Association between Cardiac Troponin Level and Coronary Flow Reserve in Patients without Coronary Artery Disease: Insight from a Thermodilution Technique Using an Intracoronary Pressure Wire

Background and Objectives: Cardiac troponins are associated with increased mortality, even among patients with no coronary artery disease. Elevated cardiac troponin levels are frequently observed in patients without significant coronary lesions, although the mechanism underlying this finding is unclear. The aim of our study was to evaluate the association between the levels of cardiac troponin and coronary flow reserve (CFR). Subjects and Methods: We evaluated serum cardiac troponin-I in 19 patients (9 female; age $61.9{\pm}10.9$ year-old). All patients had an ejection fraction >40% and angiographically normal coronary arteries. Simultaneous measurements of fractional flow reserve (FFR), the index of microcirculatory resistance (IMR), and CFR measurements using an intracoronary temperature- and pressure-sensing guidewire under basal conditions and during maximal hyperemia were performed in three vessels: the left anterior descending artery (LAD), left circumflex artery (LCX) and right coronary artery (RCA). Results: All patients were followed for a median of 13 months. FFR, IMR, and CFR measurements were performed successfully in all subjects. Mean CFRs of LAD, LCX, and RCA were $1.98{\pm}1.20$, $2.75{\pm}2.11$, and $4.44{\pm}2.51$, respectively. Mean IMRs of LAD, LCX and RCA were $33.28{\pm}18.78$, $29.11{\pm}26.70$, and $30.55{\pm}23.65$, respectively. There was a poor correlation between CFR and troponin-I values in each vessel. In selecting the lowest value of CFR in each patient as the corresponding value, the lowest CFR was not associated with troponin-I levels (r=-0.219, p=0.367). Conclusion: In patients without significant coronary lesions, the correlation between CFR and troponin-I level was not significant using a thermodilution technique. Further study of a larger population with longer-term follow-up may be needed to more fully understand microvascular dysfunction.