Relationship between local atrial fibrillation interval and refractory period in the isolated canine atrium

Machine learning based potentiating impacts of 12-lead ECG for classifying paroxysmal versus non-paroxysmal atrial fibrillation

Background

Conventional modality requires several days observation by Holter monitor to differentiate atrial fibrillation (AF) between Paroxysmal atrial fibrillation (PAF) and Non-paroxysmal atrial fibrillation (Non-PAF). Rapid and practical differentiating approach is needed.

Objective

To develop a machine learning model that observes 10-s of standard 12-lead electrocardiograph (ECG) for real-time classification of AF between PAF versus Non-PAF.

Methods

In this multicenter, retrospective cohort study, the model training and cross-validation was performed on a dataset consisting of 741 patients enrolled from Severance Hospital, South Korea. For cross-institutional validation, the trained model was applied to an independent data set of 600 patients enrolled from Ewha University Hospital, South Korea. Lasso regression was applied to develop the model.

Results

In the primary analysis, the Area Under the Receiver Operating Characteristic Curve (AUC) on the test set for the model that predicted AF subtype only using ECG was 0.72 (95% CI 0.65–0.80). In the secondary analysis, AUC only using baseline characteristics was 0.53 (95% CI 0.45–0.61), while the model that employed both baseline characteristics and ECG parameters was 0.72 (95% CI 0.65–0.80). Moreover, the model that incorporated baseline characteristics, ECG, and Echocardiographic parameters achieved an AUC of 0.76 (95% CI 0.678–0.855) on the test set.

Conclusions

Our machine learning model using ECG has potential for automatic differentiation of AF between PAF versus Non-PAF achieving high accuracy. The inclusion of  Echocardiographic parameters further increases model performance. Further studies are needed to clarify the next steps towards clinical translation of the proposed algorithm.

Exploring Refractoriness as an Adjunctive Electrical Biomarker for Staging of Atrial Fibrillation

Patients diagnosed with the same subtype of atrial fibrillation according to our current classification system may differ in symptom severity, severity of the arrhythmogenic substrate, and response to antiarrhythmic therapy. Hence, there is a need for an electrical biomarker as an indicator of the arrhythmogenic substrate underlying atrial fibrillation enabling patient‐tailored therapy. The aim of this review is to investigate whether atrial refractoriness, a well‐known electrophysiological parameter that is affected by electrical remodeling, can be used as an electrical biomarker of the arrhythmogenic substrate underlying atrial fibrillation. We discuss methodologies of atrial effective refractory period assessment, identify which changes in refractoriness‐related parameters reflect different degrees of electrical remodeling, and explore whether these parameters can be used to predict clinical outcomes.

Comprehensive evaluation of electrophysiological and 3D structural features of human atrial myocardium with insights on atrial fibrillation maintenance mechanisms

Atrial fibrillation (AF) occurrence and maintenance is associated with progressive remodeling of electrophysiological (repolarization and conduction) and 3D structural (fibrosis, fiber orientations, and wall thickness) features of the human atria. Significant diversity in AF etiology leads to heterogeneous arrhythmogenic electrophysiological and structural substrates within the 3D structure of the human atria. Since current clinical methods have yet to fully resolve the patient-specific arrhythmogenic substrates, mechanism-based AF treatments remain underdeveloped. Here, we review current knowledge from in-vivo, ex-vivo, and in-vitro human heart studies, and discuss how these studies may provide new insights on the synergy of atrial electrophysiological and 3D structural features in AF maintenance. In-vitro studies on surgically acquired human atrial samples provide a great opportunity to study a wide spectrum of AF pathology, including functional changes in single-cell action potentials, ion channels, and gene/protein expression. However, limited size of the samples prevents evaluation of heterogeneous AF substrates and reentrant mechanisms. In contrast, coronary-perfused ex-vivo human hearts can be studied with state-of-the-art functional and structural technologies, such as high-resolution near-infrared optical mapping and contrast-enhanced MRI. These imaging modalities can resolve atrial arrhythmogenic substrates and their role in reentrant mechanisms maintaining AF and validate clinical approaches. Nonetheless, longitudinal studies are not feasible in explanted human hearts. As no approach is perfect, we suggest that combining the strengths of direct human atrial studies with high fidelity approaches available in the laboratory and in realistic patient-specific computer models would elucidate deeper knowledge of AF mechanisms. We propose that a comprehensive translational pipeline from ex-vivo human heart studies to longitudinal clinically relevant AF animal studies and finally to clinical trials is necessary to identify patient-specific arrhythmogenic substrates and develop novel AF treatments.

Unsupervised Classification of Atrial Electrograms for Electroanatomic Mapping of Human Persistent Atrial Fibrillation

OBJECTIVE

Ablation treatment for persistent atrial fibrillation (persAF) remains challenging due to the absence of a 'ground truth' for atrial substrate characterization and the presence of multiple mechanisms driving the arrhythmia. We implemented an unsupervised classification to identify clusters of atrial electrograms (AEGs) with similar patterns, which were then validated by AEG-derived markers.

METHODS

956 bipolar AEGs were collected from 11 persAF patients. CARTO variables (Biosense Webster; ICL, ACI and SCI) were used to create a 3D space, and subsequently used to perform an unsupervised classification with k-means. The characteristics of the identified groups were investigated using nine AEG-derived markers: sample entropy (SampEn), dominant frequency, organization index (OI), determinism, laminarity, recurrence rate (RR), peak-to-peak (PP) amplitude, cycle length (CL), and wave similarity (WS).

