Radiofrequency ablation of atrial fibrillation: is the persistence of all intraprocedural targets necessary for long-term maintenance of sinus rhythm?

Left atrial spatial entropy: a novel tool for electrophysiological substrate characterization in atrial fibrillation

Background

Electrical remodeling has been linked to the progression and recurrence of atrial fibrillation (AF) after catheter ablation (CA). Substrate mapping based solely on a voltage amplitude electrogram (EGM) does not provide a comprehensive understanding of the left atrial (LA) disease. The aim of this study is to assess left atrial spatial entropy (LASE) from voltage maps routinely obtained during AF ablation to further characterize the LA substrate.

Materials and Methods

High-density electroanatomic maps (EAMs) of 27 patients with paroxysmal or persistent AF undergoing routine CA were prospectively collected. Computational post-processing was performed on the voltage maps. Using the Shannon entropy model, the probability distribution of the amplitude range values associated with each point of the map was used to measure LASE. Finally, correlations between LASE and clinical and electrophysiological characteristics of AF were explored.

Results

LASE differentiated between patients with paroxysmal and persistent AF (6.45 ± 0.41 vs. 5.87 ± 0.53; p = 0.028) and patients with normal and abnormal LA substrate (6.42 ± 0.42 vs. 5.87 ± 0.56; p = 0.043), independent of the basal rhythm during EM acquisition (6.33 ± 0.41 vs. 6.11 ± 0.63; p = 0.619). Accordance between LASE and EAMs was assessed by ROC analysis (AUC: 0.81; C.I.: 0.62-0.99; Youden index: 6.06; sensitivity: 80%; and specificity: 80%). Patients with the lowest LASE reported AF recurrence at the follow-up.

Conclusion

LASE may play a role in the further characterization of the LA substrate and the type of AF, independent of basal rhythm.

Clinical relevance of left atrial structural remodeling and non-pulmonary vein foci in atrial fibrillation

BACKGROUND

The mechanistic role of left atrial (LA) structural remodeling as a non-pulmonary vein (PV) trigger in the initiation of atrial fibrillation (AF) remains uncertain. This study is aimed at prospectively evaluating the association between non-PV triggers and LA structural remodeling.

METHODS

A total of 517 patients undergoing catheter ablation for AF were included. After PV isolation, a standardized protocol was implemented to reveal non-PV triggers, which included burst pacing into AF followed by cardioversion during isoproterenol infusion. If pacing-induced atrial tachycardia (AT) was observed, mapping and catheter ablation were performed.

RESULTS

The mean percentage of LA low-voltage area (LVA) < 0.5 mV incrementally increased during right atrial pacing among the no induction (n = 470), AF (n = 21), and AT (n = 26) groups (2.6 ± 5.7%, 5.5 ± 6.4%, and 18.0 ± 21.5%, respectively; P < 0.001). In the AF induction group, non-PV foci originated from the left atrium in 13 of 25 foci (52%), and 8 of 13 LA non-PV foci (62%) were located in the septal region. All except 1 focus originated from the non-LVA < 0.5 mV (8%), but 8 of the 13 LA foci originated from the LVA < 1.0 mV (62%). There were no differences in AF recurrence among the groups (log-rank, P = 0.160).

CONCLUSION

The majority of non-PV foci in the LA originated outside regions with advanced structural remodeling, thus suggesting the limited effectiveness of adjunctive ablation guided by the LVA < 0.5 mV during sinus rhythm in eliminating non-PV triggers.

Arrhythmia mechanism dependent pulmonary vein ablation in paroxysmal atrial fibrillation

Atrial fibrillation (AF) often requires invasive treatment by ablation to decrease symptom burden. The pulmonary veins (PV) are thought to trigger paroxysms of AF, and ablative PV isolation (PVI) is a cornerstone in AF treatment. However, incomplete PVI, where electrical conduction between the PV and left atrium (LA) is maintained, is curative of AF in a subset of patients. This implies that an antiarrhythmic effect other than electrical isolation between the PV and LA plays a role in AF prevention in these patients. We reason that the PV myocardium constitutes an arrhythmogenic substrate conducive to reentry in the patients with curative incomplete PVI. This PV substrate is amenable to ablation, even when conduction between the LA and PV persists. We propose that PV ablation strategies are differentiated to fit the arrhythmogenic mechanisms in the individual patient. PV substrate modification in patients with PV reentry may constitute a new therapeutic approach that is potentially simpler and more effective, in this subgroup of patients.

