Functional nature of electrogram fractionation demonstrated by left atrial high-density mapping

The temporal behavior and consistency of bipolar atrial electrograms in human persistent atrial fibrillation

The unstable temporal behavior of atrial electrical activity during persistent atrial fibrillation (persAF) might influence ablation target identification, which could explain the conflicting persAF ablation outcomes in previous studies. We sought to investigate the temporal behavior and consistency of atrial electrogram (AEG) fractionation using different segment lengths. Seven hundred ninety-seven bipolar AEGs were collected with three segment lengths (2.5, 5,and 8 s) from 18 patients undergoing persAF ablation. The AEGs with 8-s duration were divided into three 2.5-s consecutive segments. AEG fractionation classification was applied off-line to all cases following the CARTO criteria; 43% of the AEGs remained fractionated for the three consecutive AEG segments, while nearly 30% were temporally unstable. AEG classification within the consecutive segments had moderate correlation (segment 1 vs 2: Spearman’s correlation ρ = 0.74, kappa score κ = 0.62; segment 1 vs 3: ρ = 0.726, κ = 0.62; segment 2 vs 3: ρ = 0.75, κ = 0.68). AEG classifications were more similar between AEGs with 5 and 8 s (ρ = 0.96, κ = 0.87) than 2.5 versus 5 s (ρ = 0.93, κ = 0.84) and 2.5 versus 8 s (ρ = 0.90, κ = 0.78). Our results show that the CARTO criteria should be revisited and consider recording duration longer than 2.5 s for consistent ablation target identification in persAF.

Complex fractionated atrial electrograms, high dominant frequency regions, and left atrial voltages during sinus rhythm and atrial fibrillation

BACKGROUND

Ablation targeting complex fractionated atrial electrograms (CFAEs) or high dominant frequency (DF) sites is generally effective for persistent atrial fibrillation (AF). CFAEs and/or high DF sites may exist in low-voltage regions, which theoretically represent abnormal substrates. However, whether CFAEs or high DF sites reflect low voltage substrates during sinus rhythm (SR) is unknown.

METHODS

Sixteen patients with AF (8 with paroxysmal AF; 8, persistent AF) underwent high-density mapping of the left atrium (LA) with a 3-dimensional electroanatomic mapping system before ablation. The LA was divided into 7 segments and the mean bipolar voltage recorded during AF and SR, CFAEs (cycle lengths of 50-120 ms), and DF sites were assessed in each segment with either a duo-decapolar ring catheter (n=10) or a 64-pole basket catheter (n=6). Low-voltage areas were defined as those of <0.5 mV during AF and <1.0 mV during SR.

RESULTS

Regional mean voltage recorded from the basket catheter showed good correlation between AF and SR (r=0.60, p<0.01); however, the % low-voltage area in the LA recorded from the ring catheter showed weak correlation (r=0.34, p=0.05). Mean voltage was lower during AF than during SR (1.0 mV [IQR, 0.5-1.4] vs. 2.6 mV [IQR, 1.8-3.6], p<0.01). The regional and overall % low-voltage area of the LA was greater during AF than during SR (20% vs. 11%, p=0.05). CFAEs and high DF sites (>8 Hz) did not correlate with % low-voltage sites during SR; however, CFAEs sites were located in high-voltage regions during AF and high DF sites were located in low voltage regions during AF.

CONCLUSIONS

CFAEs and high DF areas during AF do not reflect damaged atrial myocardium as shown by the SR voltage. However, CFAEs and high DF sites may demonstrate different electrophysiologic properties because of different voltage amplitude during AF.

High Voltage Guided Pulmonary Vein Isolation in Paroxysmal Atrial Fibrillation

Background

Ablation of the pulmonary vein (PV) antrum using an electroanatomic mapping system is standard of care for point-by-point pulmonary vein isolation (PVI). Focused ablation at critical areas is more likely to achieve intra-procedural PV isolation and decrease the likelihood for reconnection and recurrence of atrial fibrillation (AF). Therefore this prospective pilot study is to investigate the short-term outcome of a voltage-guided circumferential PV ablation (CPVA) strategy.

Methods

We recruited patients with a history of paroxysmal atrial fibrillation (AF). The EnSite NavX system (St. Jude Medical, St Paul, Minnesota, USA) was employed to construct a three-dimensional geometry of the left atrium (LA) and voltage map. CPVA was performed; with radiofrequency (RF) targeting sites of highest voltage first in a sequential clockwise fashion then followed by complete the gaps in circumferential ablation. Acute and short-term outcomes were compared to a control group undergoing conventional standard CPVA using the same 3D system. Follow-up was scheduled at 3, 6 and 12 months.

Results

Thirty-four paroxysmal AF patients with a mean age of 40 years were included. Fourteen patients (8 male) underwent voltage mapping and 20 patients underwent empirical, non-voltage guided standard CPVA. A mean of 54 ± 12 points per PV antrum were recorded. Mean voltage for right and left PVs antra were 1.7±0.1 mV and 1.9±0.2 mV, respectively. There was a trend towards reduced radiofrequency time (40.9±17.4 vs. 48.1±15.5 mins; p=0.22).

Conclusion

Voltage-guided CPVA is a promising strategy in targeting critical points for PV isolation with a lower trend of AF recurrence compared with a standard CPVA in short-term period. Extended studies to confirm these findings are warranted.