RESULTS

Five AEG classes with distinct characteristics were identified (F = 582, P<0.0001). The presence of fractionation increased from class 1 to 5, as reflected by the nine markers. Class 1 (25%) included organized AEGs with high WS, determinism, laminarity, and RR, and low SampEn. Class 5 (20%) comprised fractionated AEGs with in low WS, OI, determinism, laminarity, and RR, and in high SampEn. Classes 2 (12%), 3 (13%) and 4 (30%) suggested different degrees of AEG organization.

CONCLUSIONS

Our results expand and reinterpret the criteria used for automated AEG classification. The nine markers highlighted electrophysiological differences among the five classes found by the k-means, which could provide a more complete characterization of persAF substrate during ablation target identification in future clinical studies.

The impact of the dominant frequency of body surface electrocardiography in patients with persistent atrial fibrillation

The dominant frequency (DF) of atrial fibrillation (AF) reflects atrial electrical activity. However, the relationship between DF measured using surface electrocardiography (ECG) and AF ablation success remains unclear. This study aimed to clarify whether the DF of surface ECG in patients with persistent AF could predict arrhythmia recurrence after catheter ablation. We investigated 125 patients with persistent AF who underwent catheter ablation between January 2009 and December 2016. Thirty-four patients (27%) had arrhythmia recurrence after catheter ablation. These patients showed a significantly high DF value in leads aVL (7.2 ± 0.7 Hz vs 6.6 ± 0.9 Hz, p < 0.001) and V1 (7.4 ± 0.8 Hz vs 6.7 ± 0.7 Hz, p < 0.001). We set the cutoff value of DF as 6.9 Hz in lead aVL (sensitivity, 80%; specificity, 63%) and as 7.1 Hz in lead V1 (sensitivity, 72%; specificity, 67%). Patients with DF < 6.9 Hz in lead aVL showed a significantly higher recurrence-free rate than those with DF ≥ 6.9 Hz (88% vs 45%; p < 0.001). Patients with DF of < 7.1 Hz in lead V1 showed a significantly higher recurrence-free rate than those with DF of  ≥ 7.1 (87% vs 47%; p < 0.001). Patients with a high DF in leads aVL and V1 showed a lower success rate of persistent AF ablation. The DF measured from surface ECG can be a useful marker to predict ablation success.

Individualised Approaches for Catheter Ablation of AF: Patient Selection and Procedural Endpoints

Pulmonary vein isolation (PVI) is the cornerstone of AF ablation, but studies have reported improved efficacy with high rates of repeat procedures. Because of the large interindividual variability in the underlying electrical and anatomical substrate, achieving optimal outcomes requires an individualised approach. This includes optimal candidate selection as well as defined ablation strategies with objective procedure endpoints beyond PVI. Candidate selection is traditionally based on coarse and sometimes arbitrary clinical stratification such as AF type, but finer predictors of treatment efficacy including biomarkers, advanced imaging and electrocardiographic parameters have shown promise. Numerous ancillary ablation strategies beyond PVI have been investigated, but the absence of a clear mechanistic and evidence-based endpoint, unlike in other arrhythmias, has remained a universal limitation. Potential endpoints include functional ones such as AF termination or non-inducibility and substrate-based endpoints such as isolation of low-voltage areas. This review summarises the relevant literature and proposes guidance for clinical practice and future research.

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.

Effects of refractory gradients and ablation on fibrillatory activity

BACKGROUND

The mechanisms involved in onset, maintenance, and termination of atrial fibrillation are not well understood. A biophysical model could be useful to determine how the events unfold.

METHOD

A two-dimensional cellular automaton consisting of 576 × 576 grid nodes was implemented to demonstrate the types of electrical activity that may occur in compromised atrial substrate. Electrical activation between nodes was made anisotropic (2:1), and the refractory period (RP) was adjusted from 74 to 192 ms in the spatial domain. Presence of collagen fibers were simulated as short lines of conduction block at many random grid sites, while ablation lesions were delineated as longer lines of block. An S1-S2 pulse from one grid corner was utilized to initiate simulated electrical activity. Simulations were done in which 1. no ablation lines, 2. random ablation lines, and 3. parallel ablation lines were added to the grid to determine how this affected the formation and annihilation of rotational activity after S1-S2 stimulation.

RESULTS

As the premature (S2) wavefront traversed the grid, rotational activity formed near boundaries where wavefronts propagated from shorter to longer refractory regions, causing unidirectional block, and were anchored by fiber clusters. Multiple wavelets appeared when wavefronts originating from different driving rotational features collided, and/or by their encounter with RP discontinuities. With the addition of randomly orientated simulated ablation lesions, followed by reinduction of fibrillatory activity, mean activation interval (AI) prolonged from a baseline level of 144.2 ms-160.3 ms (p < 0.001 in most comparisons). During fibrillatory activity, when parallel ablation lines were added to short RP regions, AI prolonged to 150.4 ms (p < 0.001), and when added to long RP regions, AI prolonged to 185.3 ms (p < 0.001). In all cases, AI prolongation after simulated ablation resulted from reduced number and/or from the isolation of local drivers, so that distant drivers in short RP regions activated long RP regions N:1, while distant drivers in long RP regions activated short RP regions at a relatively slow rate.

CONCLUSIONS

An automaton model was found useful to generate and test hypotheses concerning fibrillatory activity, which can then be validated in the clinical electrophysiology laboratory.

