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Ni H, Zhang H, Grandi E, Narayan SM, Giles WR. Transient outward K + current can strongly modulate action potential duration and initiate alternans in the human atrium. Am J Physiol Heart Circ Physiol 2019; 316:H527-H542. [PMID: 30576220 PMCID: PMC6415821 DOI: 10.1152/ajpheart.00251.2018] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/19/2018] [Revised: 07/27/2018] [Accepted: 08/15/2018] [Indexed: 01/14/2023]
Abstract
Efforts to identify the mechanisms for the initiation and maintenance of human atrial fibrillation (AF) often focus on changes in specific elements of the atrial "substrate," i.e., its electrophysiological properties and/or structural components. We used experimentally validated mathematical models of the human atrial myocyte action potential (AP), both at baseline in sinus rhythm (SR) and in the setting of chronic AF, to identify significant contributions of the Ca2+-independent transient outward K+ current ( Ito) to electrophysiological instability and arrhythmia initiation. First, we explored whether changes in the recovery or restitution of the AP duration (APD) and/or its dynamic stability (alternans) can be modulated by Ito. Recent reports have identified disease-dependent spatial differences in expression levels of the specific K+ channel α-subunits that underlie Ito in the left atrium. Therefore, we studied the functional consequences of this by deletion of 50% of native Ito (Kv4.3) and its replacement with Kv1.4. Interestingly, significant changes in the short-term stability of the human atrial AP waveform were revealed. Specifically, this K+ channel isoform switch produced discontinuities in the initial slope of the APD restitution curve and appearance of APD alternans. This pattern of in silico results resembles some of the changes observed in high-resolution clinical electrophysiological recordings. Important insights into mechanisms for these changes emerged from known biophysical properties (reactivation kinetics) of Kv1.4 versus those of Kv4.3. These results suggest new approaches for pharmacological management of AF, based on molecular properties of specific K+ isoforms and their changed expression during progressive disease. NEW & NOTEWORTHY Clinical studies identify oscillations (alternans) in action potential (AP) duration as a predictor for atrial fibrillation (AF). The abbreviated AP in AF also involves changes in K+ currents and early repolarization of the AP. Our simulations illustrate how substitution of Kv1.4 for the native current, Kv4.3, alters the AP waveform and enhances alternans. Knowledge of this "isoform switch" and related dynamics in the AF substrate may guide new approaches for detection and management of AF.
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Affiliation(s)
- Haibo Ni
- Biological Physics Group, School of Physics and Astronomy, University of Manchester , Manchester , United Kingdom
- Department of Pharmacology, University of California , Davis, California
| | - Henggui Zhang
- Biological Physics Group, School of Physics and Astronomy, University of Manchester , Manchester , United Kingdom
| | - Eleonora Grandi
- Department of Pharmacology, University of California , Davis, California
| | - Sanjiv M Narayan
- Division of Cardiology, Cardiovascular Institute, Stanford University , Stanford, California
| | - Wayne R Giles
- Faculties of Kinesiology and Medicine, University of Calgary , Calgary, Alberta , Canada
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Porta A, Bari V, De Maria B, Baumert M. A network physiology approach to the assessment of the link between sinoatrial and ventricular cardiac controls. Physiol Meas 2017; 38:1472-1489. [PMID: 28430108 DOI: 10.1088/1361-6579/aa6e95] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
OBJECTIVE A network physiology approach to evaluate the strength of the directed interactions among cardiac controls at sinoatrial and ventricular levels and respiration (R) is proposed. APPROACH The network is composed of three nodes (i.e. sinoatrial and ventricular cardiac controls and R) and their activity is exemplified by the variability of heart period (HP), the variability of the duration of the electrical activity of the heart approximated as the temporal distance between Q-wave onset and T-wave end or apex (i.e. QTe or QTa) and thoracic movements respectively. Model-based transfer entropy provided the estimate of the strength of the causal link from the source to the destination conditioned on the remaining node activity. The interactions were monitored in 15 healthy subjects aged from 24 to 54 years (9 males). Increasing levels of sympathetic activity were induced by graded head-up tilt with table inclination of 0, 15, 30, 45, 60, 75°. MAIN RESULTS We found that: (i) the strength of the causal link from HP to QTe gradually decreases with tilt table angle, while that in the reverse direction is weak, even though significant, and constant; (ii) the action of R on HP is stronger than that from R to QTe; (iii) the strength of the relation from R to HP is weakly related to tilt table inclination, while that from R to QTe does not depend on it; (iv) while QTe cannot affect R, a weak causal dependence of R on HP is detected; (v) the network computed over QTa is qualitatively similar to that over QTe, even though the strength of the causal relations might be different. SIGNIFICANCE The proposed network physiology approach provides a comprehensive picture of the directed links among relevant cardiac regulatory mechanisms and their evolution with sympathetic tone usable to identify pathological conditions.
