Alfentanil

Study objectives: This study was conducted to evaluate the value of serum troponin T, myoglobin, and creatine kinase (CK)-MB mass concentrations for ruling out perioperative myocardial infarction (poMI) early after cardiac surgery.

Design: Retrospective study.

Setting: Cardiothoracic surgery department in a university hospital.

Patients: One hundred eighty-one patients undergoing coronary artery bypass grafting (CABG) with cardiopulmonary bypass were included.

Methods: Serum concentrations of troponin T, myoglobin, and CK-MB mass were measured preoperatively (baseline), on arrival at the cardiosurgical ICU (CICU), and at 2, 4, 8, 12, 16, and 20 h after arrival at the CICU. The strength of markers studied for ruling out poMI was studied using receiver operating characteristics curves. Based on these curves, the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for each marker at every time point were calculated.

Results: poMI developed in 14 patients. On arrival at the CICU, all markers were significantly increased from baseline concentrations in both patient groups. In patients with poMI, serum concentrations of troponin T, myoglobin, and CK-MB mass were significantly higher than in control patients from 8, 2, and 0 h after arrival on the CICU, respectively. CK-MB mass was the earliest marker, and its NPV reached 98.6% 12 h after arrival at the CICU. On arrival at the CICU, the NPV for CK-MB mass already reached 96.7%. The NPV for myoglobin reached 98.4% 12 h after arrival at the CICU. Troponin T was not an early marker for ruling out poMI, with an NPV reaching 98.6% 12 h after arrival on the CICU. During the first 8 h after arrival at the CICU, sensitivity, specificity, PPV, and NPV of CK-MB mass exceeded those of myoglobin and troponin T. In later measurements (until 20 h after arrival at the CICU), troponin T gave the most sensitive definition of poMI.

Conclusions: For ruling out poMI on the CICU after CABG, CK-MB mass is a better marker than myoglobin and troponin T during the first 12 h after arrival on the CICU. Using these markers, postoperative treatment of cardiac surgical patients might be further improved.

Key words: coronary artery bypass grafting; creatine kinase-MB mass; myoglobin; perioperative myocardial infarction; ruling out; troponin T

Abbreviations: AMI = acute myocardial infarction; ASAT = aspartate aminotransferase; CABG = coronary artery bypass grafting; CICU = cardiosurgical ICU; CK = creatine kinase; CPB = cardiopulmonary bypass; FABP = fatty acid-binding protein; NPV = negative predictive value; poMI = perioperative myocardial infarction; PPV = positive predictive value; ROG = receiver operating characteristics

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In patients undergoing coronary artery bypass grafting (CABG), early diagnosis of perioperative myocardial infarction (poMI) is important because it remains a serious complication. (1,2) Currently, the diagnosis of poMI is based on changes in the ECG and increased release of biochemical markers. Previously, several biochemical markers for detection of myocardial damage have been proposed. We showed that cardiac marker proteins (fatty acid-binding protein [FABP] and myoglobin) release can be used to determine myocardial tissue loss due to the surgical procedure. (3) In addition, we showed that these proteins can be used to discriminate surgery-related myocardial injury from tissue loss caused by poMI. FABP was shown to allow diagnosis of poMI as soon as 4 h after removal of the aortic cross-clamp.

However, next to early diagnosis, markers used for the detection of poMI should also be sensitive and specific. In this respect, FABP and myoglobin do not fulfill these recommendations. Troponin T and creatine kinase (CK)-MB mass have been shown to be promising candidates. (1,4-9) As being part of the tropomyosin complex of myocardial tissue, troponin T is highly cardiac specific, which could improve the diagnosis of poMI in cardiac surgical patients.

In many studies, the emphasis of the diagnostic properties of biochemical markers has been on the detection rather than the ruling out of poMI. However, postoperative treatment of cardiac surgical patients could be improved in case poMI could be ruled out as early as possible after surgery. The aim of the present study was to evaluate whether troponin T, myoglobin, and CK-MB mass measurements enable a sensitive and early rule-out of poMI after surgery.

MATERIALS AND METHODS

Patients

One hundred eight-one adult patients undergoing elective CABG with the use of cardiopulmonary bypass (CPB) were enrolled. Age boundaries were set between 35 years and 80 years. Exclusion criteria were as follows: (1) poMI or ongoing infarction; (2) treatment with fibrinotytics within 48 h prior to surgery; (3) hepatic disease as indicated by aspartate aminotransferase (ASAT) and alanine aminotransferase levels > 2 times the upper limit of normal, or by bilirubin levels > 1.5 times the upper limit of normal; and (4) severe coagulation abnormalities. The study was performed according to the rules of the local medical ethical committee.

