Broadly classified, there are 3 main types of myocardial infarction (heart attacks), also called Acute Coronary Syndrome (ACS).
- ST elevation myocardial infarction
- Non ST elevation myocardial infarction
- Unstable angina
Heart attacks are caused by a decrease in blood supply to the heart muscle. This decrease causes damage to the heart muscle and can affect the way it functions. The degree of damage is variable and depends on what degree the blood supply was reduced.
Let’s take a brief look at the different types of heart attacks.
‘ST elevation’ heart attacks
These are commonly called STEMI (ST Elevation Myocardial Infarction) by doctors. It is called so due to the changes seen on the ECG. We have discussed normal ECGs elsewhere.
In this kind of heart attack, the blood supply is cut off to a part of the heart muscle. The common reason for this is the development of a blood clot within the coronary arteries which stops the blood flowing to a particular part of the heart. Depending on which artery is blocked and what part of the heart is not receiving blood supply, there are 4 main kinds of heart attacks.
1. Anterior myocardial infarction
Here, the heart attack affects the front surface of the heart (anterior = front). This often takes place when the large artery that lies on the front of the heart is blocked (left anterior descending artery), or may occur when the main artery is blocked (left main stem).
2. Posterior myocardial infarction
This affects the back of the heart (posterior = back). They are slightly harder to diagnose. They often accompany inferior myocardial infarction and occur due to blockage of the right coronary artery.
3. Inferior myocardial infarction
This affects the under-surface of the heart (inferior = under). It usually occurs when the circumflex or the right coronary artery is blocked.
4. Lateral myocardial infarction
This affects the sides of the heart.
Many times, patients may have a combination of 2 different areas. For example, an infero-posterior MI affects the bottom and back of the heart.
‘Non ST elevation’ heart attacks
These are sometimes called NSTEMI. Here, the symptoms of the patient are typical of a heart attack or angina, but the ECG changes are different to a STEMI. In addition, blood tests help diagnose this condition.
Patients who develop an NSTEMI are usually at risk of developing a full STEMI if treatment is not offered soon. In a way, an NSTEMI is a ‘warning’ attack, though its effects on the heart can sometimes be drastic.
This is a clinical condition where patients who have disease in the coronary arteries develop symptoms on a regular basis and on minimal exertion. Angina occurs a lot more frequently than usual. Patients who already have heart disease may notice themselves getting more and more chest pain despite taking their medication regularly.
Patients with unstable angina need aggressive management. This is because it can lead to a heart attack if not treated promptly. Tests such as a coronary angiogram may need to be performed.
Other terms you may hear
1. Stunned myocardium
This is a phenomenon where the heart muscle that has regained its blood supply (after a period of lack of blood supply) fails to pump adequately.
2. Hibernating myocardium
In hearts that have had the blood supply cut off, there is a possibility that a part of it will recover if the blood supply is restored. This might take a few days, and during that time the heart muscle is ‘resting’. This is called a ‘hibernating’ myocardium.