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1.	Corino, Valentina D.A., et al. (författare) A Mathematical Model of The Atrioventricular Node during Atrial Fibrillation 2010 Ingår i: [Host publication title missing]. - 0276-6574. ; 37, s. 117-120 Konferensbidrag (refereegranskat)abstract The atrioventricular (AV) node plays a crucial role during atrial fibrillation (AF). The aim of this study is to present an AV node model which can be fitted to short-term ECG recordings in order to infer certain AV node characteristics. The proposed model is characterized by: i) the arrival rate of atrial impulses; ii) two different refractory periods, corresponding to dual AV nodal paths; iii) the probability of an atrial impulse choosing either of these pathways; iv) a parameter modeling prolongation of the refractory period due to different physiological reasons. The model was tested on atrial fibrillatory ECGs recorded from 33 patients; the average normalized absolute error between the normalized RR histogram and the estimated model probability density function was 0.0023 ± 0.0016, (20-ms bin size, 0–2 s interval). These preliminary results are encouraging as AV nodal properties can be noninvasively assessed by a set of statistical parameters with a simple electrophysiological interpretation.
2.	Corino, Valentina D. A., et al. (författare) An Atrioventricular Node Model for Analysis of the Ventricular Response During Atrial Fibrillation 2011 Ingår i: IEEE Transactions on Biomedical Engineering. - 1558-2531. ; 58:12, s. 3386-3395 Tidskriftsartikel (refereegranskat)abstract This paper introduces a model of the atrioventricular node function during atrial fibrillation (AF), and describes the related ECG-based estimation method. The proposed model is defined by parameters that characterize the arrival rate of atrial impulses, the probability of an impulse choosing either one of the two atrioventricular nodal pathways, the refractory periods of these pathways, and the prolongation of the refractory periods. These parameters are estimated from the RR intervals using maximum likelihood estimation, except for the shorter refractory period which is estimated from the RR interval Poincare plot, and the mean arrival rate of atrial impulses by the AF frequency. Simulations indicated that 200-300 RR intervals are generally needed for the estimates to be accurate. The model was evaluated on 30-min ECG segments from 36 AF patients. The results showed that 88% of the segments can be accurately modeled when the estimated probability density function (PDF) and an empirical PDF were at least 80% in agreement. The model parameters were estimated during head-up tilt test to assess differences caused by sympathetic stimulation. Both refractory periods decreased as a result of stimulation, and the likelihood of an impulse choosing the pathway with the shorter refractory period increased.
3.	Corino, Valentina D. A., et al. (författare) Association between Atrial Fibrillatory Rate and Heart Rate Variability in Patients with Atrial Fibrillation and Congestive Heart Failure 2013 Ingår i: Annals of Noninvasive Electrocardiology. - : Wiley. - 1082-720X. ; 18:1, s. 41-50 Tidskriftsartikel (refereegranskat)abstract Background Even if atrial fibrillatory rate (AFR) has been related to clinical outcome in patients with atrial fibrillation (AF), its relation with ventricular response has not been deeply studied. The aim of this study was to investigate the relation between AFR and RR series variability in patients with AF. Methods Twenty-minute electrocardiograms in orthogonal leads were processed to extract AFR, using spatiotemporal QRST cancellation and time frequency analysis, and RR series in 127 patients (age 69 +/- 11 years) with congestive heart failure (NYHA IIIII) enrolled in the MUSIC study (MUerte Subita en Insufficiencia Cardiaca). Heart rate variability and irregularity were assessed by time domain parameters and entropy-based indices, respectively and their correlation with AFR investigated. Results Variability measures seem not to be related to AFR, while irregularity measures do. A significant correlation between AFR and variability parameters of heart rate variability during AF was found only in patients not treated with antiarrhythmics drugs (correlation = 0.56 P < 0.05 for pNN50), while this correlation was lost in patients taking rate- or rhythm-control drugs. A significant positive correlation between AFR and indices of RR irregularity was found, showing that a higher AFR is related to a less organized RR series (correlation = 0.33 P < 0.05 for regularity index for all patients, correlation increased in subgroups of patients treated with the same drug). Conclusions These results suggest that a higher AFR is associated with a higher degree of irregularity of ventricular response that is observed regardless of the use of rate-controlling drugs. Ann Noninvasive Electrocardiol 2013;18(1):41-50
4.	Corino, Valentina D. A., et al. (författare) Atrioventricular nodal function during atrial fibrillation: Model building and robust estimation 2013 Ingår i: Biomedical Signal Processing and Control. - : Elsevier BV. - 1746-8094. ; 8:6, s. 1017-1025 Tidskriftsartikel (refereegranskat)abstract Statistical modeling of atrioventricular (AV) nodal function during atrial fibrillation (AF) is revisited for the purpose of defining model properties and improving parameter estimation. The characterization of AV nodal pathways is made more detailed and the number of pathways is now determined by the Bayesian information criterion, rather than just producing a probability as was previously done. Robust estimation of the shorter refractory period (i.e., of the slow pathway) is accomplished by a Hough-based technique which is applied to a Poincare plot of RR intervals. The performance is evaluated on simulated data as well as on ECG data acquired from AF patients during rest and head-up tilt test. The simulation results suggest that the refractory period of the slow pathway can be accurately estimated even in the presence of many artifacts. They also show that the number of pathways can be accurately determined. The results from ECG data show that the refined AV node model provides significantly better fit than did the original model, increasing from 85 +/- 5% to 88 +/- 4% during rest, and from 86 +/- 5% to 87 +/- 3% during tilt. When assessing the effect of sympathetic stimulation, the AF frequency increased significantly during tilt (6.25 +/- 0.58 Hz vs. 6.32 +/- 0.61 Hz, p <0.05, rest vs. tilt) and the prolongation of the refractory periods of both pathways decreased significantly (slow pathway: 0.23 +/- 0.20 s vs. 0.11 +/- 0.10 s, p <0.001, rest vs. tilt; fast pathway: 0.24 +/- 0.31 s vs. 0.16 +/- 0.19s, p <0.05, rest vs. tilt). The results show that AV node characteristics can be assessed noninvasively for the purpose of quantifying changes induced by autonomic stimulation. (C) 2012 Elsevier Ltd. All rights reserved.
