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Dahlberg P, Axelsson K, Jensen SM, Lundahl G, Vahedi F, Perkins R, Gransberg L, Bergfeldt L. Accelerated QT adaptation following atropine-induced heart rate increase in LQT1 patients versus healthy controls: A sign of disturbed hysteresis. Physiol Rep 2022; 10:e15487. [PMID: 36324292 PMCID: PMC9630760 DOI: 10.14814/phy2.15487] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2022] [Revised: 09/08/2022] [Accepted: 09/19/2022] [Indexed: 06/16/2023] Open
Abstract
Hysteresis, a ubiquitous regulatory phenomenon, is a salient feature of the adaptation of ventricular repolarization duration to heart rate (HR) change. We therefore compared the QT interval adaptation to rapid HR increase in patients with the long QT syndrome type 1 (LQT1) versus healthy controls because LQT1 is caused by loss-of-function mutations affecting the repolarizing potassium channel current IKs , presumably an important player in QT hysteresis. The study was performed in an outpatient hospital setting. HR was increased in LQT1 patients and controls by administering an intravenous bolus of atropine (0.04 mg/kg body weight) for 30 s. RR and QT intervals were recorded by continuous Frank vectorcardiography. Atropine induced transient expected side effects but no adverse arrhythmias. There was no difference in HR response (RR intervals) to atropine between the groups. Although atropine-induced ΔQT was 48% greater in 18 LQT1 patients than in 28 controls (p < 0.001), QT adaptation was on average 25% faster in LQT1 patients (measured as the time constant τ for the mono-exponential function and the time for 90% of ΔQT; p < 0.01); however, there was some overlap between the groups, possibly a beta-blocker effect. The shorter QT adaptation time to atropine-induced HR increase in LQT1 patients on the group level corroborates the importance of IKs in QT adaptation hysteresis in humans and shows that LQT1 patients have a disturbed ultra-rapid cardiac memory. On the individual level, the QT adaptation time possibly reflects the effect-size of the loss-of-function mutation, but its clinical implications need to be shown.
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Affiliation(s)
- Pia Dahlberg
- Department of Molecular and Clinical MedicineInstitute of Medicine, Sahlgrenska Academy, University of GothenburgGothenburgSweden
- Region Västra Götaland, Department of CardiologySahlgrenska University HospitalGothenburgSweden
| | - Karl‐Jonas Axelsson
- Department of Molecular and Clinical MedicineInstitute of Medicine, Sahlgrenska Academy, University of GothenburgGothenburgSweden
- Region Västra Götaland, Department of CardiologySahlgrenska University HospitalGothenburgSweden
| | - Steen M. Jensen
- Department of Public Health and Clinical Medicine, and Heart CentreUmeå UniversityUmeåSweden
| | - Gunilla Lundahl
- Department of Molecular and Clinical MedicineInstitute of Medicine, Sahlgrenska Academy, University of GothenburgGothenburgSweden
| | - Farzad Vahedi
- Department of Molecular and Clinical MedicineInstitute of Medicine, Sahlgrenska Academy, University of GothenburgGothenburgSweden
- Region Västra Götaland, Department of CardiologySahlgrenska University HospitalGothenburgSweden
| | - Rosie Perkins
- Department of Molecular and Clinical MedicineInstitute of Medicine, Sahlgrenska Academy, University of GothenburgGothenburgSweden
| | - Lennart Gransberg
- Department of Molecular and Clinical MedicineInstitute of Medicine, Sahlgrenska Academy, University of GothenburgGothenburgSweden
| | - Lennart Bergfeldt
- Department of Molecular and Clinical MedicineInstitute of Medicine, Sahlgrenska Academy, University of GothenburgGothenburgSweden
- Region Västra Götaland, Department of CardiologySahlgrenska University HospitalGothenburgSweden
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Axelsson KJ, Gransberg L, Lundahl G, Vahedi F, Bergfeldt L. Adaptation of ventricular repolarization time following abrupt changes in heart rate: comparisons and reproducibility of repeated atrial and ventricular pacing. Am J Physiol Heart Circ Physiol 2020; 320:H381-H392. [PMID: 33164576 DOI: 10.1152/ajpheart.00542.2020] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Adequate adaptation of ventricular repolarization (VR) duration to changes in heart rate (HR) is important for cardiac electromechanical function and electrical stability. We studied the QT and QTpeak adaptation in response to abrupt start and stop of atrial and ventricular pacing on two occasions with an interval of at least 1 mo in 25 study subjects with permanent pacemakers. Frank vectorcardiography was used for data collection. Atrial or ventricular pacing was performed for 8 min aiming at a cycle length (CL) of 500 ms. We measured the immediate response (IR), the time constant (τ) of the exponential phase, and T90 End, the time to reach 90% change of