Catheter Ablation of Nonparoxysmal Atrial Fibrillation Using Electrophysiologically Guided Substrate Modification During Sinus Rhythm After Pulmonary Vein Isolation

Box Isolation of fibrotic areas: A substrate modification approach in atrial fibrillation patients

In the last years, atrial fibrosis was shown to be an independent predictor of procedural failure in patients with paroxysmal and persistent atrial fibrillation. Ablation strategies have been developed to improve the outcome of catheter ablation by targeting detected areas of fibrosis, based either on endocardial voltage mapping or cardiac magnetic resonance. Box isolation of fibrotic areas (BIFA) is a new and promising patient-tailored ablation strategy for atrial fibrillation patients targeting substantial fibrotic areas by circumferential isolation of left atrial fibrosis.

Scar Homogenization in Atrial Fibrillation Ablation: Evolution and Practice

Atrial fibrillation (AF) ablation has emerged as the preferred rhythm control strategy for symptomatic paroxysmal AF refractory or intolerant to at least one class I or III antiarrhythmic medication. Since the initial observation by Haissaguerre and colleagues, of pulmonary vein triggers initiating atrial fibrillation (AF), pulmonary vein isolation (PVI) has become the cornerstone for paroxysmal AF ablation therapy.

Low-voltage areas detected by high-density electroanatomical mapping predict recurrence after ablation for paroxysmal atrial fibrillation

INTRODUCTION

We aimed to evaluate the extent of atrial fibrosis in paroxysmal atrial fibrillation (AF) and the correlation with ablation outcomes after pulmonary vein antral isolation (PVΑI) using a mapping system with high-resolution and high-spatial sampling.

METHODS AND RESULTS

We prospectively enrolled 80 consecutive patients (45 males, median age 60.26 years) with symptomatic paroxysmal AF who were scheduled for PVAI. Prior to PVAI, high-density bipolar voltage mapping (median number of 2,485 points) was carried out during sinus rhythm in all patients. Criteria for an adequate left atrium (LA) shell were > 2,000 points. Each acquired point was classified according to the peak-to-peak bipolar voltage electrogram based on two criteria (criterion A: healthy > 0.8 mV, border zone: 0.4-0.8 mV and scarred: < 0.4 mV, criterion Β: healthy: > 0.5 mV, border zone: 0.25-0.5 mV and scarred: < 0.25 mV). The extent of low-voltage area < 0.4 mV significantly predicted atrial tachyarrhythmia recurrence after the blanking period (P = 0.002). In univariate analysis, the presence of LA voltage areas < 0.4 mV more than 10% of the total surface area was the only significant predictor of arrhythmia recurrence. The analysis based on window B cutoff values failed to demonstrate any predictors of arrhythmia recurrence.

CONCLUSION

These data demonstrate that the existence of LA voltage areas < 0.4 mV more than 10% of the total LA surface area predicts arrhythmia recurrence following PVAI for paroxysmal AF.

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.

Beyond Pulmonary Vein Isolation: the Role of Additional Sites in Catheter Ablation of Atrial Fibrillation

PURPOSE OF REVIEW

Pulmonary vein (PV) isolation is the cornerstone of atrial fibrillation (AF) ablation. However, the long-term procedural outcome remains suboptimal and there is a frequent need for repeat ablation procedure, especially in patients with non-paroxysmal AF. The review article summarizes the rationales, recent evidences, and strategies of ablation of extra-PV sites and its clinical outcomes.

RECENT FINDINGS

It is a consensus that durable PV isolations are a definite therapy in patients with paroxysmal AF. In non-paroxysmal AF, many laboratories still believe that adequate substrate ablation outside PVs is definitely required. Empirical linear ablation is not recommended because of difficulty in achieving complete linear block, unless macro-reentry atrial tachycardia developed during procedure. Most of laboratories applied complex fractionated atrial electrogram (CFAE) ablation after PV isolation in non-paroxysmal AF, but the efficacy is limited in the long-term follow-up studies. A combined approach using CFAE, non-linear similarity, and phase mapping strategy to identify rotors or focal sources for substrate modification increases the ablation outcome, when compared to CFAE ablation alone. Provocative test with mapping of non-PV triggers is also recommended in all patients to improve long-term ablation success. Ablation beyond PV isolation is important, especially in non-paroxysmal AF patients, to modify the diseased atrial substrate and eliminate the non-PV triggers, which in turn improve the ablation outcome.

