Transmural characteristics of atrial fibrillation in canine models of structural and electrical atrial remodeling assessed by simultaneous epicardial and endocardial mapping

A novel diagnostic tool to identify atrial endo-epicardial asynchrony using signal fingerprinting

OBJECTIVE

Patients with persistent atrial fibrillation (AF) have more electrical endo-epicardial asynchrony (EEA) during sinus rhythm (SR) than patients without AF. Prior mapping studies indicated that particularly unipolar, endo- and/or epicardial electrogram (EGM) morphology may be indicators of EEA. This study aim to develop a novel method for estimating the degree of EEA by using unipolar EGM characteristics recorded from either the endo- and/or epicardium.

METHODS

Simultaneous endo-epicardial mapping during sinus rhythm was performed in 86 patients. EGM characteristics, including unipolar voltages, low-voltage areas (LVAs), potential types (single, short/long double and fractionated potentials: SP, SDP, LDP and FP) and fractionation duration (FD) of double potentials (DP) and FP were compared between EEA and non-EEA areas. Asynchrony Fingerprinting Scores (AFS) containing quantified EGM characteristics were constructed to estimate the degree of EEA.

RESULTS

Endo- and epicardial sites of EEA areas are characterized by lower unipolar voltages, a higher number of LDPs and FPs and longer DP and FP durations. Patients with AF have lower potential voltages in EEA areas, along with alterations in the potential types. The EE-AFS, containing the proportion of endocardial LVAs and FD of epicardial DPs, had the highest predictive value for determining the degree of EEA (AUC: 0.913). Endo- and epi-AFS separately also showed good predictive values (AUC: 0.901 and 0.830 respectively).

CONCLUSIONS

EGM characteristics can be used to identify EEA areas. AFS can be utilized as a novel diagnostic tool for accurately estimating the degree of EEA. These characteristics potentially indicate AF related arrhythmogenic substrates.

Endocardial-Epicardial Phase Mapping of Prolonged Persistent Atrial Fibrillation Recordings

Background:

Endocardial-epicardial dissociation and focal breakthroughs in humans with atrial fibrillation (AF) have been recently demonstrated using activation mapping of short 10-second AF segments. In the current study, we used simultaneous endo-epi phase mapping to characterize endo-epi activation patterns on long segments of human persistent AF.

Methods:

Simultaneous intraoperative mapping of endo- and epicardial lateral right atrium wall was performed in patients with persistent AF using 2 high-density grid catheters (16 electrodes, 3 mm spacing). Filtered unipolar and bipolar electrograms of continuous 2-minute AF recordings and electrodes locations were exported for phase analyses. We defined endocardial-epicardial dissociation as phase difference of ≥20 ms between paired endo-epi electrodes. Wavefronts were classified as rotations, single wavefronts, focal waves, or disorganized activity as per standard criteria. Endo-Epi wavefront patterns were simultaneously compared on dynamic phase maps. Complex fractionated electrograms were defined as bipolar electrograms with ≥5 directional changes occupying at least 70% of sample duration.

Results:

Fourteen patients with persistent AF undergoing cardiac surgery were included. Endocardial-epicardial dissociation was seen in 50.3% of phase maps with significant temporal heterogeneity. Disorganized activity (Endo: 41.3% versus Epi: 46.8%, P =0.0194) and single wavefronts (Endo: 31.3% versus Epi: 28.1%, P =0.129) were the dominant patterns. Transient rotations (Endo: 22% versus Epi: 19.2%, P =0.169; mean duration: 590±140 ms) and nonsustained focal waves (Endo: 1.2% versus Epi: 1.6%, P =0.669) were also observed. Apparent transmural migration of rotational activations (n=6) from the epi- to the endocardium was seen in 2 patients. Electrogram fractionation was significantly higher in the epicardium than endocardium (61.2% versus 51.6%, P <0.0001).

Conclusions:

Simultaneous endo-epi phase mapping of prolonged human persistent AF recordings shows significant Endocardial-epicardial dissociation marked temporal heterogeneity, discordant and transitioning wavefronts patterns and complex fractionations. No sustained focal activity was observed. Such complex 3-dimensional interactions provide insight into why endocardial mapping alone may not fully characterize the AF mechanism and why endocardial ablation may not be sufficient.

Graphic Abstract:

A graphic abstract is available for this article.

