What are Cardiac Enzymes?
Enzymes are proteins that manage the body’s metabolism and other chemical processes. The heart releases cardiac enzymes or cardiac biomarkers in case of heart damage or stress due to a lack of oxygen. Elevated heart enzyme levels can indicate a heart attack or other conditions like ischemia or acute coronary syndrome.
Types of Cardiac Enzymes
The types of cardiac biomarkers or enzymes include creatine kinase, troponin, and myoglobin. Historically, LDH, or lactate dehydrogenase, was also used as a cardiac biomarker but is non-specific. When myocardial necrosis occurs, cardiac enzymes are released into the body's circulation, as seen in a heart attack or an MI (myocardial infarction).
1. Myoglobin
Myoglobin is released into the circulation after damage caused to the muscle tissue, including myocardial necrosis. Since skeletal muscle contains myoglobin, this measurement becomes non-specific for myocardial infarction. The benefit of myoglobin is that a considerable increase is seen in its levels just after 30 minutes of an injury, unlike creatine kinase and troponin, which can take around three to four hours. However, in day-to-day practice, this is not used as a biomarker as it lacks specificity and can be elevated in any muscle injury.
2. Troponin
The enzymes troponin T and I play a significant role in cardiac myocyte’s contractile apparatus. These proteins are released into the bloodstream three to four hours after myocardial infarction. It remains detectable for 10 – 14 days after the occurrence of a heart attack. The prolonged half-life allows for late diagnosis of MI, which makes it challenging to detect re-infarction, as in the case of acute stent thrombosis after PCI (Percutaneous Coronary Intervention). Though these markers have high specificity, these markers can also be elevated in certain other conditions and must be ruled out while making a diagnosis.
3. Creatine Kinase (CK) MB
Creatine kinase or creatine phosphokinase is a muscle enzyme that exists as an isoenzyme. The level of the enzyme creatine kinase increases three to four hours after myocardial infarction and remains elevated for approximately three to four days. This characteristic makes it useful for detecting re-infarction within four to ten days.
What Is a Cardiac Enzyme Test?
A cardiac enzyme test measures cardiac marker enzymes in a person’s blood and detects if an individual has experienced a heart attack. The test may also be recommended in case of symptoms that indicate a blockage in the heart’s arteries, such as chest pain, fatigue, dizziness, shortness of breath, sweating and nausea.
Purposes of a Cardiac Biomarker Test
A few important purposes of a cardiac biomarker test are:
Screen for heart conditions
Diagnose heart conditions that cause symptoms like shortness of breath and chest pain
Manage how well heart surgery and medications work
Predict a prognosis for heart problems
What Happens During a Cardiac Enzyme Test?
A suspected heart attack is the most common reason for conducting a cardiac enzyme or troponin test. During a heart attack, the artery supplying blood to the heart gets blocked, and the heart muscle doesn’t get enough oxygen. As the heart muscle cells die, they release troponin into the blood. Cardiac troponin is one of the most specific and commonly used biomarkers to determine a heart attack. It can be measured in two primary forms: troponin I (cTnI) and T (cTnT).
Doctors typically test for both cTnI and cTnT as these enzymes are the most specific to a heart attack. In some situations, the level of creatine phosphokinase MB may also be tested. A healthcare professional inserts a needle into an individual’s arm and draws a blood sample. The sample will then be sent to the lab, where it undergoes an analysis for cardiac marker enzymes. No special preparation or fasting is required to undergo a cardiac troponin test. However, some critical information that an individual must share with the doctor is if they take biotin or vitamin B7, as it can lower troponin levels.
What Do Elevated Cardiac Enzymes Indicate?
In a cardiac enzyme test, doctors measure the blood’s troponin content in nanograms per millilitre (ng/ml). The higher the nanograms per millilitre, the greater the chances of a heart attack. Suppose an individual’s cardiac enzyme test is positive for troponin levels greater than 0.04 ng/ml. In that case, he/she is likely to have experienced a heart attack or an injury to the heart. In addition to this, a cardiac enzyme test helps doctors assess the level of damage caused due to a heart attack. Also, a cardiac enzyme test is usually repeated around four to nine hours after a heart attack or a suspected injury.
What Are the Possible Causes of Elevated Cardiac Enzymes?
Apart from a heart attack, here are a few other factors that may cause the cardiac enzyme level to be elevated:
How are Stress and High Cardiac Enzyme Levels Related?
Stress cardiomyopathy, also known as broken heart syndrome, mimics a heart attack. It is most often triggered by severe physical or emotional stress, such as intense trauma. Cardiac enzymes such as troponin, are released into the blood when a heart muscle is damaged. Stress cardiomyopathy can also lead to a rise in these enzyme levels, as it results in a temporary weakening of the heart muscle.
Read more: Stress and Its Connection to Heart Diseases
Treatments for Elevated Cardiac Enzymes
If a doctor determines that a heart attack has caused elevated cardiac enzymes, then he will advise for a coronary angiogram. Further treatment will depend upon the result of the coronary angiogram.
1. Medications
The medications that can be prescribed for elevated cardiac enzyme levels caused by a heart attack include:
2. Interventional procedure
The interventional procedure may include Percutaneous Transluminal Coronary Artery (PTCA) stenting of the coronary artery (also commonly called coronary artery stenting) or Coronary Artery Bypass Grafting (CABG):
Percutaneous Transluminal Coronary Artery (PTCA)/ Coronary artery angioplasty
Also known as percutaneous coronary intervention (PCI), it is a minimally invasive procedure that aims to reopen blocked arteries and improve blood flow. It is either done through the artery in the leg or the hand. Catheters are placed through which the arteries of the heart are accessed. The blocked segment is then crossed with a wire. First, the blocked segment is ballooned with a balloon, and finally, a stent is placed in that segment so patency is maintained.
Most of the time, the patient does not require ventilatory support and is usually fit to go home the day after the procedure.
CABG (Coronary Artery Bypass Grafting)
CABG is a surgical method of treating coronary artery blockage in which a new passage is created by bypassing the blocked segment by opening the chest. The patient requires ventilatory support and may also require heart-lung support during the procedure. Usually, the patient requires 5-8 days of hospitalisation.
Article By Dr. Amit Kumar Chaurasia
Chief Cath Lab & TAVI (Unit I) - Cardiology
Artemis Hospitals