QT and QTpeak from baseline to steady state during and after pacing. During atrial pacing, the CL decreased on average 45% from mean (SD) 944 (120) to 518 (46) ms and QT decreased on average 18% from 388 (20) to 318 (17) ms. For QT, T90 End was 103 (24) s and 126 (15) s after start versus stop of atrial pacing; a difference of 24 (27) s (P = 0.006). The response pattern was similar for τ but IR did not differ significantly between pacing start and stop. The response pattern was similar for QTpeak and also for QT and QTpeak following ventricular pacing start and stop. The coefficients of variation for repeated measures were 7%-21% for T90 End and τ. In conclusion, the adaptation of VR duration was significantly more rapid following increasing than decreasing HR and intraindividually a relatively reproducible process.NEW & NOTEWORTHY We studied the duration of ventricular repolarization (VR) adaptation and its hysteresis, following increasing and decreasing heart rate by abrupt start and stop of 8-min atrial or ventricular pacing in study subjects with permanent pacemakers and repeated the protocol with ≥1 mo interval, a novel approach. VR adaptation was significantly longer following decreasing than increasing heart rate corroborating previous observations. Furthermore, VR adaptation was intraindividually a reproducible and, hence, robust phenomenon, a novel finding.
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Affiliation(s)
- Karl-Jonas Axelsson
- Department of Molecular and Clinical Medicine, Institute of Medicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden.,Department of Cardiology, Region Västra Götaland, Sahlgrenska University Hospital, Gothenburg Sweden
| | - Lennart Gransberg
- Department of Molecular and Clinical Medicine, Institute of Medicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden
| | - Gunilla Lundahl
- Department of Molecular and Clinical Medicine, Institute of Medicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden
| | - Farzad Vahedi
- Department of Molecular and Clinical Medicine, Institute of Medicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden.,Department of Cardiology, Region Västra Götaland, Sahlgrenska University Hospital, Gothenburg Sweden
| | - Lennart Bergfeldt
- Department of Molecular and Clinical Medicine, Institute of Medicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden.,Department of Cardiology, Region Västra Götaland, Sahlgrenska University Hospital, Gothenburg Sweden
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Importance of QT/RR hysteresis correction in studies of drug-induced QTc interval changes. J Pharmacokinet Pharmacodyn 2018; 45:491-503. [PMID: 29651591 PMCID: PMC5953973 DOI: 10.1007/s10928-018-9587-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2017] [Accepted: 04/09/2018] [Indexed: 11/30/2022]
Abstract
QT/RR hysteresis and QT/RR adaptation are interlinked but separate physiological processes signifying how quickly and how much QT interval changes when heart rate changes, respectively. While QT interval duration is, as a rule, corrected for heart rate in terms of the QT/RR adaptation, the correction for QT/RR hysteresis is frequently omitted in studies of drug-induced QTc changes. This study used data from previously conducted thorough QT studies to investigate the extent of QTc errors caused by omitting the correction for QT/RR hysteresis, particularly in small clinical investigations. Statistical modeling approach was used to generate 11,000 simulated samples of 10-subject studies in which mixed effect PK/PD models were used to estimate drug-induced QTc changes at mean maximum plasma concentration of investigated compounds. Calculations of QTc intervals involving and omitting QT/RR hysteresis correction were compared. These comparisons showed that ignoring QT/RR hysteresis has two undesirable effects: (A) In the design of subject-specific heart rate corrections (needed in studies of drugs that change heart rate) omission of QT/RR hysteresis may lead to signals of QTc prolongation of more than 10 ms to be missed. (B) Irrespective of whether the investigated drug changes heart rate, omission of QT/RR hysteresis causes the widths of the confidence intervals of the PK/PD predicted QTc interval changes to be increased by 20–30% on average (exceeding 50% in some cases). This may lead to a failure of excluding meaningful QTc prolongation which would be excluded if using hysteresis correction. The study concludes that correction for QT/RR hysteresis should be incorporated into future studies of drug-induced QTc changes. Subject-specific heart rate corrections that omit hysteresis correction may lead to erroneously biased conclusions. Even when using universal (e.g. Fridericia) heart rate correction, hysteresis correction decreases the confidence intervals of QTc changes and thus helps avoiding false positive outcomes.
