|
|
||||||||
Division of Cardiac and Vascular Surgery, Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada
Accepted for publication December 31, 2007.
* Address correspondence to Dr Nesher, 2075 Bayview Ave, H410, Toronto, Ontario, M4N 3M5, Canada (Email: nachumnesher{at}yahoo.com).
| Abstract |
|---|
|
|
|---|
Methods: The study included 1918 consecutive patients undergoing adult cardiac operations, including 1515 isolated coronary procedures, 229 valvular operations, and 174 combined coronary/valve procedures. Peak troponin T (normal value < 0.1 µg/L) was measured at less than 24 hours postoperatively. Excluded were 506 patients with a recent myocardial infarction (< 30-days of operation). The primary outcome was a composite of death, electrocardiogram-defined infarction, and low output syndrome (MACE).
Results: Mortality rates were 1.4%, 6.1%, and 7% in the coronary bypass, valve, and combined groups, respectively (p < 0.001). The rates of MACE were 17%, 35%, and 44% (p < 0.0001), and mean troponin T levels were 0.9 ± 1.5, 1.2 ± 2.9, and 1.3 ± 1.2 µg/L (p < 0.001), in the coronary bypass, valve, and combined groups, respectively. All patients were divided into quintiles based on their peak postoperative troponin level (Q1, 0.0 to 0.39; Q2, 0.4 to 0.59; Q3, 0.6 to 0.79; Q4, 0.8 to 1.29; and Q5, > 1.3 µg/L). Adverse outcomes were similar and stable in the lower quintiles. A stepwise increase in adverse outcomes was observed in the higher quintiles. Receiver operating characteristic curve analysis revealed a troponin cutoff of 0.8 µg/L was the most discriminatory for MACE (area under the curve, 0.7). Multivariable analyses showed a troponin value of more than 0.8 µg/L was independently associated with MACE.
Conclusions: Moderate elevations in troponin are common after cardiac operations; troponin is a well-described predictor of outcomes. Troponin levels exceeding 0.8 µg/L are associated with increased MACE in patients without a history of preoperative myocardial infarction within 30 days of operation.
| Introduction |
|---|
|
|
|---|
The prognostic significance of CK-MB after cardiac operations is fairly well established. The association between increased postoperative troponin release and hard clinical postoperative outcomes is controversial [6–9]; troponin may be an overly sensitive marker of cardiac injury in this setting. The cutoff value for detection of a significant amount of myocardial damage in this setting is still unresolved. The primary objective of our study was to determine whether cardiac-specific troponin T (TnT) correlates with major adverse cardiac events (MACE) after cardiac operations. The secondary objective was to determine a threshold value of troponin associated with these outcomes.
| Material and Methods |
|---|
|
|
|---|
Operative Management
Alpha-stat acid-base management was used during cardiopulmonary bypass (CPB). Heparin (300 U/kg) was administered to maintain an activated clotting time exceeding 480 seconds. During CPB, the body temperature was allowed to drift inferiorly (32° to 34°C). Cardiac arrest was induced and maintained with antegrade/retrograde cold/tepid blood cardioplegia. Protamine was administered to reverse heparin in the standard manner (1 mg/1 mg total heparin) Tranexamic acid or aprotinin were administered before and during the operation to minimize postoperative bleeding; aprotinin was used for patients at high risk for bleeding due to recent preoperative antiplatelet medications or the extent of the planned procedure (redo, multiple valve, or combined procedure).
Postoperative Management
Patients received aspirin (325 mg) and unfractionated heparin (5000 U) 12 hours postoperatively in the absence of significant mediastinal bleeding. Warfarin was started after chest tube removal for patients after mechanical valve replacement or any mitral valve procedure.
Serum CK level (normal range, 24 to 195 IU/L) and CK-MB level (normal range, 2 to 6 µg/L) were measured by standard methods. Measurement of TnT was within 24 hours after the operation. Troponin T was measured quantitatively by a one-step enzyme immunoassay based on electrochemiluminescence technology (Elecsys 2010; Roche, Mannheim, Germany). The lower detection limit of this assay is 0.1 µg/L (normal < 0.1 µg/L).