5.	Corino, Valentina D. A., et al. (författare) Beta-blockade and A1-adenosine receptor agonist effects on atrial fibrillatory rate and atrioventricular conduction in patients with atrial fibrillation 2014 Ingår i: Europace. - : Oxford University Press (OUP). - 1532-2092 .- 1099-5129. ; 16:4, s. 587-594 Tidskriftsartikel (refereegranskat)abstract Reduced irregularity of RR intervals in permanent atrial fibrillation (AF) has been associated with poor outcome. It is not fully understood, however, whether modification of atrioventricular (AV) conduction using rate-control drugs affects RR variability and irregularity measures. We aimed at assessing whether atrial fibrillatory rate (AFR) and variability and irregularity of the ventricular rate are modified by a selective A1-adenosine receptor agonist tecadenoson, beta-blocker esmolol, and their combination. Twenty-one patients (age 58 7 years, 13 men) with AF were randomly assigned to either 75, 150, or 300 g intravenous tecadenoson. Tecadenoson was administered alone (Dose Period 1) and in combination (Dose Period 2) with esmolol (100 g/kg/min for 10 min then 50 g/kg/min for 50 min). Heart rate (HR) and AFR were estimated for every 10 min long recording segment. Similarly, for every 10 min segment, the variability of RR intervals was assessed, as standard deviation, pNN20, pNN50, pNN80, and the root of the mean squared differences of successive RR intervals, and irregularity was assessed by non-linear measures such as regularity index (R) and approximate entropy. A marked decrease in HR was observed after both tecadenoson injections, whereas almost no changes could be seen in the AFR. The variability parameters were increased after the first tecadenoson bolus injection. In contrast, the irregularity parameters did not change after tecadenoson. When esmolol was infused, all the variability parameters further increased. Modification of AV node conduction can increase RR variability but does not affect regularity of RR intervals or AFR.
6.	Corino, Valentina D A, et al. (författare) Circadian variation of variability and irregularity of heart rate in patients with permanent atrial fibrillation: Relation to symptoms and rate-control drugs. 2015 Ingår i: American Journal of Physiology: Heart and Circulatory Physiology. - : American Physiological Society. - 1522-1539 .- 0363-6135. ; 309:12, s. 2152-2157 Tidskriftsartikel (refereegranskat)abstract The aim of this study is to evaluate the diurnal variation of the variability and irregularity of the heart rate (HR) in patients with permanent atrial fibrillation (AF), with and without rate-control drugs. Thirty-eight patients with permanent AF were part of an investigator-blind cross-over study, comparing diltiazem, verapamil, metoprolol, and carvedilol. We analyzed five Holter recordings per patient: at baseline (no rate-control drug) and with each of the four drug regimens. HR, variability (standard deviation, pNN20, pNN50, pNN80, and rMSSD) and irregularity (approximate (APEn) and sample entropy) parameters were computed in 20-minute long non-overlapping segments. Circadian rhythmicity was evaluated using the cosinor analysis to each parameter series, that is characterized by the 24-h mean (MESOR) and the excursion over the mean (the amplitude). Arrhythmia-related symptoms were assessed by a questionnaire measuring symptoms severity (SS) and frequency (SF). HR and variability parameters showed a significant circadian variation in most patients, whereas only a small minority of the patients had circadian variation of irregularity parameters. The patients with circadian ApEn at baseline had more severe symptoms (SS = 9±4 vs. 6±5, p<0.05; circadian vs. non-circadian variation). All drugs decreased the MESOR of HR and increased the MESOR of variability parameters. Only carvedilol and metoprolol decreased the normalized amplitude over the 24-h of all parameters and HR. In conclusion, HR and RR variability parameters present a circadian variation in patients with permanent AF, whereas few patients demonstrated circadian fluctuations in irregularity parameters, suggesting different physiological mechanisms.
7.	Corino, Valentina D.A., et al. (författare) Clinical use and limitations of non-invasive electrophysiological tests in patients with atrial fibrillation 2016 Ingår i: Journal of Atrial Fibrillation. - 1941-6911. ; 9:1, s. 62-67 Tidskriftsartikel (refereegranskat)abstract Atrial fibrillation (AF) is a complex arrhythmia, that has been studied non-invasively assessing atrial refractory period, atrioventricular node (AV) node refractory period, and ventricular response. The AV node plays a fundamental role as it filters many of the numerous irregular atrial impulses bombarding the node. Despite its importance, the electrophysiological (EP) characteristics of the AV node are not routinely evaluated since conventional EP techniques for assessment of refractory period or conduction velocity of the AV node are not applicable in AF. Since rate-control drugs control ventricular response through their effect on the AV node, noninvasive assessment of AV node electrophysiology may be useful. The RR series, though being highly irregular, contains information that can be used for risk stratification and prediction of outcome. In particular, RR irregularity measures during AF have been shown to be related to clinical outcome. This paper reviews the attempts done to noninvasively characterize the AV node and the ventricular response, highlighting clinical applications and limitations of the noninvasive techniques.
