The role of empiric superior vena cava isolation in atrial fibrillation: a systematic review and meta-analysis of randomized controlled trials

Empirical superior vena cava electrical isolation guided by quantitative ablation index improves outcomes of radiofrequency catheter ablation for paroxysmal atrial fibrillation

BACKGROUND

The value of empirical superior vena cava isolation (SVCI) following pulmonary vein isolation (PVI) to improve the efficacy of radiofrequency catheter ablation (RFCA) for paroxysmal atrial fibrillation (PAF) remains controversial.

OBJECTIVE

To evaluate the efficacy and safety of quantitative ablation index (AI)-guided empirical SVCI, in addition to PVI, for patients with PAF.

METHODS

Patients with symptomatic PAF who underwent RFCA between October 2021 and May 2023 were retrospectively analysed. Patients were categorised into PVI-only group and PVI+SVCI group based on the intraoperative ablation strategy. RFCA was guided by quantitative AI in both groups. Regular clinical follow-ups were conducted to detect AF recurrence, defined as any episode of atrial fibrillation, atrial flutter or atrial tachycardia lasting >30 s.

RESULTS

A total of 246 patients were enrolled, with 108 patients in the PVI group and 138 patients in the PVI+SVCI group. Compared with the PVI group, patients in the PVI+SVCI group had a higher prevalence of coronary artery disease (p=0.04), stroke (p=0.02) and a smaller left atrial diameter (p<0.01). After a follow-up period of 16±6 months, the ablation success rate was significantly higher in the SVCI+PVI group compared with the PVI group (91.3% vs 81.5%, p=0.02). Multivariable logistic regression analysis indicated that SVCI was an independent predictor of reduced AF recurrence postablation (Relative Risk [RR] 0.4, 95% CI 0.19 to 0.90, p=0.026). No significant difference in complication rates was observed between the groups.

CONCLUSION

Quantitative AI-guided empirical SVCI, in addition to PVI, improves the success rate of RFCA for PAF without increasing the risk of complications.

Ablation Strategies for Persistent Atrial Fibrillation: Beyond the Pulmonary Veins

Despite advances in ablative therapies, outcomes remain less favorable for persistent atrial fibrillation often due to presence of non-pulmonary vein triggers and abnormal atrial substrates. This review highlights advances in ablation technologies and notable scientific literature on clinical outcomes associated with pursuing adjunctive ablation targets and substrate modification during persistent atrial fibrillation ablation, while also highlighting notable future directions.

Usefulness of empiric superior vena cava isolation in paroxysmal atrial fibrillation ablation: a meta-analysis of randomized clinical trials

BACKGROUND

The long-term success rate of pulmonary vein isolation (PVI) is suboptimal due to the presence of non-pulmonary vein (PV) foci that can trigger atrial fibrillation (AF) in up to 11%. Among non-PV triggers, the superior vena cava (SVC) is a major site of origin of ectopic beats initiating AF.

OBJECTIVE

To compare data from randomized controlled trials (RCTs) assessing PVI + empiric SVC isolation (SVCI) versus PVI alone in terms of AF recurrence, procedure-related complications, and fluoroscopic and procedural times.

METHODS

A search of online scientific libraries (from inception to April 1, 2024) was performed. Four RCTs were considered eligible for the meta-analysis totaling 600 patients of whom 287 receiving PVI + SVCI and 313 receiving PVI alone.

RESULTS

In the overall population, SVCI + PVI was associated with a non-significant reduction of AF recurrence at follow-up (0.66 [0.43;1.00], p = 0.05, I2 0%). In patients with paroxysmal AF (PAF), a significant reduction of AF recurrence was related to SVCI + PVI (11.7%) as compared to PVI alone (19.9%) (0.54 [0.32;0.92], p = 0.02, I2 0%). No statistical differences were found among the groups in terms of fluoroscopic (3.31 [- 0.8;7.41], p = 0.11, I2 = 91%), procedural times (5.69 [- 9.78;21.16], p = 0.47, I2 = 81%), and complications (1.06 [0.33;3.44], p = 0.92, I2 = 0%).

