Journal articles: 'QT variability'

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Berger, Ronald D. "QT variability." Journal of Electrocardiology 36 (December 2003): 83–87. http://dx.doi.org/10.1016/j.jelectrocard.2003.09.019.

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Dobson, Craig P., Andrew Kim, and Mark Haigney. "QT Variability Index." Progress in Cardiovascular Diseases 56, no. 2 (September 2013): 186–94. http://dx.doi.org/10.1016/j.pcad.2013.07.004.

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Berger, Ronald D. "QT Interval Variability." Journal of the American College of Cardiology 54, no. 9 (August 2009): 851–52. http://dx.doi.org/10.1016/j.jacc.2009.06.007.

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Magnano, Massimo, Cristina Gallo, Pier Paolo Bocchino, Marco Briguglio, Anna Rivetti, Fiorenzo Gaita, and Matteo Anselmino. "QT prolongation and variability." Journal of Cardiovascular Medicine 20, no. 4 (April 2019): 180–85. http://dx.doi.org/10.2459/jcm.0000000000000773.

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Zareba, Wojciech, and Antoni Bayes de Luna. "QT Dynamics and Variability." Annals of Noninvasive Electrocardiology 10, no. 2 (April 2005): 256–62. http://dx.doi.org/10.1111/j.1542-474x.2005.10205.x.

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Tereshchenko, Larisa G., and Ronald D. Berger. "Towards a better understanding of QT interval variability." Therapeutic Advances in Drug Safety 2, no. 6 (September 27, 2011): 245–51. http://dx.doi.org/10.1177/2042098611421209.

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The International Conference on Harmonization of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH) Guideline E14 recommends ‘Thorough QT Study’ as a standard assessment of drug-induced QT interval prolongation. At the same time, the value of drug-induced QTc prolongation as a surrogate marker for risk of life-threatening polymorphic ventricular tachycardia known as torsades des pointes remains controversial. Beat-to-beat variability of QT interval was recently proposed as an alternative metric. The following review addresses mechanisms of beat-to-beat QT variability, methods of QT interval variability measurements, and its prognostic value in clinical studies.

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Yunisova, A. S. "Athletic heart and QT variability." Academy of medicine and sports 2, no. 4 (January 20, 2022): 20–23. http://dx.doi.org/10.15829/2712-7567-2021-38.

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This review provides detailed data on the diagnosis, prevalence, classification, and etiology. The variety of causes leading to long QT syndrome (LQTS) creates difficulties in the differential diagnosis of this condition and, as a result, LQTS often remains outside the sports medicine physicians’ attention. As a result, it is necessary to introduce non-invasive screening methods for studying the cardiac electrophysiological characteristics and select high-risk groups.

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HAIGNEY, MARK C. P., SHAMA ALAM, SCOT TEBO, GREGARY MARHEFKA, AHMED ELKASHEF, ROBERTA KAHN, C. NORA CHIANG, FRANK VOCCI, and LOUIS CANTILENA. "Intravenous Cocaine and QT Variability." Journal of Cardiovascular Electrophysiology 17, no. 6 (June 2006): 610–16. http://dx.doi.org/10.1111/j.1540-8167.2006.00421.x.

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Baumert, Mathias, Gavin W. Lambert, Tye Dawood, Elisabeth A. Lambert, Murray D. Esler, Mariee McGrane, David Barton, and Eugene Nalivaiko. "QT interval variability and cardiac norepinephrine spillover in patients with depression and panic disorder." American Journal of Physiology-Heart and Circulatory Physiology 295, no. 3 (September 2008): H962—H968. http://dx.doi.org/10.1152/ajpheart.00301.2008.

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Suggestions were made that increased myocardial sympathetic activity is reflected by elevated QT variability (dynamic changes in QT interval duration). However, the relationship between QT variability and the amount of norepinephrine released from the cardiac sympathetic terminals is unknown. We thus attempted to assess this relationship. The study was performed in 17 subjects (12 with major depressive disorder and 5 with panic disorder). Cardiac norepinephrine spillover (measured by direct catheter technique coupled with norepinephrine isotope dilution methodology) was assessed before and 4 mo after treatment with selective serotonin reuptake inhibitor (SSRI) antidepressants. The distribution of the cardiac norepinephrine spillover was bimodal, with the majority of patients having values of ≤10 ng/min. There was a positive correlation between cardiac norepinephrine spillover and corrected QT interval ( r = 0.7, P = 0.03) but not with any of the QT variability measures. However, in a subgroup of five patients who had high levels of cardiac norepinephrine spillover (>20 ng/min) a tendency for a strong positive correlation with variance of QT intervals ( r = 0.9, P = 0.08) was observed. There were significant correlations between the severity of depression and QT variability indexes normalized to the heart rate [QTVi and QT interval/R-R interval (QT/RR) coherence] and between the severity of anxiety and the QT/RR residual and regression coefficient, respectively. Treatment with SSRI antidepressants substantially reduced depression score but did not affect any of the QT variability indexes. We conclude that in depression/panic disorder patients with near-normal cardiac norepinephrine levels QT variability is not correlated with cardiac norepinephrine spillover and is not affected by treatment with SSRI.

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Yunisova, A. S., and A. V. Smolensky. "QT interval variability and athlete's heart remodeling." Clinical Medicine (Russian Journal) 100, no. 7-8 (October 31, 2022): 377–81. http://dx.doi.org/10.30629/0023-2149-2022-100-7-8-377-381.

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At present, the prevention of sudden cardiac death in athletes is of great interest. A large amount of literature data concerning the correlation between the length of the QT interval and the proarrhythmic potential of the myocardium has been accumulated. However, new potential predictors of the fatal arrhythmias occurrence in athletes have emerged in recent years — an increase in the dispersion of the QT interval, as well as short-term variability in repolarization. This review provides detailed data on the diagnosis, prevalence, classifi cation, etiology of long QT as one of the manifestations of QT variance. The variety of causes leading to long QT syndrome (LQTS) causes diffi culties in the diff erential diagnosis of this condition and, and as a result, LQTS often remains outside the attention of practitioners. The data of recent studies of the athlete’s heart remodelling are presented as well.

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Andršová, Irena, Katerina Hnatkova, Martina Šišáková, Ondřej Toman, Peter Smetana, Katharina M. Huster, Petra Barthel, Tomáš Novotný, Georg Schmidt, and Marek Malik. "Heart Rate Influence on the QT Variability Risk Factors." Diagnostics 10, no. 12 (December 16, 2020): 1096. http://dx.doi.org/10.3390/diagnostics10121096.