Basket-Type Catheters: Diagnostic Pitfalls Caused by Deformation and Limited Coverage

Whole-chamber mapping using a 64-pole basket catheter (BC) has become a featured approach for the analysis of excitation patterns during atrial fibrillation. A flexible catheter design avoids perforation but may lead to spline bunching and influence coverage. We aim to quantify the catheter deformation and endocardial coverage in clinical situations and study the effect of catheter size and electrode arrangement using an in silico basket model. Atrial coverage and spline separation were evaluated quantitatively in an ensemble of clinical measurements. A computational model of the BC was implemented including an algorithm to adapt its shape to the atrial anatomy. Two clinically relevant mapping positions in each atrium were assessed in both clinical and simulated data. The simulation environment allowed varying both BC size and electrode arrangement. Results showed that interspline distances of more than 20 mm are common, leading to a coverage of less than 50% of the left atrial (LA) surface. In an ideal in silico scenario with variable catheter designs, a maximum coverage of 65% could be reached. As spline bunching and insufficient coverage can hardly be avoided, this has to be taken into account for interpretation of excitation patterns and development of new panoramic mapping techniques.

Ablation of Persistent Atrial Fibrillation Targeting Low-Voltage Areas With Selective Activation Characteristics

BACKGROUND

Complex-fractionated atrial electrograms and atrial fibrosis are associated with maintenance of persistent atrial fibrillation (AF). We hypothesized that pulmonary vein isolation (PVI) plus ablation of selective atrial low-voltage sites may be more successful than PVI only.

METHODS AND RESULTS

A total of 85 consecutive patients with persistent AF underwent high-density atrial voltage mapping, PVI, and ablation at low-voltage areas (LVA < 0.5 mV in AF) associated with electric activity lasting > 70% of AF cycle length on a single electrode (fractionated activity) or multiple electrodes around the circumferential mapping catheter (rotational activity) or discrete rapid local activity (group I). The procedural end point was AF termination. Arrhythmia freedom was compared with a control group (66 patients) undergoing PVI only (group II). PVI alone was performed in 23 of 85 (27%) patients of group I with low amount (< 10% of left atrial surface area) of atrial low voltage. Selective atrial ablation in addition to PVI was performed in 62 patients with termination of AF in 45 (73%) after 11 ± 9 minutes radiofrequency delivery. AF-termination sites colocalized within LVA in 80% and at border zones in 20%. Single-procedural arrhythmia freedom at 13 months median follow-up was achieved in 59 of 85 (69%) patients in group I, which was significantly higher than the matched control group (31/66 [47%], P < 0.001). There was no significant difference in the success rate of patients in group I with a low amount of low voltage undergoing PVI only and patients requiring PVI+selective low-voltage ablation (P = 0.42).

CONCLUSIONS

Ablation of sites with distinct activation characteristics within/at borderzones of LVA in addition to PVI is more effective than conventional PVI-only strategy for persistent AF. PVI only seems to be sufficient to treat patients with left atrial low voltage < 10%.

Percolation as a mechanism to explain atrial fractionated electrograms and reentry in a fibrosis model based on imaging data

BACKGROUND

Complex fractionated atrial electrograms (CFAEs) have long been associated with proarrhythmic alterations in atrial structure or electrophysiology. Structural alterations disrupt and slow smoothly propagating wavefronts, leading to wavebreaks and electrogram (EGM) fractionation, but the exact nature and characteristics for arrhythmia remain unknown. Clinically, in atrial fibrillation (AF) patients, increases in frequency, whether by pacing or fibrillation, increase EGM fractionation and duration, and reentry can occur in relation with the conduction disturbance. Recently, percolation has been proposed as an arrhythmogenic mechanism, but its role in AF has not been investigated.

OBJECTIVE

We sought to determine if percolation can explain reentry formation and EGM behavior observed in AF patients.

METHODS

Computer models of fibrotic tissue with different densities were generated based on late gadolinium-enhanced magnetic resonance images, using pixel intensity as a fibrosis probability to avoid an arbitrary binary threshold. Clinical pacing protocols were followed to induce AF, and EGMs were computed.

RESULTS

Reentry could be elicited, with a biphasic behavior dependent on fibrotic density. CFAEs were recorded above fibrotic regions, and consistent with clinical data, EGM duration and fractionation increased with more rapid pacing.

CONCLUSION

These findings confirm percolation as a potential mechanism to explain AF in humans and give new insights into dynamics underlying conduction distortions and fractionated signals in excitable media, which correlate well with the experimental findings in fibrotic regions. The greater understanding of the different patterns of conduction changes and related EGMs could lead to more individualized and effective approaches to AF ablation therapy.

Is Mapping of Complex Fractionated Electrograms Obsolete?