Atrial fibrillation: mechanisms, therapeutics, and future directions

Atrial fibrillation (AF) is the most prevalent cardiac arrhythmia, affecting 1% to 2% of the general population. It is characterized by rapid and disorganized atrial activation leading to impaired atrial function, which can be diagnosed on an EKG by lack of a P-wave and irregular QRS complexes. AF is associated with increased morbidity and mortality and is a risk factor for embolic stroke and worsening heart failure. Current research on AF support and explore the hypothesis that initiation and maintenance of AF require pathophysiological remodeling of the atria, either specifically as in lone AF or secondary to other heart disease as in heart failure-associated AF. Remodeling in AF can be grouped into three categories that include: (i) electrical remodeling, which includes modulation of L-type Ca(2+) current, various K(+) currents and gap junction function; (ii) structural remodeling, which includes changes in tissues properties, size, and ultrastructure; and (iii) autonomic remodeling, including altered sympathovagal activity and hyperinnervation. Electrical, structural, and autonomic remodeling all contribute to creating an AF-prone substrate which is able to produce AF-associated electrical phenomena including a rapidly firing focus, complex multiple reentrant circuit or rotors. Although various remodeling events occur in AF, current AF therapies focus on ventricular rate and rhythm control strategies using pharmacotherapy and surgical interventions. Recent progress in the field has started to focus on the underlying substrate that drives and maintains AF (termed upstream therapies); however, much work is needed in this area. Here, we review current knowledge of AF mechanisms, therapies, and new areas of investigation.

Ability of magnetocardiography to detect regional dominant frequencies of atrial fibrillation

BACKGROUND

Lead V1 on electrocardiography (ECG) can detect the dominant frequency (DF) of atrial fibrillation (AF) in the right atrium (RA). Paroxysmal AF is characterized by a frequency gradient from the left atrium (LA) to the right atrium (RA). We examined the ability of magnetocardiography (MCG) to detect regional DFs in both the atria.

METHODS

Study subjects comprised 18 consecutive patients referred for catheter ablation of persistent AF. An MCG system with 64 magnetic sensors was used to perform MCG in the frontal, lateral, and back planes prior to the ablation procedure in each patient. DFMCG and organization index (OIMCG) were calculated using fast Fourier transformation. Intracardiac electrograms (ICEs) in both the atria and the coronary sinus (CS) were mapped at 17 sites. Regional DFsICE were also determined.

RESULTS

Mean LA DFICE was higher than mean RA DFICE (6.40±0.66 versus 6.16±0.80 Hz, P=0.03). DFMCG in the channel having the highest OIMCG was 6.61±0.88 Hz in the frontal plane, 6.52±0.64 Hz in the lateral plane, and 6.42±0.62 Hz in the back plane (P=0.3). In each plane, DFMCG correlated with DFICE at the RA appendage (R=0.95, P<0.0001), the LA appendage (R=0.91, P<0.0001), and the CS (R=0.93, P<0.0001). DFECG in V5 modestly correlated with DFICE at the LA appendage (R=0.82, P<0.0001).

CONCLUSIONS

MCG could more precisely detect the DFs in the LA and the CS than ECG. However, the usefulness of pre-procedural detection of the AF frequency gradient for ablation therapy needs to be evaluated in future prospective studies.

Lack of Correlations between Electrophysiological and Anatomical-Mechanical Atrial Remodeling in Patients with Atrial Fibrillation

BACKGROUND

Atrial fibrillation (AF) progressively leads to electrical remodeling (ER) and anatomical-mechanical remodeling (AR), whose relationships in humans remain poorly known.

METHODS

ER and AR were compared in patients undergoing percutaneous radiofrequency (RF) ablation for AF. ER was defined by right and left appendage activation rates as a surrogate for atrial refractory periods. AR was approached by left atrial (LA) diameters and area and left atrial appendage (LAA) area and contractile function (mean emptying flow velocity) (LAAFV) before RF ablation. Mean duration between successive LAA contractions was considered as LAA mechanical rate.

RESULTS

Forty-one patients (31 men, age: 64 ± 9 years) with paroxysmal (27%), persistent (61%), or long-persistent AF (12%) were prospectively included (ejection fraction: 44 ± 16%). Parameters exploring AR were highly correlated to each other: LA area (28 ± 7 cm(2) ), LAA area (5.7 ± 2.25 cm(2) ), LA transverse (49 ± 7 mm), and anteroposterior diameter (59 ± 13 mm) or LAAFV (29 ± 13 cm/s; P < 0.05 for each comparison). Parameters exploring ER were also highly correlated: right atrial appendage (RAA; 181 ± 39 ms) and LAA (176 ± 33 ms) activation rates (P < 0.0001). There was no significant correlation between any ER and AR parameter. Only LAA mechanical rate (174 ± 36 ms) was correlated to LAA or RAA activations rates (P ≤ 0.01).

CONCLUSION

ER and AR are not mutually related, atrial activation rate being not correlated to LA or LAA size or function. Thus, the mechanisms leading to AF-induced atrial remodeling may differ for anatomical and electrophysiological aspects.

Impact of baseline atrial fibrillation cycle length on acute and long-term outcome of persistent atrial fibrillation ablation

BACKGROUND

A short baseline atrial fibrillation (AF) cycle length (CL) has been associated with a worse outcome after catheter ablation for AF, whereas the impact of a long baseline AFCL is unknown. We investigated the influence of AFCL on acute and long-term success in a large series of patients undergoing catheter ablation for persistent AF.

METHODS

Overall, 177 consecutive patients undergoing catheter ablation of persistent AF using a sequential ablation approach were included in the analysis. AFCL was measured in the left atrial appendage (LAA) at baseline and following each ablation step. The primary endpoint was freedom from any atrial arrhythmia off antiarrhythmic drugs (AAD) with a single ablation procedure after 12 months.

RESULTS

Mean AFCL was 164 ± 24 ms. A shorter AFCL was associated with longer AF duration, larger LA diameter, and longer procedure duration. Termination to sinus rhythm (SR) was achieved in 57 (32 %) patients. Baseline AFCL was shorter (161 ± 24 ms) in patients without AF termination compared to patients with AF termination (169 ± 23 m, p = 0.03). The primary endpoint was reached less frequently in patients with a short (<155 ms) AFCL (18 vs. 38.5 %, p = 0.006). Patients with an AFCL between 155 and 200 ms had the best outcome compared to patients with AFCL <155 or ≥200 ms (40 vs. 18 %, p = 0.003).