8.	Corino, Valentina D. A., et al. (författare) Improved Time-Frequency Analysis of Atrial Fibrillation Signals Using Spectral Modeling 2008 Ingår i: IEEE Transactions on Biomedical Engineering. - 1558-2531. ; 55:12, s. 2723-2730 Tidskriftsartikel (refereegranskat)abstract In patients with atrial fibrillation (AF), the fibrillatory frequency trend and the time-dependent spectral characteristics can be investigated using a spectral profile technique. The spectral profile is updated by fitting each short-time spectrum. The aim of this study is to develop model-based means for stricter control on the update of the spectral profile. A spectral model defined by a superposition of Gaussian functions is suggested for describing the fundamental and harmonics of the atrial waves during AF, thereby accounting for basic characteristics of the typical AF spectrum. The model parameters are obtained from weighted least squares fitting of the model to the observed spectrum. The method was tested on simulated signals as well as on 48 ECG recordings from 15 patients with persistent AF. Using simulated signals, we assessed the accuracy in terms of magnitude and width or the spectral peaks. For SNR = 0 dB, the maximum normalized error was less than 0.2 when estimating magnitude of both the fundamental and the harmonics, whereas it was less than 0.15 for the fundamental and 0.7 for the harmonics with respect to the estimation of the width. We observed a marked Improvement while tracking the main fibrillatory frequency as the error was reduced by more than 50% In comparison with the original method. Analyzing ECGs, reliable spectral profiles were obtained In all recordings, even In those cases (5/48) that were not well characterized by the original method.
9.	Corino, Valentina D.A., et al. (författare) Non-invasive evaluation of the effect of metoprolol on the atrioventricular node during permanent atrial fibrillation 2014. - January Ingår i: Computing in Cardiology 2014. - : Oxford University Press (OUP). - 2325-8861. - 9781479943463 - 9781479943470 ; 41, s. 889-892 Konferensbidrag (refereegranskat)abstract The aim of this study was to evaluate changes in AV nodal properties during administration of metoprolol, using a novel ECG-based method for parameter estimation. The AV nodal parameters account for the probability of an impulse not passing through the fast pathway, the absolute refractory periods of the slow and fast pathways (aRPs and aRPf), representing the functional refractory period, and related prolongation in the respective refractory periods. Twenty patients (age 71±8 years, 14 men) with permanent AF from the RATe control in Atrial Fibrillation (RATAF) database were included in this study. Recordings during baseline and metoprolol administration were analyzed. Furthermore, simulated RR series were generated mimicking metoprolol administration. During metoprolol administration, aRP was significantly prolonged in both pathways (aRPs: 342±39 vs. 408±81 ms, p<0.001; aRPf: 432±74 vs. 527±83 ms, p<0.001). Similar results were found for the simulated RR series: both aRPs and aRPf were significantly prolonged with metoprolol. The AV nodal parameters reflect expected changes after metoprolol administration, i.e., a prolongation in functional refractory period. The simulations suggest that aRP may serve as an estimate of the functional refractory period.
10.	Corino, Valentina D. A., et al. (författare) Noninvasive Assessment of Atrioventricular Nodal Function: Effect of Rate-Control Drugs during Atrial Fibrillation 2015 Ingår i: Annals of Noninvasive Electrocardiology. - : Wiley. - 1082-720X. ; 20:6, s. 534-541 Tidskriftsartikel (refereegranskat)abstract Background: During atrial fibrillation (AF), conventional electrophysiological techniques for assessment of refractory period or conduction velocity of the atrioventricular (AV) node cannot be used. We aimed at evaluating changes in AV nodal properties during administration of tecadenoson and esmolol using a novel ECG-based method. Methods: Fourteen patients (age 58 +/- 8 years, 10 men) with AF were randomly assigned to either 75 or 300 mu g intravenous tecadenoson. After tecadenoson wash-out, patients received esmolol continuously (100 mu g/kg per min for 10 mins, then 50 mu g/kg per min for 50 mins). Atrial fibrillatory rate (AFR) and heart rate (HR) were assessed in 15-min segments. Using the novel method, we assessed the absolute refractory periods of the slow and fast pathways (aRPs and aRPf) of the AV node to produce an estimate of the functional refractory period. Results: During esmolol infusion, AFR and HR were significantly decreased and the absolute refractory period was significantly prolonged in both pathways (aRPs: 387 +/- 73 vs 409 +/- 62 ms, P < 0.05; aRPf: 490 +/- 80 vs 529 +/- 58 ms, P < 0.05). During both tecadenoson doses, HR decreased significantly and AFR was unchanged. Both aRPs and aRPf were prolonged for a 75 mu g dose (aRPs: 322 +/- 97 vs 476 +/- 75 ms, P < 0.05; aRPf: 456 +/- 102 vs 512 +/- 55 ms, P < 0.05) whereas a trend toward prolongation was observed for a 300 mu g dose. Conclusions: The estimated parameters reflect expected changes in AV nodal properties, i.e., slower conduction through the AV node for tecadenoson and prolongation of the AV node refractory period for esmolol. Thus, the proposed approach may be used to assess drug effects on the AV node in AF patients.