How disruption of endo-epicardial electrical connections enhances endo-epicardial conduction during atrial fibrillation

Aims

Loss of side-to-side electrical connections between atrial muscle bundles is thought to underlie conduction disturbances predisposing to atrial fibrillation (AF). Putatively, disruption of electrical connections occurs not only within the epicardial layer but also between the epicardial layer and the endocardial bundle network, thus impeding transmural conductions (‘breakthroughs’). However, both clinical and experimental studies have shown an enhancement of breakthroughs during later stages of AF. We tested the hypothesis that endo-epicardial uncoupling enhances endo-epicardial electrical dyssynchrony, breakthrough rate (BTR), and AF stability.

Methods and Results

In a novel dual-layer computer model of the human atria, 100% connectivity between the two layers served as healthy control. Atrial structural remodelling was simulated by reducing the number of connections between the layers from 96 to 6 randomly chosen locations. With progressive elimination of connections, AF stability increased. Reduction in the number of connections from 96 to 24 resulted in an increase in endo-epicardial dyssynchrony from 6.6 ± 1.9 to 24.6 ± 1.3%, with a concomitant increase in BTR. A further reduction to 12 and 6 resulted in more pronounced endo-epicardial dyssynchrony of 34.4 ± 1.15 and 40.2 ± 0.52% but with BTR reduction. This biphasic relationship between endo-epicardial coupling and BTR was found independently from whether AF was maintained by re-entry or by ectopic focal discharges.

Conclusion

Loss of endo-epicardial coupling increases AF stability. There is a biphasic relation between endo-epicardial coupling and BTR. While at high degrees of endo-epicardial connectivity, the BTR is limited by the endo-epicardial synchronicity, at low degrees of connectivity, it is limited by the number of endo-epicardial connections.

Focal activation patterns: breaking new grounds in the pathophysiology of atrial fibrillation

INTRODUCTION

High-resolution atrial mapping studies have provided novel insights in the pathophysiology of atrial fibrillation (AF) in the last few years. Increasing attention is being drawn to the so-called focal activation patterns (FAPs); however, there is no consensus on criteria to identify and characterize these patterns. Areas covered: In this expert review, an overview of definitions and criteria used to examine FAPs obtained from atrial mapping studies is provided and studies reporting on the underlying mechanisms are discussed. Expert commentary: High-resolution cardiac mapping has revealed the importance of FAPs in the pathophysiology of AF. There is increasing evidence supporting the concept of endo-epicardial (E-E) asynchrony enabling transmural conduction of electrical waves resulting in FAPs. Uniform reports of FAPs in future studies are needed to provide more knowledge on its clinical importance.

The effect of activation rate on left atrial bipolar voltage in patients with paroxysmal atrial fibrillation

INTRODUCTION

Bipolar voltage is used during electroanatomic mapping to define abnormal myocardium, but the effect of activation rate on bipolar voltage is not known. We hypothesized that bipolar voltage may change in response to activation rate. By examining corresponding unipolar signals we sought to determine the mechanisms of such changes.

METHODS AND RESULTS

LA extrastimulus mapping was performed during CS pacing in 10 patients undergoing first time paroxysmal atrial fibrillation ablation. Bipolar and unipolar electrograms were recorded using a PentaRay catheter (4-4-4 spacing) and indifferent IVC electrode, respectively. An S1S2 pacing protocol was delivered with extrastimulus coupling interval reducing from 350 to 200 milliseconds. At each recording site (119 ± 37 per LA), bipolar peak-to-peak voltage, unipolar peak to peak voltage and activation delay between unipole pairs was measured. Four patterns of bipolar voltage/extrastimulus coupling interval curves were seen: voltage attenuation with plateau voltage >1 mV (48 ± 15%) or <1 mV (22 ± 15%), and voltage unaffected by coupling interval with plateau voltage >1 mV (17 ± 10%) or <1 mV (13 ± 8%). Electrograms showing bipolar voltage attenuation were associated with significantly greater unipolar voltage attenuation at low (25 ± 28 mV/s vs. 9 ± 11 mV/s) and high (23 ± 29 mV/s vs. 6 ± 12 mV/s) plateau voltage sites (P < 0.001). There was a small but significant increase in conduction delay between unipole pairs at sites showing bipolar voltage attenuation (P = 0.026).

CONCLUSIONS

Bipolar electrogram voltage is dependent on activation rate at a significant proportion of sites. Changes in unipolar voltage and timing underlie these effects. These observations have important implications for use of voltage mapping to delineate abnormal atrial substrate.

