Correlation of corrected QT interval with quantitative cardiac troponin-I levels and its prognostic role in Non-ST-elevation myocardial infarction.

Background: Non-ST-elevation Myocardial Infarction (NSTEMI) subgroup of ACS has wide variability in patient prognosis. Risk stratification in NSTE-ACS is essential for deciding about early management. Corrected QT interval estimation is one tool which has utility in bedside risk stratification. Whether it differentiates NSTEMI patients into different risk groups is the contention of this study.

Objective: To assess (1) correlation between maximum corrected QT interval (QTc) and cardiac Troponin I (cTnI) levels; (2) if prolonged corrected QT interval is an independent predictor of higher MACE in NSTEMI patients.

Methods: We prospectively studied 301 NSTEMI patients. cTnI level and QTc were measured at 0, 12, 24 and 48h post-admission. Patients were followed for 30days post-discharge for incidence of major adverse cardiac events (MACE) defined as composite of cardiac death, non-fatal MI and urgent revascularization. We assessed correlation between cTnI level and maximum QTc value. Regression analysis was performed to identify independent predictors of MACE.

Results: We found a strong positive linear correlation between maximum QTc interval and cTnI level with a correlation coefficient of 0.637 (p<0.001). Cut-off value of QTc>468ms predicted poor prognosis in form of MACE with 72% sensitivity and 61% specificity. Multivariate analysis revealed that after adjusting for different prognostic variables, TIMI score>2 and QTc>468ms, were the only independent predictors of MACE.

Conclusion: QTc-max interval has a strong positive linear correlation with cTnI level. Prolonged QTc has utility as an independent high risk predictor in NSTEMI population.