11.	Corino, Valentina D A, et al. (författare) Noninvasive characterization of atrioventricular conduction in patients with atrial fibrillation. 2015 Ingår i: Journal of Electrocardiology. - : Elsevier BV. - 1532-8430 .- 0022-0736. ; 48:6, s. 938-942 Tidskriftsartikel (refereegranskat)abstract The atrioventricular (AV) node plays a fundamental role in patients with atrial fibrillation (AF), acting as a filter to the numerous irregular atrial impulses which bombard the node. A phenomenological approach to better understand AV nodal electrophysiology is to analyze the ventricular response with respect to irregularity. In different cohorts of AF patients, such analysis has been performed with the aim to evaluate the association between ventricular response characteristics and long-term clinical outcome and to determine whether irregularity is affected by rate-control drugs. Another approach to studying AV nodal characteristics is to employ a mathematical model which accounts for the refractory periods of the two AV nodal pathways. With atrial fibrillatory rate and RR intervals as input, the model has been considered for analyzing data during (i) rest and head-up tilt test, (ii) tecadenoson and esmolol, and (iii) rate-control drugs. The present paper provides an overview of our recent work on the characterization and assessment of AV nodal conduction using these two approaches.
12.	Corino, Valentina D. A., et al. (författare) Rate-Control Drugs Affect Variability and Irregularity Measures of RR Intervals in Patients with Permanent Atrial Fibrillation 2015 Ingår i: Journal of Cardiovascular Electrophysiology. - : Wiley. - 1540-8167 .- 1045-3873. ; 26:2, s. 137-141 Tidskriftsartikel (refereegranskat)abstract Heart Rate Variability and Irregularity During AF IntroductionIrregularity measures have been suggested as risk indicators in patients with atrial fibrillation (AF); however, it is not known to what extent they are affected by commonly used rate-control drugs. We aimed at evaluating the effect of metoprolol, carvedilol, diltiazem, and verapamil on the variability and irregularity of the ventricular response in patients with permanent AF. Methods and ResultsSixty patients with permanent AF were part of an investigator-blind cross-over study, comparing 4 rate-control drugs (diltiazem, verapamil, metoprolol, and carvedilol). We analyzed five 20-minute segments per patient: baseline and the 4 drug regimens. On every segment, heart rate (HR) variability and irregularity of RR series were computed. The variability was assessed as standard deviation, pNN20, pNN50, pNN80, and rMSSD. The irregularity was assessed by regularity index, approximate (ApEn), and sample entropy. A significantly lower HR was obtained with all drugs, the HR was lowest using the calcium channel blockers. All drugs increased the variability of ventricular response in respect to baseline (as an example, rMSSD: baseline 171 47 milliseconds, carvedilol 229 +/- 58 milliseconds; P < 0.05 vs. baseline, metoprolol 226 +/- 66 milliseconds; P < 0.05 vs. baseline, verapamil 228 +/- 84; P < 0.05 vs. baseline, diltiazem 256 +/- 87 milliseconds; P < 0.05 vs. baseline and all other drugs). Only -blockers significantly increased the irregularity of the RR series (as an example, ApEn: baseline 1.86 +/- 0.13, carvedilol 1.92 +/- 0.09; P < 0.05 vs. baseline, metoprolol 1.93 +/- 0.08; P < 0.05 vs. baseline, verapamil 1.86 +/- 0.22 ns, diltiazem 1.88 +/- 0.16 ns). ConclusionModification of AV node conduction by rate-control drugs increase RR variability, while only -blockers affect irregularity.
13.	Corino, Valentina D A, et al. (författare) Statistical modeling of atrioventricular nodal function during atrial fibrillation : An update 2013 Ingår i: BIOSIGNALS 2013 - Proceedings of the International Conference on Bio-Inspired Systems and Signal Processing. - 9789898565365 ; , s. 25-29 Konferensbidrag (refereegranskat)abstract This paper introduces a number of advancements of our recently proposed model of atrioventricular (AV) node function during atrial fibrillation (AF). The model is defined by parameters characterizing the arrival rate of atrial impulses, the probability of an impulse choosing either one of the two AV nodal pathways, the refractory periods of these pathways, and their prolongation. In the updated model, the characterization of AV nodal pathways is made more detailed and the number of pathways is determined by the Bayesian information criterion. The performance is evaluated on ECG data acquired from twenty-five AF patients during rest and head-up tilt test. The results show that the refined AV node model provides significantly better fit than did the original model. During tilt, the AF frequency increased (6.25 ±0.58 Hz vs. 6.32 ±0.61 Hz, p < 0.05, rest vs. tilt) and the prolongation of the refractory periods decreased for both pathways (slow pathway: 0.23 ±0.20 s vs. 0.11 ±0.10 s, p < 0.001, rest vs. tilt; fast pathway: 0.24±0.31 s vs. 0.16±0.19 s, p < 0.05, rest vs. tilt). These results show that AV node characteristics can be assessed noninvasively for the purpose of quantifying changes induced by autonomic stimulation.