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QT interval variability, mostly expressed by QT variability index (QTVi), has repeatedly been used in risk diagnostics. Physiologic correlates of QT variability expressions have been little researched especially when measured in short 10-second electrocardiograms (ECGs). This study investigated different QT variability indices, including QTVi and the standard deviation of QT interval durations (SDQT) in 657,287 10-second ECGs recorded in 523 healthy subjects (259 females). The indices were related to the underlying heart rate and to the 10-second standard deviation of RR intervals (SDRR). The analyses showed that both QTVi and SDQT (as well as other QT variability indices) were highly statistically significantly (p < 0.00001) influenced by heart rate and that QTVi showed poor intra-subject reproducibility (coefficient of variance approaching 200%). Furthermore, sequential analysis of regression variance showed that SDQT was more strongly related to the underlying heart rate than to SDRR, and that QTVi was influenced by the underlying heart rate and SDRR more strongly than by SDQT (p < 0.00001 for these comparisons of regression dependency). The study concludes that instead of QTVi, simpler expressions of QT interval variability, such as SDQT, appear preferable for future applications especially if multivariable combination with the underlying heart rate is used.

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Baumert, Mathias, Markus P. Schlaich, Eugene Nalivaiko, Elisabeth Lambert, Carolina Ika Sari, David M. Kaye, Murray D. Elser, Prashanthan Sanders, and Gavin Lambert. "Relation between QT interval variability and cardiac sympathetic activity in hypertension." American Journal of Physiology-Heart and Circulatory Physiology 300, no. 4 (April 2011): H1412—H1417. http://dx.doi.org/10.1152/ajpheart.01184.2010.

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Elevated QT interval variability is a predictor of malignant ventricular arrhythmia, but the underlying mechanisms are incompletely understood. A recent study in dogs with pacing-induced heart failure suggests that QT variability is linked to cardiac sympathetic nerve activity. The aim of this study was to determine whether increased cardiac sympathetic activity is associated with increased beat-to-beat QT interval variability in patients with essential hypertension. We recorded resting norepinephrine (NE) spillover into the coronary sinus and single-lead, short-term, high-resolution, body-surface ECG in 23 patients with essential hypertension and 9 normotensive control subjects. To assess beat-to-beat QT interval variability, we calculated the overall QT variability (QTVN) as well as the QT variability index (QTVi). Cardiac NE spillover (12.2 ± 6.5 vs. 20.7 ± 14.7, P = 0.03) and QTVi (−1.75 ± 0.36 vs. −1.42 ± 0.50, P = 0.05) were significantly increased in hypertensive patients compared with normotensive subjects. QTVN was significantly correlated with cardiac NE spillover ( r2 = 0.31, P = 0.001), with RR variability ( r2 = 0.20, P = 0.008), and with systolic blood pressure ( r2 = 0.16, P = 0.02). Linear regression analysis identified the former two as independent predictors of QTVN. In conclusion, elevated repolarization lability is directly associated with sympathetic cardiac activation in patients with essential hypertension.

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Goldenberg, Ilan, Jehu Mathew, Arthur J. Moss, Scott McNitt, Derick R. Peterson, Wojciech Zareba, Jesaia Benhorin, et al. "Corrected QT Variability in Serial Electrocardiograms in Long QT Syndrome." Journal of the American College of Cardiology 48, no. 5 (September 2006): 1047–52. http://dx.doi.org/10.1016/j.jacc.2006.06.033.

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PICCIRILLO, Gianfranco, Mauro CACCIAFESTA, Marco LIONETTI, Marialuce NOCCO, Vincenza DI GIUSEPPE, Antonio MOISÈ, Camilla NASO, and Vincenzo MARIGLIANO. "Influence of age, the autonomic nervous system and anxiety on QT-interval variability." Clinical Science 101, no. 4 (September 20, 2001): 429–38. http://dx.doi.org/10.1042/cs1010429.

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As QT variability increases and heart rate variability diminishes, the QT variability index (QTVI)-a non-invasive measure of beat-to-beat fluctuations in QT interval on a single ECG lead-shows a trend towards positive values. Increased QT variability is a risk factor for sudden death. Aging lengthens the QT interval and reduces RR-interval variability. In the present study we investigated the influence of aging and the autonomic nervous system on QT-interval variability in healthy subjects. We studied 143healthy subjects, and divided them into two age ranges (younger and older than 65 years). For each subject we measured two QTVIs: from the q wave to the end of the T wave (QTeVI) and to the apex of the T wave (QTaVI). Both indexes were calculated at baseline and after sympathetic stress. In 10 non-elderly subjects, both QTVIs were determined after β-adrenoreceptor blockade induced by intravenous infusion of propranolol or sotalol. The QTVI was higher in elderly than in younger subjects (P < 0.001). QTVIs obtained during sympathetic stress remained unchanged in the elderly, but became more negative in the younger group (P < 0.05). QTeVI and QTaVI at baseline were correlated positively with age (P < 0.01) and anxiety scores (P < 0.05), but inversely with the low-frequency spectral power of RR-interval variability (P < 0.001). QTVIs were higher in subjects with higher anxiety scores. In younger subjects, sotalol infusion increased both QTVIs significantly, whereas propranolol infusion did not. In conclusion, aging increases QT-interval variability. Whether this change is associated with an increased risk of sudden death remains unclear. The association of abnormal QT-interval variability with anxiety and with reduced low-frequency spectral power of heart rate variability merits specific investigation. In healthy non-elderly subjects, acute sympathetic stress (tilt) decreases the QTVI. β-Adrenoreceptor blockade inhibits this negative trend, thus showing its sympathetic origin. Because a negative trend in QTVI induced by sympathetic stress increases only in younger subjects, it could represent a protective mechanism that is lost with aging.

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Patel, Salma, Wojciech Zareba, Jean-Philippe Couderc, Xiaojuan Xia, Raymond Woosley, Imran Patel, Daniel Combs, Saif Mashaqi, and Sairam Parthasarathy. "479 The association of QTc and QT Variability with Severity of Sleep Disordered Breathing." Sleep 44, Supplement_2 (May 1, 2021): A189. http://dx.doi.org/10.1093/sleep/zsab072.478.

