Optimal cut-off value for cardiac troponin I in ruling out Type 5 myocardial infarction.
OBJECTIVE
The clinical classification of myocardial infarction (MI) into five types was introduced in 2007 as a component of the universal definition. A Type 5 MI was defined as a MI related to coronary artery bypass surgery. In a setting of patients undergoing elective coronary artery bypass grafting, we set out (i) to describe the pattern of multiple serial cardiac troponin I (cTnI) measurements within 72 h postoperatively and (ii) to determine the optimal cardiac troponin I cut-off value in ruling in or ruling out a Type 5 MI.


METHODS
In 2011-2012, patients with two- and three-vessel disease scheduled for elective on-pump coronary artery bypass grafting were considered. Samples for cTnI were drawn before and 0, 2, 4, 6, 12, 24, 48 and 72 h after surgery. Analysis for cardiac troponin I was performed by use of the Abbott Architect c16000 system with an upper reference limit (URL) of 30 ng/l. The diagnosis of a Type 5 MI was prospectively made by a consultant cardiologist and was based on clinical, electrocardiographic and imaging data together with routine sampling and measurements of cTnI, but without knowledge of the results of serial study cTnI measurements.


RESULTS
Of the 141 eligible patients, 99 (70%) qualified for final enrollment. In 8 patients (8%), the clinical diagnosis of a Type 5 MI was made. Patients without Type 5 MI (n = 91) had a median cTnI peak value of 7675 ng/l compared with 20 500 ng/l in Type 5 MI patients (P = 0.01). By use of receiver operating characteristic curves, optimal cut-off values for identifying Type 5 MI were defined as 7970 ng/l (corresponding to 266 times the URL) 12 h postoperatively and 9950 ng/l (corresponding to 331 times the URL) 24 h postoperatively. These cut-off values resulted in negative predictive values of 0.99 (12 h) and 0.99 (24 h). Positive predictive values were 0.23 (12 h) and 0.35 (24 h).


CONCLUSIONS
In clinically stable patients undergoing elective coronary artery bypass grafting, measurements of cTnI are useful in ruling out a Type 5 MI.
Department of Cardiology, Odense University Hospital, Odense C, Denmark.
Peter Hartmund
PH
Jørgensen
Mads
M
Nybo
Marianne Kjær
MK
Jensen
Poul Erik
PE
Mortensen
Tina Svenstrup
TS
Poulsen
Axel Cosmus Pyndt
AC
Diederichsen
Hans
H
Mickley
D000368:Aged; D019540:Area Under Curve; D015415:Biomarkers / Q000097:blood; D002315:Cardiopulmonary Bypass / Q000009:adverse effects; D001026:Coronary Artery Bypass / Q000009:adverse effects; D003324:Coronary Artery Disease / Q000097:blood / Q000150:complications / Q000175:diagnosis / Q000601:surgery*; D017558:Elective Surgical Procedures; D004562:Electrocardiography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009203:Myocardial Infarction / Q000097:blood / Q000145:classification / Q000175:diagnosis* / Q000209:etiology; D011237:Predictive Value of Tests; D012372:ROC Curve; D012307:Risk Factors; D013997:Time Factors; D016896:Treatment Outcome; D019210:Troponin I / Q000097:blood*
D015415:Biomarkers; D019210:Troponin I
Coronary artery bypass grafting; Myocardial infarction; Postoperative complications; Troponin I; Universal definition