Regulation of QT interval during postural transitory changes in heart rate in normal subjects

Yamada, Akira; Hayano, Junichiro; Horie, Kenji; Ieda, Kouichi; Mukai, Sonoyo; Yamada, Masami; Fujinami, Takao

doi:10.1016/0002-9149(93)90922-y

Cited by 28 publications

(19 citation statements)

References 10 publications

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“…Two studies have shown QTc lengthening (with either 70m upright tilting or on standing) and one study has shown QTc interval shortening [7][8][9]. The study reported here found no change in QTc interval with standing in subjects with normal left ventricular function.…”

Section: Discussioncontrasting

confidence: 43%

“…If nocturnal QT interval lengthening is due to posture change rather than to the circadian rhythm, different strategies will be needed. Previous studies have examined the effect of posture in a number of conditions [6][7][8][9][10]. However, these previous studies did not examine posture-related changes in the QT interval in two common conditions associated with arrhythmias, left ventricular hypertrophy and chronic heart failure.…”

Section: Introductionmentioning

confidence: 99%

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Influence of posture and handgrip on the QT interval in left ventricular hypertrophy and in chronic heart failure

Davey

1999

Clinical Science

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In certain disease states prolongation of the QT interval has been shown to be arrhythmogenic. Whether QTc interval changes with position and thus whether certain positions are more arrhythmogenic than others is not known for different diseases that predispose to arrhythmias, and was therefore studied. Patients with left ventricular hypertrophy and heart failure, and the appropriate matched controls, were recruited. Subjects were studied in the lying, sitting, standing and squatting positions and had QT intervals determined by computer algorithm 2 min after each position change. After resting, QT interval was determined while the subjects performed maximum handgrip exercise with their dominant hand. QT intervals were rate-corrected using Bazett's method. QTc interval is prolonged in heart failure patients compared with either left ventricular hypertrophy or control subjects in the lying and sitting position, but not in the standing or squatting position. The QTc intervals for heart failure and control subjects were, respectively, 443+/-7 ms versus 421+/-6 ms when lying (P<0.05), 451+/-10 ms versus 419+/-6 ms when sitting (P<0.05), 429+/-10 versus 414+/-7 ms when standing (P not significant) and 437+/-10 versus 419+/-8 ms when squatting (P not significant). The values for patients with hypertrophy did not differ from control values. Maximum handgrip does not affect the QTc interval in heart failure, but prolongs it in both the hypertrophy and control groups. Position and static exercise are important modifiers of QTc interval and their effect depends on the condition of the left ventricle.

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Section: Discussioncontrasting

confidence: 43%

Section: Introductionmentioning

confidence: 99%

Influence of posture and handgrip on the QT interval in left ventricular hypertrophy and in chronic heart failure

Davey

1999

Clinical Science

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“…Although the ARX RR X R AR model provided the best prediction of RT variability, the goodness of fit was far from 1 at rest, especially when RT e variability was considered (i.e., 0.83 and 0.69 in the case of RT a and RT e variabilities, respectively, at rest), thus suggesting that RT dynamics contain dynamic features that cannot be accounted by the structure of this model. Among these features, we recall nonlinear dynamics, e.g., due to effects of QT-RR hysteresis (17,38), adjustments according to long time scales (i.e., several minutes) that might need more specific model structures to be reliably resolved (13), and feedback effects activated by cardiac neural afferents. In addition, the goodness of fit was not constant during the experimental protocol: indeed, it progressively decreased with tilt table inclination, thus suggesting that RT dynamics became more and more complex and the best model structure tended to become more and more inadequate.…”

Section: Discussionmentioning

confidence: 99%

RT variability unrelated to heart period and respiration progressively increases during graded head-up tilt

