Detection of ischemic myocardial injury in patients with normal, or moderately elevated, serum CK and AST activities
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A serum creatine kinase-MB (CK-MB) fraction of 6% or greater, observed when enzyme activities double within 24 hours, strongly suggests acute myocardial infarction. Lower CK-MB levels indicate no myocardial infarction.
Area of Science:
- Cardiology
- Biochemistry
- Clinical Medicine
Background:
- The clinical significance of elevated serum creatine kinase-MB (CK-MB) levels in diagnosing irreversible myocardial damage remains debated.
- Assessing enzyme activity changes in the early hours post-admission is crucial for patients with suspected myocardial ischemia.
Purpose of the Study:
- To investigate the diagnostic value of serum CK-MB fraction levels in identifying acute myocardial infarction.
- To determine if a specific CK-MB threshold, particularly when enzyme activities double, correlates with irreversible myocardial damage.
Main Methods:
- Serum samples from patients with suspected myocardial ischemia were analyzed for creatine kinase (CK) and aspartate transaminase (AST) activities over 24 hours.
- Enzyme isoenzymes were fractionated when CK and AST activities doubled, even within normal ranges.
- A comparative study included 102 patients without enzyme doubling but with higher average activities.
Main Results:
- In 30 patients exhibiting enzyme doubling within 24 hours, a CK-MB fraction of 6% or greater was found in 26 admissions, correlating with acute subendocardial infarction diagnoses.
- None of the 5 patients with a CK-MB fraction below 6% received a diagnosis of acute myocardial infarction.
- A comparative group of 102 patients without enzyme doubling did not show CK-MB fractions of 6% or greater and were not diagnosed with acute myocardial infarction.
Conclusions:
- A serum CK-MB fraction of 6% or greater, particularly when associated with a doubling of enzyme activity within 24 hours, is a reliable indicator of acute subendocardial infarction.
- Lower CK-MB fractions (<6%) in this context suggest the absence of acute myocardial infarction.
Abstract:
It is still undecided in clinical medicine if an increased serum CK-MB level indicates irreversible myocardial damage. We measured CK and AST activities on three serum samples obtained during the first 24 hours following admission of patients with a clinical history suggesting myocardial ischemia. Isoenzymes were not separated when CK and AST activities were less than 300 U/L and 35 U/L respectively, but were fractionated when the enzyme activities doubled during the first 24 hours even within their normal ranges. Over a three-year period this doubling occurred in 30 patients, one of whom was admitted twice to the hospital. The serum CK-MB fractions of these patients were 6% or greater in 26 and less than 6% in 5 admissions. The final clinical diagnosis given to the patients on 20 of these 26 admissions was acute subendocardial infarction. None of the five patients with a CK-MB fraction less than 6% had a clinical diagnosis of acute myocardial infarction. A comparative study of 102 patients with higher average enzyme activities but without doubling of both enzymes during a 24-hour period, did not yield a CK-MB of 6% or greater. None of this group of patients was diagnosed clinically as having had acute myocardial infarction.