A 53-year-old banker, presents to the ER on Saturday evening complaining of persistent left shoulder, arm and neck pain that started in the morning. The pain started during a "pickup football game" with some friends that morning. He concedes that he may have "run around a bit more than he was used to" and "probably pulled some muscles" in his arm and neck. He has tried different positions, heat, Acetaminophen and ibuprofen to alleviate the pain without success. The pain has worsened throughout the day and now is bad enough that he feels "weak and sweaty".
He is mildly diaphoretic ("sweaty") but not in obvious distress. His vital signs are stable except for a mild tachycardia (fast heart beat) of 123 beats per minute. There is no tenderness to palpitation of his arm and neck muscles and there is full range of motion at all of the joints. His lungs are clear, his abdomen soft without tenderness and while there was tachycardia on cardiac examination, no murmurs were heard.
Laboratory examination revealed:
Blood Count: normal
Electrolytes: normal
Urinalysis: normal
Cardiac Troponins (T and I) I 15 mg/L; T 0.6 mg/L (nl: I < 10 mg/L; T 0-0.1 mg/L)
Total Creatine Kinase (CK) 4,552 U/L (nl:<190)
MB fraction comprising 18% of the total (nl: 4-6%)
1. What is your diagnosis?
Myocardial infarction, heart attack
2. How do you explain the location of his pain?
Referred pain, meaning the pain is not always in the chest but can be in the arms, shoulders, neck and jaw
3. What additional studies should you use to confirm your diagnosis?
Lactate Dehydrogenase (LDH)- H4 isozyme may persist for two weeks
Aspartate Amino
Transferase (AST)- peaks at 2 days, returns to normal by 4 days.
(mitochondrial/cytoplasmic isozyme)
EKG, Angiography
4. How did the creatine kinase isoenzymes help in your diagnosis?
Isozyme: MB, cardiac muscle, fraction is elevated
5. Explain the biochemistry of these isoenzymes?
Creatine Phosphokinase (CPK):
Creatine + ATP -----> Phosphocreatine + ADP
Tissue specific
isozyme, dimer consisting of two subunits, M and B
MM isozyme - muscle
BB isozyme - brain
MB isozyme - heart
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