Frequency Measures Obtained from the Surface Electrocardiogram in Atrial Fibrillation Research and Clinical Decision‐Making

Relationship between dominant frequency, organization index, and left atrial size in patients with atrial fibrillation

INTRODUCTION

Frequency domain analysis is a methodology for quantifying the organization of atrial fibrillation (AF) pattern to understand the pathophysiology of the electrical mechanism. We aimed to investigate whether the dominant frequency (DF) and organization index (OI) can indicate left atrial (LA) dilatation in patients with AF.

METHODS AND RESULTS

This observational, retrospective, single-center cohort study assessed 100 patients with persistent AF. The study population was divided into two groups based on an anterior-posterior LA dimension (LAD of 50 mm) measured by transthoracic echocardiography. The groups were one-to-one propensity score-matched. Frequency domain analysis was performed using signals at leads II and V1 on surface electrocardiogram to calculate the DF and OI. In all patients, the DF was shown to have an inverse relationship with LAD (R = -.369, p < .001 in lead II; R = -.330, p = .001 in lead V1), while the OI was directly associated with LAD (R = .234, p = .190 in lead II; R = .283, p = .004 in lead V1). However, no significant relationship between the signal amplitude and LAD was observed. Compared to patients with LAD ≤ 50 mm, those with LAD > 50 mm had a lower DF (5.057 ± 0.740 vs. 4.542 ± 0.898, p = .002) and higher OI (0.261 ± 0.104 vs. 0.322 ± 0.116, p = .007) in lead V1. These findings were consistent with those found in lead II.

CONCLUSION

Patients with persistent AF and a larger LA size had a significantly higher OI and lower DF than those with a smaller LA size. Atrial electrical properties of structural remodeling are associated with increased organization of atrial signals.

Early differentiation of long-standing persistent atrial fibrillation using the characteristics of fibrillatory waves in surface ECG multi-leads

We characterized the f-waves in atrial fibrillation (AF) in the surface ECG by quantifying the amplitude, irregularity, and dominant rate of the f-waves in leads II, aVL, and V₁, and investigated whether those parameters of the f-waves could discriminate long-standing persistent AF (LPeAF) from non-LPeAF. A total of 224 AF patients were enrolled: 112 with PAF (87 males), 48 with PeAF (38 males), and 64 with LPeAF (47 males). The f-waves in surface ECG leads V₁, aVL, and II, which reflect well electrical activity in the right atrium (RA), the left atrium (LA), and both atria, respectively, were analyzed. The f-waves for LPeAF had lower amplitudes in II and aVL, increased irregularity and a higher dominant rate in II and V₁ compared to PAF and PeAF (all p < 0.02). In a multivariate analysis, a low amplitude in lead II (<34.6 uV) and high dominant rate in lead V₁ (≧390/min) (p < 0.00₁) independently discriminated LPeAF from the other AF types. The f-waves combined with both a low amplitude in lead II and high dominant rate in lead V₁ were significantly associated with LPeAF (OR 6.27, p < 0.001). Characteristics of the f-waves on the surface ECG could discriminate LPeAF from other types of AF.

Noninvasive Assessment of Atrial Fibrillation Complexity in Relation to Ablation Characteristics and Outcome

Background: The use of surface recordings to assess atrial fibrillation (AF) complexity is still limited in clinical practice. We propose a noninvasive tool to quantify AF complexity from body surface potential maps (BSPMs) that could be used to choose patients who are eligible for AF ablation and assess therapy impact.

Methods: BSPMs (mean duration: 7 ± 4 s) were recorded with a 252-lead vest in 97 persistent AF patients (80 male, 64 ± 11 years, duration 9.6 ± 10.4 months) before undergoing catheter ablation. Baseline cycle length (CL) was measured in the left atrial appendage. The procedural endpoint was AF termination. The ablation strategy impact was defined in terms of number of regions ablated, radiofrequency delivery time to achieve AF termination, and acute outcome. The atrial fibrillatory wave signal extracted from BSPMs was divided in 0.5-s consecutive segments, each projected on a 3D subspace determined through principal component analysis (PCA) in the current frame. We introduced the nondipolar component index (NDI) that quantifies the fraction of energy retained after subtracting an equivalent PCA dipolar approximation of heart electrical activity. AF complexity was assessed by the NDI averaged over the entire recording and compared to ablation strategy.

Results: AF terminated in 77 patients (79%), whose baseline AF CL was 177 ± 40 ms, whereas it was 157 ± 26 ms in patients with unsuccessful ablation outcome (p = 0.0586). Mean radiofrequency emission duration was 35 ± 21 min; 4 ± 2 regions were targeted. Long-lasting AF patients (≥12 months) exhibited higher complexity, with higher NDI values (≥12 months: 0.12 ± 0.04 vs. <12 months: 0.09 ± 0.03, p < 0.01) and short CLs (<160 ms: 0.12 ± 0.03 vs. between 160 and 180 ms: 0.10 ± 0.03 vs. >180 ms: 0.09 ± 0.03, p < 0.01). More organized AF as measured by lower NDI was associated with successful ablation outcome (termination: 0.10 ± 0.03 vs. no termination: 0.12 ± 0.04, p < 0.01), shorter procedures (<30 min: 0.09 ± 0.04 vs. ≥30 min: 0.11 ± 0.03, p < 0.001) and fewer ablation targets (<4: 0.09 ± 0.03 vs. ≥4: 0.11 ± 0.04, p < 0.01).

