Myocardial Infarction or Heart Attack

what is a myocardial infarction?

A myocardial infarction(MI) or heart attack is the death(infarct) of a portion of heart muscle due to sudden loss of blood supply.

Heart and coronary arteries.

The heart has four major arteries. Blood is pumped out through the largest of these arteries, the aorta, which circulates it through the body. The pulmonary artery supplies blood to the lungs. The right and left coronary arteries bring oxygen rich blood to the heart itself.

Like any other muscle, the heart muscle needs a good blood supply.The coronary arteries take blood to the heart muscle. The main coronary arteries branch off from the aorta.The main coronary arteries divide into smaller branches which takes blood to all parts of the heart muscle.

Causes of myocardial infarction.

The most common cause is atherosclerosis ("hardening of the arteries"), a build-up of fatty deposits called plaque. Over time, plaque clogs and narrows the arteries and other blood vessels, and slows or blocks the flow of blood to the heart and elsewhere. Sometimes, the surface of plaques can rupture or tear, which can cause blood clots to form that block the arteries. A complete or near-complete blockage of the coronary arteries blocks the blood flow to a part of the heart which results in MI.

Other causes:Various other uncommon conditions can block a coronary artery and cause an MI. For example: inflammation of the coronary arteries (rare); a stab wound to the heart; a blood clot forming elsewhere in the body (for example, in a heart chamber) and travelling to a coronary artery where it gets stuck; cocaine abuse which can cause a coronary artery to go into spasm; complications from heart surgery; and some other rare heart problems.

Symptoms of myocardial infarction.

Many heart attacks start slowly, usually with a feeling of pain or discomfort in the chest that lasts more than a few minutes, or goes away and returns. Pain from an MI generally lasts for more than 30 minutes, and may continue for several hours. The longer the pain lasts, the greater the risk of muscle damages.Chest pain due to a reduced blood supply to the heart is called angina.(Angina usually goes off after a few minutes. MI pain usually lasts more than 15 minutes - sometimes several hours.)

People may feel different symptoms during a heart attack or MI - and some people feel no unusual symptoms.Usually described symptoms are;

An intense pain in the left side or center of the chest. The pain may also travel up into the neck, back, arms or jaw.A feeling of extreme pressure, fullness, or tightness in the chest. Nausea, dizziness, weakness, shortness of breath, or a cold sweat also can be experienced.

Not everyone experiences acute chest pain and some may have a combination of symptoms. Other MI survivors report a vague feeling that their heart or health is "not quite right." There may be only a slight discomfort. About one-quarter of all heart attacks occur without producing any noticeable warning signs. These "silent" heart attacks may go undiscovered until they show up during routine heart tests such as an electrocardiogram (ECG).

How serious is a myocardial infarction.

An MI is potentially very serious. It can lead to a chronic disabling condition because it can cause heart failure, or it can lead to full recovery. In some, it is rapidly fatal mainly because if the heart’s rhythm is disturbed, permanent brain damage and death can occur unless blood flow is quickly resumed.In many cases only a small part of the heart muscle is damaged (infarcts or dies) which heals as a small patch of scar tissue. The heart can usually function normally with a small patch of scar tissue. A larger MI is more likely to be life-threatening or cause complications.

How is myocardial infarction treated.

Medical treatment is aimed to open the blocked artery and restore blood flow to the affected area of heart muscle (doctors call this reperfusion). Treatment is also aimed at preventing further damage and the chance of repeat heart attacks in the future.

The part of the heart muscle starved of blood does not die ('infarct') immediately. If blood flow is restored within a few hours, much of the heart muscle that would have been damaged will survive. This is why an MI is a medical emergency, and treatment is given urgently. The quicker the blood flow is restored, the better the outlook. There are two treatments that can be done to restore blood flow back through the blocked artery.

Emergency angioplasty is, ideally, the best treatment if it is available and can be done within a few hours of symptoms starting. In this procedure a tiny wire with a balloon at the end is put into a large artery in the groin or arm. It is then passed up to the heart and into the blocked section of a coronary artery using special x-ray guidance. The balloon is blown up inside the blocked part of the artery to open it wide again. A stent may be left in the widened section of the artery. A stent is like a wire mesh tube which gives support to the artery and helps to keep the artery widened.

An injection of a 'clot busting' drug is an alternative to emergency angioplasty. In reality, this is the more common treatment as it can be given easily and quickly in most situations. Commonly used drug is streptokinase.

Once the artery is open, the heart attack is generally halted and the patient becomes pain free.

The patient is most likely to make a good recovery if reperfusion can be established in the first 4-6 hours of a heart attack.

Anti-platelet medicines, for example aspirin, reduce the tendency of platelets (a type of blood cell) in the blood to clump and clot. These medicines help to prevent the arteries from becoming blocked again.

Nitroglycerin, a vasodilator (blood vessel dilator), widens the blood vessel by relaxing the muscular wall of the blood vessel.

ACE (angiotensin converting enzyme) inhibitors, another type of vasodilator, improve the heart muscle healing process. They do this by blocking the production of a hormone (chemical signal carried in the blood) called angiotensin II.

Beta-blocking agents interfere with the nerves controlling the heart by blocking the action of a chemical they release called noradrenaline. They also block a hormone (chemical carried in the blood) called adrenaline. This makes the heart beat more slowly and less forcibly, which decreases the amount of muscle damage and can help to prevent serious arrhythmias.

A statin drug to lower the cholesterol level in your blood.

After having a myocardial infarction.

After recovering from an MI, it is natural to wonder if there are any 'dos and don'ts'. In the past, well-meaning but bad advice to "rest and take it easy from now on" caused some people to become over-anxious about their hearts. Some people gave up their jobs, hobbies, and any activity that caused exertion for fear of 'straining the heart'. However, quite the opposite is true for most people who recover from an MI. Regular exercise and getting back to normal work and life is usually advised.

How to prevent myocardial infarction.

Everybody has a risk of developing atherosclerosis which can lead to an MI. However, certain 'risk factors' increase the risk and include:

Preventable or treatable risk factors: Smoking, hypertension, poor diet, lack of exercise, high cholesterol level, obesity, excess alcohol.

Having diabetes. But if you have diabetes, the increased risk of heart disease is minimised by good control of the blood sugar level, and reducing blood pressure if it is high.

Briefly, if you can reduce any risk factors, it reduces your risk of having an MI (or of having a further MI if you have already had one).