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Gravel H, Jacquemet V, Dahdah N, Curnier D. Clinical applications of QT/RR hysteresis assessment: A systematic review. Ann Noninvasive Electrocardiol 2017; 23. [PMID: 29083088 DOI: 10.1111/anec.12514] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/25/2017] [Accepted: 09/17/2017] [Indexed: 12/15/2022] Open
Abstract
BACKGROUND QT/RR hysteresis (QT-hys) is an index of the time accommodation of ventricular repolarization to heart rate changes. This report comprehensively reviews studies addressing QT-hys as a biomarker of medical conditions. METHODS This is a secondary analysis of data from a recent systematic review pertaining to methods of assessment of QT-hys. Articles included in the former review were filtered in order to select original articles investigating the association of QT-hys with medical conditions in humans. RESULTS Nineteen articles fulfilled our inclusion criteria. Given the heterogeneity of the methods and investigated conditions, no pooled analysis of data could be implemented. QT-hys was mostly studied as a risk marker of severe arrhythmias, as a predictor of the long QT syndrome (LQTS) phenotypes and genotypes and as a marker of exercise-induced ischemia. An increased QT-hys appears to be implicated in arrhythmogenesis, although the evidence in this regard relies on few human studies. An augmented QT-hys was reported in the LQTS, predominantly in the LQT2 genotype, but conflicting results were obtained between studies using different methods of assessment. In addition, QT-hys appears to be a useful marker of stress-induced myocardial ischemia in patients suspected of coronary artery disease. CONCLUSIONS QT-hys evaluation has potential clinical utility in at least some clinical conditions. Further studies of the clinical validity of QT-hys assessment are warranted, particularly condition specific studies based on QT-hys evaluation methods that provide separate estimates of QT-hys and QT/RR dependency.
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Affiliation(s)
- Hugo Gravel
- Department of Kinesiology, University of Montreal, Montreal, QC, Canada
| | - Vincent Jacquemet
- Department of Pharmacology and Physiology, Faculty of Medicine, University of Montreal, Montreal, QC, Canada
| | - Nagib Dahdah
- Division of Pediatric Cardiology and CHU Ste-Justine Research Center, CHU Ste-Justine, Montreal, QC, Canada
| | - Daniel Curnier
- Department of Kinesiology, University of Montreal, Montreal, QC, Canada
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Jacquemet V, Gravel H, Curnier D, Vinet A. Theoretical and experimental comparison of lag-based and time-based exponential moving average models of QT hysteresis. Physiol Meas 2017; 38:1885-1905. [PMID: 28885987 DOI: 10.1088/1361-6579/aa8b59] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
OBJECTIVE In the electrocardiogram, adaptation of the QT interval to variations in heart rate is not instantaneous. Quantification of this hysteresis phenomenon relies on mathematical models describing the relation between the RR and QT time series. These models reproduce hysteresis through an effective RR interval computed as a linear combination of the history of past RR intervals. This filter depends on a time constant parameter that may be used as a biomarker. APPROACH The most common hysteresis model is based on an autoregressive filter with an impulse response that decreases exponentially with the beat number (lag-based model). Recognizing that the QT time series is unevenly spaced, we propose two exponential moving average filters (time-based models) to define the effective RR interval: one with an impulse response that decreases exponentially with time in seconds, and one with a step response that relaxes exponentially with time in seconds. These two filters are neither linear nor time-invariant. Recurrence formulas are derived to enable efficient implementation. MAIN RESULTS Application to clinical signals recorded during tilt table test, exercise and 24 h Holter demonstrates that the three models perform similarly in terms of goodness-of-fit. When comparing the hysteresis time constant in two conditions with different heart rates, however, the time-based models are shown to reduce the bias on the hysteresis time constant caused by heart rate acceleration and deceleration. SIGNIFICANCE Time-based models should be considered when intergroup differences in both heart rate and QT hysteresis are expected.