Conclusions: AF complexity can be noninvasively quantified by PCA in BSPMs and correlates with ablation outcome and AF pathophysiology.

P Wave Analysis in the Era of Atrial Fibrillation Ablation

The common arrhythmia atrial fibrillation (AF) is incompletely understood. The mechanism of initiation and the perpetuation of AF remain speculative. This article summarizes current knowledge of the complex relationship between arrhythmias triggering AF and their long-term effects on atrial tissue, leading to perpetuation of tachycardia. It focuses on the role of the electrocardiogram (ECG) from AF diagnosis to identification of sinus P wave abnormalities predicting future occurrences. The role of ambulatory ECG recordings in managing AF and the use of frequency analysis determining degree of organization and identification of AF triggers are discussed.

Novel non-invasive algorithm to identify the origins of re-entry and ectopic foci in the atria from 64-lead ECGs: A computational study

Atrial tachy-arrhytmias, such as atrial fibrillation (AF), are characterised by irregular electrical activity in the atria, generally associated with erratic excitation underlain by re-entrant scroll waves, fibrillatory conduction of multiple wavelets or rapid focal activity. Epidemiological studies have shown an increase in AF prevalence in the developed world associated with an ageing society, highlighting the need for effective treatment options. Catheter ablation therapy, commonly used in the treatment of AF, requires spatial information on atrial electrical excitation. The standard 12-lead electrocardiogram (ECG) provides a method for non-invasive identification of the presence of arrhythmia, due to irregularity in the ECG signal associated with atrial activation compared to sinus rhythm, but has limitations in providing specific spatial information. There is therefore a pressing need to develop novel methods to identify and locate the origin of arrhythmic excitation. Invasive methods provide direct information on atrial activity, but may induce clinical complications. Non-invasive methods avoid such complications, but their development presents a greater challenge due to the non-direct nature of monitoring. Algorithms based on the ECG signals in multiple leads (e.g. a 64-lead vest) may provide a viable approach. In this study, we used a biophysically detailed model of the human atria and torso to investigate the correlation between the morphology of the ECG signals from a 64-lead vest and the location of the origin of rapid atrial excitation arising from rapid focal activity and/or re-entrant scroll waves. A focus-location algorithm was then constructed from this correlation. The algorithm had success rates of 93% and 76% for correctly identifying the origin of focal and re-entrant excitation with a spatial resolution of 40 mm, respectively. The general approach allows its application to any multi-lead ECG system. This represents a significant extension to our previously developed algorithms to predict the AF origins in association with focal activities.

Atrial tachy-arrhythmias are associated with irregular excitation waves arising from re-entrant excitation, multiple wavelets or rapid focal activity. Identifying the origin of the irregular activity may be vital for diagnosis and treatment of the disorder. Where invasive and non-invasive methods provide approaches for such identification, both have associated disadvantages. In this study, we used a biophysically detailed model of the human atria and torso to develop an algorithm based on the correlation between the electrocardiogram (ECG) signal from a 64-lead vest and the location of rapid focal and re-entrant excitation. Using the properties of the atrial activation and the ECG signals, we developed a focus-location algorithm which is able to distinguish rapid focal activity from re-entrant scroll waves centred in the same location. Based on simulated data, the algorithm had success rates of 93% and 76% for correctly identifying the origin of focal and re-entrant excitation, respectively, and 88% for distinguish focal and re-entrant excitation, with no false positives. Inherited from our previous algorithm, it is also easily generalizable to any multi-lead ECG system.

Developing time-frequency features for prediction of the recurrence of atrial fibrillation after electrical cardioversion therapy

External electrical cardioversion has been used as a therapeutic option to terminate atrial fibrillation (AF) and restore sinus rhythm (SR). However, identifying patients who would benefit from this therapy is still an active area of research. In this study, we develop new time-frequency features to characterize the atrial activity (AA) and to predict the success of electrical cardioversion therapy by identifying the AF patients who will maintain SR in the long term. New features are extracted from the surface AA using a matching pursuit (MP) decomposition with various combinations of wavelet families. The performance of the features is validated using a dataset of AF patients who underwent electrical cardioversion therapy. Results indicate that the developed features are significantly (p-value <; 0.05) correlated with SR maintenance which suggests that the MP decomposition captures detailed morphological information of AA that may potentially be used to guide the therapy of AF patients.