Primary End Point
The objective of the study was to correlate TnT with perioperative MACE, which was defined as a composite end point of all-cause in hospital death, low-output syndrome (defined as inotropic or intraaortic balloon pump support, or both, to maintain the cardiac index > 2.0 L/min/m2) or perioperative MI (defined as new, persistent Q-waves
0.04 ms or R-wave reduction
25% in at least two contiguous anterior leads, or ischemic electrocardiographic ST/T wave changes with CK-MB mass elevation > 50 µg/L, in at least two consecutive daily electrocardiograms). Troponin levels were not considered for the diagnosis of perioperative MI.
Statistical Analysis
Categoric variables were summarized as frequencies and percentages, and continuous variables as means ± standard deviations or median and interquartile ranges. Categorical variables were compared using the Pearson
2 test for independent proportions, and the Student t test was used to compare continuous variables. A single troponin cutoff best associated with adverse clinical events was identified according to the maximum area under the receiver operating characteristic (AUROC) curve. The study cohort was divided into quintiles by peak postoperative TnT level, and adverse events were determined in each quintile. Stepwise logistic regression was used to evaluate the effect of peak TnT on outcomes, adjusting for preoperative and operative variables (Table 1). All statistical tests were two-tailed with p < 0.05 indicating statistical significance. Statistical software SAS 8.2 (SAS Institute, Cary, NC) was used for analyses.
|
| Results |
|---|
|
|
|---|
Patient characteristics and outcomes according to the type of operation are reported in Table 1. Early outcomes were better in the isolated CABG cohort than the other patient groups. Patients in the combined group were older, had operations more frequently, and were predominately women compared with the CABG-only cohort. The operative times as well as lengths of stay in the intensive care unit and the hospital were significantly prolonged. All adverse cardiac events were increased in the combined group. Patients in the isolated valve group generally underwent elective operations and most were women. Outcomes were intermediate between the CABG and combined groups.
Troponin Level and Outcome
To establish a clinically important threshold value of troponin, the results were dichotomized, and the best cutoff value was determined according to the AUROC curve. Our analyses yielded a TnT cutoff of more than 0.8 µg/L as the most predictive, with the maximum discriminatory performance between those who presented with MACE and those who did not for the entire cohort of patients (Fig 1). A TnT value of 0.8 µg/L was also most discriminatory for patients specifically in the isolated CABG and isolated valve groups; a value of 1.3 µg/L was the threshold value most discriminatory for the patients who underwent a combined procedure (Fig 1).
|
|
|
|
|
| Comment |
|---|
|
|
|---|
The present study demonstrated that elevated TnT levels above the normal value (0.1 µg/L) were observed in more than 90% of patients within 24 hours after cardiac operations. However, a TnT elevation exceeding eight times upper limit of normal (ie, > 0.8 µg/L) was found to be an independent predictor of increased MACE after isolated coronary operations (odds ratio, 2.7; 95% confidence interval, 2.1 to 3.5; p < 0.0001). A higher threshold value of more than 1.3 µg/L was found to predict MACE after higher-risk combined cardiac operations. Other significant independent predictors of MACE included age older than 70 years, female sex, preoperative stroke history, left ventricular dysfunction, NYHA heart failure exceeding II, and prolonged CPB times. Notably, TnT levels of more than 0.8 µg/L had the largest odds risk ratio for poor outcome compared with the other independent predictors elucidated.
Previous Studies
The controversy surrounding the clinical interpretation of troponin levels after cardiac operations also arises as studies report results using the two different troponin isoforms, troponin T and troponin I. According to a meta-analysis performed in acute coronary syndrome patients, the two biomarkers have been shown to be equally as specific and sensitive to predicting MI and cardiac death [11]. Most studies report troponin I rather than troponin T values.
Historically, troponin I assays were manufactured by several companies, and the assays could be generally be implemented in hospital laboratories using existing hardware; thus, the troponin assay was usually more affordable and became more widely adopted [11, 12]. Problematically, much wider variation has occurred in the reporting of troponin I using assays from different manufacturers; for example, other investigators have reported threshold values of troponin I for MACE after cardiac operations ranging from less than 1 ng/mL to more than 40 ng/mL [7, 13–16].
