Identification of atrial fibrillation episodes in ambulatory electrocardiographic recordings: validation of a method for obtaining labeled R-R interval files

ESC Working Group on e-Cardiology Position Paper: accuracy and reliability of electrocardiogram monitoring in the detection of atrial fibrillation in cryptogenic stroke patients : In collaboration with the Council on Stroke, the European Heart Rhythm Association, and the Digital Health Committee

The role of subclinical atrial fibrillation as a cause of cryptogenic stroke is unambiguously established. Long-term electrocardiogram (ECG) monitoring remains the sole method for determining its presence following a negative initial workup. This position paper of the European Society of Cardiology Working Group on e-Cardiology first presents the definition, epidemiology, and clinical impact of cryptogenic ischaemic stroke, as well as its aetiopathogenic association with occult atrial fibrillation. Then, classification methods for ischaemic stroke will be discussed, along with their value in providing meaningful guidance for further diagnostic efforts, given disappointing findings of studies based on the embolic stroke of unknown significance construct. Patient selection criteria for long-term ECG monitoring, crucial for determining pre-test probability of subclinical atrial fibrillation, will also be discussed. Subsequently, the two major classes of long-term ECG monitoring tools (non-invasive and invasive) will be presented, with a discussion of each method's pitfalls and related algorithms to improve diagnostic yield and accuracy. Although novel mobile health (mHealth) devices, including smartphones and smartwatches, have dramatically increased atrial fibrillation detection post ischaemic stroke, the latest evidence appears to favour implantable cardiac monitors as the modality of choice; however, the answer to whether they should constitute the initial diagnostic choice for all cryptogenic stroke patients remains elusive. Finally, institutional and organizational issues, such as reimbursement, responsibility for patient management, data ownership, and handling will be briefly touched upon, despite the fact that guidance remains scarce and widespread clinical application and experience are the most likely sources for definite answers.

A Review of Atrial Fibrillation Detection Methods as a Service

Atrial Fibrillation (AF) is a common heart arrhythmia that often goes undetected, and even if it is detected, managing the condition may be challenging. In this paper, we review how the RR interval and Electrocardiogram (ECG) signals, incorporated into a monitoring system, can be useful to track AF events. Were such an automated system to be implemented, it could be used to help manage AF and thereby reduce patient morbidity and mortality. The main impetus behind the idea of developing a service is that a greater data volume analyzed can lead to better patient outcomes. Based on the literature review, which we present herein, we introduce the methods that can be used to detect AF efficiently and automatically via the RR interval and ECG signals. A cardiovascular disease monitoring service that incorporates one or multiple of these detection methods could extend event observation to all times, and could therefore become useful to establish any AF occurrence. The development of an automated and efficient method that monitors AF in real time would likely become a key component for meeting public health goals regarding the reduction of fatalities caused by the disease. Yet, at present, significant technological and regulatory obstacles remain, which prevent the development of any proposed system. Establishment of the scientific foundation for monitoring is important to provide effective service to patients and healthcare professionals.

Atrial Fibrillation Beat Identification Using the Combination of Modified Frequency Slice Wavelet Transform and Convolutional Neural Networks

Atrial fibrillation (AF) is a serious cardiovascular disease with the phenomenon of beating irregularly. It is the major cause of variety of heart diseases, such as myocardial infarction. Automatic AF beat detection is still a challenging task which needs further exploration. A new framework, which combines modified frequency slice wavelet transform (MFSWT) and convolutional neural networks (CNNs), was proposed for automatic AF beat identification. MFSWT was used to transform 1 s electrocardiogram (ECG) segments to time-frequency images, and then, the images were fed into a 12-layer CNN for feature extraction and AF/non-AF beat classification. The results on the MIT-BIH Atrial Fibrillation Database showed that a mean accuracy (Acc) of 81.07% from 5-fold cross validation is achieved for the test data. The corresponding sensitivity (Se), specificity (Sp), and the area under the ROC curve (AUC) results are 74.96%, 86.41%, and 0.88, respectively. When excluding an extremely poor signal quality ECG recording in the test data, a mean Acc of 84.85% is achieved, with the corresponding Se, Sp, and AUC values of 79.05%, 89.99%, and 0.92. This study indicates that it is possible to accurately identify AF or non-AF ECGs from a short-term signal episode.