High-resolution mapping as an alternative for exit block testing in the presence of entrance block after high-power short-duration pulmonary vein isolation

BACKGROUND

After pulmonary vein isolation (PVI) for atrial fibrillation (AF), it is common as an endpoint to demonstrate an exit block from the pulmonary veins (PVs) in addition to an entrance block into them. By using high-resolution mapping catheters, even very small signals can be detected.

OBJECTIVES

We investigated whether additional exit block testing is still necessary when using high-resolution mapping catheters after ablation in high-power short-duration (HPSD) techniques.

MATERIALS AND METHODS

Overall, 114 patients with AF (average age, 65.14 ± 11.3 years; 65.8% male) undergoing radiofrequency PVI were included in the study. Ablation was performed with the HPSD technique using a fixed protocol for energy delivery of 50 W (contact force 3-20 g). Entrance and exit block were tested with a high-resolution mapping catheter. Isolation of the PVs was achieved in all patients.

RESULTS

Capture of local PV tissue was demonstrated in all patients after PVI and exit block was present in all patients after entrance block was detected using a high-resolution mapping catheter.

CONCLUSION

Exit block testing in addition to the demonstration of an entrance block as an endpoint of PVI seems to have no additional benefit and might no longer be necessary when a high-resolution mapping catheter is used in HPSD ablation for PVI of AF.

Profibrillatory Structural and Functional Properties of the Atrial-Pulmonary Junction in the Absence of Remodeling

Background: Sole pulmonary vein (PV) isolation by ablation therapy prevents atrial fibrillation (AF) in patients with short episodes of AF and without comorbidities. Since incomplete PV isolation can be curative, we tested the hypothesis that the PV in the absence of remodeling and comorbidities contains structural and functional properties that are proarrhythmic for AF initiation by reentry.

Methods: We performed percutaneous transvenous in vivo endocardial electrophysiological studies and quantitative histological analysis of PV from healthy sheep.

Results: The proximal PV contained more myocytes than the distal PV and a higher percentage of collagen and fat tissue relative to myocytes than the left atrium. Local fractionated electrograms occurred in both the distal and proximal PVs, but a large local activation (>0.75 mV) was more often present in the proximal PV than in the distal PV (86 vs. 50% of electrograms, respectively, p = 0.017). Atrial arrhythmias (run of premature atrial complexes) occurred more often following the premature stimulation in the proximal PV than in the distal PV (p = 0.004). The diastolic stimulation threshold was higher in the proximal PV than in the distal PV (0.7 [0.3] vs. 0.4 [0.2] mA, (median [interquartile range]), p = 0.004). The refractory period was shorter in the proximal PV than in the distal PV (170 [50] vs. 248 [52] ms, p < 0.001). A linear relation existed between the gradient in refractoriness (distal-proximal) and atrial arrhythmia inducibility in the proximal PV.

Conclusion: The structural and functional properties of the native atrial-PV junction differ from those of the distal PV. Atrial arrhythmias in the absence of arrhythmia-induced remodeling are caused by reentry in the atrial-PV junction. Ablative treatment of early paroxysmal AF, rather than complete isolation of focal arrhythmia, may be limited to inhibition of reentry.

Traditional Chinese medicine as a therapeutic option for cardiac fibrosis: Pharmacology and mechanisms

Cardiovascular diseases are one of the leading causes of death worldwide and cardiac fibrosis is a common pathological process for cardiac remodeling in cardiovascular diseases. Cardiac fibrosis not only accelerates the deterioration progress of diseases but also becomes a pivotal contributor for futile treatment in clinical cardiovascular trials. Although cardiac fibrosis is common and prevalent, effective medicines to provide sufficient clinical intervention for cardiac fibrosis are still unavailable. Traditional Chinese medicine (TCM) is the natural essence experienced boiling, fry, and other processing methods, including active ingredients, extracts, and herbal formulas, which have been applied to treat human diseases for a long history. Recently, research has increasingly focused on the great potential of TCM for the prevention and treatment of cardiac fibrosis. Here, we aim to clarify the identified pro-fibrotic mechanisms and intensively summarize the application of TCM in improving cardiac fibrosis by working on these mechanisms. Through comprehensively analyzing, TCM mainly regulates the following pathways during ameliorating cardiac fibrosis: attenuation of inflammation and oxidative stress, inhibition of cardiac fibroblasts activation, reduction of extracellular matrix accumulation, modulation of the renin-angiotensin-aldosterone system, modulation of autophagy, regulation of metabolic-dependent mechanisms, and targeting microRNAs. We also discussed the deficiencies and the development direction of anti-fibrotic therapies on cardiac fibrosis. The data reviewed here demonstrates that TCM shows a robust effect on alleviating cardiac fibrosis, which provides us a rich source of new drugs or drug candidates. Besides, we also hope this review may give some enlightenment for treating cardiac fibrosis in clinical practice.