CONCLUSIONS

Patients with a baseline AFCL between 155 and 200 ms have the best outcome after a single ablation procedure for persistent AF compared to patients with an AFCL of <155 or ≥200 ms.

Atrial fibrillation cycle length and atrial size in horses with and without recurrence of atrial fibrillation after electrical cardioversion

BACKGROUND

Atrial fibrillation (AF) cycle length (CL) and atrial size have been used in humans to characterize electrical and structural remodeling to predict outcome of cardioversion of AF and risk for AF recurrence (rAF).

HYPOTHESIS

Atrial fibrillation cycle length can be determined in horses with AF, and AFCL and atrial size are related to risk for rAF.

ANIMALS

Eighteen horses with naturally occurring AF that were successfully converted to sinus rhythm (SR) by transvenous electrical cardioversion (TVEC).

METHODS

Prospective study. Horses with severe valvular regurgitation, left atrial enlargement, or that required sedation for catheter placement were excluded. In all horses intra-atrial electrograms were recorded and estimated AF duration and echocardiographic parameters were determined before TVEC. The follow-up time was 1 year after TVEC.

RESULTS

Atrial fibrillation cycle length could be determined in all horses. The AFCL and the shortest 5th percentile (p5) AFCL in horses with rAF (n = 6 or 33%) were (mean ± SD) 157 ± 28 and 134 ± 24 milliseconds, respectively, and in those maintaining SR (n = 12 or 67%) 166 ± 13 and 141 ± 13 milliseconds, respectively. Significant parameters to predict rAF were (1) the ratios of the p5AFCL to the left atrium (LA) sizes corrected to the size of aorta (AO) and (2) LA sizes corrected to the size of AO.

CONCLUSIONS AND CLINICAL IMPORTANCE

Before TVEC, assessment of LA size and atrial electrophysiologic characteristics might help to identify horses at increased risk for AF recurrence.

Relationship between the electrocardiographic atrial fibrillation cycle length and left atrial remodeling: a detailed electroanatomic mapping study

BACKGROUND/OBJECTIVE

The purpose of this study was to characterize the association between the extent of left atrial electroanatomic remodeling in atrial fibrillation and the atrial fibrillation cycle length derived from lead V₁ of the surface ECG (V1AFCL).

METHODS

Twenty-three patients in atrial fibrillation (AF) who presented for AF ablation underwent detailed electroanatomic mapping of the left atrium. The digital 12-lead ECG was exported for offline analysis, with signal filtering and QRST subtraction used to reveal the fibrillatory baseline in lead V₁. Mean V1AFCL was determined by direct annotation of the fibrillatory baseline, and the corresponding dominant V1AFCL was determined by Fourier transformation to derive the dominant frequency from the frequency power spectrum. The simultaneous AFCL from proximal and distal coronary sinus recordings was determined using the same methods. The strength of the association between various left atrial remodeling variables and V1AFCL was determined.

RESULTS

The 2 methods of deriving V1AFCL and intracardiac AFCL were found to produce highly equivalent results. V1AFCL showed significant correlation with intracardiac AFCL derived from both proximal and distal coronary sinus recordings. A longer V1AFCL was associated with slower left atrial conduction velocity and greater signal complexity but not with other remodeling variables, including left atrial size, atrial refractoriness, and mean endocardial voltage.

CONCLUSION

A longer atrial fibrillatory cycle length in surface ECG lead V1 is significantly associated with parameters of more advanced left atrial electroanatomic remodeling, specifically slower atrial conduction and more extensive electrogram fractionation.

Quantification of anaesthetic effects on atrial fibrillation rate by partial least-squares

The mechanism underlying atrial fibrillation (AF) remains poorly understood. Multiple wandering propagation wavelets drifting through both atria under hierarchical models are not understood. Some pharmacological drugs, known as antiarrhythmics, modify the cardiac ionic currents supporting the fibrillation process within the atria and may modify the AF propagation dynamics terminating the fibrillation process. Other medications, theoretically non-antiarrhythmic, may slightly affect the fibrillation process in non-defined mechanisms. We evaluated whether the most commonly used anaesthetic agent, propofol, affects AF patterns. Partial least-squares (PLS) analysis was performed to reduce significant noise into the main latent variables to find the differences between groups. The final results showed an excellent discrimination between groups with slow atrial activity during the propofol infusion.

Importance of atrial surface area and refractory period in sustaining atrial fibrillation: testing the critical mass hypothesis

OBJECTIVE

The critical mass hypothesis for atrial fibrillation (AF) was proposed in 1914; however, there have been few studies defining the relationship between atrial surface area and AF. This study evaluated the effect of tissue area and effective refractory period (ERP) on the probability of sustaining AF in an in vivo model.

METHODS

Domestic pigs (n = 9) underwent median sternotomy. Epicardial activation maps were constructed from bipolar electrograms recorded from form-fitting electrode templates placed on the atria. Baseline ERPs were determined. ERP was lowered with a continuous infusion of acetylcholine (0.005-0.04 mg/Kg/min) until AF could be sustained after burst pacing. The atria were sequentially partitioned using bipolar radiofrequency ablation. ERPs were lowered using acetylcholine until AF could be sustained in each subdivision of atrial tissue. Each subdivision was further divided until AF was no longer inducible. At study completion, the heart was excised and the surface area of each section was measured.

