- ST elevation on ECG - http://www.unm.edu
A heart attack – also called a coronary occlusion, a coronary thrombosis or an acute myocardial infarction (AMI) – takes place when one of the arteries (termed a coronary artery) supplying blood to the heart muscle becomes suddenly and completely blocked. Consequently, blood cannot flow through this artery to the heart muscle (called the myocardium) and some part of this heart muscle begins to die. Without prompt medical treatment, such damage to the heart muscle can be permanent and may even result in death of the patient.
Symptoms of Heart Attack
When a person suffers a heart attack, they typically experience symptoms of crushing chest pain that can spread to the neck or shoulder, but sometimes the only manifestation of a heart attack may be breathlessness or a vague discomfort in the chest.
In the past, if it was suspected that a patient's symptoms were due to a heart attack, doctors diagnosed the condition by identifying a typical pattern on the electrocardiogram (the ECG or EKG). If a portion of heart muscle was damaged, the ECG tracing showed an elevation of the ST segment, and this "ST Elevation" was considered pathognomic of a heart attack.
Today, cardiologists differentiate between two types of heart attacks:
- STEMI - the ST Elevation Myocardial Infarction
- NSTEMI - the Non-ST Elevation Myocardial Infarction
STEMI – the ST Elevation Myocardial Infarction
This type of heart attack is diagnosed if a patient presents with symptoms suggestive of a cutting off of the blood supply to the myocadium (referred to medically as cardiac ischemia) and also if the patient's ECG shows the typical heart attack pattern of ST elevation. The diagnosis is made therefore purely on the basis of symptoms, clinical examination and ECG changes, and doctors do not wait for the results of blood tests to initiate treatment for the heart attack because these patients have a large portion of their mycocardium at risk of damage and death due to the blocked coronary artery. Treatment involves the immediate administration of ASPIRIN® and admission to an operating theatre (often called a cardiac catheterisation laboratory or simply a "cath lab") to have a coronary angiogram performed, the blood clot occluding the blood vessel removed so that the narrowed coronary artery can be widened and kept dilated with a stent.
Ideally, restoration of blood flow to the "at risk" myocardium should be achieved within 90 minutes.
NSTEMI – the Non-ST Elevation Myocardial Infarction
In the case of a Non-ST elevation heart attack, the symptoms of chest pain can be identical to that of a STEMI, but the important difference is that the patient's ECG does not show the typical ST elevation changes traditionally associated with a heart attack. The patient often has a history of having experienced angina, but the ECG at the time of the suspected attack may show no abnormality at all. The diagnosis is suspected on the history and symptoms and is confirmed by a blood test which shows a rise in the concentration of substances called cardiac enzymes in the blood. These enzymes (the most prominent is called Troponin)are found in the cells of the heart muscle, and if these myocardial cells are damaged, the cardiac enzymes leak out of the damaged cells into the blood stream.
Patients whose heart attacks are of the Non-STEMI type do not need to be rushed into the cath lab in a time-critical manner. It is reasonable to make them stable, administer ASPIRIN® and other clot dissolving medications such as heparin or clopidrogel as well as heart protective drugs such as beta blockers and nitrates, and take them electively into the cath lab for angiography. Such patients are often found to have a critical but non occlusive narrowing of a coronary artery which can be treated with stenting.
Prognosis for STEMI and NSTEMI Patients
The survival of both STEMI and NSTEMI patients during the six months following their heart attacks are virtually no different. Long term outcomes are improved by careful adherence to continued medical therapy, and it is essential that all patients who have suffered a heart attack and been stented see their doctor regularly and continue long term therapy with medications such as:
- ASPIRIN®
- clopidrogel
- statin (cholesterol lowering) drugs
- beta blockers (medications that slow the heart rate and protect the heart muscle)
- ACE inhibitors (medications that improve myocardial function and blood flow)
Damage to the heart muscle does not always manifest as the typical crushing central chest pain usually associated with a heart attack. Even if the characteristic EKG appearance of ST elevation is not seen, heart attacks do damage heart muscle - so the best way of dealing with heart attacks is to prevent them.
Further information: Warning Signs of a Heart Attack
Sanjiva Wijesinha - Dr. Sanjiva Wijesinha, Associate Professor at Monash University medical school, writes on health, travel and medical topics.