Atrial fibrillation is the most common clinically encountered arrhythmia and catheter ablation has emerged as a viable treatment option in drug-refractory cases. Pulmonary vein isolation is widely regarded as the cornerstone for successful outcomes in paroxysmal AF given that the pulmonary veins are a frequent source of AF triggering. Ablation strategies for persistent AF are less well defined. Mapping and ablation of complex fractionated electrograms (CFAEs) is one strategy that has been proposed as a means of modifying the atrial substrate thought to be critical to the perpetuation of AF. Results of clinical studies have proved conflicting and there are now strong data to suggest that pulmonary vein isolation alone is associated with outcomes comparable to those of pulmonary vein isolation plus CFAE ablation. Several studies have demonstrated that the majority of CFAEs are passive phenomena and therefore not critical to the perpetuation of AF. Conventional mapping technologies (using a bipolar or circular mapping catheter) lack the spatiotemporal resolution to identify mechanisms of AF persistence. The development of wide-field mapping techniques allows simultaneous acquisition of activation data over large areas. This strategy has the potential to better identify regions critical to AF perpetuation, and preliminary data suggest that ablation outcomes are improved when guided by these techniques. While mapping and ablation of all CFAEs is almost certainly obsolete, better identification of regions responsible for AF persistence has the potential to improve outcomes in ablation of persistent AF.

Body Surface Mapping to Guide Atrial Fibrillation Ablation

Atrial fibrillation (AF) is the most common rhythm disorder, and is strongly associated with thromboembolic events and heart failure. Over the past decade, catheter ablation of AF has advanced considerably with progressive improvement in success rates. However, interventional treatment is still challenging, especially for persistent and long-standing persistent AF. Recently, AF analysis using a non-invasive body surface mapping technique has been shown to identify localised reentrant and focal sources, which play an important role in driving and perpetuating AF. Non-invasive mapping-guided ablation has also been reported to be effective for persistent AF. In this review, we describe new clinical insights obtained from non-invasive mapping of persistent AF to guide catheter ablation.

Effects of a high-fat diet on the electrical properties of porcine atria

Background

Because obesity is an important risk factor for atrial fibrillation (AF), we conducted an animal study to examine the effect of a high-fat diet (HFD) on atrial properties and AF inducibility.

Methods

Ten 8-week-old pigs (weight, 18–23 kg) were divided into two groups. For 18 weeks, five pigs were fed a HFD (HFD group) and five were fed a normal diet (control group). Maps of atrial activation and voltages during sinus rhythm were created for all pigs using the EnSite NavX system. Effective refractory period (ERP) and AF inducibility were also determined. When AF was induced, complex fractionated atrial electrogram (CFAE) mapping was performed. At 18 weeks, hearts were removed for comparing the results of histological analysis between the two groups. Body weight, lipid levels, hemodynamics, cardiac structures, and electrophysiological properties were also compared.

Results

Total cholesterol levels were significantly higher (347 [191–434] vs. 81 [67–88] mg/dL, P=0.0088), and left atrium pressure was higher (34.5 [25.6–39.5] vs. 24.5 [21.3–27.8] mmHg, P=0.0833) in the HFD group than in the control group, although body weight only increased marginally (89 [78–101] vs. 70 [66–91] kg, P=0.3472). ERPs of the pulmonary vein (PV) were shorter (P<0.05) and AF lasted longer in the HFD group than in the control group (80 [45–1350] vs. 22 [3–30] s, P=0.0212). Neither CFAE site distribution nor histopathological characteristics differed between the two groups.

Conclusions

The shorter ERPs for the PV observed in response to the HFD increased vulnerability to AF, and these electrophysiological characteristics may underlie obesity-related AF.

Contemporary Mapping Techniques of Complex Cardiac Arrhythmias - Identifying and Modifying the Arrhythmogenic Substrate

Cardiac electrophysiology has moved a long way forward during recent decades in the comprehension and treatment of complex cardiac arrhythmias. Contemporary electroanatomical mapping systems, along with state-of-the-art technology in the manufacture of electrophysiology catheters and cardiac imaging modalities, have significantly enriched our armamentarium, enabling the implementation of various mapping strategies and techniques in electrophysiology procedures. Beyond conventional mapping strategies, ablation of complex fractionated electrograms and rotor ablation in atrial fibrillation ablation procedures, the identification and modification of the underlying arrhythmogenic substrate has emerged as a strategy that leads to improved outcomes. Arrhythmogenic substrate modification also has a major role in ventricular tachycardia ablation procedures. Optimisation of contact between tissue and catheter and image integration are a further step forward to augment our precision and effectiveness. Hybridisation of existing technologies with a reasonable cost should be our goal over the next few years.

Effect of flecainide on the extension and localization of complex fractionated electrogram during atrial fibrillation

AIMS

Complex fractionated electrogram (CFE) ablation in addition to pulmonary vein isolation is an accepted strategy for the treatment of non-paroxysmal atrial fibrillation (AF). We sought to determine the effect of flecainide on the distribution and extension of CFE areas.

METHODS

Twenty-three non-paroxysmal AF patients were enrolled in this prospective study. A first CFE map was obtained under baseline conditions by sampling 5 s of continuous recording from the distal electrodes of the ablation catheter. Intravenous flecainide (1 mg/kg) was administered over 10 min and followed by 30-min observation time. A second CFE map was obtained with the same modalities. CFE-mean values, CFE areas, and atrial electrogram amplitude were retrieved from the electro-anatomical mapping system (Ensite NavX).