Developing a New Computer-Aided Clinical Decision Support System for Prediction of Successful Postcardioversion Patients with Persistent Atrial Fibrillation

We propose a new algorithm to predict the outcome of direct-current electric (DCE) cardioversion for atrial fibrillation (AF) patients. AF is the most common cardiac arrhythmia and DCE cardioversion is a noninvasive treatment to end AF and return the patient to sinus rhythm (SR). Unfortunately, there is a high risk of AF recurrence in persistent AF patients; hence clinically it is important to predict the DCE outcome in order to avoid the procedure's side effects. This study develops a feature extraction and classification framework to predict AF recurrence patients from the underlying structure of atrial activity (AA). A multiresolution signal decomposition technique, based on matching pursuit (MP), was used to project the AA over a dictionary of wavelets. Seven novel features were derived from the decompositions and were employed in a quadratic discrimination analysis classification to predict the success of post-DCE cardioversion in 40 patients with persistent AF. The proposed algorithm achieved 100% sensitivity and 95% specificity, indicating that the proposed computational approach captures detailed structural information about the underlying AA and could provide reliable information for effective management of AF.

Association between atrial fibrillatory rate and heart rate variability in patients with atrial fibrillation and congestive heart failure

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 II-III) 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.

Analysis of atrial fibrillatory rate during spontaneous episodes of atrial fibrillation in humans using implantable loop recorder electrocardiogram

Atrial fibrillatory rate (AFR) can predict outcome of interventions for atrial fibrillation (AF); however, AFR behavior at AF onset in humans is poorly described. We studied AFR during spontaneous AF episodes in patients with lone paroxysmal AF who received implantable loop recorders and had AF episodes of 1 hour or more recorded (n = 4). Mean AFR per minute was assessed from continuous implantable loop recorder electrocardiogram using spatiotemporal QRST cancellation and time-frequency analysis. Atrial fibrillatory rate increased from 290 ± 20 to 326 ± 39 fibrillations per minute during the first 3 hours (P<.05) and reached plateau then. Atrial fibrillatory rate beyond the initial 3 hours can, therefore, be considered stable and may be evaluated for prediction of intervention effect.

Noninvasive time and frequency predictors of long-standing atrial fibrillation early recurrence after electrical cardioversion

BACKGROUND

Several clinical factors have been studied to predict atrial fibrillation (AF) recurrence after electrical cardioversion (ECV) with limited predictive value.

METHODS

 A method able to predict robustly long-standing AF early recurrence by characterizing noninvasively the electrical atrial activity (AA) with parameters related to its time course and spectral features is presented. To this respect, 63 patients (20 men and 43 women; mean age 73.4 ± 9.0 years; under antiarrhythmic drug treatment with amiodarone) who were referred for ECV of persistent AF were studied. During a 4-week follow-up, AF recurrence was observed in 41 patients (65.1%).

RESULTS

 RR variability and the studied AA spectral features, including dominant atrial frequency (DAF), its first harmonic and their amplitude, provided poor statistical differences between groups. On the contrary, f waves power (fWP) and Sample Entropy (SampEn) of the AA behaved as very good predictors. Patients who relapsed to AF presented lower fWP (0.036 ± 0.019 vs 0.081 ± 0.029 n.u.(2) , P < 0.001) and higher SampEn (0.107 ± 0.022 vs 0.086 ± 0.033, P < 0.01). Furthermore, fWP presented the highest predictive accuracy of 82.5%, whereas SampEn provided a 79.4%. The remaining features revealed accuracies lower than 70%. A stepwise discriminant analysis (SDA) provided a model based on fWP and SampEn with 90.5% of accuracy.

CONCLUSIONS

 The fWP has proved to predict long-standing AF early recurrence after ECV and can be combined with SampEn to improve its diagnostic ability. Furthermore, a thorough analysis of the results allowed outlining possible associations between these two features and the concomitant status of atrial remodeling.

Frequency analysis of atrial fibrillation surface and intracardiac electrograms during pulmonary vein isolation

AIMS

Frequency analysis of atrial electrograms from patients diagnosed with persistent atrial fibrillation (AF) appears to be crucial in its clinical diagnosis. This work explores the fibrillatory frequency properties of both surface and intracardiac electrograms before and after pulmonary vein isolation (PVI) using three time-frequency techniques.

METHODS AND RESULTS

Surface electrocardiograms (ECGs) of 21 patients diagnosed with persistent AF undergoing PVI were recorded. Three methods, Fourier, ensemble average, and wavelet analysis, were used to identify the dominant frequency (DF) in surface ECGs. Dominant frequency was also computed in electrograms recorded within the coronary sinus (CS). Dominant frequency measured within the CS was best estimated in surface lead V1 using both Fourier (relative error: 10.94 ± 10.37%, correlation: 0.58) and wavelet analysis (relative error: 10.97 ± 11.08%, correlation: 0.53). Ensemble average gave highest relative error (21.29 ± 18.07%) and lowest correlation (0.10). Dominant frequency decreased after right PVI. This decrease was significant (P< 0.05) in most of the patients (13, 14, and 7 out of 14 when Fourier, wavelets, and ensemble average was used; 14 in CS). Further isolation of the left pulmonary veins (PVs) yielded a significant (P< 0.05) decrease in only a few of them (3, 4, and 2 out of 14 when Fourier, wavelets, and ensemble average was used; 4 in CS).

