A heart attack, also called a myocardial infarction, is typically caused by a complete blockage of one or more of the arteries supplying blood to your heart. The interruption in blood flow causes damage to that part of the heart, which can be permanent. Heart attack symptoms include crushing chest pain, pain in the jaw, shortness of breath and lightheadedness. Diagnosis is made using an electrocardiogram and a blood test to measure your cardiac enzymes, which include lactate dehydrogenase (LDH), creatine phosphokinase and troponins.
Testing Cardiac Enzymes
Cardiac enzymes are tested using a blood test specific for each enzyme. Blood is drawn from a vein in your arm or hand. The site where the phlebotomist will insert the needle is first cleansed with an antiseptic, such as an alcohol pad, to prevent any microorganisms from inadvertently getting into your bloodstream. A small, rubber tourniquet is applied above your elbow and tightened to increase the amount of blood in the vein. A needle is inserted into the vein and blood is drawn into a sterile, airtight tube, which is then sent to a laboratory for analysis.
Lactate Dehydrogenase
Lactate dehydrogenase (LDH) is an enzyme found in many cells and tissues, including the heart muscle. The levels of LDH become elevated due to a wide variety of ailments. A small amount, which is detectable using a blood test, leaks into the bloodstream following tissue damage. An LDH test is used to identify the specific cause and location of the tissue damage and is useful for detecting heart attack, cancer, liver disease, kidney disease, muscular dystrophy and stroke. It is also used to monitor how well the tissue damage is being repaired by the body. However, Lab Tests Online states that LDH testing has largely been replaced by troponin-level testing in diagnosing a suspected heart attack.
Creatine Phosphokinase
Creatine phosphokinase, also referred to as creatine kinase, is another type of cardiac enzyme. It is found in heart and skeletal muscle, as well as in brain tissue. Creatine phosphokinase levels are elevated following any condition causing tissue damage to those organs, including heart attack. Following stress or injury to body tissue, creatine phosphokinase is released into the bloodstream and can be detected by analyzing a blood sample. High creatine phosphokinase levels are used to assess tissue damage following heart attack, stroke, electric shock and heart infections, as well as muscular disorders.
Troponin
The three different types of troponins, troponin C, troponin T and Troponin I, are found in heart and skeletal muscle; they are abbreviated as TnC, TnT and TnI. Both TnT and TnI occur in forms specific to the heart and testing their levels has become the standard for diagnosing a suspected heart attack. Troponins are usually found in the bloodstream in very small amounts; higher levels of TnT and TnL are indicative of how much heart damage has occurred. According to the American Heart Association, troponin levels elevate three to four hours after a heart attack and remain high for 10 to 14 days.