14.	Corino, Valentina D. A., et al. (författare) Statistical Modeling of Atrioventricular Nodal Function During Atrial Fibrillation Focusing on the Refractory Period Estimation 2014 Ingår i: Biomedical Engineering Systems and Technologies (Biostec 2013). - Berlin, Heidelberg : Springer Berlin Heidelberg. - 1865-0929. ; 452, s. 258-268 Konferensbidrag (refereegranskat)abstract We have recently proposed a statistical AV node model defined by a set of parameters characterizing the arrival rate of atrial impulses, the probability of an impulse passing through the fast or the slow pathway, the refractory periods of the pathways, and the prolongation of refractory periods. All parameters are estimated from the RR interval series using maximum likelihood (ML) estimation, except for the mean arrival rate of atrial impulses which is estimated by the AF frequency derived from the f-waves. In this chapter, we compare four different methods, based either on the Poincare plot or ML estimation, for determining the refractory period of the slow pathway. Simulation results show better performance of the ML estimator, especially in the presence of artifacts due to premature ventricular beats or misdetected beats. The performance was also evaluated on ECG data acquired from 26 AF patients during rest and head-up tilt test. During tilt, the AF frequency increased (6.08 +/- 1.03 Hz vs. 6.20 +/- 0.99 Hz, p < 0.05, rest vs. tilt) and the refractory periods of both pathways decreased (slow pathway: 0.43 +/- 0.12 s vs. 0.38 +/- 0.12 s, p = 0.001, rest vs. tilt; fast pathway: 0.55 +/- 0.14 s vs. 0.47 +/- 0.11 s, p < 0.05, rest vs. tilt). These results show that AV node characteristics can be assessed non-invasively to quantify changes induced by autonomic stimulation.
15.	Corino, Valentina D.A., et al. (författare) Statistical modeling of the atrioventricular node during atrial fibrillation : Data length and estimator performance 2013 Ingår i: 2013 35th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, EMBC 2013. - 9781457702167 ; , s. 2567-2570 Konferensbidrag (refereegranskat)abstract The atrioventricular (AV) node plays a central role during atrial fibrillation (AF). We have recently proposed a statistical AV node model defined by parameters characterizing the arrival rate of atrial impulses, the probability of an impulse choosing either one of the dual AV nodal pathways, the refractory periods of the pathways, and the prolongation of refractory periods. All model parameters are estimated from the RR series using maximum likelihood (ML) estimation, except for the mean arrival rate of atrial impulses which is estimated by the AF frequency derived from the f-waves. The aim of this study is to present a unified approach to ML estimation which also involves the shorter refractory period, thus avoiding our previous Poincaré plot analysis which becomes biased. In addition, the number of RR intervals required for accurate parameter estimation is presented. The results show that the shorter refractory period can be accurately estimated, and that the resulting estimates converge to the true values when about 500 RR intervals are available.
16.	Halvaei, Hesam, et al. (författare) Detection of Short Supraventricular Tachycardias in Single-lead ECGs Recorded Using a Handheld Device 2022 Ingår i: Computing in Cardiology, CinC 2022. - 9798350300970 Konferensbidrag (refereegranskat)abstract Short supraventricular tachycardias (S-SVTs) have been associated with a higher risk of developing atrial fibrillation (AF). Hence, identification of participants with such arrhythmias may increase the yield of AF screening. However, the lower signal quality of ECGs recorded using handheld screening devices challenges the detection of S-SVT. In the present work, a new method for detection of S-SVT is presented, which is based on the requirement on morphologic similarity between the detected beats. Specifically, any episode with a sequence of beats of similar morphology is considered as an S-SVT candidate while any episode with detections of different morphology, either due to signal disturbances or aberrant ectopic beats, is excluded. For this purpose, a support vector machine (SVM) was trained and validated, using a simulated ECG database, to classify an episode as either consisting of beats of similar or non-similar morphologies. Episodes identified as S-SVT candidates are subject to two further rhythm criteria in order to confirm the presence of an S-SVT. The performance of the S-SVT detector is evaluated using a subset of the StrokeStop I database (305 S-SVT out of 8258), resulting in a sensitivity, specificity, and positive predictive value of 88.8%, 92.0%, and 29.9%, respectively. In conclusion, the results suggest that the detection of S-SVT in AF screening can be done at an acceptable balance between sensitivity and positive predictive value.
17.	Henriksson, Mikael, et al. (författare) A novel statistical model of the dual pathway atrioventricular node during atrial fibrillation 2016 Ingår i: Computing in Cardiology. - 9781509006854 ; 42, s. 473-476 Konferensbidrag (refereegranskat)abstract The atrioventricular (AV) node plays an important role during atrial fibrillation (AF). In particular, the refractoriness of its cells influences the conduction of atrial impulses to the ventricles and, thus, the ventricular response. This study introduces a novel statistical model of the AV node, accounting for pathway switching, which can be used for non-invasive assessment of the refractory properties of the slow and the fast AV nodal pathway during AF, using the atrial fibrillatory rate and the series of RR intervals obtained from the ECG. A number of simulated histograms is presented, illustrating that even though only four parameters are used to characterize the AV node, the model is capable of representing a wide range of different RR interval series. Estimation of model parameters is evaluated with simulated RR interval series. It is shown that a signal consisting of 2400 RR intervals is sufficient for accurate parameter estimation, with an average estimation error less than 50 ms in all parameters. It is concluded that the model offers a novel way to obtain information regarding AV nodal refractoriness from the ECG.
