Effect of Posture and Isoproterenol on Beat-to-Beat Heart Rate and QT Variability

Yeragani, Vikram K.; Pohl, Robert; Jampala, V.C.; Balon, Richard; Kay, J.; Igel, Gina

doi:10.1159/000026642

Cited by 90 publications

(80 citation statements)

References 29 publications

(34 reference statements)

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“…Closer inspection of the baseline data points towards a statistical outlier with a value of SDQT that is four times higher than in the other recordings. Increased QTV during sympathetic activation is in line with several previous reports [2,5,8].…”

Section: Discussionsupporting

confidence: 93%

“…Increased QTV is thought to be caused by a reduced repolarisation reserve, reflecting ventricular repolarisation lability and has been associated with cardiac mortality [1]. In healthy subjects sympathetic activation via orthostatic provocation or pharmacological β-adrenoceptor stimulation was shown to increase QTV [2], while the relationship between sympathetic activity and QTV during rest is less clear. In patients with cardiovascular (co-)morbidities the relationship between sympathetic activity and QTV has been insufficiently explored [3][4][5][6].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Entropy Analysis of RR and QT Interval Variability during Orthostatic and Mental Stress in Healthy Subjects

Baumert

Czippelová

Ganesan

et al. 2014

Entropy

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Autonomic activity affects beat-to-beat variability of heart rate and QT interval. The aim of this study was to explore whether entropy measures are suitable to detect changes in neural outflow to the heart elicited by two different stress paradigms. We recorded short-term ECG in 11 normal subjects during an experimental protocol that involved head-up tilt and mental arithmetic stress and computed sample entropy, cross-sample entropy and causal interactions based on conditional entropy from RR and QT interval time series. Head-up tilt resulted in a significant reduction in sample entropy of RR intervals and cross-sample entropy, while mental arithmetic stress resulted in a significant reduction in coupling directed from RR to QT. In conclusion, measures of entropy are suitable to detect changes in neural outflow to the heart and decoupling of repolarisation variability from heart rate variability elicited by orthostatic or mental arithmetic stress.

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Section: Discussionsupporting

confidence: 93%

Section: Introductionmentioning

confidence: 99%

Entropy Analysis of RR and QT Interval Variability during Orthostatic and Mental Stress in Healthy Subjects

Baumert

Czippelová

Ganesan

et al. 2014

Entropy

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“…This study identified a positive linear relationship between RT variance and tilt table inclination. Since sympathetic tone and modulation increase during head-up tilt (11,14,23,32), the gradual increase of RT variability with tilt table inclination supports the existence of a relationship between RT variance and ventricular sympathetic tone and/or modulation (26,39) and the opportunity of using the level of RT variability as an index proportional to the magnitude of ventricular sympathetic control. This result, combined with recent findings suggesting that QT variability is unrelated to sympathetic tone (4), suggests that the relationship between RT variance and ventricular sympathetic control should be limited to the amplitude of ventricular sympathetic modulation (i.e., the amplitude of the fluctuations of the sympathetic discharge around its mean value) and/or, as suggested by Berger (6), to ventricular sympathetic tone when its values are elevated, as occurs at the highest tilt table inclinations.…”

Section: Discussionmentioning

confidence: 81%

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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“…First, an elevated QTVi and elevated NE spillover have been independently found in postinfarction patients and in patients with PD and depression (2,20,22,25). Second, activation of cardiac sympathetic activity (by orthostatic challenge or isoproterenol infusion) leads to increase in QTVi (23). In contrast to these findings, ␤-adrenergic blockade did not affect QTVi at rest or during tilt (14).…”

Section: Discussionmentioning

confidence: 92%

QT interval variability and cardiac norepinephrine spillover in patients with depression and panic disorder

Baumert¹,

Lambert²,

Dawood³

et al. 2008

American Journal of Physiology-Heart and Circulatory Physiology

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Nalivaiko E. QT interval variability and cardiac norepinephrine spillover in patients with depression and panic disorder. Am J Physiol Heart Circ Physiol 295: H962-H968, 2008. First published July 3, 2008 doi:10.1152/ajpheart.00301.2008.-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 Յ10 ng/min. There was a positive correlation between cardiac norepinephrine spillover and corrected QT interval (r ϭ 0.7, P ϭ 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 (Ͼ20 ng/min) a tendency for a strong positive correlation with variance of QT intervals (r ϭ 0.9, P ϭ 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. sympathetic activity; antidepressants AN EXCESSIVE CARDIAC SYMPATHETIC activity is a recognized risk factor for cardiac morbidity and mortality. In a range of clinical contexts, elevated cardiac sympathetic outflow has been demonstrated to contribute to ventricular arrhythmias (10), sudden death (6), myocardial stunning (21), and left ventricular hypertrophy (19). Direct assessment of norepinephrine (NE) spillover (the "gold standard" for assessing cardiac sympathetic activity) is a complex, invasive procedure, and cardiac sympathetic activity is still most frequently assessed by measuring mean heart rate or assessing its dynamic variability (1). Obviously, heart rate reflects autonomic influences only at the level of the cardiac pacemaker region. Because different regions of the heart could be under independent autonomic control (7, 12, 13), it becomes increasingly evident that indexes reflecting sympathetic influences in the ventricular myocardium might be of better predictive and ...

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Effect of Posture and Isoproterenol on Beat-to-Beat Heart Rate and QT Variability

Cited by 90 publications

References 29 publications

Entropy Analysis of RR and QT Interval Variability during Orthostatic and Mental Stress in Healthy Subjects

Entropy Analysis of RR and QT Interval Variability during Orthostatic and Mental Stress in Healthy Subjects

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

QT interval variability and cardiac norepinephrine spillover in patients with depression and panic disorder

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