Decreased anxiety after catheter ablation for paroxysmal atrial fibrillation is associated with augmented parasympathetic reactivity to stress

Background

Psychological improvement after catheter ablation for atrial fibrillation (AF) has been reported, but its mechanism is unclear.

Objective

This study aimed to clarify the relationship between cardiac autonomic modification and psychological changes after catheter ablation for paroxysmal AF (PAF).

Methods

Thirty-five consecutive patients (60.5 ± 11.9 years; male, n = 24) with PAF treated by catheter ablation were enrolled. Autonomic activity and reactivity to stress and psychological status were measured before (baseline) and at 1 and 3 months after ablation. We assessed autonomic activity and reactivity to stress by measuring heart rate variability (HRV) at rest (Rest), and during (Task) and after (After) the execution of a task and assessed relationships between HRV parameters and psychological changes using the State-Trait Anxiety Inventory (STAI) and Self-Rating Depression Scale (SDS).

Results

The STAI state and trait scores significantly decreased at 3 months compared with baseline, whereas SDS scores essentially remained unchanged. The high-frequency (HF) response index (Task/Rest) and HF recovery index (After/Rest) were significantly higher than baseline at 3 months (0.40 [0.29–0.90] vs 1.30 [0.64–2.18], P = .007 for HF response index; 1.13 [0.92–2.19] vs 1.87 [1.19–2.97], P = .049 for HF recovery index). Reductions in STAI scores positively correlated with increments in the HF recovery index in the entire cohort as well as in 5 patients with recurrent AF.

Conclusions

Some augmentation of parasympathetic reactivity to stress correlated with reduced anxiety, implying that cardiac autonomic modification plays roles in psychological improvement after catheter ablation for AF.

Predictors of Recurrence after Catheter Ablation of Paroxysmal Atrial Fibrillation in Different Follow-Up Periods

Background and objectives: Pulmonary vein (PV) reconnection is a major reason for recurrence after catheter ablation of paroxysmal atrial fibrillation (PAF). However, the timing of the recurrence varies between patients, and recurrence >1 year after ablation is not uncommon. We sought to elucidate the characteristics of atrial fibrillation (AF) that recurred in different follow-up periods. Materials and Methods: Study subjects comprised 151 consecutive patients undergoing initial catheter ablation of PAF. Left atrial volume index (LAVi) and atrial/brain natriuretic peptide (ANP/BNP) levels were systematically measured annually over 3 years until AF recurred. Results: Study subjects were classified into four groups: non-recurrence group (n = 84), and short-term- (within 1 year) (n = 30), mid-term- (1–3 years) (n = 26), and long-term-recurrence group (>3 years) (n = 11). The short-term-recurrence group was characterized by a higher prevalence of diabetes mellitus (hazard ratio 2.639 (95% confidence interval, 1.174–5.932), p = 0.019 by the Cox method), frequent AF episodes (≥1/week) before ablation (4.038 (1.545–10.557), p = 0.004), and higher BNP level at baseline (per 10 pg/mL) (1.054 (1.029–1.081), p < 0.0001). The mid-term-recurrence group was associated with higher BNP level (1.163 (1.070–1.265), p = 0.0004), larger LAVi (mL/m²) (1.033 (1.007–1.060), p = 0.013), and longer AF cycle length at baseline (per 10 ms) (1.194 (1.058–1.348), p = 0.004). In the long-term-recurrence group, the ANP and BNP levels were low throughout follow-up, as with those in the non-recurrence group, and AF cycle length was shorter (0.694 (0.522–0.924), p = 0.012) than those in the other recurrence groups. Conclusions: Distinct characteristics of AF were found according to the time to first recurrence after PAF ablation. The presence of secondary factors beyond PV reconnections could be considered as mechanisms for the recurrence of PAF in each follow-up period.

Cryoballoon Ablation for the Treatment of Atrial Fibrillation: A Meta-analysis

BACKGROUND

Ablation therapy is the treatment of choice in antiarrhythmic drugrefractory atrial fibrillation (AF). It is performed by either cryoballoon ablation (CBA) or radiofrequency ablation. CBA is gaining popularity due to simplicity with similar efficacy and complication rate compared with RFA. In this meta-analysis, we compare the recurrence rate of AF and the complications from CBA versus RFA for the treatment of AF.

