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Corrected QT (QTc) interval has been reported to prolong when the myocardium is exposed to ischemia. However, little is known about the association between prolonged QTc and coronary blood flow to the infarct-related artery in the setting of non-ST-elevation myocardial infarction (NSTEMI). We hypothesized that prolonged QTc predicts impaired coronary blood flow to the infarct-related artery in patients with NSTEMI.
We performed a retrospective analysis of 481 consecutive patients with NSTEMI who underwent coronary angiography within five days after presentation. Patients with atrial fibrillation, complete bundle branch block, paced rhythm, electrolytes disturbance, history of coronary artery bypass grafting and those on antiarrhythmic medication were excluded. Electrocardiography and coronary angiography were reviewed by a blind fashion. The QT was measured manually from the onset of QRS complex to the end of T wave, and QTc was calculated using Bazett’s formula. QTc prolongation was defined as QTc greater than 450ms in men and 470ms in women. Baseline characteristics, electrocardiographic and angiographic findings including Thrombolysis In Myocardial Infarction flow grade of the infarct-related artery were compared between patients with and without prolonged QTc.
Of the 340 patients included in the final analysis, 130 patients (38.2%) had a prolonged QTc interval. With respect to baseline characteristics, there was no significant difference between the two groups. There was no significant difference in the rate of TIMI grade 0/1 flow (25.4% vs. 18.6%, p=0.14) and prevalence of obstructive coronary artery disease (76.9% vs. 75.2%, p=0.72). Median QTc was 453 ms in patients with TIMI 0/1 flow and 449 ms in those with TIMI 2/3 flow (p=0.79). There was no significant difference in the rate of angiographic thrombus (p=0.22), collateral circulation to the infarct-related artery (p=0.43) and in-hospital percutaneous or surgical revascularization (p=0.29) between patients with and without QTc prolongation. The peak troponin I values were comparable between the two groups (0.76 ng/mL vs. 0.62 ng/mL, p=0.8).
Prolonged QTc interval was observed in one-third of the NSTEMI patients in our cohort of patients. Contrary to our expectation, prolonged QTc did not have a predictive value for impaired coronary flow to the infarct-related artery in patients with NSTEMI.