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Abstract Introduction The apneas and hypopneas that characterize sleep-disordered breathing (SDB) are associated with QTc prolongation and increased QT variability. There have been mixed results as to whether QTc and QT variability increase with increasing SDB severity. This study assesses whether QTc prolongation and QT variability are likely to increase with increasing severity of SDB in a large multi-center cohort. Methods 200 subjects with no SDB and approximately 600 with three levels of SDB (mild, moderate, severe) were randomly selected from the Sleep Heart Health study and matched by age, gender and BMI. SDB was defined as an apnea/hypopnea index ≥5. Respiratory and electrocardiograms (ECG) signals from polysomnography studies were analyzed. Bazett’s heart rate correction was used to calculate QTc. QT variability was measured as standard deviation of QT intervals (SDQT) and short-term interval QT variability (STVQT), at 5-minute intervals. Subjects were excluded if there were missing data or low-quality ECG. Results Seven hundred and seventy-one subjects (age 68±10 years, 51% female, 92% Caucasian) were included. One hundred and sixty-five subjects had no SDB, 235 mild, 195 moderate and 176 had severe SDB. The mean (SD) QTc was 422(29), 411(26), 419 (34) and 418 (36) ms for the no SDB, mild, moderate, and severe SDB groups, respectively (p=0.017). The mean (SD) STVQT was 7 (9), 11 (16), 8 (9) and 9 (11) for the no SDB, mild, moderate severe SDB groups, respectively (p=<0.001). The mean (SD) STVQT was 3 (2), 4 (4), 4 (3) and 4(4) for the no SDB, mild, moderate severe SDB groups, respectively (p=<0.001). There was no statistically linear relationship between QT prolongation or QT variability and SBD severity. Conclusion QTc duration and QT variability were not increased with SDB severity. Support (if any) American Academy of Sleep Medicine Foundation (203-JF-18), National Institutes of Health (HL126140), University of Arizona Health Sciences Career Development Award (5299903), and University of Arizona Faculty Seed Grant (5833261)

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Patel, S. I., W. Zareba, J. Couderc, X. Xia, B. LaFleur, E. Torabzadeh, R. Woosley, and S. Parthasarathy. "0571 Repolarization Variability Predicts Cardiovascular Death in Obstructive Sleep Apnea." Sleep 43, Supplement_1 (April 2020): A219. http://dx.doi.org/10.1093/sleep/zsaa056.568.

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Abstract Introduction Patients with untreated obstructive sleep apnea (OSA) have a 2-3—fold increased risk of cardiovascular mortality (CVD) compared with individuals without OSA. QTc prolongation and increased QT variability among OSA patients may contribute to this association. Methods Patients with OSA from the Sleep Heart Health study were identified based on polysomnography criteria and their continuous electrocardiograms (ECG) analyzed for QTc duration and QT variability. Both Fridericia’s and Bazett’s heart rate corrections were used to calculate QTc. QT variability was measured as standard deviation of QT intervals (SDQT) and normalized QT interval variance (QTVN) at 1- and 5-minute intervals and short-term interval beat-to-beat QT variability (STVQT) was measured at 5-minute intervals. Lasso with elastic-net regularization was used as the variable/covariate selection method. Cox proportional hazards regression models were used to determine predictors of CVD. Results Data from 365 patients with OSA were screened. Ninety-seven patients were excluded from analysis due to low quality ECG data (n=50) or extremely high (> ln (10)) variability in QT/QTc and/or QT variability (n=12). Fifty two percent of the sample was male with mean age 65 years (±10). Fifty-six of these patients died of CVD. The mean (SD) QTc in the group that died was 411 (30) ms and 416 (34) ms compared to 406 (24) ms and 411 (25) ms using Fridericia (Cox LR p-value 0.055) and Bazett (p=0.090), respectively. Gender, age, race, diabetes, SDQT and STVQT were significant predictors for CVD. We fit models with the covariates and SDQT (at both 1 and 5 min) and STVQT as three models and demonstrate that both SDQT and STVQT are significantly associated with CVD death (p-values of 0.0048, 0.0089, and 0.0113, respectively) and all models had high area under the curve (0.8095, 0.8085, and 0.8125, respectively). Conclusion In patients with OSA, QT variability was associated with CVD. Support American Academy of Sleep Medicine Foundation

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DE LUNA, A. B., and X. VINOLAS. "QT dispersion and heart rate variability." European Heart Journal 17, no. 2 (February 2, 1996): 165–66. http://dx.doi.org/10.1093/oxfordjournals.eurheartj.a014827.

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Berger, Ronald D., Edward K. Kasper, Kenneth L. Baughman, Eduardo Marban, Hugh Calkins, and Gordon F. Tomaselli. "Beat-to-Beat QT Interval Variability." Circulation 96, no. 5 (September 2, 1997): 1557–65. http://dx.doi.org/10.1161/01.cir.96.5.1557.

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Yeragani, V. K., R. Pohl, V. C. Jampala, R. Balon, and C. Ramesh. "Effect of Age on QT Variability." Pediatric Cardiology 21, no. 5 (September 2000): 411–15. http://dx.doi.org/10.1007/s002460010099.

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Feild, Dirk, and Rich Gregg. "Sources of Variability In Qt Calculations." Journal of Electrocardiology 49, no. 6 (November 2016): 934. http://dx.doi.org/10.1016/j.jelectrocard.2016.09.032.

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Morita, Hiroshi. "How can we stabilize QT variability?" Heart Rhythm 8, no. 8 (August 2011): 1243–44. http://dx.doi.org/10.1016/j.hrthm.2011.04.018.

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Yeragani, Vikram Kumar, Robert Pohl, Richard Balon, V. C. Jampala, and Anusha Jayaraman. "Twenty-Four-Hour QT Interval Variability: Increased QT Variability during Sleep in Patients with Panic Disorder." Neuropsychobiology 46, no. 1 (2002): 1–6. http://dx.doi.org/10.1159/000063568.

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PICCIRILLO, Gianfranco, Giuseppe GERMANÒ, Raffaele QUAGLIONE, Marialuce NOCCO, Filippo LINTAS, Marco LIONETTI, Antonio MOISÈ, Maddalena RAGAZZO, Vincenzo MARIGLIANO, and Mauro CACCIAFESTA. "QT-interval variability and autonomic control in hypertensive subjects with left ventricular hypertrophy." Clinical Science 102, no. 3 (February 14, 2002): 363–71. http://dx.doi.org/10.1042/cs1020363.