In comparison, the TnT assay has a sole manufacturer. Consequentially, the TnT literature reports results that are consistent in their magnitude and range compared with TnI. Thus, it has been adopted by many larger and newer centers. Lehrke and colleagues [12] examined 204 patients undergoing isolated, elective CABG or valve operations, or both. Using ROC and multivariable analysis, they found TnT levels higher than a threshold of 0.6 µg/L to be a significant predictor of death. Baggish and colleagues [17] identified TnT levels exceeding 1.5 µg/L as the strongest predictor for longer intensive care unit stay in 222 patients analyzed [18]. These corroborate the external validity of our own results presented and support the benefits to using the T isoform assay.
Strengths and Limitations
The strength of this study is that it comprises a large contemporary cohort of patients undergoing adult cardiac procedures to answer this relevant research question. Using TnT also strengthens the clinical applicability of the thresholds and recommendations we have presented.
The study is limited by the inherent flaws of retrospective observational studies. The patient population is heterogeneous in the complexity of operations that were performed as well as the techniques that were used, such as myocardial protection, and the revascularization approach. Thus our results may not apply to other specific patient cohorts without further study into the various subgroups, including patients who had an acute MI within 30 days before operation and therefore were excluded from our study cohort.
Finally, our data provide no insights on the specific reasons for troponin elevation postoperatively. Nonetheless, the data suggest troponin should continue to be used for quality assurance as a means of detecting postoperative myocardial injury in order to rapidly intervene with early medical or repeat revascularization therapy to circumvent poor perioperative outcomes [2].
Conclusions
Cardiac troponin levels are frequently elevated after cardiac surgical procedures. We have shown in our study, that TnT concentrations were significantly different among the different patient groups, such as levels those undergoing isolated CABG or valve procedures being lower than patients undergoing combined operations.
A single measurement of TnT exceeding 0.8 µg/L in less than 24 hours after any isolated CABG procedure adds statistically significant, independent prognostic information for in-hospital outcomes, greater than any other predictor variable. Intuitively, these patients may benefit from increased monitoring and close medical care or specific interventions. A TnT level of less than 0.8 µg/L may be considered an innocuous event caused by heart manipulation and surgical trauma to cardiac tissue and thus of no prognostic significance.
For a decade, troponin levels measured in the emergency department revolutionized the management of acute coronary insufficiency. They were used as the guideline for diagnosis and directing treatment towards more invasive therapies. This study suggests that they should continue to play an important role in directing management of patients even after interventions such as cardiac procedures. Future prospective investigations of the predictive value of elevated levels of troponin isoforms after cardiac operations are certainly necessary in order to further improve patient outcomes.
| References |
|---|
|
|
|---|
Related Article
This article has been cited by other articles:
![]() |
J. C. Leal, O. Petrucci, M. F. Godoy, and D. M. Braile Perioperative serum troponin I levels are associated with higher risk for atrial fibrillation in patients undergoing coronary artery bypass graft surgery Interact CardioVasc Thorac Surg, January 1, 2012; 14(1): 22 - 25. [Abstract] [Full Text] [PDF] |
||||
![]() |
A. M. Ranasinghe, D. W. Quinn, M. Richardson, N. Freemantle, T. R. Graham, J. Mascaro, S. J. Rooney, I. C. Wilson, D. Pagano, and R. S. Bonser Which Troponometric Best Predicts Midterm Outcome After Coronary Artery Bypass Graft Surgery? Ann. Thorac. Surg., June 1, 2011; 91(6): 1860 - 1867. [Abstract] [Full Text] [PDF] |
