Failure of creatine kinase slope values to reliably predict acute myocardial infarction

Exclusion of acute myocardial infarction. The value of measuring creatine kinase slope

For the exclusion (and diagnosis) of acute myocardial infarction, we studied timed sequential (slope) measurements of creatine kinase and creatine kinase-MB catalytic activity concentration, creatine kinase-MB mass concentration, troponin T and myoglobin, using data from 242 patients consecutively admitted for evaluation of suspected acute myocardial infarction in the 12 hours before admission. Three biochemical strategies based on measurements in two consecutive samples obtained within 12 hours after admission were evaluated. The highest sensitivities were encountered for a biochemical strategy based on the sole measurement of creatine kinase mass concentration (98%) or troponin T (96%) and a strategy based on measurements of creatine kinase activity concentrations, which includes creatine kinase slope calculation and measurement of creatine kinase mass concentration (95%). Both strategies were applied in subgroups of patients based on the electrocardiographic findings. In patients with a normal electrocardiogram, the sensitivity of the strategy using sole measurements of creatine kinase mass concentration was 100%, but this was true for the strategy based on creatine kinase slope measurements, which is the cheaper and therefore preferred procedure for excluding myocardial infarction. This approach, however, does not account for detecting minor myocardial cell damage in patients not yet fulfilling the criteria of the World Health Organization for diagnosing acute myocardial infarction.

Timed sequential analysis of creatine kinase in the diagnosis of myocardial infarction in patients over 65 years of age

AIM

To assess the value of timed sequential analysis of creatine kinase (CK) activity for the early diagnosis of acute myocardial infarction (AMI) in patients over 65 years of age.

METHOD

Samples were collected on admission and eight to 12 hours later from 156 patients over 65 years of age. Routine cardiac enzyme activities were determined and serial electrocardiograms (ECGs) recorded. The predictive value of timed samples for CK activity, standard cardiac enzyme activities, and ECGs was compared with the final diagnosis on discharge.

RESULTS

Forty one patients had a discharge diagnosis of AMI, 83 of angina pectoris, and the remaining 32 patients had other diagnoses. Electrocardiograms had a sensitivity of 55% and a specificity of 96%, giving a predictive value of 86% for a negative and 84% for a positive ECG. Standard cardiac enzymes had a predictive value of 99% for a negative result but only 68% for a positive result. The logarithm of the rate of change of CK activity had a predictive value of 97% for a negative result and 95% for a positive result.

CONCLUSION

This study has shown that slope analysis of CK activity can be used for the early diagnosis of AMI in patients over 65 years of age, and that this was not affected by the presence of possible confounding diagnoses.

Creatine kinase isoform electrophoresis for the early confirmation of myocardial infarction detected by timed sequential CK slope analysis

Creatine kinase (CK)-MM and -MB isoforms were evaluated for the early diagnosis of myocardial infarction in patients aged over 65 years admitted to a district general hospital with acute chest pain. Samples were collected for standard cardiac enzymes, timed CK slope analysis, and CKMM and CKMB isoform analysis from 48 patients admitted with acute chest pain. CKMM and CKMB isoform analyses were conducted using a Helena Rep electrophoresis system under standard conditions supplied by the company. In addition to the results of the biochemical tests the discharge diagnosis of the patients were also recorded. CKMM isoform analysis resulted in three false-negative classifications of patients and one false-positive. The predictive value of this test was 100% for a positive result and 94% for a negative result. CKMB isoform analysis was less accurate and there were six false-negative results and five false-positive results. The predictive value of a positive result was 75% and 85% for a negative result. CK isoform analysis became unreliable when mean total CK levels in serum were 210 IU/l (+/- 171). CK isoform analysis may be of use in the investigation of patients whose samples have a total CK concentration greater than the reference range but was no better than timed CK slope analysis for the detection of myocardial infarction in patients aged more than 65 years.