18.	Henriksson, Mikael, et al. (författare) A Statistical Atrioventricular Node Model Accounting for Pathway Switching During Atrial Fibrillation 2016 Ingår i: IEEE Transactions on Biomedical Engineering. - 1558-2531. ; 63:9, s. 1842-1849 Tidskriftsartikel (refereegranskat)abstract Objective: The atrioventricular (AV) node plays a central role in atrial fibrillation (AF) as it influences the conduction of impulses from the atria into the ventricles. In the present paper, the statistical dual pathway AV node model, previously introduced by us, is modified so that it accounts for atrial impulse pathway switching even if the preceding impulse did not cause a ventricular activation. Methods: The proposed change in model structure implies that the number of model parameters subjected to maximum likelihood estimation is reduced from five to four. The model is evaluated using the data acquired in the RATe control in Atrial Fibrillation (RATAF) study, involving 24- h ECG recordings from 60 patients with permanent AF. Results: When fitting the models to the RATAF database, similar results were obtained for both the present and the previous model, with a median fit of 86%. The results show that the parameter estimates characterizing refractory period prolongation exhibit considerably lower variation when using the present model, a finding that may be ascribed to fewer model parameters. Conclusion: The new model maintains the capability to model RR intervals, while providing more reliable parameters estimates. Significance: The model parameters are expected to convey novel clinical information, and may be useful for predicting the effect of rate control drugs.
19.	Husser, Oliver, et al. (författare) Exercise testing for non-invasive assessment of atrial electrophysiological properties in patients with persistent atrial fibrillation 2007 Ingår i: Europace. - : Oxford University Press (OUP). - 1532-2092. ; 9:8, s. 627-632 Tidskriftsartikel (refereegranskat)abstract Aims Experimental studies suggest that the autonomic nervous system modulates atrial refractoriness and conduction velocity in atrial. fibrillation (AF). These modulatory effects are, however, difficult to assess in the clinical setting. This study sought to non-invasively characterize in patients with persistent AF, the influence of autonomic modulation induced by exercise on atrial fibrillatory rate as marker of atrial refractoriness and to identify clinical and electrocardiographic predictors of atrial rate response. Methods and results In 24 patients (16 mates, mean age 60 +/- 13 years) with persistent AF (16 +/- 25 months), continuous ECGs were recorded during bicycle exercise testing. Fibrillatory rate (in fibrillations per minute, fpm) was assessed at baseline and immediately after termination of exercise with spatiotemporal QRST cancellation and time-frequency analysis. Ventricular response was characterized by time-domain HRV indices. Exercise had no influence on mean fibrillatory rate (409 +/- 42 vs. 414 +/- 43 fpm, P = NS). Seven patients responded to exercise with an increase in fibrillatory rate (26 10 fpm, P < 0.001 and three with a decrease (-21 +/- 8 fpm, P < 0.001), while the remaining 14 patients did not show a response. Responders' HRV indices changed in response to exercise similarly to that of non-responders. Their baseline fibrillatory rate was, however, lower than that of non-responders (387 +/- 18 vs. 425 +/- 48 fpm, P = 0.028). No other clinical or echocardiographic variable was associated with fibrillatory rate response. Twelve weeks after cardioverson, responders were more likely to remain in sinus rhythm than non-responders (88 vs. 46 %, P = 0.04). Conclusions Exercise-induced autonomic activation produces changes in atrial. etectrophysiological properties that can be detected by time-frequency analysis. Higher baseline fibrillatory rates are associated with an impaired atrial response to exercise that suggests advanced electrical remodelling and reduced sensitivity to autonomic stimuli.
20.	Iozzia, L., et al. (författare) Atrial Impulses at the Atrioventricular Node: Arrival versus Conduction during Atrial Fibrillation 2015 Ingår i: 16th Nordic-Baltic Conference on Biomedical Engineering. - Cham : Springer International Publishing. - 9783319129662 - 9783319129679 ; , s. 100-103 Konferensbidrag (refereegranskat)abstract The atrioventricular (AV) node plays a central role during atrial fibrillation (AF).We have recently proposed a statistical AV node model defined by parameters characterizing the arrival rate of atrial impulses, the probability of an impulse choosing the slower of the two AV nodal pathways, the refractory periods of the pathways, and the prolongation of refractory periods. All model parameters are estimated from the RR series using maximum likelihood estimation, except for the mean arrival rate of atrial impulses which is estimated by the AF frequency derived from the f-waves. The aim of this study is to assess the relationship between the probability γ of an atrial impulse to arrive at the slow pathway with the probability α (used in the model) of an impulse to pass through that pathway. A theoretical equation was derived to relate α with γ and viceversa, highlighting the dependence on both refractory periods and their prolongation. Results based on simulations show that the equation was correct, with an average absolute error of 0.0034 ± 0.0008.