Intraoperative Patient Management

Standard anesthetic (lorazepam, fentanyl citrate, sufentanil citrate, alfentanil hydrochloride, midazolam hydrochloride, pancuronium bromide) and monitoring techniques (ECG, central venous/pulmonary and arterial pressure monitoring, urinary output, rectal and skin temperature monitoring) were used in all patients. Before connection of the extracorporeal circuit for CPB, heparin was administered, 300 IU/kg (Heparin Leo; Leo Pharmaceutical Products BV; Weesp, the Netherlands) in order to achieve an activated coagulation time > 480 s (Hemoehron 400; International Technidyne Corporation; Edison, NJ).

Specifications on the extracorporeal circulation circuit, CPB procedures and surgical procedures have been described previously. (10) Postoperative patient treatment in the cardiosurgical ICU (CICU) was standardized and similar for both patient groups. None of the patients received thrombolytic agents.

Blood Sampling

Blood samples were obtained preoperatively (baseline), on arrival at the CICU, and at 2, 4, 8, 12, 16, and 20 h after arrival at the CICU. All samples were collected in 10-mL integrated serum separator tubes (Corvac; Sherwood Medical; St. Louis, MO). Immediately after sampling, blood was cooled, routinely centrifuged, and serum samples were stored at -70[degrees]C until analysis.

Myocardial Infarction Diagnosis

Diagnosis of poMI was established by a cardiologist based on ECG changes (new persistent Q waves and ST-segment deviations; [greater than or equal to] 1 mm ST-segment elevation in two or more limb leads and/or [greater than or equal to] 2 mm ST-segment elevation in two or more precordial leads), and a typical rise and fall in the serum CK, CK-MB activity, and ASAT curves. This resulted in two patient groups: patients in whom poMI developed (poMI group), and patients without poMI (no-poMI group).

Analytic Techniques

The serum concentrations of CK-MB mass, myoglobin, and cardiac troponin T (third generation) were all analyzed on the Elecsys 2010 (Roche Diagnostics GmbH; Mannheim, Germany; catalog No. 1731432. 2017423m and 1820788 respectively). Routine clinical chemistry parameters ASAT, alanine aminotransferase, bilirubin, and CK-MB activity were determined on the Beckman Synchron CX7 System (Beckman Coulter; Fullerton, CA).

Data Analysis

All data are presented as mean [+ or -] SEM, A Mann-Whitney U test was used for comparisons between two variables at the same time point. A Wilcoxon matched-pairs, signed-ranks test wits used for comparisons of values from one variable between two time points. A [chi square] test was used to test nonnumeric variables. Receiver operating characteristics (ROC) curves were used to compare the performance of the biochemical diagnostic methods of poMI and to determine the appropriate cutoff values for the different cardiac markers. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated to analyze the diagnostic value of each marker. The level of significance was set at p < 0.05.

RESULTS

Clinical Characteristics

The perioperative characteristics of all patients are shown in Table 1. Fourteen patients (7.7%) showed evidence of poMI according to ECG changes and routine laboratory data. These patients had longer CPB times and a longer postoperative hospital stay than the patients without poMI.

Cardiac Marker Concentrations

Preoperative CK-MB mass concentrations in the no-poMI group and the poMI group were 1.5 [+ or -] 0.3 [micro]g/L and 1.4 [+ or -] 0.2 [micro]g/L, respectively (Fig 1, top, A). CK-MB mass concentrations in the no-poMI group and the poMI group each increased until 4 h after arrival at the CICU, and then further increased only in the poMI group. From arrival at the CICU until 20 h thereafter, CK-MB mass concentrations were significantly higher in the poMI group (p < 0.05). At the first postoperative day, CK-MB mass concentrations were 13.3 times higher in poMI patients compared to no-poMI patients. Maximal CK-MB mass serum concentrations were 20.1 [+ or -] 1.3 [micro]g/L in the no-poMI group at 4 h after arrival at the CICU, and 204.2 [+ or -] 50 [micro]g/L in the poMI group at 20 h after arrival at the CICU.

