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Diagnostic markers of acute coronary syndrome

Article-Diagnostic markers of acute coronary syndrome

heart graphics

Cardiac markers are small molecules inside the cardiac cell. Usually, there is a minimal or absence of these markers in the circulating blood in normal condition. However, if the muscle cell of the heart gets damaged because of lack of oxygen (ischemia) or strained (heart failure), some of these molecules will be released and diffused to the circulating blood. So, elevation of the level of these molecules (cardiac markers) will give us the indication of the presence and the extent of the damage of the heart muscles.

Under what conditions will these cardiac markers be helpful?

Acute coronary syndrome happens when there is a sudden decrease of blood supply to the myocardial cells. These cells will suffer from suffocation which will progress to irreversible damage of the cells unless urgent treatment of restoration of the blood supply has taken place. In the first hour or so of the ischemia, the myoglobin (MB) will be released first. After that, the creatine kinase (CK) and its MB isoenzyme (CK-MB), and subsequently, troponin T will be released.

The CK-MB usually gets elevated in 3-6 hours. The first test may be negative after acute myocardial infarction (MI), so the test needs to be repeated in 6-12 hours to rule out the MI. Usually the CK-MB peaks in the initial 12-24 hours and then goes down usually after 48 hours. On the other hand, troponin T takes 3-6 hours to get elevated, but it can last in the blood for 2 weeks. Troponin is the most specific cardiac marker for myocardial injury. Of late, new high sensitivity cardiac troponin assays are used which can detect circulating troponin 
within 1 hour and if the test is negative in 3 hours, we may safely rule out cardiac injury.

The benefits of these cardiac markers are that it confirms the diagnosis of the myocardial injury, gives the extension of the myocardial damage, and also gives a risk stratification to somebody who is presented with chest pain to the Emergency Room. If the chest pain is associated with elevated troponin T, that patient will be considered high risk and will require further urgent evaluation.

The other cardiac marker that is used for myocardial stretching in a patient with heart failure is called BNP (Brain Natriuretic Peptide). This marker can be very helpful to diagnose a patient who comes in to the Emergency Room with a complaint of shortness of breath. A normal level may make a heart failure as the cause of shortness of breath very unlikely. On the other hand, a severe significant elevated level makes the heart failure diagnosis very likely. The BNP is also very helpful in following up patients with heart failure to evaluate the efficacy of the treatment and to detect early decompensation.

Another cardiac marker is called High-Sensitivity C-reactive protein (CRP) which is an indicator of inflammatory process in the coronary atheroma. Patients with elevated High-Sensitivity CRP are at a high risk of having a cardiac event. On the other hand, there is a recent study to show that specific anti-inflammatory medications which is “Anti-Interleukin-1 Antibody” may decrease the cardiac event in patients who have coronary artery disease and High-Sensitivity CRP.

Cardiac markers not only help in confirming the diagnosis of myocardial injury and heart failure, and in following up with patients and their prognosis, but they also help in reducing medical costs by avoiding unnecessary admissions for patients with chest pain.                                                                                                     

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