RESUSCITATION FROM OUT-OF-HOSPITAL CARDIAC-ARREST - IMPLICATIONS FOR CARDIAC ENZYME ESTIMATION

Background: diagnosis of precipitating myocardial infarction is essent ial for management of victims of out-of-hospital cardiac arrest, since investigations and treatment are determined by the underlying cause. Skeletal muscle and myocardial damage from external cardiac massage an d defibrillation may complicate biochemical diagnosis of myocardial in farction. Objectives: (a) to examine the relationship between cumulati ve defibrillation energy and serum levels of cardiac troponin T and MB creatine kinase (MB-CK) mass in out-of-hospital cardiac arrest surviv ors without electrocardiographic evidence of myocardial infarction; (b ) to reassess diagnostic thresholds for myocardial infarction using MB -CK mass and troponin T in this setting. Methods: 77 victims of out-of -hospital cardiac arrest were studied. Serum was obtained for MB-CK ma ss, CK and troponin T estimation on the first 4 days of admission. Pat ients were divided into three groups using electrocardiographic criter ia: group 1, myocardial infarction, group 2, no evidence of infarction ; and group 3, equivocal electrocardiograms. Correlation coefficients were calculated for highest recorded levels of the biochemical markers versus defibrillation energy. Receiver-operating characteristic plots were used to determine optimum biochemical diagnostic thresholds for subjects in groups 1 and 2. Results: using predefined criteria, 27 pat ients had myocardial infarction, 34 did not have myocardial infarction and 16 had equivocal electrocardiograms. Significant correlations wer e found for defibrillation energy versus log troponin T (r = 0.42, P < 0.05), log MB-CK mass (r = 0.51, P < 0.01) and total CK (r = 0.68, P < 0.001) in group 2. Within groups 1 and 2, MB-CK mass and troponin T provided additional diagnostic value over MB-CK fraction (P < 0.001). Diagnostic accuracy was not improved by adjusting for shock energy. Th e optimum threshold value was 4 ng/ml for troponin T (sensitivity 88%, specificity 95%), 60 ng/ml for MB-CK mass (sensitivity 88%, specifici ty 88%) and 8% of total CK for MB-CK fraction (sensitivity 74%, specif icity 82%). These values should be interpreted with caution, since thi s study is limited by the exclusion of patients with uncertain electro cardiographic diagnoses into group 3. Conclusions: skeletal muscle and myocardial damage occurs in survivors of out-of-hospital cardiac arre st and is related to the duration of resuscitation. This complicates b iochemical diagnosis of underlying myocardial infarction. Specific hig h diagnostic threshold values for MB-CK and troponin T are needed to o ptimise diagnostic accuracy. The use of MB-CK fraction leads to greate r diagnostic error because of the variability of muscle CK release aft er resuscitation.