Ablation of long-standing persistent atrial fibrillation

Atrial fibrillation (AF) is the most commonly encountered arrhythmia in the clinical setting affecting nearly 6 million people in United States and the numbers are only expected to rise as the population continues to age. Broadly it is classified into paroxysmal, persistent and longstanding persistent AF. Electrical, structural and autonomic remodeling are some of the diverse pathophysiological mechanisms that contribute to the persistence of AF. Our review article emphasizes particularly on long standing persistent atrial fibrillation (LSPAF) aspect of the disease which poses a great challenge for electrophysiologists. While pulmonary vein isolation (PVI) has been established as a successful ablation strategy for paroxysmal AF, same cannot be said for LSPAF owing to its long duration, complexity of mechanisms, multiple triggers and substrate sites that are responsible for its perpetuation. The article explains different approaches currently being adopted to achieve freedom from atrial arrhythmias. These mainly include ablation techniques chiefly targeting complex fractionated atrial electrograms (CFAE), rotors, linear lesions, scars and even considering hybrid approaches in a few cases while exploring the role of delayed enhancement magnetic resonance imaging (deMRI) in the pre-procedural planning to improve the overall short and long term outcomes of catheter ablation.

Wavefront direction and cycle length affect left atrial electrogram amplitude

BACKGROUND

The relationship between atrial electrogram (EGM) characteristics in atrial fibrillation (AF) and those in sinus rhythm (SR) are generally unknown. The activation rate and direction may affect EGM characteristics. We examined characteristics of left atrial (LA) EGMs obtained during pacing from different sites.

METHODS

The study included 10 patients undergoing pulmonary vein isolation for AF. Atrial EGMs were recorded from a 64-pole basket catheter placed in the LA, and bipolar EGM amplitudes from the distal electrode pair (1-2) and proximal electrode pair (6-7) from 8 splines were averaged. The high right atrium (HRA), proximal coronary sinus (CSp), and distal coronary sinus (CSd) were paced at 600 ms and 300 ms.

RESULTS

When the LA voltage at SR was ≥1.5 mV, bipolar voltages of the HRA were greater than those of the CSp, which were greater than those of the CSd, regardless of the pacing cycle length. The shorter pacing cycle length resulted in a reduction of the LA EGM voltage at sites of SR voltage ≥1.5 mV, but no significant difference was seen at sites where the SR EGM amplitude was between >0.5 and <1.5 mV. No significant differences were seen in intra-basket conduction times between pacing cycle lengths of 600 ms and 300 ms at any pacing site.

CONCLUSION

The rate and direction-dependent reduction of the amplitude of atrial EGMs may explain, in part, the voltage discordance during SR and AF.

Influence of the left atrial contact areas on fixed low-voltage zones during atrial fibrillation and sinus rhythm in persistent atrial fibrillation

BACKGROUND

Atrial low-voltage zones (LVZ) are suggested as important factors for maintaining persistent atrial fibrillation (PsAF). The relationship between LVZs and left atrial (LA) contact areas (CoAs) is still unclear.

OBJECTIVE

To assess whether CoA regions were involved in atrial substrate properties maintaining PsAF.

METHODS

A total of 50 patients with PsAF (36 long-lasting) were analyzed. Three representative CoA detection areas (ascending aorta-anterior-LA, descending aorta-left pulmonary vein antrum, and vertebrae-posterior-LA) were registered on the mapping geometry. Electrograms during AF and sinus rhythm (SR) were acquired, and the fractionated electrograms (CFE; < 80milliseconds) and voltages were analyzed regarding the CoAs.

RESULTS

After SR conversion, 76% (38/50) had a significant LVZ (>5% of the total LA surface area). Patients with long-lasting PsAF versus PsAF had larger CoA areas (7.7 ± 3.0 vs. 4.5 ± 2.5cm² , P < 0.05) and overlapped-LVZs (8.2 [3.2-11.0] vs. 2.1 [0.7-3.7] cm² , P = 0.0126) between the SR-LVZs (<0.5 mV) and AF-LVZs (<0.2 mV). Overlapped-LVZs were frequently observed in CoA regions (anterior 76.4%; LIPV antrum 78.8%, and vertebrae 39.2%), and those LVZs had smaller unipolar voltages than those distant from the CoA regions (0.64 ± 0.16 vs. 2.5 ± 1.5 mV, P < 0.0001). SR-LVZ targeted ablation, including of CoA regions, rendered AF termination (n = 8, 21%), and 88% of the sites were not located immediately above, but adjacent to, the overlapped-LVZs. Significant AF slowing (6.0 ± 0.6 to 5.6 ± 0.6 Hz; P < 0.05) accompanied by unintentional CFE elimination (9.8-1.8 cm² ; P < .0001) was achieved in patients without termination.