RESULTS

Over a range of ERPs from 75 to 250 ms, the probability of AF was correlated with increasing tissue area (range, 19.5-105 cm(2)) and decreasing ERP. Logistic regression analysis identified shorter ERP (P < .001) and larger area (P = .006) as factors predictive of an increased probability of sustained AF (area under the curve of the receiver-operator characteristic = 0.878).

CONCLUSIONS

The probability of sustained AF was significantly associated with increasing tissue area and decreasing ERP. These data may lead to a greater understanding of the mechanism of AF and help to design better interventional procedures.

Characterization of atrial activation (A-A) intervals during atrial fibrillation due to a single driver: do they reflect atrial effective refractory periods?

BACKGROUND

The mean, median, and minimum local atrial activation (A-A) intervals have been used to determine the local atrial effective refractory period (AERP) during atrial fibrillation (AF), the underlying assumption being that AF is due to multiple reentrant wavelets.

OBJECTIVE

We tested the hypothesis that when AF is due to a single, rapid, stable reentrant circuit (driver), the minimum and mean local A-A intervals will be similar at sites in the reentrant circuit, but will vary widely at sites with fibrillatory conduction, making these latter intervals unreliable indicators of AERP.

METHODS

During sustained AF due to a left atrial (LA) driver in 6 sterile pericarditis dogs, electrograms were recorded from 186 bipolar electrodes from both atria. A-A intervals were measured from each recording site during 1.2 seconds of AF. Minimum A-A intervals as well as temporal (within site) and spatial (between sites) variability were determined from all sites.

RESULTS

A-A intervals from each site during AF demonstrated that (1) 90-100% of right atrial (RA) sites and 18-39% of LA sites showed considerable (SD > 6 ms) temporal variability; (2) RA and LA sites with fibrillatory conduction (SD > 6 ms) showed considerable (a) spatial variability (RA: 9-36 ms; LA: 5-27 ms) and (b) variability of the minimum A-A intervals (RA: 14-35 ms; LA 11-28 ms).

CONCLUSION

During AF due to a driver, areas with fibrillatory conduction manifested considerable variability in the mean and the minimum A-A intervals. Therefore, it is unlikely that any of the A-A intervals reflect AERP.

Increase in organization index predicts atrial fibrillation termination with flecainide post-ablation: spectral analysis of intracardiac electrograms

AIMS

The mechanism of the action of flecainide in the termination of human atrial fibrillation (AF) is not fully understood. We studied the acute effects of flecainide on AF electrograms in the time and frequency domain to identify factors associated with AF termination.

METHODS AND RESULTS

Patients who were still in AF at the end of catheter ablation for AF were given intravenous flecainide. Dominant frequency (DF) and organization index (OI) were obtained by fast Fourier transform of electrograms from the coronary sinus catheter over 10 s in AF, before and after flecainide infusion. Mean AF cycle length (CL) was also calculated. Twenty-six patients were studied (16 paroxysmal AF and 10 persistent AF). Seven converted to sinus rhythm (SR) with flecainide. In all patients, mean CL increased from 211 +/- 44 to 321 +/- 85 ms (P < 0.001). Mean DF decreased from 5.2 +/- 1.03 to 3.6 +/- 1.04 Hz (P < 0.001). Mean OI was 0.33 +/- 0.13 before and 0.32 +/- 0.11 after flecainide (P = 0.90). Comparing patients who converted to SR with those who did not, OI post-flecainide was 0.41 +/- 0.12 vs. 0.29 +/- 0.10 (P = 0.013), and the relative change in OI was 29 +/- 33 vs. -3.9 +/- 27% (P = 0.016), respectively. No significant difference was noted in the change in CL and DF in the two groups.

CONCLUSION

Increase in OI, independent of changes to CL and DF, appears critical to AF termination with flecainide. Increase in OI holds promise as a sensitive predictor of AF termination.

Surgery for Lone Atrial Fibrillation: Present State-of-the-Art

For two decades, the cut-and-sew Cox-Maze III procedure was the gold standard for the surgical treatment of atrial fibrillation (AF), and proved to be effective at curing lone AF and preventing its most dreaded complication, stroke. However, this procedure was not widely adopted due to its complexity and technical difficulty. Over the last 5-10 years, the introduction of new ablation technology has led to the development of the Cox-Maze IV procedure, as well as, more limited lesion sets, with the ultimate goal of performing a minimally-invasive lesion set on the beating heart, without the need for cardiopulmonary bypass. This review summarizes the current state of the art and future directions in the surgical treatment of lone atrial fibrillation. The hope is that as we learn more about the mechanisms of AF and develop preoperative diagnostic technologies capable of precisely locating the areas responsible for AF, it will become possible to tailor specific lesion sets and ablation modalities to individual patients, making the surgical treatment of lone AF available to a larger population of patients.

The surgical treatment of atrial fibrillation

For two decades, the cut-and-sew Cox-maze III procedure was the gold standard for the surgical treatment of atrial fibrillation (AF) and has proven to be effective at eliminating AF. The incidence of late stroke was also very low. However, this procedure was not widely adopted owing to its complexity and technical difficulty. Over the last 5-10 years, the introduction of new ablation technology has led to the development of the Cox-maze IV procedure as well as more limited lesion sets, with the ultimate goal of performing a minimally invasive lesion set on the beating heart without the need for cardiopulmonary bypass. This review summarizes the current state of the art and future directions in the stand-alone surgical treatment of AF. The hope is that as more is learned about the mechanisms of AF and with better preoperative diagnostic technologies capable of precisely locating the areas responsible for AF, it will become possible to tailor specific lesion sets and ablation modalities to individual patients, making the surgical treatment of AF available to a larger population of patients.