Porta

Tobaldini

Gnecchi‐Ruscone³

et al. 2010

American Journal of Physiology-Heart and Circulatory Physiology

104

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Porta A, Tobaldini E, Gnecchi-Ruscone T, Montano N. RT variability unrelated to heart period and respiration progressively increases during graded head-up tilt. Am J Physiol Heart Circ Physiol 298: H1406 -H1414, 2010. First published February 12, 2010 doi:10.1152/ajpheart.01206.2009.-Open-loop linear parametric models were exploited to describe ventricular repolarization duration (VRD) variability during graded head-up tilt. Surface ECG and thoracic movements were recorded in 15 healthy humans (age: 24 -54 yr, median: 28 yr; 6 women and 9 men). Tilt table inclinations ranged from 15 to 90°and were varied in steps of 15°. All subjects underwent recordings at every step in random order. Heart period was assessed as the time difference between two consecutive R-wave peaks (RR) and the respiratory signal (R) as the sampling of the thoracic movement signal at the R-wave peaks. VRD was measured automatically as the temporal difference between the R-wave peak and T-wave apex (RT a) or T-wave end (RTe). The best model decomposed RT variability as due to RR changes (RR-related RT variability) to direct respiratory-related inputs (R-related RT variability) and to unknown rhythmical sources unrelated to RR changes and R (RR-R-unrelated RT variability). Using this model, RTe variability was found to be less predictable than RTa variability and composed of a smaller fraction of RR-related RT variability and a larger fraction of RR-R-unrelated RT variability. Predictability progressively decreased with tilt table angles, suggesting increased complexity of RT regulation. RT variance progressively increased with tilt table inclination. This increase was characterized by a gradual rise of the amount of RR-R-unrelated RT variability, whereas the amount of RR-related RT variability remained unchanged. These results suggest that the amount of RT variability, complexity of RT dynamics, and amount of RR-Runrelated RT variability increase with the magnitude of the sympathetic drive directly related to tilt table inclination. We propose the utilization of the amount of RR-R-unrelated RT variability instead of overall RT variability as an indirect measure of autonomic regulation directed to ventricles. QT measurement; QT variability; QT-RR relationship; modelling; autonomic nervous system THERE IS INCREASING INTEREST in quantifying the amount of the beat-to-beat changes of ventricular repolarization duration (VRD), i.e., VRD variability (2,4,6,12,15,20,27,40). This interest is based on the original suggestion that VRD variability provides an indirect measure of the autonomic regulation directed to ventricles (7). VRD variability is usually computed from the surface ECG as the variability of the time interval between the Q-wave onset and T-wave end (QT interval) under the hypothesis that the variability of the ventricular depolarization period is negligible with respect to that of VRD. Since variability of the heart period, computed as the temporal difference between two consecutive R-wave peaks on the ECG (RR), provides indexes of the ...

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“…Both rate-dependent and rate- independent factors, mediated by autonomic tone and by circulating catecholamines, play a role in the normal circadian variation of the QT interval [17, 18, 19, 20, 21, 22, 23, 24, 25, 26]. A hysteresis in QT-RR relationship when the heart rate rapidly changes has previously been reported to occur during postural changes [27] and exercise [28]. It has also been reported that the expected shortening in QT interval in the morning lags behind the decreases in RR interval [18, 19].…”

Section: Discussionmentioning

confidence: 99%

Evaluation of a 12-Lead Digital Holter System for 24-Hour QT Interval Assessment

et al. 2006

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Background: Drug induced QT prolongation may precipitate life threatening cardiac arrhythmias. Evaluation of the QT prolonging effect of new pharmaceutical agents in a ‘thorough QT/QTc study’ is being mandated by FDA. The purpose of this study was to evaluate an automated 12-lead digital Holter system for a thorough QT/QTc study. Methods: Five healthy volunteers underwent 24-hour digital Holter monitoring. Each recording underwent a fully automated QT analysis (AQA) followed by an onscreen complete manual over read (MOR). Each recording was analyzed twice at least 2 weeks apart. The effect of data sampling (5-min segment/hour), the system sensitivity to detect 5-ms increase in QT, and the ability to assess circadian variation were evaluated. Results: The AQA resulted in identical QT for the first and second analyses, but with obvious errors in QT measurements. Compared to the complete onscreen MOR, the mean QT was longer with AQA (416 ± 41 vs. 387 ± 30 ms, p < 0.001), correlation; r = 0.3. The reproducibility of AQA with complete MOR was very good (QT: 387 ± 30 vs. 387 ± 30 ms, coefficient of variation: 0.2%, r = 0.986. The 5-min mean QT intervals correlated well with the hourly mean QT intervals (r = 0.994, p < 0.001, coefficient of variation = 1 ms) and both showed a similar circadian variation. The system was sensitive to detect a 5-ms change in QT intervals (5 ± 2 ms, coefficient of variation = 0.6%, r = 0.998, p < 0.001). Conclusions: The AQA is not an acceptable method, while the automatic analysis with complete MOR is a highly sensitive and reproducible method. Data sampling by analyzing 5-min segments per hour is sensitive and reproducible.

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Regulation of QT interval during postural transitory changes in heart rate in normal subjects

Cited by 28 publications

References 10 publications

Influence of posture and handgrip on the QT interval in left ventricular hypertrophy and in chronic heart failure

Influence of posture and handgrip on the QT interval in left ventricular hypertrophy and in chronic heart failure

RT variability unrelated to heart period and respiration progressively increases during graded head-up tilt

Evaluation of a 12-Lead Digital Holter System for 24-Hour QT Interval Assessment

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