Rise and fall of high-sensitivity cardiac troponin T after coronary artery bypass grafting surgery in relation to current definitions of myocardial infarction: a systematic review and meta-analysis
Authors: Denessen E.J.S , Heuts S , Vroemen W.H.M , Sels J.W , Segers P , Bekers O , Van 't Hof A.W.J , Maessen J.G , Van Der Horst I.C.C , Mingels A.M.A 
Published: November 2020

Abstract

Background
Cardiac troponins are the preferred biomarkers for the diagnosis of myocardial infarction (MI) and play an important role in coronary artery bypass grafting (CABG) related MI (type 5 MI). Different cut-off values, as defined by multiples of the 99th percentile upper reference limit (URL) for isolated and non-isolated troponin elevations have been proposed. Also, these definitions are based on arbitrarily chosen and varying values (3rd and 4th Universal definition: 10xURL, Society for Cardiovascular Angiography and Interventions (SCAI): 35 and 70xURL) and electrocardiographical or imaging findings. In addition to the controversy in MI definitions, the introduction of high-sensitivity cardiac troponin (hs-cTn) assays and their subsequent lower thresholds warrant a thorough re-assessment of hs-cTn dynamics after CABG.

Purpose
To evaluate the rise and fall of hs-cTn after CABG in relation to the definitions of myocardial infarction.

Methods
Studies published between 2008 and 2020 reporting hs-cTn concentrations in relation to CABG were searched through Pubmed and reviewed by 2 independent screeners. The search terms were “coronary artery bypass” AND “high-sensitivity cardiac troponin”, including alternative names and abbreviations. Inclusion criteria were the use of a hs-cTn assay in the postoperative phase, either for cardiac troponin T or I. This study was performed in agreement with the PRISMA guidelines.

Results
Out of 37 screened studies, 15 studies were included (2860 patients). The overall preoperative hs-cTnT concentration (median, 25th-75th percentile) was 43.5 (16.3–57.9) ng/L. Subsequently, in &gt;80% of CABG patients, preoperative hs-cTnT was elevated &gt;14 ng/L. Hs-cTnT was highly variable over time, with a peak of 408.7 (14.9–717.2) ng/L 6–8 h after CABG. Postoperative peak hs-cTnT concentrations rose &gt;10xURL (Universal definition) in 100% of CABG patients. Peak hs-cTnT &gt;35xURL and ±20% &gt;70xURL (SCAI definition) during the first 48 h was 30% and ∼20%, respectively (estimated from data depicted in Figure 1). Electrocardiographic and imaging findings were available for only 1 study (554 patients). Overall 30-day mortality was 1.7 (0.8–4.0)%, reported by 7 studies (2291 patients). Data regarding the association of hs-cTnT and clinical outcome was reported by 1 study. As only 4 studies (217 patients) reported on the results of hs-cTnI, using assays from different vendors, a meta-analysis for hs-cTnI could not be performed.

Conclusion
The different definitions of type 5 MI propose arbitrarily chosen cTn cut-off values, varying enormously between the definitions. The current thresholds may not apply to the majority of CABG patients, since &gt;80% had elevated preoperative hs-cTnT. Furthermore, hs-cTnT obtained within 48 h after CABG is highly variable over time. Therefore, further research is needed to establish clinically relevant hs-cTn thresholds and timing of sampling for a more accurate diagnosis of CABG procedure related MI.
Figure 1

Funding Acknowledgement
Type of funding source: Public grant(s) – National budget only. Main funding source(s): ZonMw Veni grant