Screening strategies for atrial fibrillation: a systematic review and cost-effectiveness analysis

Background

Atrial fibrillation (AF) is a common cardiac arrhythmia that increases the risk of thromboembolic events. Anticoagulation therapy to prevent AF-related stroke has been shown to be cost-effective. A national screening programme for AF may prevent AF-related events, but would involve a substantial investment of NHS resources.

Objectives

To conduct a systematic review of the diagnostic test accuracy (DTA) of screening tests for AF, update a systematic review of comparative studies evaluating screening strategies for AF, develop an economic model to compare the cost-effectiveness of different screening strategies and review observational studies of AF screening to provide inputs to the model.

Design

Systematic review, meta-analysis and cost-effectiveness analysis.

Setting

Primary care.

Participants

Adults.

Intervention

Screening strategies, defined by screening test, age at initial and final screens, screening interval and format of screening {systematic opportunistic screening [individuals offered screening if they consult with their general practitioner (GP)] or systematic population screening (when all eligible individuals are invited to screening)}.

Main outcome measures

Sensitivity, specificity and diagnostic odds ratios; the odds ratio of detecting new AF cases compared with no screening; and the mean incremental net benefit compared with no screening.

Review methods

Two reviewers screened the search results, extracted data and assessed the risk of bias. A DTA meta-analysis was perfomed, and a decision tree and Markov model was used to evaluate the cost-effectiveness of the screening strategies.

Results

Diagnostic test accuracy depended on the screening test and how it was interpreted. In general, the screening tests identified in our review had high sensitivity (> 0.9). Systematic population and systematic opportunistic screening strategies were found to be similarly effective, with an estimated 170 individuals needed to be screened to detect one additional AF case compared with no screening. Systematic opportunistic screening was more likely to be cost-effective than systematic population screening, as long as the uptake of opportunistic screening observed in randomised controlled trials translates to practice. Modified blood pressure monitors, photoplethysmography or nurse pulse palpation were more likely to be cost-effective than other screening tests. A screening strategy with an initial screening age of 65 years and repeated screens every 5 years until age 80 years was likely to be cost-effective, provided that compliance with treatment does not decline with increasing age.

Conclusions

A national screening programme for AF is likely to represent a cost-effective use of resources. Systematic opportunistic screening is more likely to be cost-effective than systematic population screening. Nurse pulse palpation or modified blood pressure monitors would be appropriate screening tests, with confirmation by diagnostic 12-lead electrocardiography interpreted by a trained GP, with referral to a specialist in the case of an unclear diagnosis. Implementation strategies to operationalise uptake of systematic opportunistic screening in primary care should accompany any screening recommendations.

Limitations

Many inputs for the economic model relied on a single trial [the Screening for Atrial Fibrillation in the Elderly (SAFE) study] and DTA results were based on a few studies at high risk of bias/of low applicability.

Future work

Comparative studies measuring long-term outcomes of screening strategies and DTA studies for new, emerging technologies and to replicate the results for photoplethysmography and GP interpretation of 12-lead electrocardiography in a screening population.

Study registration

This study is registered as PROSPERO CRD42014013739.

Funding

The National Institute for Health Research Health Technology Assessment programme.

Automatic real time detection of atrial fibrillation

Atrial fibrillation (AF) is the most common sustained arrhythmia and is associated with significant morbidity and mortality. Timely diagnosis of the arrhythmia, particularly transient episodes, can be difficult since patients may be asymptomatic. In this study, we describe a robust algorithm for automatic detection of AF based on the randomness, variability and complexity of the heart beat interval (RR) time series. Specifically, we employ a new statistic, the Turning Points Ratio, in combination with the Root Mean Square of Successive RR Differences and Shannon Entropy to characterize this arrhythmia. The detection algorithm was tested on two databases, namely the MIT-BIH Atrial Fibrillation Database and the MIT-BIH Arrhythmia Database. These databases contain several long RR interval series from a multitude of patients with and without AF and some of the data contain various forms of ectopic beats. Using thresholds and data segment lengths determined by Receiver Operating Characteristic (ROC) curves we achieved a high sensitivity and specificity (94.4% and 95.1%, respectively, for the MIT-BIH Atrial Fibrillation Database). The algorithm performed well even when tested against AF mixed with several other potentially confounding arrhythmias in the MIT-BIH Arrhythmia Database (Sensitivity = 90.2%, Specificity = 91.2%).