RESULTS

After flecainide administration, CFE-mean values increased (111.5 ± 55.3 vs. 132.3 ± 65.0 ms, p < 0.001) with a decrease of CFE area (32.9%) in all patients. Atrial electrogram amplitude decreased significantly (0.30 ± 0.31 vs. 0.25 ± 0.20 mV, p < 0.001). We observed 80.9% preservation of CFE areas. A CFE mean of 78 ms was the best cutoff for predicting stable CFE areas.

CONCLUSIONS

Flecainide reduces the extension of CFE areas while preserving their spatial localization. A CFE-mean value <80 ms may be crucial to define and locate stable CFE areas.

Catheter ablation of persistent atrial fibrillation: The importance of substrate modification

Accumulating data have shown that elimination of atrial fibrillation (AF) sources should be the goal in persistent AF ablation. Pulmonary vein isolation, linear lesions and complex fractionated atrial electrograms (CFAEs) ablation have shown limited efficacy in patients with persistent AF. A combined approach using voltage, CFAEs and dominant frequency (DF) mapping may be helpful for the identification of AF sources and subsequent focal substrate modification. The fibrillatory activity is maintained by intramural reentry centered on fibrotic patches. Voltage mapping may assist in the identification of fibrotic areas. Stable rotors display the higher DF and possibly drive AF. Furthermore, the single rotor is usually consistent with organized AF electrograms without fractionation. It is therefore quite possible that rotors are located at relatively “healthy islands” within the patchy fibrosis. This is supported by the fact that high DF sites have been negatively correlated to the amount of fibrosis. CFAEs are located in areas adjacent to high DF. In conclusion, patchy fibrotic areas displaying the maximum DF along with high organization index and the lower fractionation index are potential targets of ablation. Prospective studies are required to validate the efficacy of substrate modification in left atrial ablation outcomes.

Elimination Of Triggers Without An Additional Substrate Modification Is Not Sufficient In Patients With Persistent Atrial Fibrillation

Atrial fibrillation (AF) is a multifactorial disease with complex pathophysiology. Although restoring sinus rhythm delays the progression of atrial remodeling, non-pharmacologic intervention, such as radiofrequency catheter ablation (RFCA), should be done based on the background pathophysiology of the disease. While circumferential pulmonary vein isolation (CPVI) has been known to be the cornerstone of AF catheter ablation, a clinical recurrence rate after CPVI is high in patients with persistent AF (PeAF). Step-wise linear ablation, complex fractionate atrial electrogram (CFAE)-guided ablation, rotor ablation, ganglionate plexus ablation, and left atrial appendage isolation may improve the ablation success rate after CPVI. But, there are still substantial AF recurrences after such liberal atrial substrate ablation, and current ablation techniques regarding substrate modification still have limitations. Therefore, more understanding about AF pathophysiology and early precise intervention may improve clinical outcome of AF management. Keeping in mind "more touch, more scar," operators should generate most efficient substrate modification to achieve better long-term clinical outcome.

Dynamic approximate entropy electroanatomic maps detect rotors in a simulated atrial fibrillation model

There is evidence that rotors could be drivers that maintain atrial fibrillation. Complex fractionated atrial electrograms have been located in rotor tip areas. However, the concept of electrogram fractionation, defined using time intervals, is still controversial as a tool for locating target sites for ablation. We hypothesize that the fractionation phenomenon is better described using non-linear dynamic measures, such as approximate entropy, and that this tool could be used for locating the rotor tip. The aim of this work has been to determine the relationship between approximate entropy and fractionated electrograms, and to develop a new tool for rotor mapping based on fractionation levels. Two episodes of chronic atrial fibrillation were simulated in a 3D human atrial model, in which rotors were observed. Dynamic approximate entropy maps were calculated using unipolar electrogram signals generated over the whole surface of the 3D atrial model. In addition, we optimized the approximate entropy calculation using two real multi-center databases of fractionated electrogram signals, labeled in 4 levels of fractionation. We found that the values of approximate entropy and the levels of fractionation are positively correlated. This allows the dynamic approximate entropy maps to localize the tips from stable and meandering rotors. Furthermore, we assessed the optimized approximate entropy using bipolar electrograms generated over a vicinity enclosing a rotor, achieving rotor detection. Our results suggest that high approximate entropy values are able to detect a high level of fractionation and to locate rotor tips in simulated atrial fibrillation episodes. We suggest that dynamic approximate entropy maps could become a tool for atrial fibrillation rotor mapping.

Fractionation of electrograms is caused by colocalized conduction block and connexin disorganization in the absence of fibrosis as AF becomes persistent in the goat model

Background

Electrogram fractionation and atrial fibrosis are both thought to be pathophysiological hallmarks of evolving persistence of atrial fibrillation (AF), but recent studies in humans have shown that they do not colocalize. The interrelationship and relative roles of fractionation and fibrotic change in AF persistence therefore remain unclear.

Objective

The aim of the study was to examine the hypothesis that electrogram fractionation with increasing persistence of AF results from localized conduction slowing or block due to changes in atrial connexin distribution in the absence of fibrotic change.

Methods

Of 12 goats, atrial burst pacemakers maintained AF in 9 goats for up to 3 consecutive 4-week periods. After each 4-week period, 3 goats underwent epicardial mapping studies of the right atrium and examination of the atrial myocardium for immunodetection of connexins 43 and 40 (Cx43 and Cx40) and quantification of connective tissue.