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Affiliation(s)
- Vincent Jacquemet
- Département de Pharmacologie et Physiologie, Institut de Génie Biomédical, Université de Montréal, Montréal, Canada. Hôpital du Sacré-Coeur de Montréal, Centre de Recherche, Montréal, Canada
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Gravel H, Curnier D, Dahdah N, Jacquemet V. Categorization and theoretical comparison of quantitative methods for assessing QT/RR hysteresis. Ann Noninvasive Electrocardiol 2017; 22. [PMID: 28510313 DOI: 10.1111/anec.12463] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/14/2017] [Accepted: 03/27/2017] [Indexed: 11/27/2022] Open
Abstract
BACKGROUND In the human electrocardiogram, there is a lag of adaptation of the QT interval to heart rate changes, usually termed QT/RR hysteresis (QT-hys). Subject-specific quantifiers of QT-hys have been proposed as potential biomarkers, but there is no consensus on the choice of the quantifier. METHODS A comprehensive literature search was conducted to identify original articles reporting quantifiers of repolarization hysteresis from the surface ECG in humans. RESULTS Sixty articles fulfilled our inclusion criteria. Reported biomarkers were grouped under four categories. A simple mathematical model of QT/RR loop was used to illustrate differences between the methods. Category I quantifiers use direct measurement of QT time course of adaptation. They are limited to conditions where RR intervals are under strict control. Category IIa and IIb quantifiers compare QT responses during consecutive heart rate acceleration and deceleration. They are relevant when a QT/RR loop is observed, typically during exercise and recovery, but are not robust to protocol variations. Category III quantifiers evaluate the optimum RR memory in dynamic QT/RR relationship modeling. They estimate an intrinsic memory parameter independent from the nature of RR changes, but their reliability remains to be confirmed when multiple memory parameters are estimated. Promising approaches include the differentiation of short-term and long-term memory and adaptive estimation of memory parameters. CONCLUSION Model-based approaches to QT-hys assessment appear to be the most versatile, as they allow separate quantification of QT/RR dependency and QT-hys, and can be applied to a wide range of experimental settings.
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Affiliation(s)
- Hugo Gravel
- Department of Kinesiology, University of Montreal, Montréal, QC, Canada
| | - Daniel Curnier
- Department of Kinesiology, University of Montreal, Montréal, QC, Canada
| | - Nagib Dahdah
- Division of Pediatric Cardiology and CHU Ste-Justine Research Center, CHU Ste-Justine, Montréal, QC, Canada
| | - Vincent Jacquemet
- Department of Pharmacology and Physiology, Faculty of Medicine, University of Montreal, Montréal, QC, Canada
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Diesel Exhaust Worsens Cardiac Conduction Instability in Dobutamine-Challenged Wistar–Kyoto and Spontaneously Hypertensive Rats. Cardiovasc Toxicol 2016; 17:120-129. [DOI: 10.1007/s12012-016-9363-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
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Rabkin SW, Cheng X(J. Newer QT Correction Formulae to Correct QT for Heart Rate Changes During Exercise. Am J Med Sci 2016; 351:133-9. [DOI: 10.1016/j.amjms.2015.11.007] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2015] [Accepted: 09/01/2015] [Indexed: 11/17/2022]
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Zhang Y, Bao M, Dai M, Zhong H, Li Y, Tan T. QT hysteresis index improves the power of treadmill exercise test in the screening of coronary artery disease. Circ J 2014; 78:2942-9. [PMID: 25311775 DOI: 10.1253/circj.cj-14-0697] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
BACKGROUND QT hysteresis phenomenon exists in healthy subjects, and is more exaggerated in patients with coronary artery disease (CAD) and long QT syndrome. The purpose of this study was to establish an appropriate method to evaluate the magnitude of QT hysteresis, and assess the value of QT hysteresis index in the treadmill exercise test (TET) in predicting CAD. METHODS AND RESULTS: A total of 138 subjects with suspected CAD and referred for TET and selective coronary angiography (SCA) were divided into positive (n=77) and negative (n=61) SCA groups. Dynamic ECG were recorded during TET. QT/RR curves were constructed and QTp (Q-Tpeak) and QTe (Q-Tend) hysteresis indices were calculated for each subject. SYNTAX score in the positive SCA group was determined. The QTp and QTe hysteresis indices in the positive SCA group were significantly higher than in the negative SCA group. The combination of QTe hysteresis index and conventional TET criteria had the highest sensitivity and negative predictive value according to receiver operating characteristic curve, and was an independent predictor on multivariate logistic regression. QT hysteresis indices significantly correlated with SYNTAX score in the positive SCA group. CONCLUSIONS QTe hysteresis index enhances the specificity of predicting CAD in TET. It improves the diagnostic value of TET for CAD significantly when combined with conventional criteria and is associated with the severity of CAD.