CONCLUSION

The addition of SVCI to PVI in patients in PAF is associated with a significant lower rate of AF recurrence at follow-up, without increasing complication rates and procedural and fluoroscopy times.

Repeat catheter ablation for atrial fibrillation

Catheter ablation of atrial fibrillation (AF) is an established therapy that reduces AF burden, improves quality of life, and reduces the risks of cardiovascular outcomes. Although there are clear guidelines for the application of de novo catheter ablation, there is less evidence to guide recommendations for repeat catheter ablation in patients who experience recurrent AF. In this review, we examine the rationale for repeat ablation, mechanisms of recurrence, patient selection, optimal timing, and procedural strategies. We discuss additional important considerations, including treatment of comorbidities and risk factors, risk of complications, and effectiveness. Mechanisms of recurrent AF are often due to non-pulmonary vein (non-PV) triggers; however, there is insufficient evidence supporting the routine use of empiric lesion sets during repeat ablation. The emergence of pulsed field ablation may alter the safety and effectiveness of de novo and repeat ablation. Extrapolation of data from randomized trials of de novo ablation does not optimally inform efficacy in cases of redo ablation. Additional large, randomized controlled trials are needed to address important clinical questions regarding procedural strategies and timing of repeat ablation.

Role of electroanatomical mapping-guided superior vena cava isolation in paroxysmal atrial fibrillation patients without provoked superior vena cava triggers: a randomized controlled study

AIMS

Data about whether empirical superior vena cava (SVC) isolation (SVCI) improves the success rate of paroxysmal atrial fibrillation (PAF) are conflicting. This study sought to first investigate the characteristics of SVC-triggered atrial fibrillation and secondly investigate the impact of electroanatomical mapping-guided SVCI, in addition to circumferential pulmonary vein isolation (CPVI), on the outcome of PAF ablation in the absence of provoked SVC triggers.

METHODS AND RESULTS

A total of 130 patients undergoing PAF ablation underwent electrophysiological studies before ablation. In patients for whom SVC triggers were identified, SVCI was performed in addition to CPVI. Patients without provoked SVC triggers were randomized in a 1:1 ratio to CPVI plus SVCI or CPVI only. The primary endpoint was freedom from any documented atrial tachyarrhythmias lasting over 30 s after a 3-month blanking period without anti-arrhythmic drugs at 12 months after ablation. Superior vena cava triggers were identified in 30 (23.1%) patients with PAF. At 12 months, 93.3% of those with provoked SVC triggers who underwent CPVI plus SVCI were free from atrial tachyarrhythmias. In patients without provoked SVC triggers, SVCI, in addition to CPVI, did not increase freedom from atrial tachyarrhythmias (87.9 vs. 79.6%, log-rank P = 0.28).

CONCLUSION

Electroanatomical mapping-guided SVCI, in addition to CPVI, did not increase the success rate of PAF ablation in patients who had no identifiable SVC triggers.

REGISTRATION

ChineseClinicalTrials.gov: ChiCTR2000034532.

Radiofrequency catheter ablation of atrial fibrillation: A review of techniques

Ablation of atrial fibrillation is a key area of current research. A multitude of techniques have been tested, some of which are poorly evidenced and not recommended in routine clinical practice whilst others are more promising. Additionally, a plethora of issues exist when researching ablation techniques, from control arm ablation strategy to the relevance of outcome measures. In this review article, we discuss these issues in the context of the current evidence base.

Effective superior vena cava isolation using a novel C-shaped approach

Introduction

Superior vena cava (SVC) isolation has been proposed as part of the ablation strategy for atrial fibrillation. However, circumferential isolation of the SVC can lead to late-onset complications, such as SVC stenosis.

Methods

We describe a detailed observation of the SVC conduction pattern and present a newly developed approach for SVC isolation that involves creating a C-shaped non-circumferential ablation line while sparing the lateral segment.

Results

Twelve consecutive patients were included in the study, all of whom achieved bidirectional block during the ablation procedure.

Discussion

This approach to SVC isolation is effective and has the potential to reduce ablation related complications; however, larger studies and long-term follow-up is warranted to confirm these findings.