Results

Despite refractoriness returning to normal in between each 4-week period of AF, there was a cumulative increase in the prevalence of fractionated atrial electrograms during both atrial pacing (control and 1, 2, and 3 months period of AF 0.3%, 1.3% ± 1.5%, 10.6% ± 2%, and 17% ± 5%, respectively; analysis of variance, P < .05) and AF (0.3% ± 0.1%, 2.3% ± 1.2%, 14% ± 2%, and 23% ± 3%; P < .05) caused by colocalized areas of conduction block during both pacing (local conduction velocity <10 cm/s: 0.1% ± 0.1%, 0.3% ± 0.6%, 6.5% ± 3%, and 6.9% ± 4%; P < .05) and AF (1.5% ± 0.5%, 2.7% ± 1.1%, 10.1% ± 1.2%, and 13.6% ± 0.4%; P < .05), associated with an increase in the heterogeneity of Cx40 and lateralization of Cx43 (lateralization scores: 1.75 ± 0.89, 1.44 ± 0.31, 2.85 ± 0.96, and 2.94 ± 0.31; P < .02), but not associated with change in connective tissue content or net conduction velocity.

Conclusion

Electrogram fractionation with increasing persistence of AF results from slow localized conduction or block associated with changes in atrial connexin distribution in the absence of fibrotic change.

Impact of pulmonary vein isolation on fractionated atrial potentials and ganglionated plexi in patients with persistent atrial fibrillation

Some patients with persistent atrial fibrillation (AF) acquire long-term freedom from AF by pulmonary vein (PV) isolation alone. The aim of the present study was to evaluate the characteristics of their atrial substrate.We studied 20 patients with persistent AF to examine the distribution of fractionated atrial potentials (FAP) and that of the anatomic sites of ganglionated plexi (GPs) with vagal reflexes elicited by high frequency stimulation (HFS) with the use of the CARTO system before and after the PV isolation.Both the %FAP area defined as a proportion of the FAP area to the total left atrial area (34.3 ± 10.3 to 21.5 ± 10.2%; P < 0.0001) and number of GP sites with vagal reflexes (4.0 [3.0, 5.0] to 2.0 [1.0, 2.8]; P < 0.0001) were markedly decreased after the PV isolation. Seven (35%) patients had AF recurrences, and they had a greater %FAP area after the PV isolation than those without (32.8 [22.1, 37.3] versus 13.8 [10.9, 19.9]%; P = 0.0049). A %FAP area after the PV isolation of > 20% was significantly associated with an AF recurrence (odds ratio 20.0, 95% confidence interval 2.26470.34; P = 0.018). No significant difference was found between the patients with and without AF recurrence in the reduction rate of anatomic sites of GPs with a vagal reflex induced by the HFS.A more marked reduction in the FAP area by the PV isolation was significantly associated with a better outcome in patients with persistent AF.

Mechanisms of Atrial Fibrillation - Reentry, Rotors and Reality

Atrial fibrillation (AF) is the most common sustained arrhythmia encountered in clinical practice, yet our understanding of the mechanisms that initiate and sustain this arrhythmia remains quite poor. Over the last 50 years, various mechanisms of AF have been proposed, yet none has been consistently observed in both experimental studies and in humans. Recently, there has been increasing interest in understanding how spiral waves or rotors - which are specific, organised forms of functional reentry - sustain human AF and how they might be therapeutic targets for catheter-based ablation. The following review describes the historical understanding of reentry and AF mechanisms from earlier in the 20th century, advances in our understanding of mechanisms that are able to sustain AF with a focus on rotors and complex fractionated atrial electrograms (CFAEs), and how the study of AF mechanisms has resulted in new strategies for treating AF with novel forms of catheter ablation.

Tailored atrial substrate modification based on low-voltage areas in catheter ablation of atrial fibrillation

BACKGROUND

Reduced electrogram amplitude has been shown to correlate with diseased myocardium. We describe a novel individualized approach for catheter ablation of atrial fibrillation (AF) based on low-voltage areas (LVAs) in the left atrium (LA). We sought to assess (1) the incidence of LVAs in patients undergoing AF catheter ablation, (2) the distribution of LVAs within the LA, and (3) the effect of an individualized ablation strategy on long-term rhythm outcomes.

METHODS AND RESULTS

In 178 patients with paroxysmal or persistent AF, LA voltage maps were created during sinus rhythm after circumferential pulmonary vein isolation. Subsequent substrate modification was confined to the presence of LVA (<0.5 mV) and inducible regular atrial tachycardias. LVAs were identified in 35% and 10% of patients with persistent and paroxysmal AF, respectively. The LA roof and the anterior, septal, and posterior wall LA were most often affected. The 12-month atrial tachycardias/AF-free survival was 62% for patients without LVAs and 70% for patients with LVAs and tailored substrate modification (P=0.3). Success rate in a comparison group of 26 LVA patients without further substrate modification was 27%.

CONCLUSIONS

LVAs can be found at preferred sites in 10% of patients with paroxysmal AF and in 35% of patients with persistent AF. This is the first clinical report describing a consistent voltage-based approach for substrate modification in addition to circumferential pulmonary vein isolation irrespective of AF type. Application of this limited individualized approach may have the potential to compensate for the impaired 12-month outcome of patients with endocardial structural defects.