The role of myocardial wall thickness in atrial arrhythmogenesis

Changes in the structure and electrical behaviour of the left atrium are known to occur with conditions that predispose to atrial fibrillation (AF) and in response to prolonged periods of AF. We review the evidence that changes in myocardial thickness in the left atrium are an important part of this pathological remodelling process. Autopsy studies have demonstrated changes in the thickness of the atrial wall between patients with different clinical histories. Comparison of the reported tissue dimensions from pathological studies provides an indication of normal ranges for atrial wall thickness. Imaging studies, most commonly done using cardiac computed tomography, have demonstrated that these changes may be identified non-invasively. Experimental evidence using isolated tissue preparations, animal models of AF, and computer simulations proves that the three-dimensional tissue structure will be an important determinant of the electrical behaviour of atrial tissue. Accurately identifying the thickness of the atrial may have an important role in the non-invasive assessment of atrial structure. In combination with atrial tissue characterization, a comprehensive assessment of the atrial dimensions may allow prediction of atrial electrophysiological behaviour and in the future, guide radiofrequency delivery in regions based on their tissue thickness.

Atrial fibrillation driver mechanisms: Insight from the isolated human heart

Although there have been great technological advances in the treatment of atrial fibrillation (AF), current therapies remain limited due to a narrow understanding of AF mechanisms in the human heart. This review will highlight our recent studies on explanted human hearts where we developed and employed a novel functional-structural mapping approach by integrating high-resolution simultaneous endo-epicardial and panoramic optical mapping with 3D gadolinium-enhanced MRI to define the spatiotemporal characteristics of AF drivers and their structural substrates. The results allow us to postulate that the primary mechanism of AF maintenance in human hearts is a limited number of localized intramural microanatomic reentrant AF drivers anchored to heart-specific 3D fibrotically insulated myobundle tracks, which may remain hidden to clinical single-surface electrode mapping. We suggest that ex vivo human heart studies, by using an integrated 3D functional and structural mapping approach, will help to reveal defining features of AF drivers as well as validate and improve clinical approaches to detect and target these AF drivers in patients with cardiac diseases.

Quantification of the transmural dynamics of atrial fibrillation by simultaneous endocardial and epicardial optical mapping in an acute sheep model

BACKGROUND

Therapy strategies for atrial fibrillation based on electric characterization are becoming viable personalized medicine approaches to treat a notoriously difficult disease. In light of these approaches that rely on high-density surface mapping, this study aims to evaluate the presence of 3-dimensional electric substrate variations within the transmural wall during acute episodes of atrial fibrillation.

METHODS AND RESULTS

Optical signals were simultaneously acquired from the epicardial and endocardial tissue during acute fibrillation in ovine isolated left atria. Dominant frequency, regularity index, propagation angles, and phase dynamics were assessed and correlated across imaging planes to gauge the synchrony of the activation patterns compared with paced rhythms. Static frequency parameters were well correlated spatially between the endocardium and the epicardium (dominant frequency, 0.79 ± 0.06 and regularity index, 0.93 ± 0.009). However, dynamic tracking of propagation vectors and phase singularity trajectories revealed discordant activity across the transmural wall. The absolute value of the difference in the number, spatial stability, and temporal stability of phase singularities between the epicardial and the endocardial planes was significantly >0 with a median difference of 1.0, 9.27%, and 19.75%, respectively. The number of wavefronts with respect to time was significantly less correlated and the difference in propagation angle was significantly larger in fibrillation compared with paced rhythms.

CONCLUSIONS

Atrial fibrillation substrates are dynamic 3-dimensional structures with a range of discordance between the epicardial and the endocardial tissue. The results of this study suggest that transmural propagation may play a role in atrial fibrillation maintenance mechanisms.

Application of phase coherence in assessment of spatial alignment of electrodes during simultaneous endocardial-epicardial direct contact mapping of atrial fibrillation

AIMS

Mapping and interpretation of wave conduction patterns recorded during simultaneous mapping of the electrical activity on both endocardial and epicardial surfaces are challenging because of the difficulty of reconstruction of reciprocal alignment of electrodes in space. Here, we suggest a method to overcome this difficulty using a concept of maximized endo-epicardial phase coherence.