CONCLUSION

Wavelet and Fourier analysis are good tools for estimating the atrial fibrillatory rate from surface ECG. A drop was observed in the DF value after isolation of the right PV. However, after left PVI this decrease was smaller.

Atrial fibrillation disorganization is reduced by catheter ablation: a standard ECG study

Selection of candidates to catheter ablation (CA) of long-lasting persistent atrial fibrillation (AF) is challenging, since success is not guaranteed. In this study, we put forward an automated method for noninvasively evaluating the reduction of the complexity of the AF organization following CA. Complexity is meant as the amount of disorganization observed on the ECG, supposed to be directly correlated to the number and interactions of atrial wavefronts. By means of PCA, the complexity of the AF organization is evaluated quantitatively from a 12-lead ECG recording. Preliminary results show that CA is able to reduce the complexity of AF organization in the atrial wavefront pattern propagation, despite the persistence of AF in most cases. This can be viewed as a first clinical validation of this parameter. Whether AF complexity and its reduction by CA are predictive of long-term outcome is thus still to be determined.

Use of frequency analysis on the ECG for the prognosis of low energy cardioversion treatment of atrial fibrillation

Electric cardioversion is the most effective therapy for restoring sinus rhythm in patient with atrial fibrillation (AF), however, there is not a guiding criteria for advising on when and in whom it will be successful. The objective of this study was to employ frequency analysis on the surface electrocardiogram (ECG) to predict the outcome of low energy internal cardioversion in patients with AF. Thirty nine patients with AF, for elective DC cardioversion were included in this study. One catheter was positioned in the right atrial appendage and another in the coronary sinus. A voltage step-up protocol (50-300 V) was used for patient cardioversion. Prior to shock delivery, residual atrial activity signal (RAAS) was derived from 60 seconds of surface ECG from defibrillator pads, by bandpass filtering and ventricular activity (QRST) cancellation. Dominant atrial fibrillatory frequency (DAFF) was estimated from the RAAS power spectrum as the dominant frequency within the 3-12 Hz band. DAFF was calculated from whole 60 seconds segment (DAFF_L) and from the finals 10 seconds segment (DAFF_S) of the RAAS. Lower DAFF_L and DAFF_S were found in successfully cardioverted patients than in those nonsuccessful ones, with energy < or =3 and < or =6 joules. Therapy result (employing 3J or less) was predicted in 35/39 (89.7%) patients with DAFF_L=5.40Hz, and DAFF_L was > or =5.75Hz in a 100% of noncardioverted patients. In conclusion, frequency analysis of the RAAS could be useful for predicting success of low energy internal cardioversion of patients with atrial fibrillation.

Time and frequency recurrence analysis of persistent atrial fibrillation after electrical cardioversion

Electrical cardioversion (ECV) has become a mainstay of therapy for the treatment of persistent atrial fibrillation (AF), which is an arrhythmia that affects up to 1% of the general population. The procedure is initially effective, but it is also characterized by a high rate of AF recurrence. As a consequence, it would be clinically useful to predict normal sinus rhythm (NSR) maintenance after ECV before it is attempted. In this respect, several clinical, echocardiographic and demographic parameters have been analyzed by other authors. However, these indices are weak predictors of ECV outcome. In this work, surface electrocardiographic (ECG) recordings were used to extract the atrial activity (AA) signal and parametrize the fibrillatory (f) waves, both in time and frequency, to obtain AF recurrence predictors. Parameters as f waves amplitude (fWA), AA mean power, dominant atrial frequency (DAF), its first harmonic, etc were studied. Obtained results showed that fWA was the most significant predictor of AF recurrence 1 month later. Concretely, 72.73% of the patients resulting in NSR, 83.87% relapsing to AF and 80.0% with unsuccessful ECV, were correctly identified. Therefore, fWA classified satisfactorily 79.37% of the analyzed patients. In addition, a forward stepwise discriminant analysis, with a leave-one-out cross validation approach, proved that fWA and DAF combination provided an improved diagnostic ability of 85.71%. In this case 86.36%, 83.87% and 90% of the patients who resulted in NSR, relapsed to AF and with unsuccessful ECV, were correctly discerned, respectively. In conclusion, fWA could be considered as a promising predictor of ECV outcome during the first month following the procedure. Additionally, time and frequency indices could yield complementary information useful to predict the cardioversion outcome. Finally, further studies are needed to validate the robustness of these parameters and the repeatability of the obtained results on wider databases.