Optimization of superior vena cava isolation with aid of ablation index guidance

INTRODUCTION

To investigate the optimal range of quantitative ablation index (AI) value during superior vena cava (SVC) electrical isolation by radiofrequency catheter ablation (RFCA).

METHODS

First, in a development cohort of patients with atrial fibrillation (AF), the RFCA with 40 W was performed to complete SVC isolation guided by the conduction breakthrough point from the right atrium to SVC. Then, the range of AI value was calculated by offline analysis on different segments of SVC. Lastly, for the validation of AF patients, the safety and effectiveness of SVC isolation with the optimized target range of AI value were evaluated with an additional adenosine test.

RESULTS

A total of 101 patients with AF were included in the study (44 patients in the development cohort/57 in the validation cohort). The segmental ablation strategy was applied in 70% of the patients. According to the offline analysis of the AI values in the development cohort, the target AI value range was set as 350-400. The success rate of SVC isolation in the validation cohort was significantly higher than that in the exploration cohort (100% vs. 90.9%, p = .02), and no complications occurred in the exploration cohort. During the adenosine test, the recovery rate of electrical conduction in SVC was significantly lower than that in the pulmonary vein (3.5% vs. 17.5%).

CONCLUSION

The target AI value with a range from 350 to 400 is safe and effective for high-power RFCA to complete SVC isolation.

Role of non-pulmonary vein triggers in persistent atrial fibrillation

Pulmonary vein isolation is an well-established treatment strategy for atrial fibrillation (AF), and it is especially effective for patients with paroxysmal AF. However, the success rate is limited for patients with persistent AF, because non-pulmonary vein triggers which increase AF recurrence are frequently found in these patients. The major non-pulmonary vein triggers are from the left atrial posterior wall, left atrial appendage, ligament of Marshall, coronary sinus, superior vena cava, and crista terminalis, but other atrial sites can also generate AF triggers. All these sites have been known to contain atrial myocytes with potential arrhythmogenic electrical activity. The prevalence and clinical characteristics of these non-pulmonary vein triggers are well studied; however, the clinical outcome of catheter ablation for persistent AF is still unclear. Here, we reviewed the current ablation strategies for persistent AF and the clinical implications of major non-pulmonary vein triggers.

Role of empirical isolation of the superior vena cava in patients with recurrence of atrial fibrillation after pulmonary vein isolation-a multi-center analysis

BACKGROUND

Non-pulmonary vein (PV) triggers play a role in the initiation of atrial fibrillation (AF), with the superior vena cava (SVC) being a common location. The aim of the current study was to investigate a strategy of empirical SVC isolation (SVCI) in addition to re-isolation of PV in patients with recurrence of AF after index PV isolation (PVI).

METHODS

We retrospectively analyzed consecutive patients from two centers with recurrence of AF after index PVI, undergoing a repeat ablation. Whereas only a re-isolation of the PV was intended in patients with reconnections of equal or more than two PV (PVI group), an additional SVCI was aimed for in patients with < 2 isolated PV in addition to the re-isolation of the PV (PVI + group). Analysis was performed as-treated and per-protocol.

RESULTS

Of the 344 patients included in the study (age 60 ± 10 years, 73% male, 66% paroxysmal AF), PVI only was performed in 269 patients (77%) and PVI plus SVCI (PVI +) in 75 patients (23%). Overall, freedom from AF/AT after repeat PVI was 80% (196 patients) in the PVI group and 73% in the PVI + group (p = 0.151). In multivariable Cox regression analysis, presence of persistent AF (HR 2.067 (95% CI 1.389-3.078), p < 0.001) and hypertension (HR 1.905 (95% CI 1.218-2.980), p = 0.005) were identified as only significant predictors of AF/AT recurrence. The per-protocol results did not differ from this observation.

CONCLUSIONS

A strategy of an empirical additional SVCI at repeat PVI ablation for recurrence of AF/AT does not improve outcome compared to a PVI only approach.