Rapidly detecting disorder in rhythmic biological signals: a spectral entropy measure to identify cardiac arrhythmias

We consider the use of a running measure of power spectrum disorder to distinguish between the normal sinus rhythm of the heart and two forms of cardiac arrhythmia: atrial fibrillation and atrial flutter. This spectral entropy measure is motivated by characteristic differences in the power spectra of beat timings during the three rhythms. We plot patient data derived from ten-beat windows on a "disorder map" and identify rhythm-defining ranges in the level and variance of spectral entropy values. Employing the spectral entropy within an automatic arrhythmia detection algorithm enables the classification of periods of atrial fibrillation from the time series of patients' beats. When the algorithm is set to identify abnormal rhythms within 6 s, it agrees with 85.7% of the annotations of professional rhythm assessors; for a response time of 30 s, this becomes 89.5%, and with 60 s, it is 90.3%. The algorithm provides a rapid way to detect atrial fibrillation, demonstrating usable response times as low as 6s. Measures of disorder in the frequency domain have practical significance in a range of biological signals: the techniques described in this paper have potential application for the rapid identification of disorder in other rhythmic signals.

Effect of C-reactive protein reduction on paroxysmal atrial fibrillation

BACKGROUND

C-reactive protein (CRP) lowering is associated with a reduction in recurrent and permanent atrial fibrillation. This study sought to determine whether CRP lowering also results in a reduction of paroxysmal atrial fibrillation (PAF) during daily life.

METHODS AND RESULTS

We enrolled 80 patients with proven PAF, CRP between 0.8 and 13 mg/L, and at least 1 episode of PAF on ambulatory electrocardiographic monitoring. Forty patients were randomized to placebo (placebo group) and 40 to atorvastatin (treatment group). Plasma CRP levels and ambulatory monitoring were repeated after 4 to 6 months of therapy. The 2 groups were comparable with respect to baseline characteristics, number of episodes of PAF, and baseline plasma CRP levels. The treatment group had lower median CRP levels at study end and experienced a significant reduction in the number of episodes of PAF compared with the placebo group. Paroxysmal atrial fibrillation was completely resolved in 26 (65%) of 40 patients in the treatment group versus 4 (10%) of 40 in the placebo group. The treatment group exhibited a highly significant reduction in PAF (P < .001). By logistic regression, treatment with atorvastatin was an independent predictor of PAF resolution.

CONCLUSIONS

C-reactive protein lowering with atorvastatin appears to be effective in eliminating PAF during daily life in a significant proportion of patients.

Automatic detection of atrial fibrillation using the coefficient of variation and density histograms of RR and deltaRR intervals

The paper describes a method for the automatic detection of atrial fibrillation, an abnormal heart rhythm, based on the sequence of intervals between heartbeats. The RR interval is the interbeat interval, and deltaRR is the difference between two successive RR intervals. Standard density histograms of the RR and deltaRR intervals were prepared as templates for atrial fibrillation detection. As the coefficients of variation of the RR and deltaRR intervals were approximately constant during atrial fibrillation, the coefficients of variation in the test data could be compared with the standard coefficients of variation (CV test). Further, the similarities between the density histograms of the test data and the standard density histograms were estimated using the Kolmogorov-Smirnov test. The CV test based on the RR intervals showed a sensitivity of 86.6% and a specificity of 84.3%. The CV test based on the deltaRR intervals showed that the sensitivity and the specificity are both approximately 84%. The Kolmogorov-Smirnov test based on the RR intervals did not improve on the result of the CV test. In contrast, the Kolmogorov-Smirnov test based on the ARR intervals showed a sensitivity of 94.4% and a specificity of 97.2%.

Double-blind placebo-controlled trial of digoxin in symptomatic paroxysmal atrial fibrillation

BACKGROUND

Digoxin is commonly prescribed in symptomatic paroxysmal atrial fibrillation (AF) but has never been evaluated in this condition.