Study of surface electrocardiogram spectrum before and after pulmonary vein ablation in patients with persistent atrial fibrillation

Atrial fibrillation (AF) is the most common clinical cardiac arrhythmia and is usually treated with the electrical isolation of the pulmonary veins from the atria. However, it is estimated that about 30% of the patients undergoing this therapy will develop AF again. The purpose of this study was to test the dynamic changes of the spectra calculated in surface electrocardiograms (ECGs) before and after the ablation of the pulmonary veins. Surface ECGs of 14 patients with persistent AF undergoing this intervention were considered for this study. The QRS-T waves were subtracted from the ECGs using common spatial pattern, isolating the electrical activity of the atrium. The spectrum was then calculated and the main frequency peaks were identified. The smaller peaks with amplitude below 50% of the maximum were discarded. Eleven of the patients were followed up after the intervention for 1 to 6 months. Two of the patients developed AF again; the other 9 remained in sinus rhythm. For most of the patients, the spectrum showed more order after the intervention. However, the main frequency did not experience a significant decrease in average (5.1 Hz [+/-1.3] to 4.9 Hz [+/-1.0]). Interestingly, the increment or decrease of the main frequency did not correlate with the recurrence of AF or not.

Atrial fibrillatory rate and risk of left atrial thrombus in atrial fibrillation

AIMS

In atrial fibrillation (AF), a relation between electrocardiogram (ECG) fibrillatory wave amplitude and thrombus formation has been sought for long with conflicting results. In contrast, the possible relation between atrial fibrillatory rate obtained from the surface ECG and left atrial thrombus formation in patients with AF is unknown and was consequently evaluated in this study.

METHODS AND RESULTS

One-hundred and twenty-five patients (mean age 64 +/- 12 years, 72% male) with persistent non-valvular AF (mean duration 28 +/- 80 days) undergoing transesophageal echocardiography were studied. In all patients, standard 12-lead ECG recordings were acquired before the examination. Atrial fibrillatory rate was determined using spatiotemporal QRST cancellation and time-frequency analysis of lead V1. Atrial fibrillatory rate measured 401 +/- 63 fibrillations per minute (fpm, range 235-566 fpm) and was related with age (R = -0.326, P < 0.001), ventricular rate (R = -0.202, P = 0.024), gender (407 +/- 62 in males vs. 387 +/- 64 fpm in females, P = 0.038) but not AF duration (R = 0.088, P = 0.374), presence of lone AF (408 +/- 66 vs. 394 +/- 58 fpm, P = 0.228), or beta-blocker or calcium channel blocker treatment (398 +/- 63 vs. 405 +/- 62 fpm, P = 0.556). Age was the only independent predictor of fibrillatory rate (B = -1.714, P < 0.001). In patients with left atrial thrombus (n = 10), spontaneous echo contrast (SEC) was more frequently present (70 vs. 29 %, p = 0.007) and left atrial appendage (LAA) outflow velocity was lower (26 +/- 20 vs. 37 +/- 15 cm/s, P = 0.012) than in patients without thrombus (n = 115). In contrast, mean fibrillatory rate, which showed a weak inverse correlation with LAA velocity (R = -0.118, P = 0.048) was not different between both groups (380 +/- 56 vs. 403 +/- 63 fpm, P = 0.226). Similarly, presence of thrombus and SEC combined was not related with fibrillatory rate.

CONCLUSION

Atrial fibrillatory rate obtained from surface ECG lead V1 is not a risk marker for left atrial thrombus formation in AF.

Electrocardiographic characteristics of fibrillatory waves in new-onset atrial fibrillation

AIMS

In atrial fibrillation (AF), fibrillatory waves of surface electrocardiograms (ECG) vary among patients with respect to waveform and repetition rate. The purpose of this study was to (i) explore clinical determinants of new-onset AF and (ii) determine prognostic significance to predict initial treatment outcome of electrocardiographic fibrillatory wave characteristics in new-onset AF.

METHODS AND RESULTS

Twenty-five patients (15 male, mean age 69 +/- 16 years) with new-onset AF (median AF duration 8 days) were studied. Fibrillatory rate and exponential decay defined as decay of the curve that connects power maxima of dominant and harmonic frequency components were obtained by spatiotemporal QRST cancellation and time-frequency analysis of the index ECG (before treatment initiation). Baseline AF rate was 380 +/- 50 fibrillations per minute (fpm) (range 222-494); patients' age (beta = - 1.747, P = 0.003) and AF duration (beta = 0.726, P = 0.036) were independently related with fibrillatory rate. AF terminated within 24 h in seven patients, while it was persistent in the other 18 patients. Terminating AF had lower atrial rate (333 +/- 66 vs. 398 +/- 40 fpm, P = 0.005) and exponential decay (1.03 +/- 0.36 vs. 1.40 +/- 0.37, P = 0.041) than persisting AF. Multivariate analysis revealed fibrillatory rate to be the only independent predictor of AF termination or persistence (beta = 0.031, P = 0.031). Sensitivity and specificity for predicting AF termination were strongly related to fibrillatory rate (area under the curve = 0.817). Sensitivity and specificity were 89% and 71% for a fibrillatory rate of 355 fpm.