Analyzing the electrophysiological effects of local epicardial temperature in experimental studies with isolated hearts

As a result of their modulating effects upon myocardial electrophysiology, both hypo- and hyperthermia can be used to study the mechanisms that generate or sustain cardiac arrhythmias. The present study describes an original electrode developed with thick-film technology and capable of controlling regional temperature variations in the epicardium while simultaneously registering its electrical activity. In this way, it is possible to measure electrophysiological parameters of the heart at different temperatures. The results obtained with this device in a study with isolated and perfused rabbit hearts are reported. An exploration has been made of the effects of local temperature changes upon the electrophysiological parameters implicated in myocardial conduction. Likewise, an analysis has been made of the influence of local temperature upon ventricular fibrillation activation frequency. It is concluded that both regional hypo- and hyperthermia exert reversible and opposite effects upon myocardial refractoriness and conduction velocity in the altered zone. The ventricular activation wavelength determined during constant pacing at 250 ms cycles is not significantly modified, however. During ventricular fibrillation, the changes in the fibrillatory frequency do not seem to be transmitted to normal temperature zones.

Electrical atrial fibrillation induction affects the characteristics of induced arrhythmia

Several methods are being used to induce atrial fibrillation (AF) in experimental investigations, which may affect the electrophysiologic parameters of the induced arrhythmia. The aim of our study was the investigation of temporal characteristics of AF during and after electrical induction. Direct current and high-frequency stimulation was used for induction in bipolar biatrial, right and left atrial appendage configurations in 6 dogs. Atrial and ventricular electrical activity was recorded near the bundle of His. Seven statistical parameters were calculated to analyze the temporal characteristics of electrical activity of both chambers. The induction method affected 5 atrial and no ventricular electrophysiologic parameters during stimulation, and the effect disappeared after ceasing induction, during the induced transient or persistent AF. Electrical stimulation affects the properties of the induced arrhythmia during the induction; thus, the investigation of AF is recommended only after ceasing the induction to avoid bias.

Spectral Analysis of Atrial Fibrillation Cycle Lengths Comparison Between Fast Fourier Transform Analysis and Autocorrelation Function Analysis Using Multipurpose Physio-Informatic Analysis Software

BACKGROUND

Fast Fourier transform (FFT) analysis is a popular method of spectral analysis of atrial fibrillation cycle lengths (AFCL). Autocorrelation function (ACF) analysis is also available, so the aim of this study was to elucidate the relationship between FFT and ACF analyses in the spectral analysis of AFCLs.

METHODS AND RESULTS

A total of 75 atrial fibrillation (AF) data from 39 patients were subjected to analysis. The dominant frequencies (DFs) from 4 different spectral resolutions of the FFT and peak AFCL from the ACF analysis were compared. In the FFT analysis using rectified signals, the DF was influenced by spectral resolution, no matter how the signals were tapered by the Hanning or Hamming window or filtered with the low-pass filter. There was a significant relationship between the DF from each spectral resolution and the peak AFCL. The DF from the 4,096-point FFT analysis had the strongest relationship to the peak AFCL with the smallest difference, when using 30-s AF data. In a study of the different lengths of the atrial fibrillation data, the DF also had a strong correlation to the peak AFCL with a small difference.

CONCLUSIONS

The peak AFCL obtained from ACF analysis was not of the same quality as that from FFT analysis, but had the same value as the DF from FFT analysis.

The stepwise ablation approach for chronic atrial fibrillation—Evidence for a cumulative effect

Treatment options for atrial fibrillation (AF) have evolved from simple, fluoroscopy-guided pulmonary vein isolation for those patients with paroxysmal AF to complex, multi-modality procedures targeting not only anatomic structures but also electrophysiologic phenomena including complex fractionated electrograms, sites of dominant frequency and local non-venous drivers in patients with persistent and permanent AF. The stepwise ablation approach is a novel technique whereby structures contributing to initiation and maintenance of AF are sequentially targeted by radiofrequency ablation. Broadly divided into pulmonary veins, left atrial (LA) roof, left atrium (incorporating all anatomic regions of the chamber), mitral isthmus and non-LA structures, each region is targeted in sequence and the impact of ablation upon the global fibrillatory process assessed by measurement of AF cycle length (AFCL) at a site remote from the ablation target. In addition to pulmonary vein electrical disconnection and demonstrable complete conduction block across the roof and mitral isthmus lines (when performed), ablation is performed at those sites displaying continuous electrical and complex fractionated activity, with the endpoint of local organization, as well as at sites displaying electrograms consistent with focal sources driving AF. Ablation is accompanied by a cumulative increase in the AFCL prior to termination of AF by conversion either directly to sinus rhythm or to an atrial tachycardia which is then mapped conventionally and ablated. There is a ceiling of ablation within the LA beyond which further ablation is unlikely to result in a clinical benefit and should prompt evaluation of the contribution of the right atrium to maintenance of AF. The stepwise approach benefits from the integration of anatomic and electrophysiologic information to achieve a high level of success in termination of chronic AF by catheter ablation.

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.

Transthoracic Tissue Doppler Imaging of the Atria: A Novel Method to Determine the Atrial Fibrillation Cycle Length

BACKGROUND

The atrial fibrillation cycle length (AFCL) is a critical parameter for the perpetuation and termination of AF. In the present study, we evaluated a new method to measure the AFCL based on transthoracic tissue Doppler imaging (TDI) of the right atrium (RA) and left atrium (LA).

METHODS

Twenty patients with AF (6 acute AF, 14 persistent or permanent AF) were studied. A quadripolar catheter was positioned at RA or LA to measure AFCL (AFCL(EGM), gold standard). Transthoracic echocardiography (apical 4-chamber view) was used to perform pulsed wave TDI at the free wall of RA or LA. AFCL(TDI) was defined as the time interval between two consecutive positive to negative crossings of the baseline of the atrial time velocity curves. AFCL(EGM) and AFCL(TDI) were measured at baseline and during a 10-minute infusion of flecainide (1.5 mg/kg).

