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 : Early diagnosis. Prognosis: Assessment of the success of reperfusion after thrombolytic therapy. Detection of re-infarctions. Determination of infarct size.

Acceptable biochemical markers of ischemic heart disease are now considered to include Myoglobin, CK-MB, Total CK, 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