What is a heart attack?
A heart attack is an acute event where the essential blood supply to our heart muscle is insufficient, causing damage to those muscle cells. The heart muscle – the myocardium – receives its blood supply through vessels called coronary arteries. A narrowing or blockage somewhere within one or more coronary arteries restricts or cuts off blood flow to the heart muscle, resulting in areas of damage or cell death. We call this a heart attack.
There are three main coronary arteries which branch off to supply every part of the heart muscle with oxygen-rich blood. Each artery supplies a different area of the heart muscle, so different parts of the heart can be damaged.
A heart attack is usually – but not always – accompanied by chest pain which may radiate into the neck, jaw, or left arm, and shortness of breath. Some people feel heart pain in different ways so diagnosis is based on several different features and tests.
A suspected heart attack is a medical emergency.
The heart is a hollow, muscular organ whose main job is to pump oxygenated blood around the body.
There are two halves to the heart, and each half has a top and a bottom chamber – the atrium and the ventricle. The left atrium receives oxygenated blood from the lungs then delivers it into the left ventricle, which pumps it into the body. The oxygen and nutrients in the blood are used up as it circulates through the body. This deoxygenated blood then re-enters the heart through the right atrium, and then into the right ventricle, which pumps the deoxygenated blood into the lungs. As this de-oxygenated blood circulates through the lungs, waste carbon dioxide is exchanged for oxygen from the air we breathe.
The severity of a heart attack is determined by several factors, including:
- The amount of restriction of blood supply – whether an artery was totally or partially occluded.
- The length of time that the blood flow was restricted – this can mean the difference between cell damage and cell death.
- The amount of muscle affected – a blockage higher up the circulatory system will cause damage to more muscle than a blockage in one of the smaller branched vessels.
- The area of the heart affected – damage to different areas of the muscle can affect the way the pumping action of the heart and can also affect the way the heart beats by disrupting the electrical conduction system of the heart.
The effect that a heart attack has on an individual can also depend on whether they have other serious health conditions and their baseline general health. The type and timeliness of intervention given, and a person’s adherence to ongoing treatment all influence outcomes.
When our heart beats, it is because an electrical impulse is automatically generated near the top of the heart. This impulse tells the heart muscle to contract so that blood is pumped into our body and lungs. The fibres and cells of the heart conduct the electrical impulse down throughout the heart muscle in a set pattern to control the speed and order of the muscle contraction – the different areas of muscle should contract in a set pattern, with the top half of the heart squeezing a split second before the bottom half. If an area of tissue is damaged, it loses the ability to conduct that electricity and can disrupt the natural order of movement of the heart muscle, as well as damaging that part of the muscle itself. These changes in electrical conduction activity are one of the signs that helps diagnose a heart attack and are measured on an electrocardiogram (ECG).
How do we diagnose a myocardial infarction?
When someone is having a heart attack, they may have classic symptoms such as clutching their chest with crushing central chest pain and being unable to catch their breath. They may also have very atypical symptoms, and simply think they have indigestion, toothache, a pulled muscle, or feel generally unwell. Some people have no suspicious cardiac symptoms at all and are at risk of a misdiagnosis or missed MI. Symptoms can help doctors work out what the problem might be, but there are other tests available to help make an accurate diagnosis. This includes:
The electrocardiogram (ECG) is one of the first tests performed when someone is suspected of having an MI. Ten wires are attached to the skin with sticky pads – six on the chest and one on each limb. An ECG is a safe and painless test which traces the electrical activity of the heart. The wires, or leads, are positioned carefully to show the way the current flows through different areas of the heart, so an ECG can show which area of the heart is damaged. It may also show whether the damage is old, new, or ongoing. If the damage is ongoing, the ECG may be repeated at intervals to monitor the evolution of the MI.
The ECG also gives some indication of how severe the heart attack is, and myocardial infarctions are categorised into two types – called STEMI and NSTEMI – according to the ECG findings.
Routine blood tests can help guide treatment, but specific blood tests are also done to determine and measure damage to the heart muscle. The current standard blood test to confirm or rule out a heart attack is a ‘Troponin’ test. This is a marker in the blood of a protein released by the heart muscle when damaged. A baseline troponin level will be taken immediately, then repeated a number of hours later; the difference between the two (or more) results can give some idea of the extent of the damage and whether this is an evolving event.
Both a diagnostic investigation and a treatment intervention, an angiogram involves the insertion of a small wire into a tiny puncture wound, usually in the wrist or the side of the groin. This wire is guided up to the coronary arteries. During an angiogram, a dye is injected into the coronary arteries to try and identify the position and nature of the narrowings or blockages.
What causes heart attacks?