||||
![]() |
S. R. Moonesinghe, M. G. Mythen, and M. P. W. Grocott Review Article: High-Risk Surgery: Epidemiology and Outcomes Anesth. Analg., April 1, 2011; 112(4): 891 - 901. [Abstract] [Full Text] [PDF] |
||||
![]() |
N. J. Howell, H. Ashrafian, N. E. Drury, A. M. Ranasinghe, H. Contractor, H. Isackson, M. Calvert, L. K. Williams, N. Freemantle, D. W. Quinn, et al. Glucose-Insulin-Potassium Reduces the Incidence of Low Cardiac Output Episodes After Aortic Valve Replacement for Aortic Stenosis in Patients With Left Ventricular Hypertrophy: Results From the Hypertrophy, Insulin, Glucose, and Electrolytes (HINGE) Trial Circulation, January 18, 2011; 123(2): 170 - 177. [Abstract] [Full Text] [PDF] |
||||
![]() |
G. P. Dobson Membrane polarity: A target for myocardial protection and reduced inflammation in adult and pediatric cardiothoracic surgery J. Thorac. Cardiovasc. Surg., December 1, 2010; 140(6): 1213 - 1217. [Full Text] [PDF] |
||||
![]() |
S. Talwar, J. A. Sandeep, S. K. Choudhary, D. Velayoudham, R. Lakshmy, J. M. Kasthuri, and A. S. Kumar Effect of preoperative administration of allopurinol in patients undergoing surgery for valvular heart diseases Eur J Cardiothorac Surg, July 1, 2010; 38(1): 86 - 90. [Abstract] [Full Text] [PDF] |
||||
![]() |
B. Braathen and T. Tonnessen Cold blood cardioplegia reduces the increase in cardiac enzyme levels compared with cold crystalloid cardioplegia in patients undergoing aortic valve replacement for isolated aortic stenosis J. Thorac. Cardiovasc. Surg., April 1, 2010; 139(4): 874 - 880. [Abstract] [Full Text] [PDF] |
||||
![]() |
Y. van Geene, H. A. van Swieten, and L. Noyez Cardiac troponin I levels after cardiac surgery as predictor for in-hospital mortality Interact CardioVasc Thorac Surg, March 1, 2010; 10(3): 413 - 416. [Abstract] [Full Text] [PDF] |
||||
![]() |
G. A. Lurati Buse, M. T. Koller, M. Grapow, D. Bolliger, M. Seeberger, and M. Filipovic The prognostic value of troponin release after adult cardiac surgery -- a meta-analysis Eur J Cardiothorac Surg, February 1, 2010; 37(2): 399 - 406. [Abstract] [Full Text] [PDF] |
||||
![]() |
G. A. Lurati Buse, M. T. Koller, M. Grapow, C. M. Bruni, J. Kasper, M. D. Seeberger, and M. Filipovic 12-Month Outcome After Cardiac Surgery: Prediction by Troponin T in Combination With the European System for Cardiac Operative Risk Evaluation Ann. Thorac. Surg., December 1, 2009; 88(6): 1806 - 1812. [Abstract] [Full Text] [PDF] |
||||
![]() |
S. K. Singh and S. E. Fremes Invited Commentary Ann. Thorac. Surg., December 1, 2009; 88(6): 1812 - 1813. [Full Text] [PDF] |
||||
![]() |
A. A. Mohammed, A. K. Agnihotri, R. R.J. van Kimmenade, A. Martinez-Rumayor, S. M. Green, R. Quiroz, and J. L. Januzzi Jr Prospective, Comprehensive Assessment of Cardiac Troponin T Testing After Coronary Artery Bypass Graft Surgery Circulation, September 8, 2009; 120(10): 843 - 850. [Abstract] [Full Text] [PDF] |
||||
![]() |
L. Petaja, M. Salmenpera, K. Pulkki, and V. Pettila Biochemical Injury Markers and Mortality After Coronary Artery Bypass Grafting: A Systematic Review Ann. Thorac. Surg., June 1, 2009; 87(6): 1981 - 1992. [Abstract] [Full Text] [PDF] |
||||
![]() |
R. A. Fowler, N. K. J. Adhikari, D. C. Scales, W. L. Lee, and G. D. Rubenfeld Update in Critical Care 2008 Am. J. Respir. Crit. Care Med., May 1, 2009; 179(9): 743 - 758. [Full Text] [PDF] |
||||
![]() |
O. Assar, J. Bagheri, M. H. Mandegar, and F. Roshanali Time of Measurement of Troponin is Essential When We Think About Prediction or Phenomena Ann. Thorac. Surg., November 1, 2008; 86(5): 1721 - 1721. [Full Text] [PDF] |
||||
![]() |
V. Jeevanandam Invited Commentary Ann. Thorac. Surg., April 1, 2008; 85(4): 1354 - 1354. [Full Text] [PDF] |
||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| ANN THORAC SURG | ASIAN CARDIOVASC THORAC ANN | EUR J CARDIOTHORAC SURG |
| J THORAC CARDIOVASC SURG | ICVTS | ALL CTSNet JOURNALS |