METHODS AND RESULTS

From a multicenter registry, 43 representative patients with frequent symptomatic AF episodes were recruited into a randomized, double-blind crossover comparison of digoxin (serum concentration, 1.29+/-0.35 nmol/L) and placebo. The study end point was the occurrence of 2 AF episodes (documented by patient-activated monitors), censored at 61 days. The median time to 2 episodes was 13.5 days on placebo and 18.7 days on digoxin (P<0. 05). The relative risk (95% CI) of 2 episodes (placebo:digoxin) was 2.19 (1.07 to 4.50). A similar effect was seen on the median time to 1 episode: increased from 3.5 to 5.4 days (P<0.05), relative risk 1. 69 (0.88 to 3.24). The mean+/-SD ventricular rates during AF recordings during placebo and digoxin treatment were 138+/-32 and 125+/-35 bpm, respectively (P<0.01). Twenty-four-hour ambulatory ECG recordings did not show significant differences in the frequency or duration of AF or in ventricular rate.

CONCLUSIONS

Digoxin reduces the frequency of symptomatic AF episodes. However, the estimated effect is small and may be due to a reduction in the ventricular rate or irregularity rather than an antiarrhythmic action.

Evolution of changes in the ventricular rhythm during paroxysmal atrial fibrillation

Changes in the RR interval within episodes of paroxysmal atrial fibrillation (PAF) have not been fully characterized. A database of 177 24-hour Holter recordings were created from patients with PAF in the CRAFT studies. PAF episodes of > or = 1 minute duration containing < or = 20% noise and preceded by > or = 1 minute of sinus rhythm with < or = 20% noise were selected. Sections of each AF episode containing 10 and 25 RR intervals were identified at the onset, middle, and termination of each episode. Descriptive characteristics (mean, SD, and RMSSD of RR intervals) were calculated within each section, and compared using a nonparametric, paired Wilcoxon test. In 25 patients (17 men, 60.6 +/- 12.2 years old), 231 episodes from 44 recordings met the selection criteria. The mean RR interval increased slightly between the onset and mid-portion of AF episodes (565.9 +/- 128.3 vs 580.3 +/- 144.7 ms, P < 0.001). The RR interval at the termination of AF was significantly greater than that at the start (627.1 +/- 156.1 vs 565.9 ms, P < 10-11) or mid-portion (627.1 +/- 156.1 vs 580.3 +/- 144.7 ms, P < 10-13). SD of the RR interval increased significantly between onset and mid-portion (111.1 +/- 60.2 vs 118.2 +/- 66.7 ms, P < 0.001) and more substantially between mid-portion and termination (118.2 +/- 66.7 vs 201.8 +/- 93.7 ms, P < 10-21). During paroxysms of AF, the mean RR interval and the variability of RR intervals increases. Termination of a paroxysm is preceded by a marked increase in RR interval variability.

Circadian variation in atrial fibrillation in patients with frequent paroxysms

Determinants of the duration of episodes of atrial fibrillation (AF) in patients with paroxysmal atrial fibrillation (PAF) are poorly understood. However, autonomic tone shows circadian variation and is known to affect atrial electrophysiology. We therefore compared the duration of episodes of AF with an onset during the day (08:00-22:00) to those with an onset during the night in a database of 24-hour ECG recordings in patients with frequent symptomatic PAF. The heart rate in the 30 seconds prior to AF onset was also compared. From 42 recordings, 296 episodes of AF > 30 seconds duration and preceded by > 60 seconds sinus rhythm were identified. The 165 nocturnal episodes tended to be shorter (median = 1.15 min) than the 131 diurnal episodes (median = 1.5 min) and the distribution of nocturnal and diurnal durations was significantly different (P = 0.007; Kolgomorov-Smirnov test). This was also true in recordings containing at least 1 diurnal and at least 1 nocturnal episode. The mean heart rate prior to AF onset was lower at night (62.2 +/- 11.8 vs 75.6 +/- 16.4 beats/min; P < 0.0001 Wilcoxon test). These findings suggest that in patients with frequent symptomatic PAF, autonomic influences affect the duration of episodes of AF and has pathphysiological and therapeutic implications.

Age and gender influences on rate and duration of paroxysmal atrial fibrillation

The influence of age and gender on the character of paroxysmal atrial fibrillation (PAD) has not been described.

