damaged and thickened due to the accumulation of fatty material called atheroma (made up predominantly of cholesterol). This process is known as atherosclerosis.
Previously it was thought that a progressive narrowing in a coronary artery caused heart attacks. It is now clear that this process can sometimes occur in coronary arteries that have minor narrowings when cracks or fissures develop in plaques. The exposed, damaged inner lining of the coronary artery wall causes blood cells called platelets to stick to the damaged area and start the formation of blood clots within the artery. These blood clots prevent the flow of blood, vital for the heart muscle to survive. If the artery is blocked for more than a few minutes the muscle cells beyond the blockage may become permanently damaged.
It remains unknown why heart attacks happen when they do, sometimes affecting people who seem to have been perfectly well. Certain factors are known to increase the risk of having a heart attack:
- Family history of heart disease at a young age
- High blood pressure
- Elevated cholesterol levels
- Lack of physical exercise
The heart muscle that is injured by this blockage may become irritable and can cause irregularity in the heart rhythm. This can be fatal, by causing a cardiac arrest, even when it appears that very little heart muscle has been damaged. This is why it is very important that if you think you are having a heart attack you should call for an ambulance. If having taken GTN (two puffs at 5-minute intervals up to 15 minutes) your symptoms have not resolved, you should call an ambulance without delay.
The damaged heart muscle eventually heals with a scar but may not be able to pump quite as much as it did before. In the majority of patients however, there is enough good muscle left for the heart to function adequately and for recovery to be complete.
How is a heart attack diagnosed?
A heart attack is diagnosed on the basis of evaluating the:
- Patient’s symptoms
- Changes on the electrocardiogram (ECG)
- Blood tests
Typically, a heart attack is associated with symptoms of severe chest pain lasting for more than 15 minutes that can spread to the:
- Arms, or
- Through to the upper back
It is usually (but not always) associated with:
- Nausea and / or vomiting
- Burping or a feeling of indegestion
The electrocardiogram looks at the electrical activity produced by the heart muscle contracting. A heart attack produces a characteristic series of changes on the ECG. These changes do not always occur immediately and in some patients it can initially be difficult to see a difference from the changes seen with anginal symptoms.
Blood tests are used to confirm the diagnosis of a heart attack. When the heart muscle is damaged it releases certain chemicals into the bloodstream. These chemicals, known as cardiac enzymes are usually found only in small amounts in the blood. After a heart attack larger amounts can be detected, often for several days. The levels can be measured from a series of blood tests taken over a period of time.
How is a heart attack treated?
A heart attack poses a significant risk to life particularly if the heart stops beating (called a cardiac arrest). This is why a heart attack is always treated as an emergency.
Patients having a heart attack are usually in pain and are frightened or anxious. The first priority is to relieve the pain, provide oxygen if needed, and to give reassurance. The ambulance crew or hospital staff will give:
- Pain relief either as an injection into a vein or a gas mixture (called Entonox) through a face mask.
- Aspirin to chew. This reduces the stickiness of the blood cells called platelets that are responsible for forming blood clots.
- Oxygen is given via a face mask to those patients who need it.
Rapid admission to hospital is important so that drugs that break down the blood clot (‘clot busters’ or ‘thrombolysis’ to use the medical term) can be given if required. These drugs are administered by an injection through a vein. The sooner these drugs are given, the greater the likelihood they will work and reduce the amount of heart muscle damaged. Not all patients are suitable for treatment with thrombolysis. Occasionally procedures using balloon-stretching of the blocked artery (called angioplasty or PTCA) are needed. These procedures aim to improve the blood supply to the surviving heart muscle.
Once in hospital you will usually be admitted to a coronary care unit (also known as the CCU). Tests will be performed to help decide on the best treatment for you and may include:
- Blood tests.
- A chest X ray.
- An ultrasound scan of the heart called an echocardiogram.
- A treadmill walking test, called an exercise tolerance test.
- An X ray dye test, called a coronary angiogram, to look at the heart arteries in more detail.
Before discharge you may be started on drugs to:
- Reduce the risk of further heart attacks (for example beta blockers, aspirin, clopidogrel, anticoagulants and cholesterol-lowering drugs known as statins).
- Reduce the risk of or to relieve the symptoms of breathlessness (for example diuretics or ACE-inhibitors).
- Reduce angina (for example beta blockers, nitrates, calcium antagonists or potassium channel openers).
Tests may show that drug treatment alone is unlikely to be successful and you may be advised to have coronary angioplasty and stenting or coronary artery bypass surgery.
Following discharge from hospital you may be invited to attend a cardiac rehabilitation programme. This covers areas such as:
- Information on lifestyle modification and treatments
These classes aim to restore confidence and promote your recovery, helping you back to normal activities.