METHODS AND RESULTS

Endo-epicardial mapping was performed in six humans during induced atrial fibrillation (AF) in right atria using two sets of 8 × 8 electrode plaques. For each electrode, mean phase coherence (MPC) with all electrodes on the opposite side of the atrial wall was calculated. Localization error was defined as a distance between the directly opposing electrode and the electrode with the maximal MPC. Overall, there was a linear correlation between MPC and distance between electrodes with R(2) = 0.34. Localization error obtained for electrodes of the plaque in six patients resulted in a mean 2.3 ± 1.9 mm for 25 s electrogram segment length. Eighty-four per cent of the measurements resulted in error smaller than 3.4 mm. The duration of the recording used to compute MPC was negatively correlated with localization error; however, the effect reached plateau for segment durations longer than 15 s.

CONCLUSION

Application of the concept of maximized endo-epicardial phase coherence to electrograms during AF allows reconstruction of reciprocal alignment of the electrodes on the opposite side of the atrial wall. This approach may be especially useful in settings where the spatial position of endo- and epicardial electrodes for intracardiac mapping cannot otherwise be determined.

Catheter ablation of atrial fibrillation in patients with concomitant left ventricular impairment: a systematic review of efficacy and effect on ejection fraction

INTRODUCTION

Catheter ablation of atrial fibrillation (AF) is an established rhythm control strategy; however, the impact of co-existing LV systolic dysfunction (LVSD) on ablation success is less well understood. This systematic review compiles the outcomes of catheter ablation of atrial fibrillation in patients with LVSD.

METHODS

An electronic database (Pubmed, Scopus, Embase) search using the keywords 'atrial fibrillation AND ablation AND (ventricular dysfunction OR heart failure OR cardiomyopathy)' was performed for English scientific literature up to 01/01/2014. 2484 references were retrieved and evaluated for relevance by three reviewers. Reviews and reference lists of retrieved articles were also examined to ensure all relevant studies were included. Data was extracted from 19 studies, including a total of 914 patients.

RESULTS

Single-procedure success in LVSD patients for AF ablation was 56.5% (95% CI: 48%-64%). Overall multiple-procedure (including the use of anti-arrhythmic drugs) in LVSD patients for AF ablation was 81.8% (95% CI: 75%-87%). The mean increase in LVEF following AF ablation was 13.3% (95% CI: 10.8%-15.9%). Seven studies reported improvements in exercise capacity and quality of life information using standardised criteria. The pooled rate of serious adverse events was 5.5% (95% CI: 3.7%-8.1%).

CONCLUSIONS

Catheter ablation may be an effective therapy in AF patients with left ventricular systolic impairment, and can be associated with improvements in left ventricular function, quality of life, exercise capacity, and modest rates of serious adverse events.

Surface and intramural reentrant patterns during atrial fibrillation in the sheep

INTRODUCTION

This article is part of the Focus Theme of Methods of Information in Medicine on "Biosignal Interpretation: Advanced Methods for Studying Cardiovascular and Respiratory Systems".

BACKGROUND

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia in humans and is predicted to dramatically increase its prevalence in the future. High-resolution mapping data and Fourier power spectral analysis with its dominant frequency support the hypothesis that AF in the structurally normal sheep heart and in some patients often presents organized drivers in the form of periodic surface re-entries or breakthroughs. Nevertheless, the dynamics of those surface patterns of activity, as well as their intramural components are still poorly understood.

OBJECTIVE

To present data on AF waves from the surface of isolated sheep hearts and discuss the interpretation of their intramural patterns.

METHODS

We used a combination of endocardial-epicardial optical mapping with phase and spectral analysis as well as computer simulation of the re-entrant activity in the myocardial wall.

RESULTS

Analysis of the surfaces' optical mapping data in the phase domain reveals that activation of the posterior left atrium (PLA) consisted of alternating patterns of breakthroughs and reentries. The patterns on the endocardial and epicardial PLA surface at any given moment of time of the AF could be either identical or not identical, and the activity in the thickness of the PLA wall is hypothesized to conform to either ectopic discharge or reentrant scroll waves, but a definite evidence for the presence of such mechanisms is currently lacking. A universal minimal-principle theory is shown in a computer model to result in a tendency of the axis of the scroll waves to align with the myocardial fibers inside the wall.

CONCLUSION

The tendency of filaments of scroll waves to align with myocardial fibers may contribute to the variety and intermittency of surface rotors seen in AF.