Empirical superior vena cava isolation in patients undergoing repeat catheter ablation procedure after recurrence of atrial fibrillation

BACKGROUND

Although the ectopic foci responsible for initiating atrial fibrillation (AF) are usually located in the pulmonary veins (PVs), non-PV sources may initiate AF in approximately 11% of unselected patients with paroxysmal or persistent AF. The superior vena cava (SVC) is one of the most frequent non-PV origins for initiating AF. This study aims to investigate the effect of empirical SVC isolation in redo AF ablation procedures.

METHODS

Consecutive patients undergoing redo AF ablation procedures using a high-power short-duration protocol (HPSD) (50 W; ablation index guided; target AI 350 for posterior wall ablation, AI 450 for anterior wall ablation; CARTO 3 mapping system) were included. Patients with SVC isolation were compared to patients without SVC isolation. Periprocedural parameters and complications were recorded and analyzed. Short-term endpoints included intrahospital AF recurrence, midterm endpoint AF freedom after 3 months, and long-term endpoint AF freedom after 12 months.

RESULTS

A total of 276 patients underwent repeat ablation for recurrent AF (67 ± 10 years; 57% male; 31.5% paroxysmal AF). The patients were divided into two groups: redo procedures with SVC isolation vs redo procedure without SVC isolation. Additional LA substrate modification was done based on intraprocedural voltage maps. Baseline characteristics did not differ significantly between the two groups. Median procedure time was 85.4 ± 27.1 min with ablation times of 14.0 ± 8.5 min. Intrahospital AF recurrence occurred in 32 patients (12%) with no difference among both groups: 17 patients (13%) SVC vs 15 patients (10%) No-SVC; p = 0.416. At 3-month follow-up, 47 (17%) presented an AF recurrence during the blanking period: 25 patients (19%) SVC vs 22 patients (15%) No-SVC; p = 0.304). After 12 months, 202 (73%) of all patients were in stable sinus rhythm with no significant difference between the two groups: 93 patients (73%) SVC vs 109 patients (74%) No-SVC; p = 0.853). No significant differences were noted when dividing the patients in paroxysmal or persistent AF with and without SVC isolation.

CONCLUSIONS

In our series of repeat AF ablation procedures, the addition of empirical SVC isolation to Re-PVI and LA substrate modification did not influence AF recurrence rates. This strategy can however be safe and useful in patients in whom SVC is identified as a trigger of AF.

An impact of superior vena cava isolation in non-paroxysmal atrial fibrillation patients with low voltage areas

BACKGROUND

This study aimed to investigate the correlation between left atrial low-voltage areas (LVAs) and an arrhythmogenic superior vena cava (SVC) and the impact on the efficacy of an empiric SVC isolation (SVCI) along with a pulmonary vein isolation (PVI) of non-paroxysmal atrial fibrillation (non-PAF) with or without LVAs.

METHODS

We retrospectively enrolled 153 consecutive patients with non-PAF who underwent a PVI alone (n = 51) or empiric PVI plus an SVCI (n = 102). Left atrial voltage maps were constructed during sinus rhythm to identify the LVAs (<0.5 mV). An arrhythmogenic SVC was defined as firing from the SVC and an SVC associated with the maintenance of AF-like rapid SVC activity.

RESULTS

An arrhythmogenic SVC and LVAs were identified in 28% and 65% of patients with a PVI alone and 36% and 73% of patients with a PVI plus SVCI, respectively (P = .275 and P = .353). In the multivariate analysis a female gender, higher pulmonary artery systolic pressure (PAPs), and arrhythmogenic SVC were associated with the presence of LVAs. In the PVI plus SVCI strategy, there was no significant difference in the atrial tachyarrhythmia/AF-free survival between the patients with and without LVAs after initial and multiple sessions (50% vs. 61%; P = .386, 73% vs. 79%; P = .530), however, differences were observed in the PVI alone group (27% vs. 61%; P = .018, 49% vs. 78%; P = .046).

CONCLUSIONS

The presence of LVAs was associated with an arrhythmogenic SVC. An SVCI may have the potential to compensate for an impaired outcome after a PVI in non-PAF patients with LVAs.

Superior vena cava isolation with 50 W high power, short duration ablation strategy

INTRODUCTION

The optimal ablation strategy is unknown regarding a superior vena cava isolation (SVCI). This study aimed to examine the feasibility and safety and to analyze the lesion characteristics of the SVCI using high-power, short-duration (HPSD) ablation.

