Cardiac enzymes and cardiac

proteins

Dr. Nabil Bashir

Introduction

• Diagnostic accuracy of biochemical markers for AMI can be enhanced by combining the most sensitive and the most specific tests.

• The temporal pattern of marker protein release is of diagnostic importance .

• The ideal marker of myocardial injury would provide :

A. Early diagnosis.

B. Prognosis: Assessment of the success of reperfusion after thrombolytic therapy.

C. Detection of re-infarctions.

D. Determination of infarct size.

• Acceptable biochemical markers of ischemic heart disease are now considered to include

A. Myoglobin,

B. CK-MB,

C. Total CK,

D. Cardiac troponins T and I.

Creatine Kinase

• Enzyme CK has three isoforms composed of two chains (M and B chains), MM, MB and BB

• The MB fraction is found predominantly in cardiac muscle.

• It is important to show both a rise in the serum concentration of CK-MB, and a rise in the ratio of CK-MB to total CK to diagnose MI.

• Typically, CK-MB begins to rise 4-8 hours after the MI, peaks within the first 24 hours, and can be used to establish the diagnosis of the MI.

• The CK-MB returns to normal range after 48-72 hours. Case 2 illustrates the use of this marker to confirm clinical diagnosis, as mentioned above.

• It can also be used for follow up, as an additional tool in evaluation of cardiac patients

Troponin I

• Troponin I is the subunit of the troponin complex that binds actin and inhibits actomyosin ATPase activity in the absence of calcium

• Three isoforms of troponin I have been described, one cardiac (cTnI), and two skeletal muscle (slow twitch, sTnI, and fast twitch, fTnI) .

• Each of the three TnI isoforms is encoded by different genes located on different chromosomes.

• Unlike CK-MB, cardiac troponins are not found in serum from healthy people.

• This make cTnI an excellent biochemical marker for detection of myocardial injury.

• cTnI has been shown to be a very sensitive and specific marker for acute MI.

• It can be detected within 4-8 hrs after the onset of symptoms.

• cTnI peaks between 14-36 hrs after onset of AMI and remains elevated for 5-7 days after AMI.

• Due to long duration of increase of cTnI following onset of chest pain, it could replace LD-2 isoenzyme for the detection of late presenting AMI patients.

• Additionally, recent studies demonstrate that cTnI is more sensitive than the LD1/LD2 ratio.

• cTnI has proved to be a diagnostic and prognostic marker for myocardial damage with high diagnostic sensitivity and specificity.

myoglobin

• One of earliest markers, which is very sensitive but, lacks specificity.

• Its diagnostic value is primarily due to its early appearance.

case

LABORATORY DATA

Cardiac enzyme levels

DAY TIMET CPK (normal 0-200 IU/L) MB CPK (normal <7 IU/L) RI(normal <3) TROPONIN I(normal < 1.5 ng/mL) Day 1 00:15AM 1494 33.9 2.3 66.6

Day 110:40 AM 1544 54.2 3.5 83.1

Day 105:24 PM 2286 64.5 2.8 125.7

Day 211:40 PM 2536 65.4 2.6 141.7

Old biomarkers

• Aspartate aminotransferase

• Lactate dehydrogenase

Lactate dehydrogenase

• Rises in 12 to 24 hours following MI,

• Peaks in 2 to 3 days

• Gradually disappearing in 5 to 14 days

Tissue distribution of LDH

Normal LD1:LD2 = 0.5-0.75

MI LD1:LD2 > 1