Atrial fibrillation therapy now and in the future: drugs, biologicals, and ablation

Atrial fibrillation (AF) is a complex disease with multiple inter-relating causes culminating in rapid, seemingly disorganized atrial activation. Therapy targeting AF is rapidly changing and improving. The purpose of this review is to summarize current state-of-the-art diagnostic and therapeutic modalities for treatment of AF. The review focuses on reviewing treatment as it relates to the pathophysiological basis of disease and reviews preclinical and clinical evidence for potential new diagnostic and therapeutic modalities, including imaging, biomarkers, pharmacological therapy, and ablative strategies for AF. Current ablation and drug therapy approaches to treating AF are largely based on treating the arrhythmia once the substrate occurs and is more effective in paroxysmal AF rather than persistent or permanent AF. However, there is much research aimed at prevention strategies, targeting AF substrate, so-called upstream therapy. Improved diagnostics, using imaging, genetics, and biomarkers, are needed to better identify subtypes of AF based on underlying substrate/mechanism to allow more directed therapeutic approaches. In addition, novel antiarrhythmics with more atrial specific effects may reduce limiting proarrhythmic side effects. Advances in ablation therapy are aimed at improving technology to reduce procedure time and in mechanism-targeted approaches.

Simultaneous epicardial and noncontact endocardial mapping of the canine right atrium: simulation and experiment

Epicardial high-density electrical mapping is a well-established experimental instrument to monitor in vivo the activity of the atria in response to modulations of the autonomic nervous system in sinus rhythm. In regions that are not accessible by epicardial mapping, noncontact endocardial mapping performed through a balloon catheter may provide a more comprehensive description of atrial activity. We developed a computer model of the canine right atrium to compare epicardial and noncontact endocardial mapping. The model was derived from an experiment in which electroanatomical reconstruction, epicardial mapping (103 electrodes), noncontact endocardial mapping (2048 virtual electrodes computed from a 64-channel balloon catheter), and direct-contact endocardial catheter recordings were simultaneously performed in a dog. The recording system was simulated in the computer model. For simulations and experiments (after atrio-ventricular node suppression), activation maps were computed during sinus rhythm. Repolarization was assessed by measuring the area under the atrial T wave (ATa), a marker of repolarization gradients. Results showed an epicardial-endocardial correlation coefficients of 0.80 and 0.63 (two dog experiments) and 0.96 (simulation) between activation times, and a correlation coefficients of 0.57 and 0.46 (two dog experiments) and 0.92 (simulation) between ATa values. Despite distance (balloon-atrial wall) and dimension reduction (64 electrodes), some information about atrial repolarization remained present in noncontact signals.

Ectopic and reentrant activation patterns in the posterior left atrium during stretch-related atrial fibrillation

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia in humans and is predicted to dramatically increase its prevalence in the future. There is experimental evidence that increasing stretch increases the dominance of the pulmonary veins (PVs) during AF in isolated hearts and ectopic activity in the isolated PVs, but the ionic mechanisms underlying such effects are not clear and the ability of the PVs to favorably host functional reentry during stretch cannot be excluded. We used a combination of endocardial-epicardial optical mapping with phase and spectral analysis to study stretch-related AF (SRAF) in normal isolated sheep hearts. We have found rapid AF sources in the posterior left atrium (PLA) and PV region and their activation frequency and level of organization correlated with intra-atrial pressure. Analysis of the surfaces' optical mapping data in the phase domain reveals that activation of the PLA consisted of alternating patterns of breakthroughs, reentries and relatively simple waves swiping across the mapped field. The patterns on the endocardial and epicardial PLA surface at any given moment of time of the SRAF could be either identical or not identical, and the activity in the thickness of the PLA wall is hypothesized to conform to either ectopic discharge or scroll waves, but a definite evidence for the presence of such mechanisms is currently lacking. Thus the understanding of the manner by which the mechano-electric feedback effects in the PLA, including the PVs, become important in the initiation and maintenance of AF requires further detailed investigation.

Time course and mechanisms of endo-epicardial electrical dissociation during atrial fibrillation in the goat

AIMS

This study aims to determine the degree and mechanisms of endo-epicardial dissociation of electrical activity during atrial fibrillation (AF) and endo-epicardial differences in atrial electrophysiology at different stages of atrial remodelling.

METHODS AND RESULTS

Simultaneous high-density endo-epicardial mapping of AF was performed on left atrial free walls of goats with acute AF, after 3 weeks, and after 6 months of AF (all n = 7). Endo-epicardial activation time differences and differences in the direction of conduction vectors were calculated, endocardial and epicardial effective refractory periods (ERP) were determined, and fractionation of electrograms was quantified. Histograms of endo-epicardial activation time differences and differences in the direction of conduction vectors revealed two distinct populations, i.e. dissociated and non-dissociated activity. Dyssynchronous activity (dissociated in time) increased from 17 ± 7% during acute AF to 39 ± 17% after 3 weeks, and 68 ± 13% after 6 months of AF. Dissociation was more pronounced in thicker parts of the atrial wall (thick: 49.3 ± 21.4%, thin: 42.2 ± 19.0%, P < 0.05). At baseline, endocardial ERPs were longer when compared with epicardial ERPs (ΔERP, 21.8 ± 18 ms; P < 0.001). This difference was absent after 6 months of AF. The percentage of fractionated electrograms during rapid pacing increased from 9.4 ± 1.9% (baseline) to 18.6 ± 0.6% (6 months).