CONCLUSIONS

Fibrillatory rates vary substantially among patients to new-onset AF and are related to patients' age and AF duration. Lower fibrillatory rates indicate higher chances of spontaneous AF termination within 24 h.

Validation and clinical application of time-frequency analysis of atrial fibrillation electrocardiograms

INTRODUCTION

Fibrillatory rates can reliably be obtained from surface ECGs during atrial fibrillation (AF) and correspond with right atrial (RA) and coronary sinus (CS) rates, while both the relation with pulmonary venous (PV) rates and determinants of fibrillatory waveform are unknown. Class III antiarrhythmic drugs prolong atrial refractoriness and decrease its dispersion, effects that may be reflected in ECG parameters. Consequently, this study sought (1) to investigate the relation between ECG fibrillatory rate and waveform characteristics with intraatrial/PV fibrillatory activity and (2) to noninvasively monitor class III antiarrhythmic drug effects in patients with AF.

METHODS AND RESULTS

Thirty-six patients with drug-refractory AF who underwent catheter-based pulmonary vein isolation and had AF at the beginning of the procedure were studied. A positive correlation between V1 rates obtained by time-frequency analysis and RA (R = 0.97, P < 0.001), CS (R = .71, P < 0.001), and PV rates (R = 0.65, P = 0.001) was found. Exponential decay defined as decay of the curve that connects power maxima of dominant and harmonic frequency components correlated with RA rate dispersion (R = 0.53, P = 0.004). In amiodarone-treated patients (n = 7), V1 rate (286 +/- 64 vs. 371 +/- 40 fpm, P < 0.001) and exponential decay (1.06 +/- 0.29 vs. 1.38 +/- 0.38, P = 0.034) were lower than in patients without amiodarone (n = 29). In 19 additional patients with persistent AF, oral dofetilide treatment decreased mean fibrillatory rate from 377 +/- 57 to 294 +/- 50 fpm (P < 0.001) and exponential decay from 1.24 +/- 0.43 to 0.85 +/- 0.22 (P = 0.002).

CONCLUSIONS

Fibrillatory waves of surface ECG lead V1 closely reflect right atrial, and, to a lesser degree, left atrial activity. Time-frequency analysis allows noninvasive monitoring of antiarrhythmic drug effects on fibrillatory rate and waveform.

Electroatriography – Time-frequency analysis of atrial fibrillation from modified 12-lead ECG configurations for improved diagnosis and therapy

Current atrial fibrillation (AF) management guidelines suggest that initially a decision must be made to apply either a rate control or rhythm control strategy in the individual patient. However, patients' selection remains substantially empirical and the strategy initially chosen often proves unsuccessful and alternative therapies must be adopted. Thus, it seems desirable to develop and apply tests that quantify AF disease state and guide AF management. The overall hypothesis of this paper is that time-frequency analysis of AF from modified 12-lead ECG configurations will improve AF management beyond current diagnostic and therapeutic standards. In particular, we present a novel concept in which 12-lead ECG configurations are modified for time-frequency analysis of AF (electroatriography). While five electrodes (VR, VL, VF, V1, V2) are placed in the conventional position, the other four electrodes (V3, V4, V5, V6) are empirically repositioned anterior or posterior over the atria. By applying spatiotemporal QRST cancellation and time-frequency analysis to these recordings in 19 patients with persistent AF, fibrillatory rate dispersion among individual anterior (25+/-14 fibrillations per minute, fpm) and posterior leads (16+/-11fpm) as well as individual anterior/posterior rate gradients ranging between -24 and +116fpm could be identified. Consequently, the portrayed techniques may form the conceptual basis for individualized noninvasive characterization of AF. Initiation of further studies using the described techniques in different AF subsets, for comparisons with intracardiac recordings and outcome of different therapies, e.g. cardioversion, antiarrhythmic drug and ablation therapy may be stimulated.

Analysis of surface electrocardiograms in atrial fibrillation: techniques, research, and clinical applications