METHODS

The heart rate (HR) during PAF in patients receiving placebo or antiarrhythmic therapy was analyzed. Data from 177 24-hour Holter recordings were analyzed to mark the onset and termination of PAF and converted into RR interval files. PAF episodes lasting at least 2 minutes and containing < or = 20% noise were included. HR during the first 30-second segment versus during the remainder of the episode, and the duration of PAF episodes were compared among groups of different ages and sex (Wilcoxon test).

RESULTS

236 episodes from 55 recordings in 32 patients (all patients: 61.4 +/- 12.8 years; men (19): 58.5 +/- 12.6 years; women (13) 65.5 +/- 12.4 years, P = ns for difference in age) fulfilled the inclusion criteria. Women had a higher mean heart rate at AF onset (123 +/- 35 beats/min vs 115 +/- 20 beats/min, P = 0.02) and during the remainder of the episode (120 +/- 25 beats/min vs 112 +/- 22 beats/min at the start, P = 0.01, and 116 +/- 26 beats/min vs 108 +/- 18 beats/min subsequently, P = 0.01). Episodes tended to be longer in women (mean 89.8 min vs 50.5 min, P = NS) and in the aged (mean 83.8 min vs 46.9 min, P = NS).

CONCLUSION

PAF episodes are associated with faster heart rates and last longer in women, which may reflect differing autonomic responses to AF. A slower ventricular rate during PAF in older patients probably reflects an increasing prevalence of impaired atrioventricular conduction.

Mid- and long-term similarity of ventricular response to paroxysmal atrial fibrillation: digoxin versus placebo

The effects of digoxin on ventricular response during atrial fibrillation (AF) and consequent effects on arrhythmic symptoms have still not been fully explained. This study investigated whether the treatment by digoxin contributes to mid- and long-term stabilization of ventricular cycles in patients with paroxysmal AF. A population of 45 patients with paroxysmal AF underwent 24-hour ECG recordings during each arm of a randomized crossover trial comparing digoxin and placebo. This yielded 30 Holter recordings from 22 patients that contained AF episodes lasting in excess of 2 minutes and with acceptably low Holter noise. Each AF episode was divided into nonoverlapping segments of 30 seconds and the distribution of RR intervals in each segment was compared with the distribution of all other AF segments in the same recording using the Kolmogorov-Smirnov test. The percentage of tests that revealed significant differences at levels of P < or = 0.01, and P < or = 0.001 were sorted according to the time between the segments compared. The comparisons of these results were performed between: (a) all recordings on placebo (n = 16) and all recordings on digoxin (n = 14), and (b) between recordings on placebo and on digoxin in 8 patients in whom paired analysis was possible. Adjacent AF segments (distance 0) differed significantly only in < 30% of both recordings on placebo and on digoxin. However, with increasing the distance between segments, the proportion of the significant differences between RR interval distributions increased more with placebo than with digoxin (P < 10(-300), Chi-square test). Paired data revealed larger differences between placebo and digoxin with increasing distance between segments. Thus in patients with paroxysmal AF, digoxin leads to more reproducible patterns of ventricular cycles that may be better tolerated clinically.

Analysis of the cardiac rhythm preceding episodes of paroxysmal atrial fibrillation

AIMS

This study seeks to elucidate whether there was a common mode of initiation of paroxysmal atrial fibrillation (PAF) episodes that might suggest new therapies.

METHODS

A library of 177 digitized and analyzed 24-hour Holter recordings from PAF pharmacotherapy trials was studied. All noise-free PAF episodes > or =0.5 minutes were identified. PAF episodes and the preceding 2 minutes of sinus rhythm were printed as tachograms and visually inspected. Heart rate and ectopic beat behavior were used to characterize modes of PAF onset by comparing half-minute segments of the final 2 minutes of sinus rhythm.

RESULTS

Thirty-four recordings (from 19 patients, aged 61.7 +/- 11.5 years) provided 231 PAF episodes suitable for analysis. No patients had a consistent mode of PAF onset. This was confirmed by systematic analysis of the five patients with the most episodes. Overall, a highly significant increase in ectopic beats, from 1.34 to 6.52 min(-1) (p < 0.001) was found, but heart rate did not significantly change (mean heart rate at onset = 64 beats/min). PAF was initiated by a solitary ectopic beat in more than half of the cases. No consistent evidence for short-long-short sequences, seen in ventricular arrhythmias, was found.