RESULTS

Measurement of AFCL(TDI) was feasible in all but one patient. At baseline, AFCL(EGM) was 170 +/- 22 ms, AFCL(TDI) 172 +/- 22 ms (difference 2 +/- 5 ms). AFCL(TDI) correlated significantly with AFCL(EGM) (R = 0.91, P < 0.0001). Bland-Altman analysis showed a bias of -2 ms with a 95% limit of agreement between -26 ms and +22 ms. During flecainide, the AFCL(TDI) method yielded an AFCL prolongation from 176 +/- 23 ms at baseline to 279 +/- 68 ms (P < 0.01) after 10 minutes of infusion (57 +/- 26%).

CONCLUSIONS

(1) Tissue Doppler imaging of the atria during transthoracic echocardiography can be used to reliably determine the AFCL during both acute and persistent or permanent AF. (2) Continuous measurement of AFCL with TDI can be used to monitor the effect of antiarrhythmic drugs on atrial rate during AF. (3) This novel method is attractive because of the ease of acquiring the data and its noninvasive character.

Indices of Electrical and Contractile Remodeling During Atrial Fibrillation in Man

BACKGROUND

Atrial electrical and contractile remodeling have been demonstrated to coincide during atrial fibrillation (AF) in experimental studies. We explored whether electrical and contractile remodeling correlate in man and explored its clinical implications.

METHODS

Forty-nine patients with persistent AF were studied. Electrical remodeling was assessed noninvasively using spectral analysis to estimate the average fibrillatory rate (AFR). Atrial contractility was assessed by transesophageal echocardiography (TEE) measurement of left atrial appendage outflow velocity (LAAOV).

RESULTS

The AFR was 403+/-43 fibrillations per minute (fpm) and the LAAOV was 0.27+/-0.14 m/s. A significant correlation was found between AFR and LAAOV (r=-0.47, P=0.001). In patients with a LAAOV>or=0.25 m/s, the AFR was 387+/-48 fpm compared to 419+/-31 fpm among patients with LAAOV<0.25 m/s (P<0.01).

CONCLUSIONS

This study demonstrates that indices of electrical and contractile remodeling are strongly correlated in persistent AF in man. The interindividual overlap, however, is too large to allow predictions of LAAOV based on fibrillatory frequency alone.

Prediction of sinus rhythm maintenance following DC-cardioversion of persistent atrial fibrillation - the role of atrial cycle length

Background

Atrial electrical remodeling has been shown to influence the outcome the outcome following cardioversion of atrial fibrillation (AF) in experimental studies.

The aim of the present study was to find out whether a non-invasively measured atrial fibrillatory cycle length, alone or in combination with other non-invasive parameters, could predict sinus rhythm maintenance after cardioversion of AF.

Methods

Dominant atrial cycle length (DACL), a previously validated non-invasive index of atrial refractoriness, was measured from lead V1 and a unipolar oesophageal lead prior to cardioversion in 37 patients with persistent AF undergoing their first cardioversion.

Results

32 patients were successfully cardioverted to sinus rhythm. The mean DACL in the 22 patients who suffered recurrence of AF within 6 weeks was 152 ± 15 ms (V1) and 147 ± 14 ms (oesophagus) compared to 155 ± 17 ms (V1) and 151 ± 18 ms (oesophagus) in those maintaining sinus rhythm (NS). Left atrial diameter was 48 ± 4 mm and 44 ± 7 mm respectively (NS). The optimal parameter predicting maintenance of sinus rhythm after 6 weeks appeared to be the ratio of the lowest dominant atrial cycle length (oesophageal lead or V1) to left atrial diameter. This ratio was significantly higher in patients remaining in sinus rhythm (3.4 ± 0.6 vs. 3.1 ± 0.4 ms/mm respectively, p = 0.04).

Conclusion

In this study neither an index of atrial refractory period nor left atrial diameter alone were predictors of AF recurrence within the 6 weeks of follow-up. The ratio of the two (combining electrophysiological and anatomical measurements) only slightly improve the identification of patients at high risk of recurrence of persistent AF. Consequently, other ways to asses electrical remodeling and / or other variables besides electrical remodeling are involved in determining the outcome following cardioversion.

Rapid fluctuations in atrial fibrillatory electrophysiology detected during controlled respiration

Heart rate during sinus rhythm is modulated through the autonomic nervous system, which generates short-term oscillations. The high-frequency components in these oscillations are associated with respiration, causing sinus arrhythmia, mediated by the parasympathetic nervous system. In this study, we evaluated whether slow, controlled respiration causes cyclic fluctuations in the frequency of the fibrillating atria. Eight patients (four women; median age 63 yr, range 53-68 yr) with chronic atrial fibrillation (AF) and third-degree atrioventricular block treated by permanent pacemaker were studied. ECG was recorded during baseline rest, during 0.125-Hz frequency controlled respiration, and finally during controlled respiration after full vagal blockade. We calculated fibrillatory frequency using frequency analysis of the fibrillatory ECG for overlapping 2.5-s segments; spectral analysis of the resulting frequency trend was performed to determine the spectrum of variations of fibrillatory frequency. Normalized spectral power at respiration frequency increased significantly during controlled respiration from 1.4 (0.76-2.0) (median and range) at baseline to 2.7 (1.2-5.8) (P = 0.01). After vagal blockade, the power at respiration frequency decreased to 1.2 (0.23-2.8) (P = 0.01). Controlled respiration causes cyclic fluctuations in the AF frequency in patients with long-duration AF. This phenomenon seems to be related to parasympathetic modulations of the AF refractory period.

