A heart attack (also known as myocardial infarction) occurs when there is a sudden obstruction of blood flow in the coronary artery. The heart is a fist-size organ which lies in the centre of the chest. Its main function is to pump blood to the lungs where the blood is replenished with oxygen and then subsequently to pump blood to the rest of the body to allow it to function properly. In order for the heart itself to function properly, it receives blood rich with oxygen via blood vessels called coronary arteries.
During a heart attack, a person usually experiences severe central chest pain, classically described as heavy or crushing sensation. The chest pain is very similar to angina pain but it is more prolonged (>30 mins) and not relieved with rest or usual medications for angina. This condition is usually accompanied by nausea, sweating and apprehension. However, 25% of heart attacks are clinically silent.
Atherosclerosis is the process that causes gradual buildup in the inner lining of the artery and therefore narrowing of the coronary artery. Although its exact mechanism is unknown, certain factors in a person increase the likelihood of this process. These include smoking, diabetes mellitus, high blood pressure, cholesterol and strong family history.
When the narrowing inside the lumen of the artery is severe, the amount of blood supply is unable to meet the demand of the heart muscle, especially when the person is exerting or exercising. The condition whereby the heart muscle is starved of essential nutrients is called myocardial ischaemia. When myocardial ischaemic occurs only upon exertion, it is called angina (i.e. chest pain). Stable angina is not life threatening and is usually promptly relieved by rest to reduce heart muscle demand or medications to dilate the coronary artery to increase the blood supply.
Conversely, heart attack is due to sudden, complete blockage of the coronary artery causing permanent damage to part of the heart muscle (myocardial infarction). This is usually due to sudden breakage of the lining of a narrowing (plaque rupture) inside the artery. This causes clot formation at the site of rupture (a process known as Atherothrombosis) and subsequent complete blockage of the artery. Myocardial ischaemia occurs at rest and if the artery is not opened promptly, heart muscle cells will die within minutes. If ischaemia persists for more than 6 hours, majority of the muscles supplied by that artery will be permanently damaged.
When a heart attack occurs, the patient will usually feel severe chest discomfort.
In spite of treatment given, there is still a 10% mortality rate in patients with heart attack. This is usually caused by abnormal heart rhythm (ventricular fibrillation) due to electrical instability of the heart or heart failure due to massive heart attack. Occasionally, heart muscle can rupture after a heart attack and this is usually fatal.
The diagnosis of heart attack is based on three findings: characteristics of chest pain, ECG and blood test. If two of the three findings are present, it will confirm the diagnosis of heart attack. ECG is the most useful test as it usually shows characteristic changes within minutes of heart attack.
The eventual confirmation of heart attack is the blood tests, which detect proteins released into the blood stream when part of the heart muscle dies. However, these proteins (cardiac enzymes) can only be detected four to six hours after heart attack, which may be too late to implement treatment if treatment of heart attack is based on this alone.
The goal of treatment of heart attack is early diagnosis and to open up the blocked artery quickly and effectively to minimise the extent of damage to the heart muscle. Currently, there are two treatment options to unblock the artery. The fastest way to treat heart attack is to give a powerful blood thinning medication (thrombolytic agents) to dissolve the clot and therefore unblock the artery. Any qualified physician can give this immediately upon diagnosis of heart attack. However, it is only effective in slightly more than 50% in opening the blocked artery and may cause serious bleeding complications from other areas, including the brain.
A more effective way to unblock the artery is by inserting a balloon or stent through a small puncture in the groin or wrist to open up the artery, known as coronary angioplasty. It is successful in more than 90% of the cases. The disadvantage of this treatment is that the procedure needs to be performed in the procedure suite and requires experienced operators. There is also a delay in time in getting the whole angioplasty team in the hospital, especially after office hours. At the National Heart Centre Singapore, emergency angioplasty for patients who are admitted for heart attack is available round the clock.
The patient should follow the medication regimen as prescribed even if he feels well. He should tell the doctor if he has any side effects from the medication. The patient should also tell the doctor if he finds the dosing inconvenient or if he finds it difficult to take his medication regularly.
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