Atrial fibrillation (AF) is the most common arrhythmia encountered in clinical practice. Neither the natural history of AF nor its response to therapy is sufficiently predictable by clinical and echocardiographic parameters. The purpose of this article is to describe technical aspects of novel electrocardiogram (ECG) analysis techniques and to present research and clinical applications of these methods for characterization of both the fibrillatory process and the ventricular response during AF. Atrial fibrillatory frequency (or rate) can reliably be assessed from the surface ECG using digital signal processing (extraction of atrial signals and spectral analysis). This measurement shows large inter-individual variability and correlates well with intra-atrial cycle length, a parameter which appears to have primary importance in AF maintenance and response to therapy. AF with a low fibrillatory rate is more likely to terminate spontaneously and responds better to antiarrhythmic drugs or cardioversion, whereas high-rate AF is more often persistent and refractory to therapy. Ventricular responses during AF can be characterized by a variety of methods, which include analysis of heart rate variability, RR-interval histograms, Lorenz plots, and non-linear dynamics. These methods have all shown a certain degree of usefulness, either in scientific explorations of atrioventricular (AV) nodal function or in selected clinical questions such as predicting response to drugs, cardioversion, or AV nodal modification. The role of the autonomic nervous system for AF sustenance and termination, as well as for ventricular rate responses, can be explored by different ECG analysis methods. In conclusion, non-invasive characterization of atrial fibrillatory activity and ventricular response can be performed from the surface ECG in AF patients. Different signal processing techniques have been suggested for identification of underlying AF pathomechanisms and prediction of therapy efficacy.

Electrophysiological and antiarrhythmic effects of the novel antiarrhythmic agent AZD7009: a comparison with azimilide and AVE0118 in the acutely dilated right atrium of the rabbit in vitro

AIMS

To compare the electrophysiological and antiarrhythmic effects of AZD7009, azimilide, and AVE0118 in the acutely dilated rabbit atria in vitro.

METHODS AND RESULTS

In the isolated Langendorf-perfused rabbit heart, the atrial effective refractory period (AERP) and the inducibility of atrial fibrillation (AF) were measured at increasing concentrations of AZD7009 (0.1-3 microM), azimilide (0.1-3 microM), and AVE0118 (0.3-10 microM). In separate groups of atria, termination of sustained AF was assessed. In non-dilated atria, the AERP was 82+/-1.3 ms (mean+/-SEM) and AF could not be induced. Dilation significantly reduced the AERP to 49+/-1.0 ms (P<0.001) and 92% of the atria became inducible. Perfusion with AZD7009, azimilide, and AVE0118 concentration-dependently increased the AERP and reduced the AF inducibility. At the highest concentrations of AZD7009, azimilide, and AVE0118, AERP and AF inducibility changed from 50+/-4.5 to 136+/-6.6 ms and 80 to 0% (both P<0.001) from 51+/-3.0 to 105+/-9.9 ms (P<0.001) and 80 to 0% (P<0.01) and from 46+/-2.8 to 85+/-6.0 ms and 90 to 0% (both P<0.001). Restoration of sinus rhythm was seen in 6/6, 5/6, and 5/6 hearts perfused with AZD7009, azimilide, and AVE0118, respectively.

CONCLUSION

In the dilated rabbit atria, AZD7009, azimilide, and AVE0118 concentration-dependently increased AERP, effectively prevented AF induction, and rapidly restored sinus rhythm.

Pilot study: Noninvasive monitoring of oral flecainide's effects on atrial electrophysiology during persistent human atrial fibrillation using the surface electrocardiogram

BACKGROUND

The relation between flecainide's plasma level and its influence on human atrial electrophysiology during acute and maintenance therapy of atrial fibrillation (AF) is unknown. Therefore, this study determined flecainide plasma levels and atrial fibrillatory rate obtained from the surface ECG during initiation and early maintenance of oral flecainide in patients with persistent lone AF and assessed their relationship.

METHODS AND RESULTS

In 10 patients (5 males, mean age 63 +/- 14 years, left atrial diameter 46 +/- 3 mm) with persistent lone AF, flecainide was administered as a single oral bolus (day 1) followed by 200-400 mg/day (days 2-5). The initial 300 mg flecainide bolus resulted in therapeutic plasma levels in all patients (range 288-629 ng/ml) with no side effects. Flecainide plasma levels increased on day 3 and remained stable thereafter. Day 5 plasma levels were lower (508 +/- 135 vs 974 +/- 276 ng/ml, P = 0.009) in patients with daily mean flecainide doses of 200 mg compared to patients with higher maintenance doses. Fibrillatory rate obtained from the surface electrocardiogram measuring 378 +/- 17 fpm at baseline was reduced to 270 +/- 18 fpm (P < 0.001) after the flecainide bolus but remained stable thereafter. Fibrillatory rate reduction was independent of flecainide plasma levels or clinical variables.

CONCLUSION

A 300 mg oral flecainide bolus is associated with electrophysiologic effects that are not increased during early maintenance therapy in persistent human lone AF. In contrast to drug plasma levels, serial analysis of fibrillatory rate allows monitoring of individual drug effects on atrial electrophysiology.