CONCLUSION

During AF, pronounced dissociation of electrical activity occurs between the epicardial layer and the endocardial bundle network. The increase in dissociation is due to owing to progressive uncoupling between the epicardial layer and the endocardial bundles and correlates with increasing stability and complexity of the AF substrate.

Electrophysiological differences between the epicardium and the endocardium of the left atrium

BACKGROUND

Electrophysiological properties of the atrial endocardium compared to epicardium are not well understood. The purpose of this study was to compare the electrophysiological properties and vulnerability to arrhythmia induction from these regions.

METHODS AND RESULTS

Transseptal endocardial and percutaneous epicardial mapping were performed in a porcine model (n = 7). Two opposing 4-mm electrophysiological catheters were positioned endocardially and epicardially. A circular mapping catheter (CMC) was positioned at the ostium of the common inferior pulmonary vein (CIPV) recording left atrial (LA)-PV potentials. Endocardial and epicardial effective refractory periods (ERPs) at two basic cycle lengths (CLs) of 600 and 400 ms were recorded from four anatomic locations (CIPV, LA appendage, right superior PV, and LA posterior wall). Atrial repetitive response (ARR) induction was also tested from endocardial and epicardial sites. Overall, 254 ERP measurements (mean 36.3 per animal) and 84 induction attempts (mean 12 per animal) were performed. The ERP was significantly shorter in the epicardium compared to the endocardium at basic CL of 400 ms (P = 0.006) but not at CL of 600 ms (P = 0.2). In addition, only the epicardium demonstrated ERP shortening when the CL of the basic drive was shortened (P = 0.03). ARR could be induced more often from the epicardium (P = 0.002) and fibrillatory activity with epicardial/endocardial dissociation was recorded (n = 3). Also, the earliest PV activation site on the CMC was noted to be different in 16.5% of cases during epicardial and endocardial pacing.

CONCLUSION

The electrophysiological characteristics of the atrial epicardium are different from the endocardium with a shorter ERP and more frequent ARR induction by programed stimulation.

Fibrillatory conduction in the atrial free walls of goats in persistent and permanent atrial fibrillation

BACKGROUND

Over a time course of months, the stability of atrial fibrillation (AF) gradually increases and the efficacy of pharmacological cardioversion declines both in humans and in animal models. Changes in fibrillatory conduction over this period largely are unexplored.

METHODS AND RESULT

Goats were instrumented with an atrial endocardial pacemaker lead and a burst pacemaker. AF was maintained for 3 weeks (short-term AF [ST], n = 10) or 6 months (long-term AF [LT], n = 7). AF could be cardioverted pharmacologically at the early time point (persistent AF), but not at the later time point (permanent AF). At follow-up, a high-resolution mapping electrode was used to record epicardial conduction patterns in the free walls of the right atrium (RA) and left atrium (LA). A new method for mapping of fibrillation waves was used to describe AF conduction patterns. Wavefronts propagated uniformly during slow pacing in both groups, although conduction velocity was significantly lower in the LT group (LA, 93 ± 14 versus 72 ± 10 cm/s; RA, 94 ± 8 versus 78 ± 8 cm/s). Median AF cycle length (AFCL) was not significantly different between the groups. However, the LT group showed highly complex activation patterns during AF, with an increased number of simultaneously propagating waves (LT group RA, 8.4 ± 3.0 waves/AFCL; LA, 12.8 ± 2.4 waves/AFCL; versus ST group RA, 4.3 ± 2.2 waves/AFCL; LA, 4.5 ± 2.5 waves/AFCL). Fibrillation waves in the LT group showed pronounced dissociation with large activation time differences. The incidence of waves newly appearing within the recording area also was increased in both atria. These alterations in conduction were accompanied by myocyte hypertrophy and increased endomysial fibrosis.

CONCLUSIONS

Long-term AF in goats leads to dissociated conduction in the atrial free walls that may contribute to increased AF stability.