METHODS AND RESULTS

A total of 100 patients underwent an index SVCI using HPSD (n = 50, HPSD group) or conventional lower-power and longer-duration (n = 50, LPLD group) ablation, using the Thermocool Smarttouch SF. In the HPSD group, ablation was performed with a power of 50 W for 7 s, and was limited to 4 s at the lateral segment close to the right phrenic nerve. The ablation setting used in the LPLD group was 20-25 W for 20-30 s and was limited to 10-20 W for 15-30 s at the lateral segment when diaphragmatic capture was seen. An electrical SVCI was achieved in all patients. The HPSD group required a significantly shorter procedure time (10.8 ± 3.2 vs. 14.8 ± 6.4 min; p < .01), shorter radiofrequency duration (49 ± 16 vs. 282 ± 124 s; p < .01), fewer lesions (8.3 ± 2.5 vs. 10.4 ± 4.4; p < .01), and lower ablation index (316 ± 38 vs. 356 ± 62; p < .001) than the LPLD group. The incidence of a postprocedural asymptomatic mild diaphragmatic elevation was comparable (2% in the HPSD group vs. 6% in the LPLD group; p = .61).

CONCLUSION

The 50-W HPSD ablation strategy allowed for a successful, fast, and safe SVCI with the fewer ablation lesions and the lower ablation index.

The susceptibility of the rat pulmonary and caval vein myocardium to the catecholamine-induced ectopy changes oppositely in postnatal development

KEY POINTS

The developmental changes of the caval (SVC) and pulmonary vein (PV) myocardium electrophysiology are traced throughout postnatal ontogenesis. The myocardium in SVC as well as in PV demonstrate age-dependent differences in the ability to maintain resting membrane potential, to manifest automaticity in a form of ectopic action potentials in basal condition and in responses to the adrenergic stimulation. Electrophysiological characteristics of two distinct types of thoracic vein myocardium change in an opposite manner during early postnatal ontogenesis with increased proarrhythmicity of pulmonary and decreased automaticity in caval veins. Predisposition of PV cardiac tissue to proarrhythmycity develops during ontogenesis in time correlation with the establishment of sympathetic innervation of the tissue. The electrophysiological properties of caval vein cardiac tissue shift from a pacemaker-like phenotype to atrial phenotype in accompaniment with sympathetic nerve growth and adrenergic receptor expression changes.

ABSTRACT

The thoracic vein myocardium is considered as a main source for atrial fibrillation initiation due to its high susceptibility to ectopic activity. The mechanism by which and when pulmonary (PV) and superior vena cava (SVC) became proarrhythmic during postnatal ontogenesis is still unknown. In this study, we traced postnatal changes of electrophysiology in a correlation with the sympathetic innervation and adrenergic receptor distribution to reveal developmental differences in proarrhythmicity occurrence in PV and SVC myocardium. A standard microelectrode technique was used to assess the changes in ability to maintain resting membrane potential (RMP), generate spontaneous action potentials (SAP) and adrenergically induced ectopy in multicellular SVC and PV preparations of rats of different postnatal ages. Immunofluorescence imaging was used to trace postnatal changes in sympathetic innervation, β1- and α1A-adrenergic receptor (AR) distribution. We revealed that the ability to generate SAP and susceptibility to adrenergic stimulation changes during postnatal ontogenesis in an opposite manner in PV and SVC myocardium. While SAP occurrence decreases with age in SVC myocardium, it significantly increases in PV cardiac tissue. PV myocardium starts to demonstrate RMP instability and proarrhythmic activity from the 14th day of postnatal life which correlates with the appearance of the sympathetic innervation of the thoracic veins. In addition, postnatal attenuation of SVC myocardium automaticity occurs concomitantly with sympathetic innervation establishment and increase in β1-ARs, but not α1A-AR levels. Our results support the contention that SVC and PV myocardium electrophysiology change during postnatal development, resulting in higher PV proarrhythmicity in adults.