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Affiliation(s)
- Yijie Zhang
- Department of Cardiology, Wuhan University, Renmin Hospital
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Akyuz A, Alpsoy S, Akkoyun DC, Degirmenci H, Guler N. Maximal Exercise-Corrected QT as a Predictor of Coronary Artery Disease: Comparison of Simpler Heart Rate Corrections. Korean Circ J 2013; 43:655-63. [PMID: 24255649 PMCID: PMC3831011 DOI: 10.4070/kcj.2013.43.10.655] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2013] [Revised: 07/19/2013] [Accepted: 08/29/2013] [Indexed: 11/26/2022] Open
Abstract
Background and Objectives The relationship between QT prolongation and myocardial ischemia is widely known. Due to the limited value of ST depression, we aimed to evaluate, by using four simpler heart rate corrections (Bazett, Framingham, Fridericia and Hodges), the value of maximal exercise-QTc prolongation in the diagnosis of coronary artery disease (CAD) presence and severity. Subjects and Methods We enrolled 234 subjects (mean age 57.3±9 years, 143 men) who had undergone exercise testing and coronary angiography due to a suspicion of CAD in the study. Evaluating CAD severity with Gensini scoring, the CAD group (n=122) and controls with non-CAD were compared in terms of corrected QT duration at maximal exercise. Results Age, gender, hypertension, dyslipidemia, smoking, exercise duration, resting, and peak heart rate were similar between the two groups (all p>0.05). The CAD group had higher raw QT values than the controls {268 (169-438) vs. 240 (168-348), p<0.001}. Although Framingham QTc of ≥350 ms and Fridericia QTc of ≥340 ms were seen to be useful for the diagnosis of CAD, there was no additive diagnostic value of exercise QTc in addition to ST depression. Maximal exercise-QTc Bazett (r=0.163, p=0.01), Framingham (r=0.239, p=0.001), and Fridericia (r=0.206, p=0.001) equations were weakly positively correlated with Gensini scoring. Conclusion The patients with CAD have longer QTc intervals at peak heart rates during exercise. This finding provides insufficient evidence to support routine incorporation of QTc at peak heart rates into exercise test interpretation.
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Affiliation(s)
- Aydın Akyuz
- Department of Cardiology, Namık Kemal University Medical School, Tekirdag, Turkey
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Fletcher GF, Ades PA, Kligfield P, Arena R, Balady GJ, Bittner VA, Coke LA, Fleg JL, Forman DE, Gerber TC, Gulati M, Madan K, Rhodes J, Thompson PD, Williams MA. Exercise standards for testing and training: a scientific statement from the American Heart Association. Circulation 2013; 128:873-934. [PMID: 23877260 DOI: 10.1161/cir.0b013e31829b5b44] [Citation(s) in RCA: 1205] [Impact Index Per Article: 109.5] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
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Pelchovitz DJ, Ng J, Chicos AB, Bergner DW, Goldberger JJ. QT-RR hysteresis is caused by differential autonomic states during exercise and recovery. Am J Physiol Heart Circ Physiol 2012; 302:H2567-73. [PMID: 22542617 DOI: 10.1152/ajpheart.00041.2012] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
QT-RR hysteresis is characterized by longer QT intervals at a given RR interval while heart rates are increasing during exercise and shorter QT intervals at the same RR interval while heart rates are decreasing during recovery. It has been attributed to a lagging QT response to different directional changes in RR interval during exercise and recovery. Twenty control subjects (8 males, age 51 ± 6 yr), 16 subjects with type 2 diabetes (12 males, age 56 ± 8 yr), 71 subjects with coronary artery disease (CAD) and preserved left ventricular ejection fraction (LVEF) (≥50%) (51 males, age 59 ± 12 yr), and 17 CAD subjects with depressed LVEF (<50%) (13 males, age 57 ± 10 yr) underwent two 16-min exercise tests followed by recovery. In session 2, parasympathetic blockade with atropine (0.04 mg/kg) was achieved at end exercise. QT-RR hysteresis was quantified as: 1) the area bounded by the QT-RR relationships for exercise and recovery in the range of the minimum RR interval at peak exercise to the minimum RR interval + 100 ms and 2) the difference in QT interval duration between exercise and recovery at the minimum RR interval achieved during peak exercise plus 50 ms (ΔQT). The effect of parasympathetic blockade was assessed by substituting the QT-RR relationship after parasympathetic blockade. QT-RR hysteresis was positive in all groups at baseline and reversed by parasympathetic blockade (P < 0.01). We conclude that QT-RR hysteresis is not caused by different directional changes in RR interval during exercise and recovery. Instead, it is predominantly mediated by differential autonomic nervous system effects as the heart rate increases during exercise vs. as it decreases during recovery.