New Insights On Ablation Of Persistent Atrial Fibrillation: Evidence From The SARA Trial

Since Haissaguerre et al first described the pathogenic role of pulmonary vein firing as a crucial mechanism triggering atrial fibrillation, catheter ablation has been recommended as a curative treatment. Several trials have demonstrated that ablation is an effective treatment in most patients with paroxysmal atrial fibrillation and low-grade remodelled atria. In patients with persistent AF, there is substantially less evidence, mostly based on non-randomized studies, supporting this recommendation. The available scientific evidence as well as the current approaches to treating persistent AF patients are discussed in this article. Further, we describe the main findings of the SARA trial and put them into perspective.

Impact of left atrial appendage ridge ablation on the complex fractionated electrograms in persistent atrial fibrillation

BACKGROUND

The left atrial appendage (LAA) is a possible key contributor to the maintenance of persistent atrial fibrillation (PsAF). The effect of LAA ostial ablation on global left atrial higher-frequency sources remains unclear.

METHODS

Complex fractionated electrograms (CFEs) and dominant frequency (DF) maps acquired with a NavX system in 58 PsAF patients were enrolled and examined before and after LAA posterior ridge ablation, which followed a stepwise linear ablation.

RESULTS

High-density left atrial mapping identified continuous CFE sites in 50 % and high-DFs (≥ 8 Hz) in 53 % of patients at the LAA posterior ridge. In 44 patients in whom AF persisted despite pulmonary vein isolation (PVI) and linear ablation, LAA ablation significantly increased the mean CFE cycle length from 98 ± 29 to 108 ± 30 ms (P<0.0001) and decreased DF from 6.1 ± 0.8 to 5.9 ± 0.8 Hz (P<0.005) within the coronary sinus (CS). A multivariate analysis showed single-procedure failures could be predicted by the left atrial volume index and absence of continuous CFEs at the LAA posterior ridge region. The percent decrease in the global left atrial DF after LAA posterior ridge ablation was significantly lower in the patients with than in those without an enlarged left atrium (LA) (>90 mL/m(2)) (median 0 vs 4.8 %; P<0.01) and significantly lower in the patients with than in those without the absence of continuous CFEs in the LAA posterior ridge region (median 0.6 vs 4.8 %; P<0.05).

CONCLUSION

These findings suggested that an approach incorporating an LAA posterior ridge ablation was effective in modifying higher-frequency sources in the global LA in PsAF patients, but a lesser effect was documented in patients with electroanatomical remodeling of the LA.

The logical operator map identifies novel candidate markers for critical sites in patients with atrial fibrillation

The identification of suitable markers for critical patterns during atrial fibrillation (AF) may be crucial to guide an effective ablation treatment. Single parameter maps, based on dominant frequency and complex fractionated electrograms, have been proposed as a tool for electrogram-guided ablation, however the specificity of these markers is debated. Experimental studies suggest that AF critical patterns may be identified on the basis of specific rate and organization features, where rapid organized and rapid fragmented activities characterize respectively localized sources and critical substrates. In this paper we introduce the logical operator map, a novel mapping tool for a point-by-point identification and localization of AF critical sites. Based on advanced signal and image processing techniques, the approach combines in a single map electrogram-derived rate and organization features with tomographic anatomical detail. The construction of the anatomically-detailed logical operator map is based on the time-domain estimation of atrial rate and organization in terms of cycle length and wave-similarity, the logical combination of these indexes to obtain suitable markers of critical sites, and the multimodal integration of electrophysiological and anatomical information by segmentation and registration techniques. Logical operator maps were constructed in 14 patients with persistent AF, showing the capability of the combined rate and organization markers to identify with high selectivity the subset of electrograms associated with localized sources and critical substrates. The precise anatomical localization of these critical sites revealed the confinement of rapid organized sources in the left atrium with organization and rate gradients towards the surrounding tissue, and the presence of rapid fragmented electrograms in proximity of the sources. By merging in a single map the most relevant electrophysiological and anatomical features of the AF process, the logical operator map may have significant clinical impact as a direct, comprehensive tool to understand arrhythmia mechanisms in the single patient and guide more conservative, step-wise ablation.

Importance of pericardial fat in the formation of complex fractionated atrial electrogram region in atrial fibrillation

BACKGROUND/OBJECTIVES

Pericardial fat (PF) and complex fractionated atrial electrogram (CFAE) are both associated with atrial fibrillation (AF). Therefore, we examined the relation between PF and CFAE area in AF.

METHODS

The study population included 120 control patients without AF and 120 patients with AF (80 paroxysmal AF and 40 persistent AF) who underwent catheter ablation. Total cardiac PF volume, representing all adipose tissue within the pericardial sac, was measured by contrast-enhanced computed tomography. The location and distribution of CFAE region were identified by left atrial endocardial mapping using a three-dimensional mapping system. We analyzed the significance of total cardiac PF volume and total area of CFAE region on AF, persistence of AF from paroxysmal to persistent form, and the relation between total cardiac PF volume and total CFAE area. We also evaluated the regional distribution of PF volume and CFAE area in five areas of the left atrium (LA).