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Left ventricular hypertrophy is a risk factor for sudden death. Malignant ventricular arrhythmias originate from altered cardiac repolarization. Ample data have described spatial abnormalities in cardiac repolarization [QT interval (QT) dispersion] in subjects with hypertension; more data are needed on temporal changes. This study was designed to assess the QT variability index (QTVI), the slope between QT and the RR interval (QT-RRslope) and spectral QT variability in subjects with arterial hypertension. The results were compared with those from a population at high risk of sudden death, i.e. patients with hypertrophic cardiomyopathy (HCM) who had received an implantable cardioverter/defibrillator (ICD), and those from normotensive control subjects. A total of 44 hypertensive subjects, six patients with HCM and an ICD and 33 control subjects underwent simultaneous short-term recording (256 beats) of QT, RR and systolic blood pressure variability, in the supine position, during controlled breathing. QTVI and spectral components of QT variability in the hypertensive group were significantly higher than in normotensive control subjects (P < 0.001), but significantly lower than in patients with HCM and an ICD (P < 0.001). The severity of left ventricular hypertrophy correlated significantly with QTVI and the ratio of low-frequency (LF) to high-frequency (HF) power obtained from the RR variability spectra (RRLF/HF, slope = 0.24, P < 0.05; QTVI, slope = 4.06, P < 0.0001; intercept, slope = 2.40, P < 0.05; χ2 = 38.8; P < 0.0001). The QT-RR slope was significantly higher only in patients with HCM and an ICD (P < 0.001). In conclusion, the increased QTVI and the correlation of this index with left ventricular hypertrophy indicates that hypertension increases temporal cardiac repolarization abnormalities. At the level of the cardiac sinus node, this alteration is associated with increased sympathetic and reduced vagal modulation. As already noted in patients with HCM, the increased QTVI could be a factor responsible for triggering malignant ventricular arrhythmias in subjects with hypertension.

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BOETTGER, SILKE, CHRISTIAN PUTA, VIKRAM K. YERAGANI, LARS DONATH, HANS-JOSEF MÜLLER, HOLGER H. W. GABRIEL, and KARL-JÜRGEN BÄR. "Heart Rate Variability, QT Variability, and Electrodermal Activity during Exercise." Medicine & Science in Sports & Exercise 42, no. 3 (March 2010): 443–48. http://dx.doi.org/10.1249/mss.0b013e3181b64db1.

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Batchvarov, Velislav N., Azad Ghuran, Peter Smetana, Katerina Hnatkova, Monica Harries, Polychronis Dilaveris, A. John Camm, and Marek Malik. "QT-RR relationship in healthy subjects exhibits substantial intersubject variability and high intrasubject stability." American Journal of Physiology-Heart and Circulatory Physiology 282, no. 6 (June 1, 2002): H2356—H2363. http://dx.doi.org/10.1152/ajpheart.00860.2001.

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Recently, it was demonstrated that the QT-RR relationship pattern varies significantly among healthy individuals. We compared the intra- and interindividual variations of the QT-RR relationship. Twenty-four-hour 12-lead digital electrocardiograms (ECGs; SEER MC, GE Marquette; 10-s ECG recorded every 30 s) were obtained at baseline and after 24 h, 1 wk, and 1 mo in 75 healthy subjects (42 women, 33 men, age 27.9 ± 9.6 vs. 26.8 ± 7.5 yr, P = not significant). QT interval was measured automatically in each ECG by six different algorithms, and the mean of the six measurements was analyzed. In each recording of each individual, QT-RR relationship was assessed by 10 different regression models including linear (QT = β + α × RR) and parabolic (QT = β × RRα) models. Standard deviations (SDs) of regression parameters α and β of consecutive recordings of each individual were compared with SD of the individual means. Intrasubject stability and interindividual variability were further tested by ANOVA. With all models, intraindividual SDs of the regression parameters were highly significantly smaller than SD of individual means ( P < 10−5–10−9). The intrasubject stability was further confirmed by ANOVA ( P < 10−19–10−30). The QT-RR relationship exhibits substantial intersubject variability as well as a high intrasubject stability. This has practical implications for a precise estimation of the heart rate-corrected QT interval in which optimized subject-specific rate correction formulas should be used.

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Dobson, Craig P., Maria Teresa La Rovere, Cara Olsen, Marino Berardinangeli, Marco Veniani, Paolo Midi, Luigi Tavazzi, and Mark Haigney. "24-Hour QT variability in heart failure." Journal of Electrocardiology 42, no. 6 (November 2009): 500–504. http://dx.doi.org/10.1016/j.jelectrocard.2009.06.021.

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Hasan, Muhammad A., Derek Abbott, Mathias Baumert, and Sridhar Krishnan. "Increased beat-to-beat T-wave variability in myocardial infarction patients." Biomedical Engineering / Biomedizinische Technik 63, no. 2 (March 28, 2018): 123–30. http://dx.doi.org/10.1515/bmt-2015-0186.

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AbstractThe purpose of this study was to investigate the beat-to-beat variability of T-waves (TWV) and to assess the diagnostic capabilities of T-wave-based features for myocardial infarction (MI). A total of 148 recordings of standard 12-lead electrocardiograms (ECGs) from 79 MI patients (22 females, mean age 63±12 years; 57 males, mean age 57±10 years) and 69 recordings from healthy subjects (HS) (17 females, 42±18 years; 52 males, 40±13 years) were studied. For the quantification of beat-to-beat QT intervals in ECG signal, a template-matching algorithm was applied. To study the T-waves beat-to-beat, we measured the angle between T-wave max and T-wave end with respect to Q-wave (∠α) and T-wave amplitudes. We computed the standard deviation (SD) of beat-to-beat T-wave features and QT intervals as markers of variability in T-waves and QT intervals, respectively, for both patients and HS. Moreover, we investigated the differences in the studied features based on gender and age for both groups. Significantly increased TWV and QT interval variability (QTV) were found in MI patients compared to HS (p<0.05). No significant differences were observed based on gender or age. TWV may have some diagnostic attributes that may facilitate identifying patients with MI. In addition, the proposed beat-to-beat angle variability was found to be independent of heart rate variations. Moreover, the proposed feature seems to have higher sensitivity than previously reported feature (QT interval and T-wave amplitude) variability for identifying patients with MI.

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Baumert, Mathias, Barbora Czippelova, Alberto Porta, and Michal Javorka. "Decoupling of QT interval variability from heart rate variability with ageing." Physiological Measurement 34, no. 11 (October 8, 2013): 1435–48. http://dx.doi.org/10.1088/0967-3334/34/11/1435.