Analysis of the surface electrocardiogram for monitoring and predicting antiarrhythmic drug effects in atrial fibrillation

Specific antiarrhythmic therapy with class I and III drugs for atrial fibrillation (AF) conversion and prevention of its recurrence is frequently utilized in clinical practice. Besides being only moderate effective, the utilization of antiarrhythmic drugs may be associated with serious side effects. In the clinical setting it is difficult to directly evaluate the effects of antiarrhythmic drugs on the individual patient's atrial electrophysiology, thereby predicting their efficacy in restoring and maintaining sinus rhythm. Analysis of the surface electrocardiogram in terms of P-wave signal averaged ECG during sinus rhythm and spectral characterization of fibrillatory waves during AF for evaluation of atrial antiarrhythmic drug effects is a new field of investigation. Both techniques provide reproducible parameters for characterizing atrial electrical abnormalities and seem to contain prognostic information regarding antiarrhythmic drug efficacy. Further research is needed which elucidates the most challenging clinical questions in AF management whom to place on antiarrhythmic drug treatment and what antiarrhythmic drug to prescribe. Analysis of the surface ECG might have the potential to answer these questions.

Drug-induced changes in fibrillation cycle length and organization index can predict chemical cardioversion of long-lasting atrial fibrillation with bepridil alone or in combination with aprindine

BACKGROUND

The aim of this study was to investigate whether drug-induced changes in fibrillation wave characteristics can predict pharmacological conversion of long lasting persistent atrial fibrillation (AF).

METHODS AND RESULTS

The study group comprised 23 consecutive patients with AF lasting > or =1 month. Patients first received bepridil (200 mg/day) for 2-4 weeks. When sinus rhythm was not restored with bepridil, oral aprindine (40 or 60 mg/day) was added to bepridil. Fast Fourier transform analysis of fibrillation waves using lead V1 was performed to calculate the fibrillation cycle length (FCL). The spectral areas were measured and the maximum area divided by the total area was termed the fibrillation organization index (FOI). Sinus rhythm was restored in 16 of 23 patients (70%); 8 of these 16 patients received only bepridil (Group I) and the other 8 responders received bepridil and aprindine (Group II). In Group I bepridil increased both FCL (p<0.001) and FOI (p<0.01) and terminated AF after 20+/-12 days. In Group II bepridil increased FCL (p<0.001), but did not change FOI. The addition of aprindine terminated AF in association with an increase in both FCL (p<0.005) and FOI (p<0.005) within 19+/-8 days. In the remaining 7 patients who did not have restoration of sinus rhythm, bepridil increased both FCL and FOI significantly, but less than in Group I, and the addition of aprindine did not further increase either of them. Chemical cardioversion of AF occurred in all patients with FCL > or =190 ms and FOI > or =45% after drug administration.

CONCLUSION

Bepridil alone or in combination with aprindine converted long lasting persistent AF in association with an increase in both FCL and FOI. The combination of FCL and FOI after drug administration is helpful in predicting chemical cardioversion of persistent AF.

Time-frequency analysis of the surface electrocardiogram for monitoring antiarrhythmic drug effects in atrial fibrillation

This study explored time-frequency analysis of surface electrocardiograms in patients with persistent atrial fibrillation for monitoring atrial drug action. Drug loading over 3 days with oral flecainide (n = 13) or amiodarone (n = 17) organized the fibrillatory process expressed by decreased atrial fibrillatory rate, increased rate stability, and decreased exponential decay. Effects were more pronounced with flecainide than with amiodarone.

Echocardiographic and electrocardiographic predictors for atrial fibrillation recurrence following cardioversion

INTRODUCTION

Identification of suitable candidates for cardioversion currently is not based on individual electrical and mechanical atrial remodeling. Therefore, this study analyzed the meaning of atrial fibrillatory rate obtained from the surface ECG (as a measure of electrical remodeling) and left atrial size (as measure of mechanical remodeling) for prediction of early atrial fibrillation (AF) recurrence following cardioversion.

METHODS AND RESULTS

Forty-four consecutive patients (26 men and 18 women, mean age 62 +/- 11 years, no antiarrhythmic medication at baseline) with persistent AF were studied. Fibrillatory rate was obtained from high-gain, high-resolution surface ECG using digital signal processing (filtering, QRST subtraction, Fourier analysis) before electrical cardioversion. Univariate and multivariate regression analysis revealed larger systolic left atrial area (Beta = 0.176, P = 0.031) obtained by precardioversion echocardiogram from the apical four-chamber view and higher atrial fibrillatory rate (Beta = 0.029, P = 0.021) to be independent predictors for AF recurrence (n = 13). Stratification based on the regression equation (electromechanical index [EMI] = 0.176 systolic left atrial area + 0.029 fibrillatory rate - 17.674) allowed identification of groups at low, intermediate, or high risk. No patient with an EMI < -1.85 had early AF recurrence, as opposed to 78% with an EMI > -0.25. Intermediate results (40% recurrence rate) were obtained when the calculated EMI ranged between -1.85 and -0.25 (P < 0.001).

CONCLUSION

Fibrillatory rate obtained from the surface ECG and systolic left atrial area obtained by echocardiography may predict early AF recurrence in patients with persistent AF. These parameters might be useful in identifying candidates with a high likelihood of remaining in sinus rhythm after cardioversion.