METHODS

We systematically searched PubMed for the articles that compared the outcome of interest. The primary outcome was to compare the recurrence rate of AF between CBA and RFA. We also included subgroup analysis with complications of pericardial effusion, phrenic nerve palsy and cerebral microemboli following ablation therapy.

RESULTS

A total of 24 studies with 3527 patients met our predefined inclusion criteria. Recurrence of AF after CBA or RFA was similar in both groups (RR: 0.84; 95% CI: 0.65, 1.07; I2=48%, Cochrane p=0.16). In subgroup analysis, heterogeneity was less in paroxysmal AF (I2=0%, Cochrane p=0.46) compared to mixed AF (I2=72%, Cochrane p=0.003). Procedure and fluoroscopy time was less by 26.37 and 5.94 minutes respectively in CBA compared to RFA. Complications, pericardial effusion, and silent cerebral microemboli, were not different between the two groups, however, phrenic nerve palsy was exclusively present only in CBA group.

CONCLUSION

This study confirms that the effectiveness of CBA is similar to RFA in the treatment of AF with the added advantages of shorter procedure and fluoroscopy times.

High-density Mapping Guided Pulmonary Vein Isolation for Treatment of Atrial Fibrillation - Two-year clinical outcome of a single center experience

Pulmonary vein isolation (PVI) as interventional treatment for atrial fibrillation (AF) aims to eliminate arrhythmogenic triggers from the PVs. Improved signal detection facilitating a more robust electrical isolation might be associated with a better outcome. This retrospective cohort study compared PVI procedures using a novel high-density mapping system (HDM) with improved signal detection vs. age- and sex-matched PVIs using a conventional 3D mapping system (COM). Endpoints comprised freedom from AF and procedural parameters. In total, 108 patients (mean age 63.9 ± 11.2 years, 56.5% male, 50.9% paroxysmal AF) were included (n = 54 patients/group). Our analysis revealed that HDM was not superior regarding freedom from AF (mean follow-up of 494.7 ± 26.2 days), with one- and two-year AF recurrence rates of 38.9%/46.5% (HDM) and 38.9%/42.2% (COM), respectively. HDM was associated with reduction in fluoroscopy times (18.8 ± 10.6 vs. 29.8 ± 13.4 min; p < 0.01) and total radiation dose (866.0 ± 1003.3 vs. 1731.2 ± 1978.4 cGy; p < 0.01) compared to the COM group. HDM was equivalent but not superior to COM with respect to clinical outcome after PVI and resulted in reduced fluoroscopy time and radiation exposure. These results suggest that HDM-guided PVI is effective and safe for AF ablation. Potential benefits in comparison to conventional mapping systems, e.g. arrhythmia recurrence rates, have to be addressed in randomized trials.

Cardiac fibrosis - A short review of causes and therapeutic strategies

Fibrotic diseases cause annually more than 800,000 deaths worldwide, whereof the majority accounts for lung and cardiac fibrosis. A pathological remodeling of the extracellular matrix either due to ageing or as a result of an injury or disease leads to fibrotic scars. In the heart, these scars cause several cardiac dysfunctions either by reducing the ejection fraction due to a stiffened myocardial matrix, or by impairing electric conductance, or they can even lead to death. Today it is known that there are several different types of cardiac scars depending on the underlying cause of fibrosis. In this review, we present an overview of what is known about cardiac fibrosis including the role of cardiac cells and extracellular matrix in this disease. We will further summarize current diagnostic tools and highlight pre-clinical or clinical therapeutic strategies to address cardiac fibrosis.

Long-term impact of a bonus freeze on clinical outcome: Analysis of effective and non-effective bonus freezes in cryoballoon ablation

Purpose

Data on bonus freeze characteristics and their impact on complication rates and long-term clinical outcome are limited.

Methods

Pulmonary vein isolation (PVI) using a 28 mm 2^nd-generation cryoballoon (CB) was performed in 169 patients (pts). The isolation temperatures, time to isolation and minimal temperatures of the cryoapplications were documented.

Results

The study included 92 pts who received one bonus freeze after PVI in group I and 77 pts who did not receive a bonus freeze in group II. After a mean follow-up time of 19.0±8.6 months in group I and 16.4±7.5 months in group II, 67 of 92 pts (72.8%) and 49 of 75 pts available to follow up (65.3%; p = 0.221) were free of atrial tachyarrhythmia, respectively. Phrenic nerve palsy occurred in 5.4% of the pts in group I (5/92 pts) and 1.3% of the pts in group II (1/77 pts; p = 0.22). Both the mean nadir temperatures of the bonus freezes and mean nadir temperatures of the isolation freezes differed significantly between the recurrent and non-recurrent pts in group I. The predilection sites of the reconduction for both groups were the inferior aspect of the inferior pulmonary veins.