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Yang, Peiran, Zhao Jing, Bingrong Sun, Lixin Wu, Bo Qiu, Ping Chang, and Sanjiv Ramachandran. "On the Upper-Ocean Vertical Eddy Heat Transport in the Kuroshio Extension. Part I: Variability and Dynamics." Journal of Physical Oceanography 51, no. 1 (January 2021): 229–46. http://dx.doi.org/10.1175/jpo-d-20-0068.1.

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AbstractOceanic eddies play a crucial role in transporting heat from the subsurface to surface ocean. However, dynamics responsible for the vertical eddy heat transport QT have not been systematically understood, especially in the mixed layer of western boundary current extensions characterized by the coincidence of strong eddy activities and air–sea interactions. In this paper, the winter (December–March) QT in the Kuroshio Extension is simulated using a 1-km regional ocean model. An omega equation based on the geostrophic momentum approximation and generalized to include the viscous and diabatic effects is derived and used to decompose the contribution of QT from different dynamics. The simulated QT exhibits a pronounced positive peak around the center of the mixed layer (~60 m). The value of QT there exhibits multi-time-scale variations with irregularly occurring extreme events superimposed on a slowly varying seasonal cycle. The proposed omega equation shows good skills in reproducing QT, capturing its spatial and temporal variations. Geostrophic deformation and vertical mixing of momentum are found to be the two major processes generating QT in the mixed layer with the former and the latter accounting for its seasonal variation and extreme events, respectively. The mixed layer instability and the net effect of frontogenesis/frontolysis contribute comparably to the geostrophic deformation induced QT. The contribution of QT from vertical mixing of momentum can be understood on the basis of turbulent thermal wind balance.

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BONNEMEIER, HENDRIK, UWE K. H. WIEGAND, WIEBKE BRAASCH, AXEL BRANDES, GERT RICHARDT, and JURGEN POTRATZ. "Circadian Profile of QT Interval and QT Interval Variability in 172 Healthy Volunteers." Pacing and Clinical Electrophysiology 26, no. 1p2 (January 2003): 377–82. http://dx.doi.org/10.1046/j.1460-9592.2003.00053.x.

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Orosz, Andrea, István Baczkó, Viktória Nagy, Henriette Gavallér, Miklós Csanády, Tamás Forster, Julius Gy Papp, András Varró, Csaba Lengyel, and Róbert Sepp. "Short-term beat-to-beat variability of the QT interval is increased and correlates with parameters of left ventricular hypertrophy in patients with hypertrophic cardiomyopathy." Canadian Journal of Physiology and Pharmacology 93, no. 9 (September 2015): 765–72. http://dx.doi.org/10.1139/cjpp-2014-0526.

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Stratification models for the prediction of sudden cardiac death (SCD) are inappropriate in patients with hypertrophic cardiomyopathy (HCM). We investigated conventional electrocardiogram (ECG) repolarization parameters and the beat-to-beat short-term QT interval variability (QT-STV), a new parameter of proarrhythmic risk, in 37 patients with HCM (21 males, average age 48 ± 15 years). Resting ECGs were recorded for 5 min and the frequency corrected QT interval (QTc), QT dispersion (QTd), beat-to-beat short-term variability of QT interval (QT-STV), and the duration of terminal part of T waves (Tpeak–Tend) were calculated. While all repolarization parameters were significantly increased in patients with HCM compared with the controls (QTc, 488 ± 61 vs. 434 ± 23 ms, p < 0.0001; QT-STV, 4.5 ± 2 vs. 3.2 ± 1 ms, p = 0.0002; Tpeak–Tend duration, 107 ± 27 vs. 91 ± 10 ms, p = 0.0015; QTd, 47 ± 17 vs. 34 ± 9 ms, p = 0.0002), QT-STV had the highest relative increase (+41%). QT-STV also showed the best correlation with indices of left ventricular (LV) hypertrophy, i.e., maximal LV wall thickness normalized for body surface area (BSA; r = 0.461, p = 0.004) or LV mass (determined by cardiac magnetic resonance imaging) normalized for BSA (r = 0.455, p = 0.015). In summary, beat-to-beat QT-STV showed the most marked increase in patients with HCM and may represent a novel marker that merits further testing for increased SCD risk in HCM.

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Dzhishambaev, E. D., S. I. Khakimova, N. O. Amanalieva, Yu A. Kroshkin, and L. M. Amurhanova. "HEART RATE AND QT VARIABILITY IN PATIENTS WITH METABOLIC SYNDROME COMPLICATED BY CARDIAC ARRHYTHMIA." Eurasian heart journal, no. 2 (June 30, 2012): 59–64. http://dx.doi.org/10.38109/2225-1685-2012-2-59-64.

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One hundred and eighty three male patients aged from 35 to 55 years were examined to study the heart rate variability and the QT dispersion at the metabolic syndrome complicated with cardiac arrhythmias. The diminution of the temporal pattern of heart rate variability, increase of the both sympathetic tone and sympathetic-vagal ratio were revealed in patients with supraventricular and ventricular rhythm disturbances. These changes were especially characteristic for patients with atrial fibrillation. QT dispersion was higher in patients with ventricular arrhythmias in comparison with other groups, although maximal corrected QT interval and its maximal dispersion was revealed in patients with combined cardiac arrhythmias (either ventricular and supraventricular arrhythmias).

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Platisa, Mirjana, Vera Gal, Zorica Nestorovic, Ida Leskosek-Cukalovic, Sasa Despotovic, Mile Veljovic, Aleksandar Petrovic, et al. "Changes in linear and nonlinear measures of RR and QT interval series after beer intake." Vojnosanitetski pregled 74, no. 12 (2017): 1107–11. http://dx.doi.org/10.2298/vsp150514316p.

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Background/Aim. There are only several studies on the acute effect of alcoholic drinks intake on heart rhythm and this phenomenon is still not well understood. We wanted to examine whether linear and nonlinear measures of RR interval and QT interval series could quantify the effect of beer in healthy subjects. Methods. Eighteen young volunteers drank 500 mL of beer (21 g of ethanol). Electrocardiogram (ECG) recordings were taken in supine position: 20 minutes before (relaxation) and 60 minutes after drink intake. The RR interval series and the QT interval series were extracted from ECG and we calculated short-term (?1) and long-term (?2) scaling exponents and sample entropy (SampEn) for both series; low frequency (LF) and high frequency (HF) spectral components from RR interval series and QT variability (QTV). Blood pressure was measured every 10 minutes. Results. It was shown that beer induced changes in variability and correlation properties of these series. Immediate effect of beer intake was detected as a transient increase in the QT variability, heart rate and blood pressure. Delayed effects of beer were shortening of the RR and QT intervals and reduction of the HF spectral component. Beer intake also increased short-term scaling exponent (?1) of the RR time series and long-term scaling exponent (?2) of the QT time series. Conclusion. Our results suggest that acute effects of beer are reduced parasympathetic control of the heart and changed dynamic complexity of the ventricular repolarization.

