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Laboratory Diagnosis of Acute Myocardial Infarction - nurse labs myocardial infarction


Laboratory Diagnosis of Acute Myocardial Infarction-nurse labs myocardial infarction

Trakia Journal of Sciences, Vol. 3, No. 1, pp 8-14, 2005
Copyright ? 2005 Trakia University
Available online at:
http://www.uni-sz.bg
ISSN 1312-1723
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LABORATORY DIAGNOSIS OF ACUTE
MYOCARDIAL INFARCTION
A. Ruseva*
Central Clinical Laboratory, University Hospital, Pleven, Bulgaria
ABSTRACT
The early recognition of cardiac ischemia and accurate placement of the patient in the risk spectrum
of the acute coronary syndrome are critical to the effective management of patients with acute
myocardial infarction (AMI). Apart from clinical history, physical examination and accurate ECG
interpretations, cardiac biomarkers are equally valuable in the initial evaluation of patients with non-
traumatic chest pain. Previously the diagnosis of an AMI was based on World Health Organisation
(WHO) criteria which defined MI as the presence of two out of three characteristics comprising:
symptoms of acute ischemia (chest pain), development of Q waves in ECG and elevated activities of
traditional serum enzymes comprising: total CK, CK-MB, ASAT and LDH. An ideal biomarker
should have the following characteristics: relatively high concentration within cardiac tissue, have no
significant tissue sources other than the heart, have high clinical sensitivity and specificity, be
detectable in the blood early after the onset of chest pain, have elevated blood levels for several days
after the onset of symptoms, and have an assay with a quick turnaround time. Since no single
biomarker fulfils all of these criteria, the NACB proposes the use of two biomarkers for the diagnosis
of AMI: an early marker - myoglobin and a definitive marker- cardiac troponins. When cardiac
troponin is not available, the next best alternative is CK-MB (measured by mass assay).
Key Words: AMI, laboratory diagnosis, troponin, myoglobin, CK-MB
When a patient presents with chest pain in the 1. To assess the probability that the patient's
emergency department, physicians must symptoms are related to acute coronary
consider a continuum of acute coronary ischemia.
syndromes which could include the 2. To assess the patient's risk of recurrent
following: non-cardiac chest pain, unstable cardiac events, including death and
angina in which oxygen deprivation occurs recurrent ischemia [5].
without permanent damage to heart muscle Diagnosis of an AMI in the past, during the
and heart attack or myocardial infarction (MI) early 1990s, utilised the World Health
with permanent heart muscle damage If Organisation (WHO) criteria defining MI as
patients with chest pain are not properly the presence of two out of three
evaluated, then some patients without an acute characteristics:
coronary event will be inappropriately ? symptoms of acute ischemia (chest pain);
admitted, while patients experiencing an AMI ? development of Q waves in ECG;
may be discharged[25]. Critical to the ? elevation of traditional enzyme activities
effective management of these patients are the in serum: total CK, CK-MB, ASAT and
early recognition of a cardiac ischemia event LDH [4, 20, 23, 24]
and the proper placement of the patient in the Creatine kinase (CK) emerged as the primary
risk spectrum of the acute coronary syndrome indicator of MI. Total CK starts to rise within
[20]. The objectives of the initial evaluation of 3 to 8 hours after MI, peaks at 10 - 24 hours
patients with non-traumatic chest pain are and returns to normal by 3 - 4 days. It can be
twofold: markedly elevated with skeletal muscle
trauma or brain injury. Other skeletal muscle
diseases including dystrophy, myopathy and
Correspondence to: Adelaida Ruseva, MD. myositis show increase. Electrical cardio-
Central Clinical Laboratory, University Hospital, version shows an increase as does cardiac
8-A G. Kotchev Str., 5800 Pleven; E-mail: catheterisation without myocardial damage.
adi_ruseva@dir.bg
8 Trakia Journal of Sciences, Vol. 3, No. 1, 2005
RUSEVA A.
Total CK is increased in hypothyroidism, pulmonary emboli, hepatic disease and also
stroke, surgery and in patients with by intramuscular injections. However, in the
convulsions who have skeletal muscle patient with a minor infarction or a non-Q-
damage. Therefore total CK is not specific for wave infarction there may be no change in the
MI. AST values [9].
Three isoenzymes in blood comprise According to the National Academy of
the total fraction of these: CK-MM (CK-1) Clinical Biochemistry (NACB), do to low
(Skeletal Muscle) > 95% of total, CK- MB specificity and the availability of more
(CK-2) (Myocardial)

What are the 5 types of myocardial infarction?Type 2 MIType 1 MI (NSTEMI)Demand ischemia onlyUnstable angina onlyOther, please specify:None of the above / Not applicable