Preoperative troponin T concentrations in the no-poMI group and the poMI group were 0.027 [+ or -] 0.014 [micro]g/L and 0.017 [+ or -] 0.012 [micro]g/L, respectively (Fig 1, center, B). Postoperative troponin T concentrations in the no-poMI group and poMI group each increased above preoperative concentrations, and were similar until 4 h after arrival at the CICU. From this time point on, postoperative troponin T in the no-poMI group steadily decreased toward the first postoperative day (20 h after arrival at the CICU), whereas the troponin T concentration in the poMI group persistently increased until 20 h after arrival at the CICU, at this time being 6.8-fold higher than in the control subjects. Thus, troponin T concentrations in the poMI group were significantly higher than in the no-poMI group from 8 h to at least 20 h after arrival at the CICU. Maximal troponin T serum concentrations were 0.90 [+ or -] 0.05 [micro]g/L in the no-poMI group at 4 h after arrival at the CICU, and 3.3 [+ or -] 0.7 [micro]g/L in the poMI group at 20 h after arrival at the CICU.

[FIGURE 1 OMITTED]

Preoperative myoglobin concentrations in the no-poMI group and the poMI group were 48 [+ or -] 4 [micro]g/L and 44 [+ or -] 4 [micro]g/L, respectively (Fig 1, bottom, C). Myoglobin concentrations increased from preoperative to the time of arrival at the CICU in both no-poMI and poMI patients. In poMI patients, myoglobin concentrations continued to increase, reaching peak levels at the first postoperative day (20 h after arrival at the CICU). At the latter time point, myoglobin concentrations were 3.5 times higher compared to no-poMI patients. A significant difference in myoglobin plasma concentrations between no-poMI and poMI patients was reached at 2 h after arrival at the CICU. Maximal myoglobin serum concentrations were 337 [+ or -] 13 [micro]g/L in the no-poMI group at arrival on the CICU, and 1,067 [+ or -] 355 [micro]g/L in the poMI group at 20 h after arrival on the CICU.

Threshold Values and Test Characteristics

The strength of correlation between standard criteria (ECG and routine laboratory CK-MB activity) and serum troponin T, myoglobin, and CK-MB mass was studied using ROC curves. The area under the curves for each marker at every time point are shown in Table 2. CK-MB mass and myoglobin showed a close correlation between standard criteria for poMI diagnosis and the cutoff values calculated using the ROC curves. For troponin T, this close correlation became evident later in the postoperative period. Cutoff values were derived from the intersection of the right bottom to left top diagonal and the ROC curve and the corresponding coordinates of the curve (Fig 2). Corresponding cutoff values for each marker at every time points are shown in Table 2. Serum levels of troponin T > 1.0 [micro]g/L 8 h after arrival at the CICU confirmed the presence of poMI with a sensitivity of 76.9%, specificity of 72.7%, PPV of 18.2%, and NPV of 97.6%. At the same time point, CK-MB mass serum levels > 22 [micro]g/L confirmed the presence of poMI with a sensitivity of 78.6%, specificity of 77.6%, PPV of 22.9%, and NPV of 97.7%. Serum myoglobin levels > 297 [micro]g/L 8 h after arrival at the CICU confirmed the presence of poMI with a sensitivity of 80%, specificity, of 80.4%, PPV of 22.2%, and NPV of 98.3%. For each marker and at every time point, the sensitivity, specificity, PPV, and NPV of a single sample were calculated (Table 3).

[FIGURE 2 OMITTED]

Comment

poMI is a serious complication after cardiac surgery, with a reported incidence of up to 26%, dependent on the criteria used to select the patient groups. (2,11) Previously, we showed that using cardiac marker proteins instead of enzymes theoretically enabled a poMI to be diagnosed earlier after surgery. (3) Furthermore, we showed that in case CPB is used, myocardial tissue injury is inevitable. (3,12) However, both routinely used enzymatic markers (CK and CK-MB) and the proteins (FABP and myoglobin) we tested thus far either failed cardiac specificity or did not enable a diagnosis of poMI early after surgery. The ideal marker for the diagnosis of poMI early after cardiac surgery would however possess both before mentioned characteristics. Troponins are highly cardiac specific, a characteristic that could improve the diagnosis of poMI in cardiac surgery. In the present study, we studied the value of serum troponin T, myoglobin, and CK-MB mass concentrations in patients undergoing CABG.

