ABC | Volume 114, Nº2, February 2020

Original Article Inanır et al. Arrhythmia predictors in type 1 diabetes mellitus Arq Bras Cardiol. 2020; 114(2):275-280 Table 2 – Electrocardiographic findings of the study population T1DM (n = 46) Control group (n = 46) p value Heart rate (bpm) 84.0 ± 16.9 68.3 ± 11.3 < 0.001 QT ms 352.6 ± 27.4 362.4 ± 22.9 0.068 QTc ms 412.9 ± 36.0 384.2 ± 24.6 < 0.001 QTd ms 29.7 ± 13.8 15.2 ± 6.0 < 0.001 QTdc ms 34.5 ± 15.0 16.1 ± 6.6 < 0.001 Tp-e ms 90.3 ± 8.1 74.8 ± 9.9 < 0.001 JT ms 275.1 ± 23.7 278.8 ± 24.7 0.456 JTc ms 321.6 ± 26.0 295.5 ± 24.7 < 0.001 Tp-e/QT 0.26 ± 0.03 0.21 ± 0.03 < 0.001 Tp-e/QTc 0.22 ± 0.03 0.20 ± 0.03 0.007 Bpm: beats per minute; JT: interval from the end of the QRS complex (J point) to the end of the T wave; JTc: corrected JT interval; ms: millisecond; QT: interval from the beginning of the QRS complex to the end of the T wave; QTc: corrected QT interval; QTd: QT dispersion, the difference between the maximum and minimum QT intervals; QTdc: corrected QT dispersion; Tp-e: T-peak to T-end interval. Table 3 – Correlations of T1DM disease duration and HbA1c levels with electrocardiographic parameters T1DM duration (years) HbA1c (%) QTc ms r = 0.417, p < 0.001 r = 0.414, p < 0.001 QTd ms r = 0.600, p < 0.001 r = 0.353, p < 0.001 QTdc ms r = 0.669, p < 0.001 r = 0.608, p < 0.001 Tp-e ms r = 0.606, p < 0.001 r = 0.602, p < 0.001 JTc r = 0.443, p < 0.001 r = 0.525, p < 0.001 Tp-e/QT r = 0.615, p < 0.001 r = 0.608, p < 0.001 Tp-e/QTc r = 0.357, p < 0.001 r = 0.352, p = 0.001 depolarization to completion of repolarization. Because QT is typically affected by heart rate, the heart rate-corrected QT interval (QTc) has been proposed as amore appropriatemeasure of QT. 17 Inmany cardiovascular and non-cardiovascular diseases, QTc was shown to be increased. 18 QTc prolongation has been suggested as an independent marker of ventricular arrhythmias, sudden death, and increased mortality in patients with T1DM as well. 17,19-22 T1DM patients have been shown to present a positive association of QTc prolongation with age, diabetes duration, and poor metabolic control. 23 Accordingly, we have also found a positive correlation between QTc and T1DM duration and HbA1c levels. QTd, which is defined as the difference between the maximum and minimum QT interval on surface 12-lead ECG, 24 represents ventricular repolarization heterogeneity and is reported as a predictor of ventricular arrhythmias. 24,25 Increased QTd has also been associated with sudden cardiac death. 26,27 Tokatli et al. reported that QTd was prolonged in patients with type 2 diabetes mellitus in comparison with controls. 28 In this paper, we found that QTd was significantly increased in T1DM patients as well, in correlation with disease duration and glycemic control measured by HbA1c. Uysal et al. have found that QTc and QTdc were prolonged in children and adolescents with T1DM. 29 This prolongation, however, was not associated with disease duration and glycemic control, which may be explained by the relatively young age and short disease duration. QT interval is composed of depolarization and repolarization components, and it is also affected by QRS period. 30 However, JT interval is the component of the QT interval that reflects ventricular repolarization alone. 31 It has been suggested that JT interval may be a more specific repolarization marker than the QT interval. 32 JT interval may also be affected by heart rate. Therefore, JTc may be more appropriate. Accordingly, Alizade et al. 33 reported that prolonged JTc was associated with ventricular arrhythmias. Tp-e interval is also a relatively new ECG parameter showing ventricular repolarization. It has been associated with ventricular arrhythmias and sudden death, even in patients with normal QTc. 34,35 Tp-e/QT ratio has also recently been used as a new electrocardiographic marker for ventricular repolarization, 36 and it has been reported to be associated with malignant ventricular arrhythmias. 37 Most studies assessing ventricular depolarization or repolarization abnormalities in T1DM have used QTc duration and QTdc. However, Tp-e, JT, JTc intervals, and Tp-e/QT and Tp-e/QTc ratios have not been studied. We have found that, in addition to QTc and QTdc, Tp-e and JTc intervals and Tp-e/QT and Tp-e/QTc ratios are increased in T1DM subjects, in association with disease duration and HbA1c levels. 277