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Affiliation(s)
- Alberto Porta
- Department of Biomedical Sciences for Health, University of Milan, Milan, Italy. Department of Cardiothoracic, Vascular Anesthesia and Intensive Care, IRCCS Policlinico San Donato, San Donato Milanese, Milan, Italy
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Baumert M, Porta A, Vos MA, Malik M, Couderc JP, Laguna P, Piccirillo G, Smith GL, Tereshchenko LG, Volders PGA. QT interval variability in body surface ECG: measurement, physiological basis, and clinical value: position statement and consensus guidance endorsed by the European Heart Rhythm Association jointly with the ESC Working Group on Cardiac Cellular Electrophysiology. Europace 2016; 18:925-44. [PMID: 26823389 PMCID: PMC4905605 DOI: 10.1093/europace/euv405] [Citation(s) in RCA: 140] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2015] [Accepted: 11/05/2015] [Indexed: 12/20/2022] Open
Abstract
This consensus guideline discusses the electrocardiographic phenomenon of beat-to-beat QT interval variability (QTV) on surface electrocardiograms. The text covers measurement principles, physiological basis, and clinical value of QTV. Technical considerations include QT interval measurement and the relation between QTV and heart rate variability. Research frontiers of QTV include understanding of QTV physiology, systematic evaluation of the link between QTV and direct measures of neural activity, modelling of the QTV dependence on the variability of other physiological variables, distinction between QTV and general T wave shape variability, and assessing of the QTV utility for guiding therapy. Increased QTV appears to be a risk marker of arrhythmic and cardiovascular death. It remains to be established whether it can guide therapy alone or in combination with other risk factors. QT interval variability has a possible role in non-invasive assessment of tonic sympathetic activity.
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Affiliation(s)
- Mathias Baumert
- School of Electrical and Electronic Engineering, The University of Adelaide, Adelaide, SA, Australia
| | - Alberto Porta
- Department of Biomedical Sciences for Health, University of Milan, Milan, Italy Department of Cardiothoracic, Vascular Anesthesia and Intensive Care, IRCCS Policlinico San Donato, Milan, Italy
| | - Marc A Vos
- Department of Medical Physiology, Division of Heart and Lungs, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Marek Malik
- St Paul's Cardiac Electrophysiology, University of London, and National Heart and Lung Institute, Imperial College, Dovehouse Street, London SW3 6LY, UK
| | - Jean-Philippe Couderc
- Heart Research Follow-Up Program, University of Rochester Medical Center, Rochester, NY, USA
| | - Pablo Laguna
- Zaragoza University and CIBER-BBN, Zaragoza, Spain
| | - Gianfranco Piccirillo
- Dipartimento di Scienze Cardiovascolari, Respiratorie, Nefrologiche, Anestesiologiche e Geriatriche, Università 'La Sapienza' Rome, Rome, Italy
| | - Godfrey L Smith
- Institute of Cardiovascular and Medical Sciences, University of Glasgow, Glasgow, UK
| | - Larisa G Tereshchenko
- Oregon Health and Science University, Knight Cardiovascular Institute, Portland, OR, USA
| | - Paul G A Volders
- Department of Cardiology, Cardiovascular Research Institute Maastricht, Maastricht University Medical Centre, Maastricht, The Netherlands
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Porta A, Bari V, Marchi A, De Maria B, Cerutti S. Wiener-Granger causality in QT-HP variability interactions. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2016; 2015:1781-4. [PMID: 26736624 DOI: 10.1109/embc.2015.7318724] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
The study exploits a Wiener-Granger causality (WGC) approach in the time domain to assess directionality of the dynamical interactions between QT interval and heart period (HP) during a graded head-up tilt protocol challenging the cardiovascular control as a function of the tilt table inclination. QT interval and HP are approximated from the surface ECG as the temporal distance between the R-wave apex and T-wave offset and between two consecutive R-wave peaks respectively. The adopted WGC approach accounts for the confounding effect of respiration (RESP) affecting both QT and HP. Causality ratios (CRs) from HP to QT given RESP (CRHP→QT|RESP) and from QT to HP given RESP (CRQT→HP|RESP) were computed and their significance was tested via F-test. We found that, regardless of the tilt table angle, CRHP→QT|RESP is significant, while CRQT→HP|RESP is negligible. CRHP→QT|RESP showed a trend towards a decrease with tilt table angle. These findings suggested that the causal direction from HP over QT is dominant compared to the reverse one and sympathetic activation induced a QT-HP uncoupling.