RESULTS

Total cardiac PF volume correlated with AF (odds ratio [OR]: 1.024, p<0.001). Total cardiac PF volume and total CFAE area were both independently associated with persistence of AF (OR: 1.018, p=0.018, OR: 1.144, p=0.002, respectively). Multivariate linear regression analysis identified total cardiac PF volume as a significant and independent determinant of total CFAE area (r=0.488, p<0.001). Furthermore, regional PF volume correlated with local CFAE area in an each LA area.

CONCLUSIONS

PF volume correlated significantly with CFAE area in patients with AF. This finding suggests that PF is directly related to the progression of CFAE area and promotes the pathogenic process of AF.

Model of Bipolar Electrogram Fractionation and Conduction Block Associated With Activation Wavefront Direction at Infarct Border Zone Lateral Isthmus Boundaries

Background—

Improved understanding of the mechanisms underlying infarct border zone electrogram fractionation may be helpful to identify arrhythmogenic regions in the postinfarction heart. We describe the generation of electrogram fractionation from changes in activation wavefront curvature in experimental canine infarction.

Methods and Results—

A model was developed to estimate the extracellular signal shape that would be generated by wavefront propagation parallel to versus perpendicular to the lateral boundary (LB) of the reentrant ventricular tachycardia (VT) isthmus or diastolic pathway. LBs are defined as locations where functional block forms during VT, and elsewhere they have been shown to coincide with sharp thin-to-thick transitions in infarct border zone thickness. To test the model, bipolar electrograms were acquired from infarct border zone sites in 10 canine heart experiments 3 to 5 days after experimental infarction. Activation maps were constructed during sinus rhythm and during VT. The characteristics of model-generated versus actual electrograms were compared. Quantitatively expressed VT fractionation (7.6±1.2 deflections; 16.3±8.9-ms intervals) was similar to model-generated values with wavefront propagation perpendicular to the LB (9.4±2.4 deflections; 14.4±5.2-ms intervals). Fractionation during sinus rhythm (5.9±1.8 deflections; 9.2±4.4-ms intervals) was similar to model-generated fractionation with wavefront propagation parallel to the LB (6.7±3.1 deflections; 7.1±3.8-ms intervals). VT and sinus rhythm fractionation sites were adjacent to LBs ≈80% of the time.

Conclusions—

The results suggest that in a subacute canine infarct model, the LBs are a source of activation wavefront discontinuity and electrogram fractionation, with the degree of fractionation being dependent on activation rate and wavefront orientation with respect to the LB.

Temporal stability in the spectral representation of complex fractionated atrial electrograms

BACKGROUND

Although local electrograms during atrial fibrillation (AF) are often spectrally analyzed over 8-second (8s) intervals, changes may be common over intervals as short as 2s. We sought to determine whether averaged 2s measurements of electrogram spectral parameters were similar to 8s measurements, and whether the 2s intervals could provide an estimate of the temporal stability of the signal frequency content in paroxysmal versus persistent AF.

METHODS

Complex fractionated atrial electrograms (CFAEs) were acquired outside the pulmonary vein ostia and from free wall sites in nine paroxysmal and 10 longstanding persistent AF patients. Using a 2s sliding calculation window, a frequency spectrum was computed every 100 ms over an interval of 8.4 seconds (82 spectra in total). The dominant frequency (DF), the dominant amplitude (DA), and the mean spectral profile (MP) were measured. The 2s measurements were compared to single 8.4-second interval measurements. Coefficients of variation (COV) were computed from the 82 spectra for each CFAE recording to determine temporal variability of parameters.

RESULTS

Over the sliding 2s computation intervals, as for fixed 8.4-second computation intervals, mean DA and DF were significantly higher in longstanding persistent AF while MP was significantly higher in paroxysmal AF (P ≤ 0.001). The COV was significantly higher for the DF parameter in paroxysmal AF (P < 0.001) and significantly higher for the MP parameter in persistent AF (P < 0.02).

CONCLUSIONS

For both paroxysmal and persistent AF data, the 2s sliding window averages provide similar results to single 8.4-second intervals, and information regarding temporal stability was additionally obtained in the process.

Catheter Ablation Targeting Complex Fractionated Atrial Electrogram in Atrial Fibrillation

The relatively low success rates seen with pulmonary vein ablation in non-paroxysmal atrial fibrillation (AF) patients as compared to those with the paroxysmal form of the arrhythmia have prompted electrophysiologists to search for newer ablative strategies. A decade has passed since the initial description of complex fractionated atrial electrogram (CFAE) ablation aimed at targeting the electrophysiological substrate in atrial fibrillation. Despite intensive research, superiority of CFAE-based ablation over other contemporary approaches could not be demonstrated. Nevertheless, the technique has an adjunctive role to pulmonary vein ablation in non-paroxysmal AF patients. Perhaps our incomplete understanding of the complex AF pathophysiology and inadequate characterization or determination of CFAE has limited our success so far. This review aims to highlight the current challenges and future role of CFAE ablation.  .

Localized rotational activation in the left atrium during human atrial fibrillation: relationship to complex fractionated atrial electrograms and low-voltage zones

BACKGROUND

In humans, the existence of rotors or reentrant sources maintaining atrial fibrillation (AF) and the underlying electroanatomic substrate has not been well defined.