CONCLUSION

The mode of onset of atrial fibrillation is inconsistent, both across a population with PAF and within individuals. This has implications for understanding the mechanisms of atrial fibrillation onset in human beings and for the treatment of the disorder.

Distribution of fast heart rate episodes during paroxysmal atrial fibrillation

OBJECTIVE

To investigate the defibrillator waiting time (time between the recognition of atrial fibrillation and the actual shock) by studying paroxysmal atrial fibrillation episodes with RR intervals shorter than a certain limit (that is, episodes during which defibrillation should not be attempted).

METHODS

Long term 24 hour Holter recordings from a digoxin v placebo crossover study in patients with paroxysmal atrial fibrillation were analysed. In all, 23 recordings with atrial fibrillation episodes of at least 1000 ventricular cycles and with < 20% Holter artefacts or noise were used (11 recorded on placebo and 12 on digoxin). For each recording, the mean ("mean waiting time") and maximum ("maximum waiting time") duration of continuous sections of atrial fibrillation episodes with all RR intervals shorter than a certain threshold were evaluated, ranging the threshold from 400 to 1000 ms in 10 ms steps. For each threshold, the mean and maximum waiting times were compared between recordings on placebo and on digoxin.

RESULTS

Both the mean and maximum waiting times increased exponentially with increasing threshold. Practically acceptable mean waiting times less than one minute were observed with thresholds below 600 ms. There were no significant differences in mean waiting times and maximum waiting times between recordings on placebo and digoxin, and only a trend towards shorter waiting times on digoxin.

CONCLUSIONS

Introduction of a minimum RR interval threshold required to deliver atrial defibrillation leads to practically acceptable delays between atrial fibrillation recognition and the actual shock. These delays are not prolonged by digoxin treatment.

A relationship between fluctuations in heart rate and the duration of subsequent episodes of atrial fibrillation

A relationship between autonomic tone and the onset of paroxysmal atrial fibrillation in some patients is recognised. Episodes of PAF may vary enormously in duration, however, from a few beats to many hours. Whether autonomic tone influences the duration of the episodes has been less well investigated. From a database of Holter recording taken from patients with symptomatic PAF, we identified all episodes of at least 30 seconds duration which were preceded by noise free sinus rhythm. This study examined the heart rate prior to AF onset, the change in heart rate over the final minute of sinus rhythm and the time of AF onset, and compared the data from those episodes of AF of more than 5 minutes duration to the shorter ones. Heart rate was slower before long episodes of AF, but this was found to predominantly represent data from separate recordings. A highly significant rise in heart rate was detected prior to long AF episodes compared to shorter ones. Daytime AF episodes were slightly longer than nocturnal ones. The most important finding was that longer AF episodes were typified by a heart rate acceleration. This suggests that, regardless of underlying aetiology, and increase in sympathetic tone may be important in the sustenance of episodes of PAF.

Electrophysiological effects of intrapericardial infusion of endothelin-1

Recently, extremely high levels of endothelin-1 (ET-1) were detected in the pericardial fluid of patients undergoing open-heart surgery. ET-1 has been suggested to have direct arrhythmogenic effect on myocardium. The aim of the present study was to examine the putative arrhythmogenic effect of intrapericardial infusion of ET-1 in anesthetized dogs (n = 15). In preliminary experiments, ET-1 (0.125-1.0 nmol/min, n = 7) was infused into the closed pericardial sack for 40 min. ET-1 induced non-sustained and/or sustained ventricular tachyarrhythmias in all but the lowest dose. For detailed arrhythmia analysis in addition to standard ECG ventricular endocardial and epicardial monophasic action potentials (MAP) were recorded. ET-1 (0.250 nmol/min, n = 7) induced mono- and polymorphic ventricular tachycardias, which degenerated into ventricular fibrillation in two instances. Moderate if any ischemic signs could be detected before the onset of arrhythmias. The arrhythmias spontaneously disappeared in all instances with the exception when ventricular fibrillation terminated the experiment. QT interval (260 +/- 23 ms vs. 317 +/- 31 ms, P < 0.05), and endo- and epicardial MAPD90 (at 300 ms cycle length) prolonged significantly (in average 182 +/- 12 ms vs. 224 +/- 25 ms, P < 0.05). Using MAP recording afterdepolarizations were detected in three instances. In control animals (n = 3) arrhythmias were not observed and all electrophysiological parameters remained unchanged. The present results show that intrapericardial administration of ET-1 can induce ventricular arrhythmias in dogs. The arrhythmogenic effect of ET-1 may be based on prolongation of MAP duration and development of afterdepolarizations. However, the elucidation of the precise mechanism needs further investigation.