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Porta A, Bari V, Badilini F, Tobaldini E, Gnecchi-Ruscone T, Montano N. Frequency domain assessment of the coupling strength between ventricular repolarization duration and heart period during graded head-up tilt. J Electrocardiol 2011; 44:662-8. [PMID: 21908003 PMCID: PMC3206996 DOI: 10.1016/j.jelectrocard.2011.08.002] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2011] [Indexed: 11/28/2022]
Abstract
We test the hypothesis that the degree of correlation between ventricular repolarization duration (VRD) and heart period (HP) carries information on cardiac autonomic regulation. The degree of correlation was assessed in the frequency domain using squared coherence function during an experimental protocol known to gradually induce a shift of sympathovagal balance toward sympathetic predominance (ie, graded head-up tilt). We observed a progressive decrease of squared coherence with tilt table inclination, thus confirming the working hypothesis. The VRD-HP uncoupling occurs in the high-frequency band, centered on the respiratory rate, thus suggesting that vagal withdrawal is responsible for the VRD-HP uncoupling.
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Affiliation(s)
- Alberto Porta
- Department of Technologies for Health, Galeazzi Orthopedic Institute, University of Milan, Milan, Italy.
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Isoprenaline increases the slopes of restitution trajectory in the conscious rabbit with ischemic heart failure. J Biol Phys 2011; 36:299-315. [PMID: 21629591 DOI: 10.1007/s10867-009-9185-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2009] [Accepted: 12/22/2009] [Indexed: 10/20/2022] Open
Abstract
Roughly speaking, restitution is the dependence of recovery time of cardiac electrical activity on heart rate. Increased restitution slope is theorized to be predictive of sudden death after heart injury such as from coronary artery occlusion (ischemia). Adrenaline analogs are known to increase restitution slope in normal hearts, but their effects in failing hearts are unknown. Twenty-six rabbits underwent coronary ligation (n = 15) or sham surgery (n = 11) and implantation of a lead in the heart for recording electrocardiograms. Eight weeks later, unanesthetized rabbits were given 0.25-2.0 ml of 1 μmol/L isoprenaline intravenously, which increased heart rate. Heart rate was quantified by time between QRS peaks (RR) and heart activity duration by R to T peak time (QTp). Ligated rabbits (n = 6) had lower ejection fraction than sham rabbits (n = 7, p < 0.0001) indicative of heart failure, but similar baseline RR (269 ± 15 vs 292 ± 23 ms, p = 0.07), QTp (104 ± 17 vs 91 ± 9 ms, p = 0.1), and isoprenaline-induced minimum RR (204 ± 11 vs 208 ± 6 ms, p = 0.4). The trajectory of QTp vs TQ plots displayed hysteresis and regions of negative slope. The slope of the positive slope region was >1 in ligated rabbits (1.27 ± 0.66) and <1 in sham rabbits (0.35 ± 0.14, p = 0.004). The absolute value of the negative slope was greater in ligated rabbits (- 0.81 ± 0.52 vs - 0.35 ± 0.14, p = 0.04). Isoprenaline increased heart rate and slopes of restitution trajectory in failing hearts. The dynamics of restitution trajectory may hold clues for sudden death in heart failure patients.
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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 2010; 298:H1406-14. [PMID: 20154259 DOI: 10.1152/ajpheart.01206.2009] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
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 degrees and were varied in steps of 15 degrees . 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 (RT(e)). 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, RT(e) variability was found to be less predictable than RT(a) 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-R-unrelated 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.
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Affiliation(s)
- Alberto Porta
- Università degli Studi di Milano, Dipartimento di Tecnologie per la Salute, Istituto Ortopedico Galeazzi, Laboratorio di Modellistica di Sistemi Complessi, Via R. Galeazzi 4, Milan, Italy.