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Zhuravlev, N. M., N. A. Shnayder, E. E. Vaiman, A. K. Abdyrakhmanova, M. M. Petrova, E. N. Bochanova, I. V. Romanova, O. A. Gavrilyuk, N. V. Lareva, and R. F. Nasyrova. "Interindividual Variability of Anticonvulsant-Induced QT Prolongation Risk." Personalized Psychiatry and Neurology 2, no. 1 (May 15, 2022): 22–45. http://dx.doi.org/10.52667/2712-9179-2022-2-1-23-45.

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In connection with the widespread use of anticonvulsants (antiepileptic drugs – AEDs) in psychiatric and neurological practice and the need for their long-term use to treat a wide range of mental disorders and neurological diseases, the question of their safety profile, including the assessment of the risk of developing life-threatening conditions and adverse reactions (ADRs), becomes relevant. In this regard, from the position of personalized medicine, it is critical to develop an interdisciplinary approach with the participation of doctors of various specialties and a new strategy of a personalized approach to predicting AED-induced prolongation of the QT interval as one of the most prognostically unfavorable cardiological ADRs (including sudden death syndrome – SDS). We searched for full-text publications for the period from 2011 to 2021 databases using the following keywords and its combination. We have found and systematized monogenic and multifactorial forms of long QT syndrome (LQTS) and candidate genes that slow down AEDs metabolism in the liver. Identification of risk alleles of single nucleotide variants (SNVs) of the candidate genes predisposing to the development of AED-induced LQTS and SDS will make it possible to adjust the choice and dosage of these drugs and prevent the development of ADRs, which will improve the quality of life of patients and prevent SDS in the patients with psychiatric and neurological disorders.

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Madias, John E. "QT-Interval Variability and/or T-Wave Alternans." Annals of Noninvasive Electrocardiology 14, no. 3 (July 2009): 309–10. http://dx.doi.org/10.1111/j.1542-474x.2009.00312.x.

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Rijnbeek, Peter R., Marten E. van den Berg, Gerard van Herpen, Henk J. Ritsema van Eck, and Jan A. Kors. "Validation of automatic measurement of QT interval variability." PLOS ONE 12, no. 4 (April 12, 2017): e0175087. http://dx.doi.org/10.1371/journal.pone.0175087.

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Huh, In Young, Dae-Young Kim, Minha Sung, Minhyun Lee, and Soon Eun Park. "Change of QT variability index during general anesthesia." Korean Journal of Anesthesiology 69, no. 3 (2016): 250. http://dx.doi.org/10.4097/kjae.2016.69.3.250.

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Carpenter, R. E., S. J. Emery, O. Uzun, D. Rassi, and M. J. Lewis. "Influence of antenatal physical exercise on heart rate variability and QT variability." Journal of Maternal-Fetal & Neonatal Medicine 30, no. 1 (March 29, 2016): 79–84. http://dx.doi.org/10.3109/14767058.2016.1163541.

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Hnatkova, Katerina, Donna Kowalski, James J. Keirns, E. Marcel van Gelderen, and Marek Malik. "Relationship of QT interval variability to heart rate and RR interval variability." Journal of Electrocardiology 46, no. 6 (November 2013): 591–96. http://dx.doi.org/10.1016/j.jelectrocard.2013.07.007.

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Hinterseer, Martin, Britt-Maria Beckmann, Morten B. Thomsen, Arne Pfeufer, Robert Dalla Pozza, Markus Loeff, Heinrich Netz, Gerhard Steinbeck, Marc A. Vos, and Stefan Kääb. "Relation of Increased Short-Term Variability of QT Interval to Congenital Long-QT Syndrome." American Journal of Cardiology 103, no. 9 (May 2009): 1244–48. http://dx.doi.org/10.1016/j.amjcard.2009.01.011.

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Baracaldo-Santamaría, Daniela, Kevin Llinás-Caballero, Julián Miguel Corso-Ramirez, Carlos Martín Restrepo, Camilo Alberto Dominguez-Dominguez, Dora Janeth Fonseca-Mendoza, and Carlos Alberto Calderon-Ospina. "Genetic and Molecular Aspects of Drug-Induced QT Interval Prolongation." International Journal of Molecular Sciences 22, no. 15 (July 28, 2021): 8090. http://dx.doi.org/10.3390/ijms22158090.

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Long QT syndromes can be either acquired or congenital. Drugs are one of the many etiologies that may induce acquired long QT syndrome. In fact, many drugs frequently used in the clinical setting are a known risk factor for a prolonged QT interval, thus increasing the chances of developing torsade de pointes. The molecular mechanisms involved in the prolongation of the QT interval are common to most medications. However, there is considerable inter-individual variability in drug response, thus making the application of personalized medicine a relevant aspect in long QT syndrome, in order to evaluate the risk of every individual from a pharmacogenetic standpoint.

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Timofeev, Eugene V., Eduard V. Zemtsovsky, and Svetlana V. Reeva. "Cardiac arrhythmias and predictors in patients of young age with marfanoid habitus." Pediatrician (St. Petersburg) 10, no. 2 (June 19, 2019): 37–46. http://dx.doi.org/10.17816/ped10237-46.

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Cardiac arrhythmias are frequent manifestations of hereditary connective tissue disorders (HCTD). Such HCTD as Marfan syndrome (MS), the primary mitral valve prolapse are characterized by frequent supraventricular and ventricular extrasystoles, prolonged PQ and QT interval, reduced heart rate variability and frequent findings of other predictors of heart arrhythmias. Cardiac arrhythmias as well as their predictors in patients of young age with marfanoid habitus (MH) were not previously evaluated. Materials and methods. A total number of 238 patients of young age were examined. All patients received phenotypic and anthropometric screening and Holter ECG. Cardiac arrhythmias, duration of QT interval (QTc), QT dispersion (QTd), heart rate variability and heart rate turbulence were estimated. Results for young people with MH as compared with the control group are characterized by frequent detection of paired (42.6% vs 9.7%, p= 0.00001), group (17.0% vs 4.2%, p = 0.01) supraventricular extrasystoles, ventricular extrasystoles in pathological quantity (10.6% vs 1.4%, p = 0.02). Pathological value of heart rate turbulence is detected significantly more frequently in individuals with MH. During evaluation of variability a significant decrease in all spectral (HF, LF, VLF), as well as most statistical (SDNN, pNN50) indicators was revealed. Patients with MH are characterized by prolonged QT interval (QTc threshold in 480 ms overcomes 21% of boys with MH, p = 0.00001) and increase the variance of the QT interval (threshold of 50 ms overcomes 37.5% of girls with MH, p = 0.0004).