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Affiliation(s)
- Daniel J Pelchovitz
- Division of Cardiology, Northwestern University Feinberg School of Medicine, Chicago, Illinois 60611, USA
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Seethala S, Shusterman V, Saba S, Mularski S, Němec J. Effect of β-adrenergic stimulation on QT interval accommodation. Heart Rhythm 2011; 8:263-70. [DOI: 10.1016/j.hrthm.2010.10.012] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/07/2010] [Accepted: 10/08/2010] [Indexed: 01/10/2023]
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Halámek J, Jurák P, Bunch TJ, Lipoldová J, Novák M, Vondra V, Leinveber P, Plachy M, Kara T, Villa M, Frána P, Soucek M, Somers VK, Asirvatham SJ. Use of a novel transfer function to reduce repolarization interval hysteresis. J Interv Card Electrophysiol 2010; 29:23-32. [PMID: 20625805 DOI: 10.1007/s10840-010-9500-x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/15/2009] [Accepted: 06/14/2010] [Indexed: 10/19/2022]
Abstract
BACKGROUND Cardiac repolarization is assessed by the QT interval on the surface electrocardiogram and varies with the heart rate. Standard QT corrections (QTc) do not account for the lag in QT change following a change in heart rate (QT hysteresis). Our group has developed and tested a transfer function (TRF) model to assess the effectiveness of a dynamic model of QT/RR coupling in eliminating hysteresis. METHODS We studied three groups: group I, healthy volunteers (n = 23, 41 ± 17 years); group II, hypertensive patients (n = 25, 45 ± 11 years); and group III, patients in a predominately paced rhythm (n = 5, 75 ± 6 years). To vary the heart rate, either exercise bicycling in the supine position (groups I and II) or manipulation of the pacemaker parameters (group III) was done. We then compared a dynamic TRF model with a model based on weighted averages of previous RR intervals. Two parameters were tested: root mean square (RMS) of the error signal between measured and computed QT and the elimination of hysteretic loops. RESULTS TRF-based measurements eliminated hysteresis in 22/23 (95%) group I patients, 21/25 (84%) group II patients, and 4/5 (80%) group III patients. When hysteresis elimination was not complete, the QT drift that followed RR intervals was different before and after bicycling (100 ms). In these patients, the corresponding QT interval did not significantly change during this period. The TRF model was found superior to the other tested models with respect to both analyzed parameters (RMS and hysteresis elimination). CONCLUSION The TRF model limited QT hysteresis in healthy, hypertensive, and pacemaker-dependent patients. In addition, an important finding of QT drift in patients with hypertension was identified. With further study in these and other diseased states, the TRF model may improve our ability to measure accurately cardiac repolarization and to determine arrhythmia risk.
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Eisner DA, Dibb KM, Trafford AW. The mechanism and significance of the slow changes of ventricular action potential duration following a change of heart rate. Exp Physiol 2009; 94:520-8. [PMID: 19270038 DOI: 10.1113/expphysiol.2008.044008] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
This article reviews the effects of changes of heart rate on the ventricular action potential duration. These can be divided into short term (fractions of a second), resulting from the kinetics of recovery of membrane currents, through to long term (up to days), resulting from changes of protein expression. We concentrate on the medium-term changes (time course of the order of 100 s). These medium-term changes occur in isolated tissues and in the intact human heart. They may protect against cardiac arrhythmias. Finally, we discuss the cellular mechanisms responsible for these changes.
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Affiliation(s)
- D A Eisner
- University of Manchester, Unit of Cardiac Physiology, 3.18 Core Technology Facility, Manchester, UK.
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Identifying coronary artery flow reduction and ischemia using quasistationary QT/RR-interval hysteresis measurements. J Electrocardiol 2007; 40:S91-6. [DOI: 10.1016/j.jelectrocard.2007.05.024] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2007] [Accepted: 05/14/2007] [Indexed: 11/17/2022]
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Affiliation(s)
- Paul Kligfield
- Division of Cardiology, Weill Medical College of Cornell University and the Cornell Center of the New York-Presbyterian Hospital, New York, NY, USA
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