Composition of circulating cardiac troponin T after on-pump and off-pump cardiac surgery

Background Cardiac troponin T (cTnT) can be found in the circulation in intact, mildly fragmented and short, highly fragmented forms. During the early stages of myocardial infarction intact and mildly fragmented long cTnT forms predominate. In contrast, in later myocardial infarction stages, as well as in renal disease, Takotsubo syndrome, atrial fibrillation and after strenuous exercise cTnT elevations are mainly due to short highly fragmented cTnT forms. However, the molecular forms contributing to postoperative cTnT elevation in cardiac surgery remain unclear. Purpose To investigate the composition of circulating cTnT after on-pump and off-pump cardiac surgery Methods Lithium-heparin plasma samples were obtained from 149 patients undergoing elective cardiac surgery preoperatively and at 3–6 hours, 1 day, and 3–7 days postoperatively. Intact and mildly fragmented cTnT forms were measured with an in-house investigational high-sensitivity (hs) long cTnT assay and hs-cTnT was measured with Roche Elecsys 5 gen assay in each sample. Statistical comparisons were performed using nonparametric tests and median values [25th-75th percentiles] are reported. Results None of the included patients met the criteria for clinical perioperative myocardial infarction. Peak hs-cTnT exceeded 70x upper reference limit (URL) in 34 (23.0%) patients with a median peak concentration of 636 ng/L. Long cTnT peaked at 3–6 h (542 [250–880] ng/L) with 79 (53.4%) patients exceeding 70x URL. Long cTnT declined rapidly reaching 11 [7–17] ng/L at 3–7 days values. Only one patient (0.7%), who developed new left bundle branch block, exceeded 10x URL at 3–7 days. In contrast, hs-cTnT remained elevated at 3–7 days (161 [100–293] ng/L), and 57% of patients exceeded 10x URL. Peak long cTnT correlated with cardiopulmonary bypass duration (r= 0.398, p<0.001) and was significantly higher after on-pump surgery vs off-pump surgery (603 [361–924] ng/L vs. 23 [11–52] ng/L, p<0.001). The ratio of long cTnT to hs-cTnT at peak release was also higher after on-pump surgery (91% [72–118] vs. 24% [13–34], p<0.001). Conclusions The results show that long cTnT constitutes the main component of early troponin release after on-pump surgery while smaller fragments dominate after off-pump surgery. The rapid decline of long cTnT may offer diagnostic advantages later in the postoperative course.