Relationship between pattern of occurrence of atrial fibrillation and surface electrocardiographic fibrillatory wave characteristics

OBJECTIVES

The purpose of this study was to assess whether surface ECG fibrillatory (f)-wave characteristics reflect clinical variables, especially pattern of occurrence.

BACKGROUND

In clinically stable patients, f waves have fairly constant quantitative characteristics. Both electrophysiologic and structural remodeling might modify f waves.

METHODS

We analyzed f waves from 238 patients (120 men and 118 women; age range 30-97 years, mean 77 +/- 12) with atrial fibrillation identified by retrospective chart review as paroxysmal, persistent, or permanent fibrillation. Analysis was performed in the time and frequency domains on ECGs after QRS-T cancellation. Student's t-test and multivariate analysis were used for comparison.

RESULTS

The f waves of 12 patients taking rhythm control drugs had lower frequency ("slower" fibrillation) than the f waves of patients not taking such drugs (5.3 +/- 0.6 vs 6.0 +/- 0.7 Hz, P < .001). Of the 226 remaining patients, 59 were paroxysmal, 30 were persistent, and 72 were permanent; 65 had an unknown pattern. Paroxysmal and persistent patients were younger than permanent (74 +/- 12 and 72 +/- 15 vs 80 +/- 9 years, P < .002 for both). Paroxysmal, persistent, and permanent patients had different f-wave frequencies of 5.7 +/- 0.7, 6.1 +/- 0.8, and 6.2 +/- 0.6 Hz, respectively (P = .01 for paroxysmal vs persistent and P < .001 for paroxysmal vs permanent). Patients older than 77 years (mean age) had lower f wave frequency than those younger 77 years (6.0 +/- 0.7 vs 6.2 +/- 0.7 Hz, P = .01). Using multivariate analysis, the overall pattern-frequency relationship was significant (p = .014). There was a statistically significant inverse correlation between frequency and age (R = .27, slope = -0.017 Hz/year, P < .001).

CONCLUSIONS

ECG f-wave frequency reflects specific clinical variables, with higher frequency in permanent than paroxysmal fibrillation but lower frequency in older than younger patients. These findings are consistent with the idea that fibrillatory waves are modified by both electrophysiologic and structural remodeling.

Mechanism of Propensity to Atrial Fibrillation in Patients Undergoing Isthmus Ablation for Typical Atrial Flutter

Mechanism of propensity to atrial fibrillation.

BACKGROUND

Patients undergoing isthmus ablation for atrial flutter (AFL) may reveal postablation atrial fibrillation (AF). The electrophysiological mechanism is unclear. In patients with idiopathic AF, enhanced spatial dispersion of right atrial refractoriness was the substrate for the initiation of AF. We hypothesize that dispersion of right atrial refractoriness in patients undergoing AFL ablation is the major cause of postablation AF.

METHODS

Consecutive patients (n=42) undergoing isthmus ablation for typical AFL were included. Twelve right atrial unipolar electrograms were recorded. Inducibility of AF was assessed by a pacing protocol, starting with one extrastimulus, followed by more aggressive pacing until AF was induced. Mean fibrillatory intervals were used to assess local refractoriness of each recording site. Spatial dispersion of right atrial refractoriness was calculated as the coefficient of dispersion (CD-value: standard deviation of the mean of all local mean fibrillatory intervals as a percentage of the overall mean fibrillatory interval). A CD-value of 3.0 or less was defined as normal, whereas CD-value greater than 3.0 was considered enhanced dispersion. PES and refractoriness analysis were followed by isthmus ablation.

RESULTS

Of the 42 patients, 29 had CD-value of 3.0 or less. In these 29 patients, AF was induced with 1 extrastimulus in only 1 patient, with 2 extrastimuli in 4 patients and burst pacing was required to induce AF in 24 of these 29 patients. Prior to the procedure, 5 of 29 patients had AF episodes, after ablation 6 of 29 patients. Of the 42 patients, 13 had CD-value greater than 3.0, AF was induced with a single extrastimulus in 11 patients, with 2 extrastimuli in the remaining 2 patients. Of the 13 patients, 11 had AF episodes both before and after ablation (P<0.001).

CONCLUSION

Enhanced spatial dispersion of right atrial refractoriness may be the substrate for propensity to AF in patients with AFL. The substrate was associated with enhanced inducibility of atrial fibrillation.

Atrial Fibrillatory Wave Characteristics on Surface Electrogram:

INTRODUCTION

Fibrillatory waves on the surface ECG have been scrutinized to allow inferences about underlying mechanisms and pathophysiology, based on the premise that fibrillatory waves do not vary "randomly" but provide a consistent reflection of the underlying state of the atria in an individual patient. This premise is untested.

METHODS AND RESULTS

Ten standard ECGs were recorded over a 24-hour period in each of 20 clinically stable inpatients with atrial fibrillation. After QRS-T cancellation, the remainder fibrillatory waves were analyzed. Interpatient versus intrapatient differences in fibrillatory wave characteristics were evaluated by analysis of variance (ANOVA). The fibrillatory wave peak-to-peak amplitude of all the patients ranged from 0.06 to 0.35 mV, whereas 1 SD of the amplitude for each patient ranged from 0.004 to 0.053 mV. Short-term peak frequencies of all the patients ranged from 4.6 to 8.0 Hz, whereas 1 SD for each patient varied from 0.2 to 0.5 Hz. For these and all other parameters tested, interpatient differences were significantly greater compared to intrapatient differences (P < 0.0001).

CONCLUSION

Fibrillatory wave characteristics are repeatable from ECG to ECG over 24 hours for clinically stable patients, whereas substantial differences are present between patients. Further study of the relationship of such characteristics to pathophysiology and management decisions is valid and warranted.