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High-Sensitivity Troponin I After CABG for Postop Decision-Making
Quick Takes
- This was a retrospective single-center study of 4,684 adult patients who underwent isolated CABG electively and had serial high-sensitivity cardiac troponin I (hs-cTnI) levels measured.
- An hs-cTnI value >500× the upper reference limit of normal measured at 12-16 hours was the optimal cut-off for discriminating between patients who required additional revascularization and those who did not.
- The cut-off exhibited the following testing characteristics: a sensitivity of 88.4%, specificity of 93.4%, PPV of 20.1%, and NPV of 99.8%.
Study Questions:
What is the optimal high-sensitivity cardiac troponin I (hs-cTnI) cut-off for post-coronary artery bypass grafting (CABG) for predicting revascularization and cardiovascular events?
Methods:
This was a retrospective single-center study of 4,684 adult (≥18 years old) patients who underwent elective isolated CABG from 2013–2019. Urgent procedures were excluded. hs-cTnI was measured 24 hours prior to surgery as well as serially at 4-hour intervals up to 48 hours post-surgery. Electrocardiographic (ECG), echocardiographic, and coronary angiography data were collected. The primary outcome was repeat revascularization (percutaneous coronary angiography or redo surgery). Receiver operating characteristic curve analyses were performed to identify the optimal cut-off value for hs-cTnI. Internal validation was performed through randomly dividing the study population into two groups. External validation was performed using data from the Alfred Hospital in Melbourne, Australia (n = 775).
Results:
A total of 4,684 consecutive patients met eligibility criteria. The study population had a mean age of 67 years, and consisted of 19.4% women; 85% of procedures were performed off-pump. A total of 161 patients (3.48%) underwent invasive coronary angiography after surgery, of whom 86 patients (53.4%) underwent repeat revascularization. The median peak postoperative hs-cTnI level was 93× the upper reference limit (URL), with a median time to peak hs-cTnI of 8.1 hours. Only peak hs-cTnI levels within 48 hours postoperatively (in quartiles), presence of new ECG or echocardiographic abnormalities, and electrical or hemodynamic instability were significantly associated with the primary outcome.
The optimal cut-off value for peak hs-cTnI in predicting revascularization was >13,000 ng/L (>500× the URL; c-statistic, 0.92; 95% confidence interval [CI], 0.87-0.96). This cut-off had a sensitivity of 88.4%, specificity of 93.4%, positive predictive value (PPV) of 20.1%, and negative predictive value (NPV) of 99.8% (accuracy, 93.3%). When stratifying by sex, the optimal cut-off values were 13,300 ng/L (>390× URL) in males and 9400 ng/L (588× URL) in females. The optimal time point for measurement was 12-16 hours post-surgery. Combining hs-cTnI with ECG abnormalities or hemodynamic instability improved discriminative performance by 4%. A decision tree analysis of serial hs-cTnI measurements showed no added benefit of hs-cTnI measurements in patients with ECG or echocardiographic abnormalities or hemodynamic instability. Use of criteria from current guidelines (troponin >70× URL) exhibited worse discrimination ability (C-statistic, 0.67; 95% CI, 0.64-0.69).
Conclusions:
hs-cTnI levels >500× the URL at 12-16 hours post-cardiac surgery was the optimal cut-off in discriminating between patients without other signs of acute coronary syndrome who required revascularization.
Perspective:
Identifying post-CABG myocardial infarction and the need for revascularization is challenging and requires the integration of various clinical parameters in a comprehensive yet timely assessment. Troponin testing represents a core component of the assessment for myocardial injury. Interpretation of high-sensitivity troponin levels in the post-cardiac surgery scenario is complicated by the occurrence of iatrogenic myocardial injury and the difficulty in differentiating that from a new vessel occlusion. The European Society of Cardiology issued recommendations to use a threshold of 70× URL of cardiac troponin in addition to ECG, echocardiographic, and hemodynamic criteria to aid in the diagnosis of post-cardiac surgery myocardial infarction based on evidence of its association with mortality.
This study examines the association between hs-cTnI and repeat revascularization to provide cut-offs that could help as a decision-making tool. The study, however, is retrospective in nature, with the decision to revascularize highly driven by the hs-cTnI level itself. Validation was performed in a small cohort. Unaccounted for factors driving the decision to revascularize are highly likely, given the complexity of the clinical scenario. Nevertheless, the proposed cut-off (500× URL) exhibited excellent NPV of 99.8%, which is promising but should not be relied solely upon in such high-risk clinical situations.
Clinical Topics: Acute Coronary Syndromes, Arrhythmias and Clinical EP, Cardiac Surgery, Invasive Cardiovascular Angiography and Intervention, Noninvasive Imaging, Implantable Devices, SCD/Ventricular Arrhythmias, Atrial Fibrillation/Supraventricular Arrhythmias, Aortic Surgery, Cardiac Surgery and Arrhythmias, Interventions and ACS, Interventions and Imaging, Angiography, Echocardiography/Ultrasound, Nuclear Imaging
Keywords: Acute Coronary Syndrome, Arrhythmias, Cardiac, Cardiac Surgical Procedures, Coronary Angiography, Coronary Artery Bypass, Diagnostic Imaging, Echocardiography, Electrocardiography, Hemodynamics, Myocardial Infarction, Myocardial Revascularization, Percutaneous Coronary Intervention, Postoperative Care, Troponin, Troponin I
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