21.	Platonov, Pyotr, et al. (författare) Atrial fibrillatory rate in the clinical context: natural course and prediction of intervention outcome. 2014 Ingår i: Europace. - : Oxford University Press (OUP). - 1532-2092 .- 1099-5129. ; 16 Suppl 4, s. 110-119 Tidskriftsartikel (refereegranskat)abstract Shortening of atrial refractory period during atrial fibrillation has been considered a hallmark of atrial electrical remodelling. The atrial fibrillatory cycle length, which is intimately related to the atrial fibrillatory rate (AFR), is generally accepted as a surrogate marker for local refractoriness. The value of using AFR to monitor the progress of atrial ablation therapy has been demonstrated and gradual slowing of AFR has consistently been observed to precede arrhythmia termination during paroxysmal or permanent atrial fibrillation ablation. Today, AFR is the key characteristic of the fibrillatory process, repeatedly validated against intracardiac recordings and extensively studied in clinical contexts. This paper provides an overview of clinical data accumulated since the method was introduced in 1998, and to present the current state of knowledge regarding ECG-derived AFR: its time course and dynamics, clinical factors affecting AFR, and available evidence of its value in the clinical context. We conclude that AFR is a promising, easily available AF characteristic that can be derived from the conventional surface ECG. It is clearly a useful tool for monitoring drug effects. Reference values for predicting intervention effect, however, are likely to be population- and context-specific and related to age, clinical types of atrial fibrillation, as well as to presence and advancement of underlying structural heart disease. Prospective studies in homogeneous patient populations are still needed to establish the clinical value of AFR.
22.	Saiz-Vivó, Javier, et al. (författare) Atrial fibrillation episode patterns as predictor of clinical outcome of catheter ablation 2023 Ingår i: Medical and Biological Engineering and Computing. - : Springer Science and Business Media LLC. - 0140-0118 .- 1741-0444. ; 61:2, s. 317-327 Tidskriftsartikel (refereegranskat)abstract Methods for characterization of atrial fibrillation (AF) episode patterns have been introduced without establishing clinical significance. This study investigates, for the first time, whether post-ablation recurrence of AF can be predicted by evaluating episode patterns. The dataset comprises of 54 patients (age 56 ± 11 years; 67% men), with an implantable cardiac monitor, before undergoing the first AF catheter ablation. Two parameters of the alternating bivariate Hawkes model were used to characterize the pattern: AF dominance during the monitoring period (log(mu)) and temporal aggregation of episodes (beta1). Moreover, AF burden and AF density, a parameter characterizing aggregation of AF burden, were studied. The four parameters were computed from an average of 29 AF episodes before ablation. The risk of AF recurrence after catheter ablation using the Hawkes parameters log(mu) and beta1, AF burden, and AF density was evaluated. While the combination of AF burden and AF density is related to a non-significant hazard ratio, the combination of log(mu) and beta1 is related to a hazard ratio of 1.95 (1.03–3.70; p < 0.05). The Hawkes parameters showed increased risk of AF recurrence within 1 year after the procedure for patients with high AF dominance and high episode aggregation and may be used for pre-ablation risk assessment.
23.	Saiz-Vivo, Javier, et al. (författare) Atrial Fibrillatory Rate Characterization Extracted from Implanted Cardiac Monitor Data 2021 Ingår i: 2021 Computing in Cardiology, CinC 2021. - 2325-8861 .- 2325-887X. - 9781665479165 ; 48 Konferensbidrag (refereegranskat)abstract The aim of this study is to characterize atrial fibrillatory rate (AFR) extracted from a cohort of continuously monitored atrial fibrillation (AF) patients as function of episode duration and onset time. The f-wave signal used to compute the AFR was extracted from a single lead ECG strip of the AF episodes stored in an Implantable Cardiac Monitor (ICM) in a cohort of 99 patients. The f-wave signals were obtained from 1400 AF episodes using a spatiotemporal QRST cancellation process and the AFR was estimated as the fundamental frequency of a model fitted to the extracted f-waves. We studied the relationship between AFR and episode duration and episode onset time, respectively. AFR (median (interquartile range)) was significantly lower (p-value<0.05) in short episodes (<20 min) (5.15 (0.66) Hz) than in longer episodes (5.30 (0.74) Hz). AFR was significantly higher for episodes with onset time at night (00-06) (5.34 (0.82) Hz) than for episodes with onset during the day (10-20) (5.21 (0.70) Hz). Significant differences were also found between the relative AFR (ratio between the AFR and the average AFR of the patient) and episode duration (Short: 99.2 (9.3) %; Long: 100.0 (8.9) %). Data extracted from ICMs shows that that nighttime AF onset and longer duration AF episodes are more common in patients with higher AFR.
24.	Saiz-Vivo, Javier, et al. (författare) Heart rate characteristic based modelling of atrial fibrillatory rate using implanted cardiac monitor data 2023 Ingår i: Physiological Measurement. - : IOP Publishing. - 0967-3334 .- 1361-6579. ; 44:3 Tidskriftsartikel (refereegranskat)abstract OBJECTIVE: The objective of the present study is to investigate the feasibility of using heart rate characteristics to estimate atrial fibrillatory rate (AFR) in a cohort of atrial fibrillation (AF) patients continuously monitored with an implantable cardiac monitor (ICM). We will use a mixed model approach to investigate population effect and patient specific effects of heart rate characteristics on AFR, and will correct for the effect of previous ablations, episode duration, and onset date and time.APPROACH: The f-wave signals, from which AFR is estimated, were extracted using a QRST cancellation process of the AF episodes in a cohort of 99 patients (67% male; 57±12 years) monitored for 9.2(0.2-24.3) months as median(min-max). The AFR from 2453 f-wave signals included in the analysis was estimated using a model-based approach. The association between AFR and heart rate characteristics, prior ablations, and episode-related features were modelled using fixed-effect and mixed-effect modelling approaches.MAIN RESULTS: The mixed-effect models had a better fit to the data than fixed-effect models showing higher coefficients of determination (R2=0.49 vs R2=0.04) when relating the variations of AFR to the heart rate features. However, when correcting for the other factors, the mixed-effect model showed the best fit (R2=0.56). AFR was found to be significantly affected by previous catheter ablations (p<0.05), episode duration (p<0.05), and irregularity of the RR interval series (p<0.05).SIGNIFICANCE: Mixed-effect models are more suitable for AFR modelling. AFR was shown to be faster in episodes with longer duration, less organized RR intervals and after several ablation procedures.