Conclusion

The impact of a bonus freeze on long-term clinical outcome was not significant for two reasons: 1) The necessity of a bonus freeze was low because the long-term clinical success rate without a bonus freeze was high; and 2) the majority of bonus freezes, especially at the predilection sites, such as the inferior PV, appeared to be ineffective.

Efficacy of adjunctive measures used to assist pulmonary vein isolation for atrial fibrillation: a systematic review

PURPOSE OF REVIEW

Pulmonary vein reconnection leading to recurrence of atrial arrhythmias after pulmonary vein isolation (PVI) for atrial fibrillation remains a significant challenge. A number of adjunctive measures during PVI have been used to attempt to reduce pulmonary vein reconnection and recurrence of atrial arrhythmias. We performed a systematic review of the literature and meta-analysis of studies evaluating the efficacy of adjunctive measures used during PVI in reducing recurrent atrial arrhythmias.

RECENT FINDINGS

Our literature search found four interventions that met the prespecified definition of adjunctive measure: adenosine testing post-PVI, contact force-guided PVI, pacing inexcitability of the ablation line during PVI and additional ablation based on the computed tomography thickness of the pulmonary vein-left atrial appendage ridge. Sixteen studies enrolling 3507 patients met all inclusion and exclusion criteria. PVI performed with adjunctive measures was shown to reduce the 1-year recurrence rate of atrial arrhythmias. The point estimate for the combined relative risk of atrial arrhythmia recurrence was 0.56 [95% confidence interval (CI): 0.43-0.73; P value <0.001] in the PVI with adjunctive measures group.

SUMMARY

PVI for atrial fibrillation assisted by adjunctive measures results in clinically significant reduction of recurrent atrial arrhythmias. Additional research is required to assess the relative efficacy of individual or combined adjunctive strategies used during PVI for atrial fibrillation.

Independent mapping methods reveal rotational activation near pulmonary veins where atrial fibrillation terminates before pulmonary vein isolation

OBJECTIVE

To investigate mechanisms by which atrial fibrillation (AF) may terminate during ablation near the pulmonary veins before the veins are isolated (PVI).

INTRODUCTION

It remains unstudied how AF may terminate during ablation before PVs are isolated, or how patients with PV reconnection can be arrhythmia-free. We studied patients in whom PV antral ablation terminated AF before PVI, using two independent mapping methods.

METHODS

We studied patients with AF referred for ablation, in whom biatrial contact basket electrograms were studied by both an activation/phase mapping method and by a second validated mapping method reported not to create false rotational activity.

RESULTS

In 22 patients (age 60.1 ± 10.4, 36% persistent AF), ablation at sites near the PVs terminated AF (77% to sinus rhythm) prior to PVI. AF propagation revealed rotational (n  =  20) and focal (n  =  2) patterns at sites of termination by mapping method 1 and method 2. Both methods showed organized sites that were spatially concordant (P < 0.001) with similar stability (P < 0.001). Vagal slowing was not observed at sites of AF termination.

DISCUSSION

PV antral regions where ablation terminated AF before PVI exhibited rotational and focal activation by two independent mapping methods. These data provide an alternative mechanism for the success of PVI, and may explain AF termination before PVI or lack of arrhythmias despite PV reconnection. Mapping such sites may enable targeted PV lesion sets and improved freedom from AF.

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.

Mini Electrodes on Ablation Catheters: Valuable Addition or Redundant Information?-Insights from a Computational Study

Radiofrequency ablation has become a first-line approach for curative therapy of many cardiac arrhythmias. Various existing catheter designs provide high spatial resolution to identify the best spot for performing ablation and to assess lesion formation. However, creation of transmural and nonconducting ablation lesions requires usage of catheters with larger electrodes and improved thermal conductivity, leading to reduced spatial sensitivity. As trade-off, an ablation catheter with integrated mini electrodes was introduced. The additional diagnostic benefit of this catheter is still not clear. In order to solve this issue, we implemented a computational setup with different ablation scenarios. Our in silico results show that peak-to-peak amplitudes of unipolar electrograms from mini electrodes are more suitable to differentiate ablated and nonablated tissue compared to electrograms from the distal ablation electrode. However, in orthogonal mapping position, no significant difference was observed between distal electrode and mini electrodes electrograms in the ablation scenarios. In conclusion, catheters with mini electrodes bring about additional benefit to distinguish ablated tissue from nonablated tissue in parallel position with high spatial resolution. It is feasible to detect conduction gaps in linear lesions with this catheter by evaluating electrogram data from mini electrodes.