CONCLUSION

Our data suggested that external structures in contact with the LA are involved in the creation of localized diseased myocardium necessary for PsAF maintenance.

Catheter ablation of atrial fibrillation with box isolation of fibrotic areas: Lessons on fibrosis distribution and extent, clinical characteristics, and their impact on long-term outcome

INTRODUCTION

The BIFA concept (box isolation of fibrotic areas) supplementing pulmonary vein isolation (PVI) was implemented in atrial fibrillation (AF) patients with fibrotic atrial cardiomyopathy (FACM) to improve catheter ablation outcomes.

METHODS AND RESULTS

Ninety-two patients with FACM underwent PVI + BIFA. We investigated patient characteristics (58 persistent/34 paroxysmal, 68 ± 8 years, LA 44 ± 7 mm, CHA₂ DS₂ -VASc 2.6 ± 1.3, FACM I: 15.2%, II: 53.3%, III: 26.1%, IV: 5.4%), periprocedural data concerning fibrosis extent/distribution, and their impact on outcome. Based on severe fibrosis areas (SFAs) of 13.5 ± 13.9 cm² detected by voltage mapping, 1.4 ± 0.5 boxes (n = 1-3, 2.2-35.3 cm² ) were applied in the left atrium. With higher grade FACM, SFAs increased and maximum voltage decreased (I/IV: 6.29/3.18 mV). Anterior (ant.) SFAs were found to be more common and larger than posterior (post.) SFAs (58.3% vs. 42.6%, ant. 8.0 ± 8.0 vs. post. 4.7 ± 6.8 cm² ). In 40 of 92 (43%) patients, both atrial walls were affected with rare cases of solely post. fibrosis (6 of 92, 6.6%). Women (39 of 92, 42%) showed FACM III+IV more often than men (P = 0.022) and can still present paroxysmal while persistent males are more likely to have FACM I-II. Single and multiple procedure (1.2/patient) success was 69% and 83% after 16 ± 8 months with an unfavorable impact of large SFA size, both-sided fibrosis and reduced maximum voltage, independently of patient characteristics and AF type.

CONCLUSION

FACM patients are a challenging AF subgroup for catheter ablation. Women seem to show FACM III+IV more often than men. The distribution of left atrial fibrosis is variable but more pronounced anteriorly. Atrial disease is characterized by SFA size but also maximum voltage reduction, both with implications on ablation outcome. Using BIFA, success rates of patients without fibrosis can be approached but are limited in FACM III+IV.

Intra-operative mapping of the atria: the first step towards individualization of atrial fibrillation therapy?

INTRODUCTION

Atrial fibrillation (AF), an age-related progressive disease, is becoming a worldwide epidemic with a prevalence rate of 33 million. Areas covered: In this expert review, an overview of important results obtained from previous intra-operative mapping studies is provided. In addition, our novel intra-operative high resolution mapping studies, its surgical considerations and data analyses are discussed. Furthermore, the importance of high resolution mapping studies of both sinus rhythm and AF for the development of future AF therapy is underlined by our most recent results. Expert commentary: Progression of AF is determined by the extensiveness of electropathology which is defined as conduction disorders caused by structural damage of atrial tissue. The severity of electropathology is a major determinant of therapy failure. At present, we do not have any diagnostic tool to determine the degree of electropathology in the individual patient and we can thus not select the most optimal treatment modality for the individual patient. An intra-operative, high resolution scale, epicardial mapping approach combined with quantification of electrical parameters may serve as a diagnostic tool to stage AF in the individual patient and to provide patient tailored therapy.

Scar homogenization in AF ablation: Evolution and practice

Laboratory studies, histology studies, image studies and the clinical studies all prove the positive correlation between atrial fibrillation and atrial fibrosis from different perspectives. Atrial fibrosis, by separating myocardial cell coupling, diminishing conduction velocity and promoting anisotropic conduction, produce the substrate to sustain atrial fibrillation (AF). These fibrotic areas can be translated into signal abnormalities (low voltage and complex electrgram), and be depicted by electroanatomic high density map. Ablation targeting these areas after circumferential pulmonary vein produces isolation as the additional substrate modification strategy has proved its beneficial results. However, the unified methodology regarding the scar definition, the mapping rhythm (AF or sinus rhythm) and the modification endpoint is yet to be negotiated. Large-scale clinical trials, long-term follow-up results are needed to prove its contribution to the overall success rate of AF ablation.