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Zaniboni M, Cacciani F, Salvarani N. Temporal variability of repolarization in rat ventricular myocytes paced with time-varying frequencies. Exp Physiol 2007; 92:859-69. [PMID: 17573414 DOI: 10.1113/expphysiol.2007.037986] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Adaptation of action potential duration (APD) to pacing cycle length (CL) has been previously characterized in isolated cardiomyocytes for sudden changes in constant CL and for pre-/postmature stimuli following constant pacing trains. However, random fluctuations characterize both physiological sinus rhythm (up to 10% of mean CL) and intrinsic beat-to-beat APD at constant pacing rate. We analysed the beat-to-beat sensitivity of each APD to the preceding CL during constant-sudden, random or linearly changing pacing trains in single patch clamped rat left ventricular myocytes, in the absence of the autonomic and electrotonic effects that modulate rate dependency in the intact heart. Beat-to-beat variability of APD at -60 mV (APD(-60 mV)), quantified as S.D. over 10-beat sequences, increased with corresponding mean APD. When measured as coefficient of variability (CV), APD(-60 mV) variability was inversely proportional to pacing frequency (from 1.2% at 5 Hz to 3.2% at 0.2 Hz). It was increased, at a basic CL (BCL) of 250 ms, by 55% by the L-type calcium current (I(CaL)) blocker nifedipine, and decreased by 23% by the transient-outward potassium current (I(to)) blocker 4-aminopyridine. Variability of APD at BCL of 250 ms prevented the detection of random changes of CL smaller than approximately 5%. Ten per cent random changes in CL were detected as a 40% increase in CV of APD and tended to correlate with it (r = 0.43). Block of I(CaL) depressed this correlation (r = 0.23), whereas block of I(to) significantly increased it (r = 0.67); this was similar with linearly changing CL ramps (ranging +/-10% and +/-20% of 250 ms). We conclude that beat-to-beat APD variability, a major determinant of the propensity for development of arrhythmia in the heart, is present in isolated myocytes, where it is dependent on mean APD and pacing rate. Action potential duration shows a beat-to-beat positive correlation with preceding randomly/linearly changing CL, which can be pharmacologically modulated.
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Affiliation(s)
- Massimiliano Zaniboni
- Dipartimento di Biologia Evolutiva e Funzionale - Sezione Fisiologia, Università degli Studi di Parma, Viale G.P. Usberti 11A, 43100 Parma, Italy.
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Larroude CE, Jensen BT, Agner E, Toft E, Torp-Pedersen C, Wachtell K, Kanters JK. Beat-to-beat QT dynamics in paroxysmal atrial fibrillation. Heart Rhythm 2006; 3:660-4. [PMID: 16731466 DOI: 10.1016/j.hrthm.2006.02.021] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/15/2005] [Accepted: 02/15/2006] [Indexed: 11/30/2022]
Abstract
BACKGROUND QT dynamics parameters are used only in sinus rhythm. However, because many patients with paroxysmal atrial fibrillation undergo antiarrhythmic treatment that changes QT, developing methods for measuring QT dynamics during atrial fibrillation is important. OBJECTIVES The purpose of this study was to evaluate whether QT dynamics in atrial fibrillation can be measured more reliably if additional RR intervals are included in the QT calculation. METHODS QT and RR intervals were measured in 15 patients with atrial fibrillation and sinus rhythm on the same 24-hour Holter recording. Full QT adaptation is not instantaneous but lags behind over several beats. To correct for this lag, we adapted a weighted average method using five successive RR intervals. Linear regression was performed on (QT, RR) and (QT, RR(modified)) pairs. Variability ratio (standard deviation of all QT intervals/standard deviation of all RR intervals) and modified variability ratio (standard deviation of all QT intervals/modified standard deviation of all RR intervals) were calculated. RESULTS QT-RR slope was reduced in atrial fibrillation compared with sinus rhythm (0.076 +/- 0.009 vs 0.113 +/- 0.0013, P = .0005). When correcting for lag, using the QT-RR(modified) slope, the slope in atrial fibrillation became similar to the slope in sinus rhythm (0.126 +/- 0.013 vs 0.126 +/- 0.013, P = .9547). The variability ratio was reduced in atrial fibrillation compared with sinus rhythm (0.175 +/- 0.017 vs 0.240 +/- 0.031, P = .009), but when correcting for the lag, the modified variability ratio was similar in atrial fibrillation and sinus rhythm (0.262 +/- 0.029 vs 0.267 +/- 0.038, P = .80). CONCLUSION The results of this study demonstrate that QT dynamics can be measured reliably in atrial fibrillation using 24-hour Holter recordings.
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Affiliation(s)
- Charlotte E Larroude
- Laboratory of Experimental Cardiology, Department of Medical Physiology, University of Copenhagen, Denmark
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