ABC | Volume 112, Nº1, January 2019

Original Article Dotta et al Regional QT dispersion as predictor of reperfusion Arq Bras Cardiol. 2019; 112(1):20-29 Methods This was an observational, prospective study. The study was approved by the local ethics committee and all patients or their legal representatives signed an informed consent form before participating in the study. Patients We selected patients with STEMI that sought medical care at public health centers in the city of Sao Paulo, Brazil, who had undergone thrombolytic therapy using TNK, referred for angiography in a tertiary hospital, regardless of electrocardiographic criterion for reperfusion (ST-segment resolution > 50%). Only patients with primary diagnostic of myocardial infarction, considered eligible to thrombolytic therapy in PIS were consecutively included. One hundred and ten patients were initially included, and six were excluded for electrocardiographic reasons. Exclusion criteria were: known contraindications to fibrinolysis, and electrocardiographic findings that could affect QT interval measurements, such as bundle branch block, atrial fibrillation or previous myocardial infarction. Thus, in the present study, 104 patients of both sexes were included, all of them with primary AMI, treated with TNK within 6 hours of symptoms’ onset at primary care centers and subsequently referred for coronary angiography at a tertiary hospital within 2-24 hours of fibrinolysis, or immediately, in situations when a rescue therapy was needed. The operation of the STEMI network in Sao Paulo has been previously published. 7,8 Clinical and demographic data of the patients were obtained. An experienced echocardiographer, who did not know about their clinical history performed the measurements of the ventricular ejection fraction on the fifth day following AMI in all patients. Electrocardiographic analysis Electrocardiographic analysis consisted of an ECG before and 60 minutes after fibrinolysis, using certified and calibrated devices, with patients in prone position. Two independent observers, unaware of patients’ clinical characteristics, analyzed the ECG results. The criteria to undergo electrocardiographic reperfusion was a reduction in ST-segment greater than 50% in the highest lead within 60 minutes of fibrinolytic administration. QT interval was manually measured using a digital caliper, with a lineal, non-contact measurement system, with a resolution of 0.1 mm/0.01’’, accuracy of ± 0,2 mm / 0.001" (< 100 mm) and ± 0.03 mm / 0.01"(>100 - 200 mm) and repeatability of 0.1 mm / 0.01". QT values were converted to milliseconds (ms) and corrected for heart rate by the Hodges’ linear method using the formula [QTc = QT + 1.75 (RR - 60)]. In order to minimize intraobserver variability, QT interval was calculated by the mean of three measurements in consecutive QRS complexes and in all ECG leads. Kappa coefficient was calculated to minimize the interobserver variability. QT measurements were performed using the tangent method, in which the end of T-wave was defined as the intersection of this tangent with the baseline, at the maximal slope at the end of theQT interval. 16 In the presence of a U-wave, the end of T wave was taken as the nadir between T and Uwaves. Additionally, we excluded from the analysis all ECG leads where some variables, particularly the T-wave, could not be clearly determined. QTcDwas defined as the difference between the maximum (QT max ) and minimum QT (QT min ) interval in 12-lead ECG. Regional dispersion was calculated as the difference between QT max and QT min only in leads with ST-segment elevation. Acute anterior wall myocardial infarction was defined as ST‑segment elevation in DI, aVL, V1-V3 or V1-V6 leads, whereas non-anterior wall myocardial infarction defined as ST-segment elevation in DII, DIII, aVF, and V 5 -V 6 leads. Angiographic analysis Angiographic analysis was performed in a tertiary hospital according to a PIS protocol previously described. Two experienced hemodynamic technicians (more than 15 years of practice), unaware of any information that could affect angiographic analysis, analyzed the epicardial flow according to TIMI flow grade, 17 and myocardial perfusion according to myocardial Blush grade. 18 Myocardial blush, defined as contrast density in myocardial microcirculation (Chart 1), was assessed only in patients with TIMI3 grade. Statistical analysis Numerical data were expressed as mean and standard deviation (SD) in case of variables with normal distribution, or as median and interquartile range (IQR) in case of quantitative variables with non-normal distribution. The normality of data distribution was tested with the Shapiro-Wilk test and the Kolmogorov-Smirnov test; kurtosis and asymmetry of data distribution were also examined. Categorical variables were expressed as number (n) and percentage (%) and compared by the Pearson’s chi-square test, or Fisher’s exact test, as Chart 1 – Definitions for myocardial perfusion (microperfusion) by Myocardial Blush Grade Grade 0 (absence of myocardial perfusion): absence of myocardial blush or contrast density Grade 1 (minimal myocardial perfusion): minimal myocardial blush or contrast density Grade 2 (partial myocardial perfusion): moderate myocardial blush or contrast density, but less than that obtained during contrast injection into a contra-lateral or ipsilateral non-infarcted-related coronary artery Grade 3 (complete myocardial perfusion): normal myocardial blush or contrast density, comparable with that obtained during contrast injection into a contra-lateral or ipsilateral non-infarcted-related coronary artery Adapted from Van ´t Hof et al. 18 21