In the present study, plasma concentrations of the cardiac markers studied show that in case a patient has undergone CABG with the use of CPB, some myocardial damage occurs in all patients. These relatively moderate elevations of the markers studied, in comparison to concentrations found in patients with acute myocardial infarction (AMI), may reflect minimal myocardial damage. Based on the plasma curves (Fig 1, bottom, C) and its fast appearance and clearance features myoglobin may be used to estimate ischemia-reperfusion injury early postoperatively. However, based on the test characteristics (Table 3), myoglobin is not the most suitable marker for ruling out poMI in patients undergoing CABG.

Although the cutoff values of cardiac markers have been reported elaborately (13-15) for patients presenting with acute chest pain, these values are not well established for patients during and after cardiac surgery. Based on the data of the patients in the present study, we found optimal cutoff values for each marker at every time point (Table 2). Carrier et al (1) recently showed acceptable test characteristics for troponin T in CABG patients 24 h after surgery, which increased toward 48 h after surgery. In the present study, however, we found optimal test characteristics for troponin T already at 12 h after arrival at the CICU. In addition, troponin T concentrations in the patients reported by Carrier et al (1) were approximately twofold the concentrations found in the patients of the present study. The latter finding can be explained by the fact that Carrier et al (1) used the first generation reagents for troponin T determinations as opposed to the third-generation reagents we used in the present study. However, using the linear regression formula provided by others, (16) and the instructions for use of the Troponin T STAT Immunoassay (Roche Diagnostics Gmbh) results in similar troponin T concentrations in the patients described by Carrier et al (1) and our patients. Nevertheless, the cutoff values in the patients of Carrier et al (1) were higher than the ones we found in our patients. Also, Swaanenburg et al (17) recently showed that the release patterns of cardiac markers after uncomplicated heart surgery depend on the type of surgery and the circumstances during surgery. Therefore, because of insufficient analytical standardization of the various cardiac marker methodologies, we strongly recommend that each institution should determine its own release patterns of cardiac markers for cardiac surgical procedures, and subsequently calculate the corresponding optimal cutoff values.

Previously it was shown by de Winter et al (9) that in patients with AMI, the size of the infarction influences the sensitivity and specificity in the early hours after onset of symptoms for CK-MB mass and troponin T, while this effected myoglobin less. Troponin T, CK-MB mass, and myoglobin levels increased earlier in patients with large infarcts. The latter finding may be one of the reasons for the fact that it is hard to find proper markers for poMI early after surgery. Our previous findings (3) and present findings show a large dispersion in postoperative cardiac marker plasma levels. Consequently, calculating optimal cutoff values based on the mean plasma levels in the control patients plus two times the SD results in cutoff values that rule out patients with small poMIs. Furthermore, the test characteristics of the marker studied will not reach appropriate values. In the present study, the test characteristics of the markers used were calculated using ROC curves. This resulted in relatively high values of particularly the NPV. The lowest NPV calculated for each marker at every time point was 93.7 (Table 3), indicating that in the worst case poMI could be ruled out with 93.7% certainty using any of the markers studied. The relatively high values of sensitivity, specificity, and NPV at all postoperative time points may be explained by the fact that in our patients the "onset of symptoms," as it is usually called in patients with AMI, is the same for all patients, supposing that the poMIs in the present study have a perioperative etiology.

Concluding Remarks

In conclusion, although the measurement of serum troponin T eventually might give the best definition of poMI, CK-MB mass is the preferred marker for ruling out poMI. The data of the present study show that in patients undergoing CABG, troponin T and CK-MB mass should be measured during the first 8 h after arrival on the CICU not to detect but rather to exclude poMI. Whether this will lead to a better management of these patients from current postoperative treatment protocols remains to be evaluated in ongoing studies.

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* From the Departments of Cardiothoracic Surgery (Drs. Fransen and Maessen) and Clinical Chemistry (Mr. Diris and Dr. van Dieijen-Visser), University Hospital Maastricht; and the Cardiovascular Research Institute Maastricht (Dr. Hermens), Maastricht, the Netherlands.

Manuscript received October 23, 2001; revision accepted April 3, 2002.

Correspondence to: Erik J. Fransen, MSc, PhD, Department of Cardiothoracic Surgery, University Hospital Maastricht, P. Debyelaan 25, 6202 AZ Maastricht, the Netherlands; e-mail: efr@scpc.azm.nl

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