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Galetta, Fabio, Ferdinando Franzoni, Poupak Fallahi, Leonardo Tocchini, Lara Braccini, Gino Santoro, and Alessandro Antonelli. "Changes in heart rate variability and QT dispersion in patients with overt hypothyroidism." European Journal of Endocrinology 158, no. 1 (January 2008): 85–90. http://dx.doi.org/10.1530/eje-07-0357.

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ObjectiveThe aim of the present study was to evaluate the effect of clinical hypothyroidism on cardiovascular autonomic function and ventricular repolarization.Design and methodsWe studied 31 patients (22 females and 9 males; mean age 53.6±11.8 years) with overt hypothyroidism (TSH=56.2±14.7 μU/ml, low free thyroxine (T4), free tri-iodothyronine (T3)) and 31 euthyroid controls, to investigate the dispersion of the QT interval in electrocardiogram (ECG) (an index of inhomogeneity of repolarization) and heart rate variability (HRV; a measure of cardiac autonomic modulation). The hypothyroid patients and controls underwent a full medical examination, standard 12-lead ECG, and 24-h ambulatory ECG monitoring. The hypothyroid patients were re-examined after 6 months of treatment with l-T4.ResultsPatients with hypothyroidism showed higher QT dispersion and lower HRV measures than controls (P<0.01 or P<0.001). In hypothyroid patients, standard deviation of all R–R intervals was inversely related (by simple regression) to serum (log)TSH levels (r=−0.47, P=0.008), while QT dispersion (r=0.50, P=0.004) and QTc dispersion (r=0.46, P=0.008) were directly related to (log)TSH. Parameters of HRV improved after 6 months of l-T4 treatment, with the correction of hypothyroidism, becoming comparable with those of the control subjects, whereas the QT and QTc dispersion results were found to be only partially restored, remaining higher than the controls.ConclusionsThe results of the study demonstrate that hypothyroidism is associated with a decreased sympatho-vagal modulation of the heart rate and with an increased inhomogeneity of ventricular recovery times. The assessment of HRV and QT dispersion in patients with overt hypothyroidism may represent a useful tool in monitoring the cardiovascular risks.

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Çakar, Nafiye E., and Ahmet İrdem. "P wave dispersion and ventricular repolarization changes in children with familial hypercholesterolemia." Cardiology in the Young 30, no. 11 (November 2020): 1643–48. http://dx.doi.org/10.1017/s1047951120003765.

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AbstractBackground:Familial hypercholesterolemia is a genetic disease with plasma total cholesterol especially low-density lipoprotein-cholesterol elevation. In this study, we aimed to examine the changes in the electrocardiographies of children with familial hypercholesterolemia.Materials and methods:Electrocardiography of 85 patients with a diagnosis of familial hypercholesterolemia, followed up from the Pediatric Metabolism and Pediatric Cardiology outpatient clinic was examined. Electrocardiography of 83 children from the control group who did not have hypercholesterolemia in a similar gender and age range were examined. Heart rate, P wave, PR interval, P wave dispersion, QRS wave, QT interval, corrected QT (calculated with Bazett formula), Tpeak-end interval, QT dispersion, corrected QT dispersion, JT interval, corrected JT (calculated with Bazett formula) were statistically compared.Results:P wave, PR interval, and P wave dispersion values were significantly higher (p < 0.05) in the children with familial hypercholesterolemia. Corrected QT, QT dispersion, corrected QT dispersion, JT interval, corrected JT, Tpeak-end interval were significantly higher than the control group (p < 0.05) in children with familial hypercholesterolemia. These statistical differences in electrocardiography parameters support the risk of atrial and/or ventricular arrhythmia in children with familial hypercholesterolemia.Conclusion:We found that high total cholesterol and low-density lipoprotein-cholesterol variables are associated with an increased risk of cardiac atrial and/or ventricular arrhythmia. The findings suggest that total cholesterol and low-density lipoprotein-cholesterol variability can be used as a new marker for the risk of cardiac arrhythmia. In this case, decreasing total cholesterol and low-density lipoprotein-cholesterol variability below certain thresholds may decrease the risk of cardiac arrhythmia.

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NĚMEC, JAN, MARIE BUNCOVÁ, VLADIMIR SHUSTERMAN, BRUCE WINTER, WIN-KUANG SHEN, and MICHAEL J. ACKERMAN. "QT Interval Variability and Adaptation to Heart Rate Changes in Patients with Long QT Syndrome." Pacing and Clinical Electrophysiology 32, no. 1 (January 2009): 72–81. http://dx.doi.org/10.1111/j.1540-8159.2009.02179.x.

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Zhang, Lu, and Brian P. Smith. "Sex Differences in QT Interval Variability and Implication on Sample Size of Thorough QT Study." Drug Information Journal 41, no. 5 (September 2007): 619–27. http://dx.doi.org/10.1177/009286150704100508.

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Patel, Salma, Wojciech Zareba, Bonnie LaFleur, Jean-Philippe Couderc, Xiaojuan Xia, Raymond Woosley, Daniel Combs, et al. "478 The Relationship between Sleep Disordered Breathing, Markers of Ventricular Repolarization and Cardiovascular Mortality." Sleep 44, Supplement_2 (May 1, 2021): A188—A189. http://dx.doi.org/10.1093/sleep/zsab072.477.

