CARDIAC ENZYME STUDIES 

Enzymes are biochemical catalysts. They are necessary to the body’s structure, function, and regulation that help chemical reactions take place. Cardiac enzymes are found in heart tissue, and they serve as catalysts for the heart’s various biochemical reactions.

Key cardiac enzymes are:

• Troponin
• Creatine Phosphokinase (CPK)

Troponin is a particularly important cardiac enzyme, because it plays a central role in how heart muscles contract. It controls how the heart muscle responds to the signal received for contraction, and it regulates the force with which the muscle contracts.

Creatine phosophokinase is also important, for it gives needed energy for movement by the heart.

Low levels of troponin and creatine phosphokinase (CPK) are normally found in blood, but if the heart muscle is injured, such as from a heart attack, the enzymes and proteins leak out of damaged heart muscle cells, and their levels in the bloodstream rise.

So, why are cardiac enzymes important and what can they tell us?

In the case of a blocked artery (i.e., heart attack), heart surgery, or any type of heart injury, the flow of oxygen-rich blood to the heart is interrupted—damaging the heart and its muscles.

Using a heart attack as an example, a coronary artery, which is an artery that supplies blood to the heart, is completely blocked by a blood clot, and the heart is deprived of oxygenated blood. When heart muscle is damaged in the case of a heart attack, high concentrations of cardiac enzymes are released into the blood stream.

Death or damage to heart muscle cells leads to disintegration of heart cell membranes, which are the outer coats of muscles cells.

Loss of cell membranes results in a “leaking” of cardiac muscle enzymes into the blood—leading to high levels of cardiac enzymes in the blood after a heart attack or other heart damage.

For heart attacks, measuring the levels of cardiac enzymes in the blood is a common test for the diagnosis of a heart attack and the amount the damage done to the heart; the medical field considers the measurement of cardiac enzyme levels in the blood to be a reliable test for a heart attack.

About measuring cardiac enzyme levels

However, one should note that cardiac enzymes leak slowly into the blood, and unusually high levels of cardiac enzymes in the blood may not appear until six or more hours after the onset of a heart attack. Thus, if a person has chest pain but has normal levels of cardiac enzymes in the blood, a heart attack cannot be ruled out. In that instance, repeated cardiac enzymes tests are normally conducted to confirm diagnosis of a heart attack.

There are separate cardiac enzyme tests for Troponin and CPK. The CPK is considered the least accurate test because the CPK enzyme is found in the heart muscles, skeletal muscles, and the brain; as such, unusually elevated CPK enzyme levels in the blood stream can be attributed to a muscle injury.

The Troponin test is considered the most accurate cardiac enzyme test in the diagnosis of a heart attack.

Cardiac enzyme studies must always be compared with symptoms, physical examination findings, and electrocardiogram (ECG) results.

Certain Enzymes are released from the heart muscle cells when it is injured (“heart attack”) such as:

• Creatine phospho kinase (CPK)
• Lactatate dehydrogenase (LDH)
• Serum glutamic oxaloacetic transaminase (SGOT) or Aspartate transaminase (AST)

These enzymes are normally found in the blood at low levels.

The abnormal elevation of these enzymes in the blood stream can occasionally be the only indicator that a heart attack (myocardial infarction) has occurred.

The physician will test the cardiac enzymes in situations where a myocardial infarction is suspected (patient with chest pain). Patients known to have had a heart attack may have cardiac enzymes monitored over several days to document improvement.

Often the cardiac enzymes will not be abnormally elevated until 24 hours after the onset of the chest pain.

An abnormal elevation in CPK is diagnostic for a heart attack, even in cases where the ECG may be normal. Increased diagnostic accuracy is found when this blood test is performed serially (over 24 hours) with the ECG.

Many medicines may affect the results of this test. Be sure to tell your health professional about all the nonprescription and prescription medicines you take.

Cardiac enzyme studies are often repeated over several hours for comparison. Blood samples for these cardiac enzyme tests are usually drawn every 8 to 12 hours for 1 to 2 days after a suspected heart attack, to look for the rise and fall in the enzyme levels.

CARDIAC TESTS: protein and enzyme tests

ENZYME TESTS