Anatomical targets and expected outcomes of catheter-based ablation of atrial fibrillation in 2020

Anatomical-based approaches, targeting either pulmonary vein isolation (PVI) or additional extra PV regions, represent the most commonly used ablation treatments in symptomatic patients with atrial fibrillation (AF) recurrences despite antiarrhythmic drug therapy. PVI remains the main anatomical target during catheter-based AF ablation, with the aid of new technological advances as contact force monitoring to increase safety and effective radiofrequency (RF) lesions. Nowadays, cryoballoon ablation has also achieved the same level of scientific evidence in patients with paroxysmal AF undergoing PVI. In parallel, electrical isolation of extra PV targets has progressively increased, which is associated with a steady increase in complex cases undergoing ablation. Several atrial regions as the left atrial posterior wall, the vein of Marshall, the left atrial appendage, or the coronary sinus have been described in different series as locations potentially involved in AF initiation and maintenance. Targeting these regions may be challenging using conventional point-by-point RF delivery, which has opened new opportunities for coadjuvant alternatives as balloon ablation or selective ethanol injection. Although more extensive ablation may increase intraprocedural AF termination and freedom from arrhythmias during the follow-up, some of the targets to achieve such outcomes are not exempt of potential severe complications. Here, we review and discuss current anatomical approaches and the main ablation technologies to target atrial regions associated with AF initiation and maintenance.

Paroxysmal atrial fibrillation recurrence after redo procedure-ablation modality impact

BACKGROUND

Atrial fibrillation recurrence (AFR) is common after pulmonary vein isolation (PVI), and the rate does not differ between radiofrequency (RF) and cryoballoon (CB) ablation. The aim of this study was to assess the impact of the ablation modality used at the index PVI on the outcome after redo PVI in patients with paroxysmal AF.

METHODS

In this prospective, single-center, non-randomized study, consecutive patients with paroxysmal AF who have undergone the index PVI with either RF ablation (RF group) or 2nd-generation CB (CB group) were included. The primary endpoint was freedom from recurrence of atrial arrhythmia lasting > 30 s.

RESULTS

A total of 105 patients undergoing redo PVI for paroxysmal AF were included (median age 61 years; 24% female; left ventricular ejection fraction (LVEF) 57 ± 8%; left atrial volume index (LAVI) 34 ± 11 mm). Index PVI was done either with focal RF (n = 81) or with CB (n = 24) and redo PVI only with focal RF. Total procedure time (139 vs. 113 min, p = 0.10) and RF delivery time (1017 vs. 870 s, p = 0.33) of the redo PVI were not significantly different. After a median follow-up of 371 (185-470) days, there were no differences between the RF and CB groups regarding the AFR rate after the second PVI (24 vs. 23%, p = 0.89). The Kaplan-Meier analysis showed no difference between the groups regarding AFR freedom time (p = 0.81). In multivariable logistic regression, only coronary artery disease was identified as an independent long-term predictor of AFR (OR 4.15, 95% CI 1.17-14.71, p = 0.027).

CONCLUSIONS

The ablation modality used at the index PVI has no impact on long-term outcome after redo PVI in patients with paroxysmal AF.

Efficacy of Ablation Lesion Sets in Addition to Pulmonary Vein Isolation for Paroxysmal Atrial Fibrillation: Findings From the SMASH - AF Meta-Analysis Study Cohort

Background

The objective was to explore the efficacy of ablation lesion sets in addition to pulmonary vein isolation (PVI) for paroxysmal atrial fibrillation. The optimal strategy for catheter ablation of paroxysmal atrial fibrillation is debated.