OBJECTIVE

Our aim was to determine the prevalence of localized rotational activation (RotA) in the left atrium (LA) during human AF and whether complex fractionated atrial electrograms (CFAEs) or low-voltage areas colocalize with RotA sites.

METHODS

We prospectively studied 32 patients (mean age 57 ± 8 years; 88% with persistent AF) undergoing AF catheter ablation. Bipolar electrograms were recorded for 2.5 seconds during AF using a roving 20-pole circular catheter in the LA. RotA was defined as sequential temporal activation of bipoles around the circular catheter. Bipolar electrogram fractionation index and bipolar voltage were used to define CFAEs and low-voltage areas, respectively.

RESULTS

In 21 (66%) patients, 47 RotA sites were identified. Few (9%) lasted 2.5 seconds (cycle length 183 ± 6 ms), while the majority (91%) were nonsustained (duration 610 ± 288 ms; cycle length 149 ± 11 ms). RotA was most common in the pulmonary vein antrum (71%) and posterior LA (25%). CFAEs were recorded from 18% ± 12% of LA area, and most (92% ± 7%) were not associated with RotA sites. However, 85% of RotA sites contained CFAEs. Very low voltage (<0.1 mV) areas comprised 12% ± 10% of LA area and were present in 23% of RotA sites.

CONCLUSIONS

In patients with predominantly persistent AF, localized RotA is commonly present but tends to be transient (<1 second). Although most CFAEs do not colocalize with RotA sites, the high prevalence of CFAEs and very low voltages within RotA sites may indicate slow conduction in diseased myocardium necessary for their maintenance.

Inverse relationship between fractionated electrograms and atrial fibrosis in persistent atrial fibrillation: combined magnetic resonance imaging and high-density mapping

OBJECTIVES

This study sought to evaluate the relationship between fibrosis imaged by delayed-enhancement (DE) magnetic resonance imaging (MRI) and atrial electrograms (Egms) in persistent atrial fibrillation (AF).

BACKGROUND

Atrial fractionated Egms are strongly related to slow anisotropic conduction. Their relationship to atrial fibrosis has not yet been investigated.

METHODS

Atrial high-resolution MRI of 18 patients with persistent AF (11 long-lasting persistent AF) was registered with mapping geometry (NavX electro-anatomical system (version 8.0, St. Jude Medical, St. Paul, Minnesota)). DE areas were categorized as dense or patchy, depending on their DE content. Left atrial Egms during AF were acquired using a high-density, 20-pole catheter (514 ± 77 sites/map). Fractionation, organization/regularity, local mean cycle length (CL), and voltage were analyzed with regard to DE.

RESULTS

Patients with long-lasting persistent versus persistent AF had larger left atrial (LA) surface area (134 ± 38 cm(2) vs. 98 ± 9 cm(2), p = 0.02), a higher amount of atrial DE (70 ± 16 cm(2) vs. 49 ± 10 cm(2), p = 0.01), more complex fractionated atrial Egm (CFAE) extent (54 ± 16 cm(2) vs. 28 ± 15 cm(2), p = 0.02), and a shorter baseline AF CL (147 ± 10 ms vs. 182 ± 14 ms, p = 0.01). Continuous CFAE (CFEmean [NavX algorithm that quantifies Egm fractionation] <80 ms) occupied 38 ± 19% of total LA surface area. Dense DE was detected at the left posterior left atrium. In contrast, the right posterior left atrium contained predominantly patchy DE. Most CFAE (48 ± 14%) occurred at non-DE LA sites, followed by 41 ± 12% CFAE at patchy DE and 11 ± 6% at dense DE regions (p = 0.005 and p = 0.008, respectively); 19 ± 6% CFAE sites occurred at border zones of dense DE. Egms were less fractionated, with longer CL and lower voltage at dense DE versus non-DE regions: CFEmean: 97 ms versus 76 ms, p < 0.0001; local CL: 153 ms versus 143 ms, p < 0.0001; mean voltage: 0.63 mV versus 0.86 mV, p < 0.0001.

CONCLUSIONS

Atrial fibrosis as defined by DE MRI is associated with slower and more organized electrical activity but with lower voltage than healthy atrial areas. Ninety percent of continuous CFAE sites occur at non-DE and patchy DE LA sites. These findings are important when choosing the ablation strategy in persistent AF.

Current hot potatoes in atrial fibrillation ablation

Atrial fibrillation (AF) ablation has evolved to the treatment of choice for patients with drug-resistant and symptomatic AF. Pulmonary vein isolation at the ostial or antral level usually is sufficient for treatment of true paroxysmal AF. For persistent AF ablation, drivers and perpetuators outside of the pulmonary veins are responsible for AF maintenance and have to be targeted to achieve satisfying arrhythmia-free success rate. Both complex fractionated atrial electrogram (CFAE) ablation and linear ablation are added to pulmonary vein isolation for persistent AF ablation. Nevertheless, ablation failure and necessity of repeat ablations are still frequent, especially after persistent AF ablation. Pulmonary vein reconduction is the main reason for arrhythmia recurrence after paroxysmal and to a lesser extent after persistent AF ablation. Failure of persistent AF ablation mostly is a consequence of inadequate trigger ablation, substrate modification or incompletely ablated or reconducting linear lesions. In this review we will discuss these points responsible for AF recurrence after ablation and review current possibilities on how to overcome these limitations.