The most common cause of heart attack is coronary artery disease; this is the gradual narrowing of arteries caused mainly by fatty deposits within the vessels. Although the narrowing happens gradually, the fatty deposits or plaques can be unstable, and may sometimes rupture or have parts sheer off. The body responds to this as it would to any rupture within a blood vessel – by beginning the clotting process. This causes a problem as a blood clot develops at the narrowed, ruptured area within the artery, reducing or blocking the blood supply to the heart muscle.
Occasionally, someone will have a positive diagnosis of a heart attack but have healthy coronary arteries. This can be due to coronary artery spasm – a temporary narrowing of the vessels which is severe enough to cause damage to the heart muscle. This is most commonly seen in the use of some illicit drugs.
As the main cause of heart attacks is coronary artery disease (CAD), looking at the causes of CAD gives us the best idea of the causes of MI. Some of the factors that make people more likely to have coronary artery disease, and therefore more likely to have a heart attack, are:
- High cholesterol
- Increasing age
- Family history of heart disease
- High alcohol intake
The main preventable risk factor for an MI caused by coronary artery spasm is the use of illicit drugs, so avoiding recreational drug use is the best way to avoid coronary artery spasm.
Heart Attack Symptoms
The symptoms of heart attacks can vary from person to person, and there are sometimes particular differences in the way men and women express heart pain.
Most of the signs of heart attack are common to both men and women, in particular chest pain, sometimes radiating to the left arm, neck and back. Some people describe a tightness, like a band around the chest or a heaviness, like something is sitting on the chest.
Nausea and vomiting are associated with the most serious heart attacks.
Heart Attack Symptoms
In addition to the classic symptoms, men are more likely to describe indigestion-type pain and back pain.
In addition to, or in place of the classic symptoms of heart attack, women are more likely than men to experience symptoms like jaw pain, nausea, shortness of breath, and fainting.
Heart Attack Treatment
In the first few days after a heart attack, some people develop arrhythmias – abnormal heart rhythms. Some of these can be dangerous, even life-threatening, so cardiac monitoring is recommended for the first two or three days.
Also called a PCI, or percutaneous coronary intervention, an angiogram is a diagnostic procedure that gives us the most information about what’s happening inside the coronary arteries and can be used to administer effective treatment. During the angiogram, a thin hollow wire is fed into an artery in the wrist or groin. A dye is injected through this wire into the coronary arteries while a series of X-rays are taken. When the problem area is identified, the same wire is used to compress or remove areas of clot and plaque. A stent is then fitted – this is like a tiny mesh tube which beds into the vessel wall and holds it open.
Severe heart attacks (STEMIs) have significantly better results the sooner they receive PCI; this rapid access PCI is referred to as Primary PCI, or PPCI.
Coronary Artery Bypass Graft (CABG) Surgery
Coronary Artery Bypass Graft (CABG, pronounced like ‘cabbage’) surgery is usually performed if one or more vessels have total or near-total blockages that cannot be reduced by less-invasive angiogram techniques. It is an open heart surgery where a vein is removed from the leg and attached to the coronary arteries in positions to reroute the blood flow past the problem area.
Medications for Myocardial Infarction
Blood thinners, or anticoagulants, are usually the first treatment given for a suspected heart attack. Aspirin is usually given immediately when a heart attack is first suspected and supplemented with other antiplatelets and anticoagulants. Different types of blood thinners can be given either as tablets or injections given intravenously – into the vein – or subcutaneously – under the skin. Anticoagulants make some people more at risk of having bleeding problems, and the benefits and risks should be weighed up for these people.
In the longer term, people who have had a heart attack usually stay on some medication for life, including blood thinners, cholesterol medications such as statins, and tablets called beta-blockers and ACE inhibitors, which have good long term evidence for preventing further heart attacks and maintaining good heart function.
Rarely, a very serious heart attack will be treated with thrombolysis – this means using a strong, clot-busting drug. This used to be used more commonly in the past but has a high risk of complications such as severe bleeding. Thrombolysis is usually only considered during the initial presentation of a STEMI where the patient cannot reach a venue that offers PCI within the first two hours.
Heart Attack Complications
People are at the highest risk of life-threatening arrhythmia in the first few days after a heart attack, which is why cardiac monitoring is frequently used in this period. An arrhythmia is an abnormal heart rhythm, such as a very fast, very slow, or irregular beat. There are different types of arrhythmia, some more worrying than others. All arrhythmia should be monitored and treatment should be considered, as some arrhythmias can lead to cardiac arrest.
A heart attack can trigger a dangerous heart rhythm, some of which may stop the heart’s pumping action completely. Having no output – no pulse, no blood flowing to vital organs – is a cardiac arrest. A cardiac arrest is an immediate, life-threatening incident. Cardiac arrests that occur in hospitals with cardiac monitoring means that individuals are able to access immediate treatment. This can lead to much better outcomes than if a cardiac arrest were to happen outside of hospital settings where treatment is likely to be delayed.