Mechanistic Insights Into Durable Pulmonary Vein Isolation Achieved by Second-Generation Cryoballoon Ablation

Background

The mechanism explaining the efficacy of cryoballoon ablation (CBA) for atrial fibrillation has not been clarified.

Methods and Results

We compared lesion characteristics between patients in whom pulmonary vein isolation (PVI) was performed by CBA (n=56) and those by contact force (CF)-based RF ablation (n=56). We evaluated the 3-dimensional PV morphology before and after cryoballoon inflation. After PVI, a 3D left atrial voltage map was created. Pacing (10 mA and 2 ms) was performed within the low voltage area from the ablation line, and electrically unexcitable ablated tissue was identified. ATP-provoked dormant conduction after PVI occurred in 9 of the 224 (4%) PVs in the CBA group and in 13 of the 224 (6%) PVs in the CF group (P=0.3935). The inflated balloon stretched the PV from the original PV ostial surface by 7.1±3.5 mm, but at sites with (vs, sites without) residual PV potential/dormant conduction, the extent of the PV distension was reduced (4.0±4.0 mm vs. 7.2±3.4 mm, P<0.0001). The unexcitable ablated tissue around the PVs was significantly wider in CB patients than in CF patients (16.7±5.1 mm vs. 5.3±2.3 mm, P<0.0001).

Conclusions

Use of the cryoballoon significantly distends the PV. Without this extensive distention, PVI may not be successful. CBA seems to yield wide unexcitable ablation zones. These factors seem to explain the durability of CBA lesions.

Pulmonary Vein Re-Isolation as a Routine Strategy Regardless of Symptoms: The PRESSURE Randomized Controlled Trial

OBJECTIVES

The goal of this study was to determine whether a strategy of early re-isolation of pulmonary vein (PV) reconnection in all patients, regardless of symptoms, would reduce the recurrence of atrial fibrillation (AF) and improve quality of life.

BACKGROUND

Lasting pulmonary vein isolation (PVI) remains elusive. PV reconnection is strongly linked to the recurrence of arrhythmia.

METHODS

A total of 80 patients with paroxysmal AF were randomized 1:1 after contact force-guided PVI to receive either standard care or undergo a repeat electrophysiology study after 2 months regardless of symptoms (repeat study). At the initial procedure, PVI was demonstrated by entrance/exit block and adenosine administration after a minimum 20-min wait. At the repeat study, all sites of PV reconnection were re-ablated. Patients recorded electrocardiograms daily and whenever symptomatic for 12 months using a handheld monitor. Recurrence was defined as ≥30 s of atrial tachyarrhythmia (AT) after a 3-month blanking period. The Atrial Fibrillation Effect on Quality-of-Life Questionnaire was completed at baseline and at 6 and 12 months.

RESULTS

All 40 patients randomized to repeat study attended for this after 62 ± 6 days, of whom 25 (62.5%) had reconnection of 41 (26%) PVs. There were no complications related to these procedures. Subjects recorded a total of 32,203 electrocardiograms (380 [335 to 447] per patient) during 12.6 (12.2 to 13.2) months of follow-up. AT recurrence was significantly lower for the repeat study group (17.5% vs. 42.5%; p = 0.03), as was AT burden (p = 0.03). Scores on the Atrial Fibrillation Effect on Quality-of-Life Questionnaire were higher in the repeat study group at 6 months (p < 0.001) and 12 months (p = 0.02).

CONCLUSIONS

A strategy of routine repeat assessment with re-isolation of PV reconnection improved freedom from AT recurrence, AT burden, and quality of life compared with current standard care. (The Effect of Early Repeat Atrial Fibrillation [AF] on AF Recurrence [PRESSURE]; NCT01942408).

Paroxysmal atrial fibrillation ablation: Achieving permanent pulmonary vein isolation by point-by-point radiofrequency lesions

Pulmonary vein isolation by point-by-point radiofrequency catheter ablation constitutes the cornerstone of catheter ablation strategies for the treatment of atrial fibrillation. However, despite advances in pulmonary vein isolation ablation strategies, long-term success rates after ablation remain suboptimal, which highlights the need to develop techniques to achieve more durable lesions. Strategies proposed to improve the durability of pulmonary vein isolation can be divided into two groups: Those addressed to improving the quality of the lesion and those that optimize the detection of acute PV reconnection during the ablation procedure. This manuscript reviews the role and potential benefits of these techniques according to current clinical evidence.

