ABC | Volume 110, Nº6, June 2018

Original Article Karaman et al Myocardial repolarization and VPC burden Arq Bras Cardiol. 2018; 110(6):534-541 Methods Study population One hundred patients with at least 1 VPC in the 12-lead ECG with diagnosis of dizziness, syncope, and palpitation without structural heart disease admitted to the Cardiology Department of our university hospital, between July 2016 and March 2017, were enrolled for this cross-sectional study. Twenty-four-hour ambulatory Holter recordings were obtained from all patients. VPC burden was calculated as the total number of VPCs divided by the number of all QRS complexes in the total recording time. A frequency of < 1% VPCs/24 h was denoted as “rare-group 1 (n = 32)”, 1–5% VPCs/24 h was denoted as “occasional-group 2 (n = 36)”, and > 5% VPCs/24 h was denoted as “frequent-group 3 (n = 32)”. The exclusion criteria for all groups were non-reliable T waves on the ECG, atrial fibrillation, bundle branch block, moderate or severe valvular heart diseases, thyroid disorders, cardiomyopathies, congenital heart diseases, malignancy, pulmonary hypertension, electrolyte disturbances, acute coronary syndromes, heart failure, history of myocardial infarction, history of coronary artery bypass grafting, implanted permanent pacemaker, and LV segmental motion defect in the echocardiographic exam. The local ethics committee approval and informed consent from all patients were obtained. Electrocardiography and Holter Recordings Twelve-lead ECGs were obtained at rest at 10 mm/mV amplitude and 25 mm/sec (Cardiofax V; Nihon Kohden Corp., Tokyo, Japan) rate, with the patient in the supine position. All ECGs were transferred to a computer through a scanner and then used for × 300% magnification using the Paint software. Holter recordings were performed by using Lifecard CF recorders (Del-Mar Reynolds). Patients were warned not to smoke and not to consume coffee and/or alcohol during the Holter recording. Measurements were performed on the computer by two cardiologists who were blinded to the clinical data of each patient. Ventricular tachycardia (VT) was defined as the line-up of at least three or more consecutive VPCs. The ventricular couplet (Vc) was defined as a sequential ordering of two VPCs. RR interval, QRS duration, QT, and QTd were measured in all derivations. QT was defined as the time from the start of the QRS to the point at which the T wave returns to the isoelectric line. The average value of at least two readings was calculated for each lead. QTc was calculated by using Bazett’s formula: 9 QTc = QT/√R – R interval. QTd was defined as the difference between the longest and the shortest QT interval of the 12leads. Subjects with U waves in their ECGs were excluded from the study. In the measurement of Tp-e interval, the tail and tangent methods can be used, but the former is a better predictor of mortality than the latter. 10 Thus, the tail method was used in this study. The tail method was defined as the interval from the peak to the end of the T wave to the point where the wave reached the isoelectric line. 9 Measurement of the Tp-e interval was obtained from leads V2 and V5, which were corrected for heart rate (cTp-e). 11 The Tp-e/QT and Tp-e/QTc ratios were calculated from these measurements. Echocardiographic examination All echocardiography examinations (General Electric Vivid S5, Milwaukee, WI, USA) were performed by an experienced cardiologist in all subjects using a 2.5–3.5 MHz transducer in the left decubitus position. Two-dimensional and pulsed Doppler measurements were obtained using the criteria of the American Society of Echocardiography and the European Association of Cardiovascular Imaging. 12 Left ventricular ejection fraction (LVEF) was assessed using Simpson’s method. Statistical analysis All tests were performed by using PASW Statistics (SPSS 18.0 for Windows, Inc., Chicago, IL, USA). Shapiro–Wilk test was used to test for normal distribution. Continuous variables were described as the mean (± standard deviation), and categorical variables were described as frequency (percentage). All continuous parameters were compared among groups by using one-way ANOVA. The post hoc Tukey’s test was used for significant intergroup differences. Categorical factors were compared among groups using the χ 2 test for independence. Correlations between two variables were performed by Pearson’s correlation. Multiple linear regression analysis was used to evaluate the association between an increased VPC burden and independent variables that differed significantly in Pearson’s correlation analyses (p < 0.1). A multivariate logistic regression analysis was performed to demonstrate the effect of presence of CAD on ECG parameters. P-values < 0.05 were considered significant. Results The baseline demographics and laboratory characteristics of the three groups are summarized in Table 1. No significant difference was found among the three groups in terms of any baseline demographic or laboratory characteristic. Some baseline and ambulatory ECG parameters among the groups are shown in Table 2. According to the comparison of the ECG parameters among the three groups in lead V2, QT interval was significantly longer in groups 2 and 3 than in group 1. Tp-e interval in group 3 was significantly longer than those in groups 1 and 2. The Tp-e/QTc ratio significantly increased in groups 2 and 3 in comparison with group 1. When the groups were compared, no significant difference was found in QTc interval and Tp-e/QT ratio (Table 2). In the comparison of ECG parameters among the three groups in lead V5, QT interval was significantly longer in group 3 than in group 1. Tp-e interval was significantly longer in group 3 than in groups 1 and 2. Tp-e/QTc ratio was significantly increased in the group 3 when compared to the group1. When the groups were compared, no significant difference was found in QTc interval and Tp-e/QT ratio (Table 2). A total of 28 patients had coronary artery disease (CAD) (7, 10, and 11 patients in groups 1, 2, and 3, respectively). Non-critical lesions that did not cause significant narrowing were evident in the angiographic reports. The presence of CAD was greater in group 3 than in groups 1 and 2, but statistical significance was not observed (p = 0.538). In the multivariate logistic regression 535