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Abstract Introduction Sleep disordered breathing (SDB) is associated with increased mortality. Obstructive apneas/hypopneas have been associated with an increase in both QTc duration and QT variability. These markers of ventricular repolarization are associated with arrhythmias and death. It is unknown whether SDB-related QTc changes are responsible for the relationship between QTc/QT variability and cardiovascular death (CVD). Methods From the Sleep Heart Health Study, we randomly selected 200 subjects in each of four groups based on overall apnea/hypopnea index: those with no SDB and those in either, mild, moderate or severe SDB at baseline, matched for gender, age and BMI. Respiratory-related channels and electrocardiograms (ECG) from each polysomnography were analyzed. QTc was calculated using Bazett’s heart rate correction. The following measures of QT variability were obtained: i) standard deviation of QT intervals (SDQT) at 1- and 5-minute intervals and ii) short-term interval QT variability (STVQT) at 5-minute intervals. Cox proportional hazards regression models were used to evaluate potential predictors of CVD. Results Twenty-nine subjects were excluded either due to missing data or low quality ECG. The 771 subjects included were 68±10 years of age, half were female. During follow-up, 220 subjects (28.5%) died of CVD among whom, 67 (30.5%) had comorbid severe SDB, 45 (20.5%) had no SDB, and the remaining CVD deaths had mild (47, 21.4%) and moderate 61 (27.7%) SDB. The CVD patients were more likely to be older(p<0.001), hypertensive (p<0.001), diabetic(p<0.001), and had increased SDQT(p<0.001), STVQT(p<0.001) and QTc (0.017). After adjusting for covariates, the presence of mild (p=0.562), moderate(p=0.439) and severe SDB (p=0.912) did not moderate the association between QTc prolongation and CVD. Additionally, mild (p=0.486), moderate(p=0.478) and severe SDB (p=0.849) did not moderate the association between SDQT and CVD. Similarly, mild (p=0.144), moderate(p=0.594) and severe SDB (p=0.508) did not moderate the association between STVQT and CVD. However, QTc, SDQT, STVQT, mild and severe SDB were individually associated with CVD (p=0.004, 0.000, 0.000, 0.014, 0.022, respectively). Conclusion SDB was not a factor in the relationship between QTc prolongation/QT variability and CVD. Support (if any) American Academy of Sleep Medicine Foundation (203-JF-18), National Institutes of Health (HL126140), University of Arizona Health Sciences Career and Development Award (5299903)

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Khan, Wali. "Frequency of QT Interval Prolongation in Chronic Liver Disease Patients." Proceedings of Shaikh Zayed Medical Complex Lahore 33, no. 4 (December 2, 2019): 1–4. http://dx.doi.org/10.47489/p000s334z7221-4mc.

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Introduction: The frequency of QT interval prolongation as published in the international and local literature has been variable. Aims & Objectives: To determine the frequency of QT interval prolongation in patients with chronic liver disease and resolve the variability in the literature. Place and duration of study: The present study was conducted in Gastroenterology and Hepatology Unit Shaikh Zayed Hospital Lahore from 1st March 2017 to 31st August 2017. Material & Methods: About 240 patients with diagnosed chronic liver disease were selected. Electrocardiography (12 lead) was performed in all patients to look for QT interval prolongation and their mean was calculated for purpose of analysis. Results: Mean age of our patients was 53.7±11.9 and male gender was dominant (55.8%). It was noted that QT interval was prolonged in 62 patients (25.8%) while rest of the 178 patients had normal QT interval. Conclusion: QT interval prolongation is frequently observed (25.8%) in chronic liver disease patients. Therefore, every patient with chronic liver disease should be investigated for QT interval prolongation. Key words: Chronic liver disease, QT interval, Electrocardiography

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Tiwari, Chandan, A. Pandey, and S. K. Singh. "Study about genetic variability, heritability and genetic advance in garlic (Allium sativum)." INTERNATIONAL JOURNAL OF PLANT SCIENCES 17, no. 2 (July 15, 2022): 232–35. http://dx.doi.org/10.15740/has/ijps/17.2/232-235.

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The study genetic variability, heritability, genetic advance analysis in garlic (Allium sativum L.) sixteen genotypes experimental trial was conducted at RRS NHRDF, Salaru, Karnal during 2016-17 and 2017-18. The experiment was conducted in Randomize Block Design with three replications. Observations were recorded for sixteen characteristics. The higher magnitude of genetic variability, heritability, genetic advance observed for plant establishment, plant stand at maturity, % marketable bulb (on wt. basis), gross yield (kg/plot), marketable yield (kg/plot), marketable yield (qt/ha), average weight of bulb (g), weight of 20 bulbs, bulb polar diameter (cm), bulb equatorial diameter (cm), T.S.S (%), average no of cloves per bulb at genotypic levels. High heritability coupled with high genetic advance in percent of mean was recorded for average no of cloves per bulb, marketable yield (kg/plot), marketable yield (qt/ha), gross yield (kg/plot), gross yield (qt/ha), that selection for these traits would be effective for the improvement of bulb yield per plant. The level of variation found in the collection showed the great potentiality of improving agronomic characters in garlic.

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Nayyar, Sachin, Kurt C. Roberts-Thomson, Muhammad A. Hasan, Thomas Sullivan, Judith Harrington, Prashanthan Sanders, and Mathias Baumert. "Autonomic modulation of repolarization instability in patients with heart failure prone to ventricular tachycardia." American Journal of Physiology-Heart and Circulatory Physiology 305, no. 8 (October 15, 2013): H1181—H1188. http://dx.doi.org/10.1152/ajpheart.00448.2013.

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QT variability (QTV) signifies repolarization lability, and increased QTV is a risk predictor for sudden cardiac death. The aim of the present study was to investigate the role of autonomic nervous system activity on QTV. This study was performed in 29 subjects: 10 heart failure (HF) patients with spontaneous ventricular tachycardia [HFVT(+)], 10 HF patients without spontaneous VT [HFVT(−)], and 9 subjects with structurally normal hearts (HNorm). The beat-to-beat QT interval was measured on 3-min records of surface ECGs at baseline and during interventions (atrial pacing and esmolol, isoprenaline, and atropine infusion). Variability in QT intervals was expressed as the SD of all QT intervals (SDQT). The ratio of the SDQT to SD of RR intervals (SDRR) was calculated as an index of QTV normalized to heart rate variability. There was a trend toward a higher baseline SDQT-to-SDRR ratio in the HFVT(+) group compared with the HFVT(−) and HNorm groups ( P = 0.09). SDQT increased significantly in the HFVT(+) and HFVT(−) groups compared with the HNorm group during fixed-rate atrial pacing ( P = 0.008). Compared with baseline, isoprenaline infusion increased SDQT in HNorm subjects ( P = 0.02) but not in HF patients. SDQT remained elevated in the HFVT(+) group relative to the HNorm group despite acute β-adrenoceptor blockade with esmolol ( P = 0.02). In conclusion, patients with HF and spontaneous VT have larger fluctuations in beat-to-beat QT intervals. This appears to be a genuine effect that is not solely a consequence of heart rate variation. The effect of acute autonomic nervous system modulation on QTV appears to be limited in HF patients.

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Journal articles on the topic 'QT variability'

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