A clinical study on the electrophysiological characteristics of patients without recurrence after ablation of persistent atrial fibrillation

BACKGROUND

The electrophysiological characteristics of patients without recurrence after ablation of persistent atrial fibrillation (AF) have not been systematically determined. This study compared the electrophysiological characteristics in patients with and without recurrence of AF after persistent AF ablation.

METHODS

Forty-five patients without recurrence of AF after persistent AF ablation were enrolled to assess electrophysiological characteristics including pulmonary vein (PV) reconnection, the mitral isthmus (MI) line and the roof line reconduction. Ninety-five patients with recurrence of AF after ablation were used as the control group.

RESULTS

Among patients without recurrence, recovery of PV conduction was observed in 37 of 45 (82.2%) patients: 3/45 (6.7%) reconnection in 4 veins, 7/45 (15.6%) in 3 veins, 11/45 (24.4%) in 2 veins, and 16/45 (35.6%) in 1 vein. No significant differences were seen in the proportion of patients with PV reconnection compared to patients with recurrence (p>0.05). Among patients without recurrence, the MI line reconduction was observed in 3/45 (6.7%) patients; the roof line conduction was observed in 5/45 (11.1%) patients. In comparison, patients with clinical recurrence of AF had recovery of the MI line conduction in 27/95 (28.4%) and recovery of the roof line conduction in 26/95 (27.4%). Significant differences were seen between these two groups (6.7% vs 28.4%, p=0.004; 11.1% vs 27.4%, p=0.031).

CONCLUSION

Although a high incidence of PV reconnection was similarly observed in patients with and without recurrence of AF, a lower incidence of lines reconduction was observed in patients without recurrence of AF.

Electrotonic coupling of excitable and nonexcitable cells in the heart revealed by optogenetics

Electrophysiological studies of excitable organs usually focus on action potential (AP)-generating cells, whereas nonexcitable cells are generally considered as barriers to electrical conduction. Whether nonexcitable cells may modulate excitable cell function or even contribute to AP conduction via direct electrotonic coupling to AP-generating cells is unresolved in the heart: such coupling is present in vitro, but conclusive evidence in situ is lacking. We used genetically encoded voltage-sensitive fluorescent protein 2.3 (VSFP2.3) to monitor transmembrane potential in either myocytes or nonmyocytes of murine hearts. We confirm that VSFP2.3 allows measurement of cell type-specific electrical activity. We show that VSFP2.3, expressed solely in nonmyocytes, can report cardiomyocyte AP-like signals at the border of healed cryoinjuries. Using EM-based tomographic reconstruction, we further discovered tunneling nanotube connections between myocytes and nonmyocytes in cardiac scar border tissue. Our results provide direct electrophysiological evidence of heterocellular electrotonic coupling in native myocardium and identify tunneling nanotubes as a possible substrate for electrical cell coupling that may be in addition to previously discovered connexins at sites of myocyte-nonmyocyte contact in the heart. These findings call for reevaluation of cardiac nonmyocyte roles in electrical connectivity of the heterocellular heart.

Novel therapeutic strategies targeting fibroblasts and fibrosis in heart disease

Our understanding of the functions of cardiac fibroblasts has moved beyond their roles in heart structure and extracellular matrix generation and now includes their contributions to paracrine, mechanical and electrical signalling during ontogenesis and normal cardiac activity. Fibroblasts also have central roles in pathogenic remodelling during myocardial ischaemia, hypertension and heart failure. As key contributors to scar formation, they are crucial for tissue repair after interventions including surgery and ablation. Novel experimental approaches targeting cardiac fibroblasts are promising potential therapies for heart disease. Indeed, several existing drugs act, at least partially, through effects on cardiac connective tissue. This Review outlines the origins and roles of fibroblasts in cardiac development, homeostasis and disease; illustrates the involvement of fibroblasts in current and emerging clinical interventions; and identifies future targets for research and development.

Organized Sources Are Spatially Conserved in Recurrent Compared to Pre-Ablation Atrial Fibrillation: Further Evidence for Non-Random Electrical Substrates

INTRODUCTION

Recurrent atrial fibrillation (AF) after ablation is associated with reconnection of initially isolated pulmonary vein (PV) trigger sites. Substrates are often targeted in addition to PVI, but it is unclear how substrates progress over time. We studied if substrates in recurrent AF are conserved or have developed de novo from pre-ablation AF.