Heart failure, sometimes referred to as congestive cardiac failure, is a chronic condition that can develop at any point after a heart attack; it can develop very quickly or come much later when someone has had damage to the heart. It affects the pumping action of the heart and particularly restricts the heart’s ability to move fluids around the body. Fluid backs up into the lungs and builds up in the lower limbs. A buildup of fluid in the tissues is known as oedema, and when it is in the lungs it is known as pulmonary oedema. People with heart failure can become very short of breath very quickly and require careful management with medications, lifestyle and monitoring. In the immediate aftermath of a heart attack, the heart’s pumping action can be severely reduced and may result in heart failure.
Sometimes the heart function is severely reduced in the immediate aftermath of an MI but resolves within a few months. This is referred to as the heart or the myocardium being ‘stunned’, and is often known as a ‘stunned heart’ or ‘stunned myocardium’. It can cause severe acute heart failure symptoms such as fluid in the lungs and severe shortness of breath, as well as extreme fatigue.
A heart attack is a shocking and life-changing event and it’s common to feel depressed after experiencing one. Someone who has had a heart attack is likely to come home with lots of new medications to take every day, have to take time off work, and may be anxious about returning to normal activities. Attending cardiac rehabilitation programmes can help improve understanding and acceptance of normal feelings after a heart attack.
Changes to heart function and structure are usually assessed by an echocardiogram – an ‘echo’ test, which should be repeated at a set interval after an MI to monitor recovery, assess the damage and minimise the risk of complications.
Cardiac Arrest vs Heart Attack
A heart attack is not the same as a cardiac arrest, though the terms are often confused in the media and public.
In a heart attack, some of your heart muscle is damaged by poor blood flow through the coronary arteries. In a cardiac arrest, you have no cardiac output. This means there’s no heartbeat and pulse. There are several common causes of cardiac arrest, and some are reversible – such as profoundly low blood sugar, or severe hypothermia. Sometimes, with immediate treatment, including chest compressions, intravenous medications and often a shock delivered by a defibrillator, a cardiac arrest is survivable. If the heart stops pumping for more than a few minutes, essential organs like the brain quickly become irreversibly damaged. Few people survive a cardiac arrest, and of those few, only a small percentage are discharged from hospital with no significant lasting effects.
If you had a heart attack, your heart did not stop beating, or stop working – unless you also had a cardiac arrest.
Another phrase often confused with heart attacks or cardiac arrests is ‘heart failure’. Heart failure is a chronic condition where the pumping action of the heart is reduced – often because of a previous heart attack. Some people live for years after a diagnosis of heart failure, though it can cause profoundly debilitating symptoms.
What is a Silent Heart Attack?
A ‘silent’ heart attack or silent MI occurs when someone experiences a heart attack with no or few symptoms or atypical symptoms that you may not normally associate with a heart attack.
Even if the initial heart attack does not show any symptoms or is undiagnosed because the symptoms didn’t suggest a cardiac cause, people very often feel very unwell in the days and weeks after an untreated heart attack. If someone goes to their GP complaining of severe fatigue or breathlessness over a short recent period, the GP could reasonably consider investigating for a missed heart attack, especially if the patient has risk factors for heart disease.
Sometimes, an SMI is only discovered during a routine check-up appointment when the doctor finds out that the individual has had a heart attack at some point in the past after performing some screening tests such as a routine ECG.
Symptoms of heart pain can be very variable from person to person, which means that doctors have to be careful not to discount the possibility of heart attacks with atypical symptoms. Diabetics are particularly likely to be found to have had a heart attack with no discernible symptoms. The variation between the symptoms experienced by men and women could also increase the risk of a misdiagnosis or missed heart attack.
Preventing Heart Attacks
A healthy lifestyle is the best thing we can do to reduce our risk of having a heart attack. We need to know what the risk factors for heart disease are, how they affect us personally, and what we can do to reduce them and help prevent heart attacks.
Following a healthy diet and getting more exercise are essential ways to prevent heart disease and other cardiovascular diseases. If you have other health conditions, managing them well can help reduce risk. Smoking puts you at high risk of lots of different diseases including heart attacks, and stopping smoking is one of the best things you can do for your health and the health of those around you.
You can also see a doctor or other healthcare professional to discuss your own personal risk factors and how to tackle them. Having regular contact with health services means that you can have regular cholesterol checks and targeted treatment, and if you have other conditions you can get help controlling and managing them. Although healthy changes are under your control, they’re not always easy. If you’re planning to lose weight, change your diet, start an exercise plan, or give up smoking, it’s okay to ask for help.
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