Performance of basic ventricular tachycardia detection algorithms in implantable cardioverter defibrillators: implications for device programming

Around 20% of patients with third generation implantable cardioverter defibrillators receive inappropriate therapy, usually triggered by atrial fibrillation. This is because the criteria used for ventricular tachycardia detection by current implantable cardioverter defibrillators are based on the analysis of a sequence of RR intervals and may be inappropriately satisfied by supraventricular tachyarrhythmias. Algorithms for ventricular tachycardia detection were challenged against the full RR interval sequences from 482 spontaneous episodes of atrial fibrillation and 260 spontaneous episodes of ventricular tachycardia to determine their ability to discriminate between the arrhythmias. The sensitivities and specificities of the algorithms were calculated over a wide range of programmable parameters. For a given window length and detection interval, the most stringent algorithms, that required all beats to be classified as "fast", were more specific than those allowing a proportion of "normal" intervals, even after adjustment for differing sensitivity. These differences were less marked for faster tachycardias. Specificity increased with the detection window length to a limit of approximately 18 beats. We conclude that ventricular tachycardia is detected with the highest specificity if all beats in an analyzed sequence are required to be "fast," even after lengthening of the tachycardia detection interval to maintain sensitivity. Further improvement in algorithm performance may require the incorporation of criteria such as tachycardia onset and stability.

Graphical representation of complex data--diurnal patterns of initiations of atrial fibrillation episodes

A construction of a purpose designed graphical display is demonstrated in a study investigating the circadian distribution of patterns of RR interval sequences preceding episodes of paroxysmal atrial fibrillation (PAF). Based on a comparison with a (80%, 120%) range around the median of preceding 10 RR intervals, each RR interval is classified as normal, short, or long. Classifications of RR intervals in n-tuplets (n = 1, ...,5) preceding PAF episodes are used to compute probabilities of individual types of sequences occurring within 4-hour periods of the day (between 1 am, 5 am, 9 am, 1 pm, 5 pm, and 9 pm). Graphical representation of the data is proposed using a hierarchy of bar graphs. The graphical system has been filled with data of 327 atrial fibrillation episodes recorded in 46 24-hour ECGs in PAF patients. The graphical analysis supports a link between PAF initiation and cardiac autonomic status.

Effect of digoxin on the ventricular rate variability during paroxysmal atrial fibrillation

This study investigated whether the irregularity of ventricular cycle length during atrial fibrillation (AF) is affected by digoxin. Patients (n = 41) with paroxysmal AF enrolled in a randomized crossover comparison of digoxin and placebo underwent 24-hour ambulatory monitoring during each treatment. Tapes containing AF episodes lasting at least 2 minutes were selected (24 recordings on placebo and 17 on digoxin). The mean (mRR) and standard deviation (SDRR) of RR intervals was calculated for each 30-second segment of AF. The resulting SDRR values were clustered according to bins of mRR values ranging from 350-650 ms in 25-ms steps. In each bin, the SDRR values of all placebo and all digoxin recordings were statistically compared for the top 5, 10, and 15 percentiles of each bin which represented the extremes of ventricular cycle length irregularity during AF. There were no significant differences between the total data of SDRR values in individual bins of mRR. However, the top 5, 10, and 15 percentiles of SDRR values corresponding to mRR values from 350-550 ms were significantly reduced by digoxin (P < 0.0001). The study concludes that although digoxin does not influence the mean variability of RR cycles during AF paroxysms, it suppresses episodes in which a fast ventricular response is associated with extreme variability of RR periods.