METHODS AND RESULTS

Of 137 patients undergoing Focal Impulse and Rotor Mapping (FIRM) at their index procedure for AF, 29 consecutive patients (60 ± 8 years, 79% persistent) recurred and were also mapped at repeat procedure (21 ± 20 months later) using carefully placed 64-pole baskets and RhythmView(TM) (Topera, Menlo Park, CA, USA) to identify AF sources and disorganized zones. Compared to index AF, recurrent AF had a longer cycle length (177 ± 21 vs. 167 ± 19 milliseconds, P = 0.01). All patients (100%) had 1 or more conserved AF rotors between procedures with surrounding disorganization. The number of sources was similar for recurrent AF post-PVI versus index AF (3.2 ± 1.4 vs. 3.1 ± 1.0, P = 0.79), but was lower for recurrent AF after FIRM+PVI versus index AF (4.4 ± 1.4 vs. 2.9 ± 1.7, P = 0.03). Overall, 81% (61/75) of AF sources lay in conserved regions, while 19% (14/75) were detected de novo.

CONCLUSION

Electrical propagation patterns for recurrent AF after unsuccessful ablation are similar in individual patients to their index AF. These data support temporospatial stability of AF substrates over 1-2 years. Trials should determine the relative benefit of adding substrate mapping and ablation to PVI for recurrent AF.

Clinical recurrence and electrical pulmonary vein reconnections after second-generation cryoballoon ablation

BACKGROUND

Electrical reconnections after pulmonary vein isolation (PVI) are less common after second-generation cryoballoon than radiofrequency ablation.

OBJECTIVE

The purpose of this study was to investigate the incidence and characteristics of pulmonary vein (PV) reconnections after second-generation cryoballoon ablation in patients with and those without clinical recurrences.

METHODS

Forty patients with paroxysmal atrial fibrillation undergoing second procedures after cryoballoon ablation were enrolled. Twenty-five patients experienced clinical recurrences, and the remaining 15 did not.

RESULTS

All 158 PVs were reevaluated a median [25th, 75th percentiles] of 6.0 [4.0-9.0] months after the initial procedure. In total, reconnections were detected in 39 PVs (24.7%) among 25 patients (62.5%). Reconnected PVs included 6 left superior (LS) (15.8%), 7 left inferior (LI) (18.4%), 5 right superior (RS) (12.5%), 20 right inferior (RI) (50.0%), and 1 left common (LC) (50.0%) PV. Reconnected PV potential conduction delays were a median of 112 [76-130], 103 [82-133], 84 [66-96], 68 [49-73], and 204 ms in the LS, LI, RS, RI, and LC PV, respectively. There was no significant difference between those with and those without clinical recurrences with regard to clinical characteristics, procedural results, incidence of reconnections (25/98 vs 14/60, P = .758), and PV conduction delays in each PV. The most common gap location was the RI PV bottom in both groups. Among 5 patients with reconnections of arrhythmogenic PVs (with atrial fibrillation initiation), 2 experienced clinical recurrences, whereas 3 did not. Non-PV foci (with atrial fibrillation initiation) were identified in a second procedures in 10 of 25 patients with clinical recurrences.

CONCLUSION

The incidence and characteristics of PV reconnections after second-generation cryoballoon ablation were similar between patients with and those without clinical recurrences. The results should be considered when discussing the optimal dose of cryoballoon applications.

The Living Scar--Cardiac Fibroblasts and the Injured Heart

Cardiac scars, often dubbed 'dead tissue', are very much alive, with heterocellular activity contributing to the maintenance of structural and mechanical integrity following heart injury. To form a scar, non-myocytes such as fibroblasts are recruited from intra- and extra-cardiac sources. Fibroblasts perform important autocrine and paracrine signaling functions. They also establish mechanical and, as is increasingly evident, electrical junctions with other cells. While fibroblasts were previously thought to act simply as electrical insulators, they may be electrically connected among themselves and, under some circumstances, to other cells including cardiomyocytes. A better understanding of these biophysical interactions will help to target scar structure and function, and will facilitate the development of novel therapies aimed at modifying scar properties for patient benefit.

Fibroblast-myocyte coupling in the heart: Potential relevance for therapeutic interventions

Cardiac myocyte-fibroblast electrotonic coupling is a well-established fact in vitro. Indirect evidence of its presence in vivo exists, but few functional studies have been published. This review describes the current knowledge of fibroblast-myocyte electrical signaling in the heart. Further research is needed to understand the frequency and extent of heterocellular interactions in vivo in order to gain a better understanding of their relevance in healthy and diseased myocardium. It is hoped that associated insight into myocyte-fibroblast coupling in the heart may lead to the discovery of novel therapeutic targets and the development of agents for improving outcomes of myocardial scarring and fibrosis.