Ventricular gradient and nondipolar repolarization components increase at higher heart rate

Abstract

.-Differences in action potential duration reflect differences in ion channel properties. These properties also determine rate dependence of action potential duration, and transmural dispersion was confirmed experimentally to increase with cycle length. While several electrocardiographic indexes characterizing repolarization abnormalities have been proposed, studies of their heart rate dependence are missing. This study therefore investigated rate relationship of two repolarization descriptors, namely, the so-called total cosine of the QRS-T angle (TCRT), proposed to characterize global repolarization heterogeneity, and the so-called relative T wave residuum (TWR), linked to regional repolarization dispersion. During 24-h holter recordings in 60 healthy subjects (27 males), a 12-lead ECG was obtained every 30 s. RR intervals, QT intervals, and TCRT and TWR were calculated in each ECG and averaged over RR interval bins ranging from 550 to 1,150 ms in 10-ms steps. Women had uniformly greater TCRT and TWR values than men did over the entire range of investigated RR intervals. Whereas the TCRT in both sexes showed marked rate dependence with higher values at long RR intervals (550 vs. 1,150 ms: women, 0.46 Ϯ 0.31 vs. 0.76 Ϯ 0.18, P ϭ 9 ϫ 10 Ϫ7 ; men, 0.08 Ϯ 0.45 vs. 0.49 Ϯ 0.35, P ϭ 9 ϫ 10 Ϫ8 ), the rate dependence of TWR was more marked in women than in men, showing higher values at shorter RR intervals (550 ms vs. 1,150 ms: women: 0.29 Ϯ 0.14% vs. 0.08 Ϯ 0.06%, P ϭ 2 ϫ 10 Ϫ8 ; men: 0.14 Ϯ 0.12% vs. 0.04 Ϯ 0.02%, P ϭ 2 ϫ 10 Ϫ15 ). This suggests that both global and regional repolarization heterogeneity are increased at faster heart rates. Whereas in women at all heart rates the sequence of repolarization more closely replicates the sequence of depolarization, localized repolarization is more heterogeneous than in men especially at fast heart rates. repolarization heterogeneity; electrocardiogram; rate dependence; gender difference ACTION POTENTIAL DURATION (APD) differs not only between myocytes of different ventricular layers (35) but also between the cardiac apex and base (25), posterior and anterior endocardial surfaces (4), and right and left ventricle (8). This APD dispersion is potentially arrhytmogenic, especially when increased by ion channel mutations in congenital and druginduced long QT syndrome (3) or by abrupt changes in cycle length (17).Differences in APD reflect differences in ion channel properties (13,35). Because these properties also determine the rate dependence of APD (13,35,42), heart rate likely influences APD dispersion across the heart. However, experimental studies confirmed significant increase with cycle length prolongation for transmural dispersion (35) that was linked to the occurrence of torsades de pointes and QT interval prolongation at slow heart rates (3). Electrocardiographic investigations of heart rate dependence of other facets of repolarization heterogeneity are missing.Several electrocardiographic indexes have recently been proposed to characterize repolarization abnormalit...

T‐Wave Morphology Parameters Based on Principal Component Analysis Reproducibility and Dependence on T−Offset Position

“…In the report of Smetana et al long-term ECG recordings had been obtained, thus providing larger RR ranges than those obtained when recording only short term 10-second resting ECGs. In addition, Smetana et al showed that Twave parameters mainly change for RR intervals shorter than 700 ms. 8 Of note, the heart rate influences on T-wave morphology parameters based on PCA are much lesser than observed for the crude QT duration (>10% with R 2 = 39% in our study). Our data suggest that for RR intervals included between 900 and 1200 ms a correction for heart rate changes is not mandatory for T-wave morphology parameters analysis.…”

“…8 In the present study, the slopes of the relationships between heart rate and PCA parameters are small (≤6 * 10 −3 ) although significant, explaining only 5-10% of the distribution of the parameters (Table 6). It is smaller than in the reports from Smetana et al 8 the discrepancy being probably related to the range of heart rate considered. In the report of Smetana et al long-term ECG recordings had been obtained, thus providing larger RR ranges than those obtained when recording only short term 10-second resting ECGs.…”

“…1,5,6 From 12-lead ECG, the so-called TWR could represent the nondipolar components of the T-wave energy and could reflect regional ventricular repolarization heterogeneities, 7,8 although this link has yet not been fully demonstrated from the standard 12-lead set. As in previous studies, we found that the TWR stands for only a small amount (i.e.…”

“…32,33 More critically, PCA of the T-wave morphology is also dependent on heart rate. 8 To take into account this physiological modulation, Smetana et al suggest running PCA analysis after heart rate stratification ("binning") from long-term ECG series. 8 In the present study, the slopes of the relationships between heart rate and PCA parameters are small (≤6 * 10 −3 ) although significant, explaining only 5-10% of the distribution of the parameters (Table 6).…”

“…8 To take into account this physiological modulation, Smetana et al suggest running PCA analysis after heart rate stratification ("binning") from long-term ECG series. 8 In the present study, the slopes of the relationships between heart rate and PCA parameters are small (≤6 * 10 −3 ) although significant, explaining only 5-10% of the distribution of the parameters (Table 6). It is smaller than in the reports from Smetana et al 8 the discrepancy being probably related to the range of heart rate considered.…”