25.	Sandberg, Frida, et al. (författare) Drug effect evaluation during permanent atrial fibrillation using an AV-node model 2013 Ingår i: Computing in Cardiology 2013, CinC 2013. - 9781479908844 ; 40, s. 1243-1246 Konferensbidrag (refereegranskat)abstract The purpose of the present study is to evaluate the effect of rate control drugs on the AV node characteristics during atrial fibrillation (AF) using a model-based approach. A statistical model of the AV nodal function is employed, defined by parameters which characterize the arrival rate of atrial impulses, the refractoriness of the fast and the slow AV-nodal pathway and the probability of atrial impulse to pass through either of the two pathways. The RATAF (RATe control in Atrial Fibrillation) study database consists of recordings from 60 patients with permanent AF at baseline and on treatment with metoprolol, verapamil, diltiazem and carvedilol, respectively. The resulting model parameter estimates indicate that the refractory period of the slow pathway as well as that of the fast pathway increased significantly during treatment with all four drugs. The results suggest that the proposed AV-node model can be used for non-invasive evaluation of the effect of rate control drugs.
26.	Sandberg, Frida, et al. (författare) Non-invasive assessment of the effect of beta blockers and calcium channel blockers on the AV node during permanent atrial fibrillation. 2015 Ingår i: Journal of Electrocardiology. - : Elsevier BV. - 1532-8430 .- 0022-0736. ; 48:5, s. 861-866 Tidskriftsartikel (refereegranskat)abstract We aimed at assessing changes in AV nodal properties during administration of the beta blockers metoprolol and carvedilol, and the calcium channel blockers diltiazem and verapamil from electrocardiographic data.
27.	Sandberg, Frida, et al. (författare) Preliminary results from clinical validation study of a method for non-invasive assessment of atrioventricular node refractoriness during atrial fibrillation 2017 Ingår i: 2017 Computing in Cardiology (CinC). - 2325-8861. ; 44, s. 1-4 Konferensbidrag (refereegranskat)abstract The purpose of this study is to evaluate our previously proposed model-based, non-invasive approach to assess atrioventricular (AV) node refractory periods during atrial fibrillation (AF) by comparing its estimates to the invasively assessed AV node refractory periods. Patients referred to the hospital for pulmonary vein isolation (PVI), being in AF upon arrival, are included in the study. Using our approach, we estimate the AV node refractory periods from the ECG before and during the PVI procedure. The refractory periods is estimated using both single and dual pathway models; Bayes Information Criterion is employed to select the most appropriate model. Following conversion to sinus rhythm, a S1S2 atrial pacing protocol is applied to invasively assess AV node refractory periods. Preliminary results suggest that the method for non-invasive assessment of AV node refractoriness is accurate, however, more data is needed to better establish performance.
28.	Östenson, Sten, et al. (författare) Autonomic influence on atrial fibrillatory process : Head-up and head-down tilting 2017 Ingår i: Annals of Noninvasive Electrocardiology. - : Wiley. - 1082-720X. ; 22:2 Tidskriftsartikel (refereegranskat)abstract Background: Changes in the autonomic nervous system (ANS) tone are present before, during, and after episodes of atrial fibrillation (AF). Atrial fibrillatory rate (AFR, the inverse of the atrial cycle length) has been used as a surrogate marker for local refractoriness and is a key characteristic of the fibrillatory process in patients with AF. Aim of this study is to assess changes in AFR, as an effect of autonomic balance change. Methods: Forty patients undergoing cardiac cardioversion for symptomatic persistent AF were included in the study. Surface ECG was recorded during rest, head-down (HDT, -30°), and head-up tilt (HUT, +60°). A median value of AFR was computed in each phase of the protocol. Results: AFR decreased during HDT compared to the baseline (B) condition in all patients but three (median AFR_B = 391 fpm vs. AFR_HDT = 377 fpm, p < .0001). HUT increased AFR, making it significantly higher than HDT and baseline conditions (median AFR_HUT = 396 fpm, p < .0001 vs. B and HDT). Heart rate (HR) increased during HUT, but had a heterogeneous behavior in the population during HDT: about one third of the patients had an HR lower during HDT than during baseline, whereas the remaining two third had an increase in HR during HDT. Conclusions: Dominant sympathetic/vagal tone during HUT/HDT significantly affects AFR, increasing/decreasing in respect to baseline. It may be worth exploring the possibility that patients with AF of shorter duration can convert to sinus rhythm during HDT.

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