Methods and Results

The SMASH‐AF (Systematic Review and Meta‐analysis of Ablation Strategy Heterogeneity in Atrial Fibrillation) study cohort includes trials and observational studies identified in PubMed, Scopus, and Cochrane databases from January 1 1990, to August 1, 2016. We included studies reporting single procedure paroxysmal atrial fibrillation ablation success rates. Exclusion criteria included insufficient reporting of outcomes, ablation strategies that were not prespecified and uniform, and a sample size of fewer than 40 patients. We analyzed lesion sets performed in addition to PVI (PVI plus) using multivariable random‐effects meta‐regression to control for patient, study, and procedure characteristics. The analysis included 145 total studies with 23 263 patients (PVI‐only cohort: 115 studies, 148 treatment arms, 16 500 patients; PVI plus cohort: 39 studies; 46 treatment arms, 6763 patients). PVI plus studies, as compared with PVI‐only studies, included younger patients (56.7 years versus 58.8 years, P=0.001), fewer women (27.2% versus 32.0% women, P=0.002), and were more methodologically rigorous with longer follow‐up (29.5 versus 17.1 months, P 0.004) and more randomization (19.4% versus 11.8%, P<0.001). In multivariable meta‐regression, PVI plus studies were associated with improved success (7.6% absolute improvement [95% CI, 2.6–12.5%]; P<0.01, I²=88%), specifically superior vena cava isolation (4 studies, 4 treatment arms, 1392 patients; 15.1% absolute improvement [95% CI, 2.3–27.9%]; P 0.02, I²=87%). However, residual heterogeneity was large.

Conclusions

Across the paroxysmal atrial fibrillation ablation literature, PVI plus ablation strategies were associated with incremental improvements in success rate. However, large residual heterogeneity complicates evidence synthesis.

Rat caval vein myocardium undergoes changes in conduction characteristics during postnatal ontogenesis

The electrophysiological properties of the superior vena cava (SVC) myocardium, which is considered a minor source of atrial arrhythmias, were studied in this study during postnatal development. Conduction properties were investigated in spontaneously active and electrically paced SVC preparations obtained from 7-60-day-old male Wistar rats using optical mapping and microelectrode techniques. The presence of high-conductance connexin 43 (Cx43) was evaluated in SVC cross-sections using immunofluorescence. It was found that SVC myocardium is excitable, electrically coupled with the atrial tissue, and conducts excitation waves at all stages of postnatal development. However, the conduction velocity (CV) of excitation and action potential (AP) upstroke velocity in SVC were significantly lower in neonatal than in adult animals and increased with postnatal maturation. Connexins Cx43 were identified in both neonatal and adult rat SVC myocardium; however, the abundance of Cx43 was significantly less in neonates. The gap junction uncoupler octanol affected conduction more profound in the neonatal than in adult SVC. We demonstrated for the first time that the conduction characteristics of SVC myocardium change from a slow-conduction (nodal) to a high-conduction (working) phenotype during postnatal ontogenesis. An age-related CV increase may occur due to changes of AP characteristics, electrical coupling, and Cx43 presence in SVC cardiomyocyte membranes. Observed changes may contribute to the low proarrhythmicity of adult caval vein cardiac tissue, while pre- or postnatal developmental abnormalities that delay the establishment of the working conduction phenotype may facilitate SVC proarrhythmia.

Persistent Atrial Fibrillation Ablation: Where Do We Go From Here?

Catheter ablation is being used increasingly for the treatment of atrial fibrillation (AF). Pulmonary vein antral isolation is considered the "cornerstone" for the ablation of AF. This approach has demonstrated consistent rates of success for paroxysmal AF, but the rates of success for persistent AF are lower. There has long been a hypothesis that additional ablation beyond pulmonary vein isolation is required to achieve better outcomes in the population with persistent AF. However, large clinical trials have demonstrated recently that such approaches as empiric linear ablation and/or ablation of complex fractionated electrograms may add no benefit over pulmonary vein isolation alone in persistent AF. Furthermore, new technologies are improving the durability and outcome of pulmonary vein isolation alone. These observations have endorsed a search for new potential targets for adjuvant ablation, which currently include ablation of dynamic phenomena during AF such as rotational and focal activations, ablation of scar regions in the atria, isolation of the left atrial posterior wall, and ablation of nonpulmonary vein triggers. Whether any of these additional approaches will add to the success of ablation for persistent AF is unknown. Smaller study results are mixed. Only the performance of large-scale randomized trials will definitively answer whether additional ablation over pulmonary vein isolation alone with improve outcomes for persistent AF.

Complications of Atrial Fibrillation Cryoablation

Catheter ablation either by using radiofrequency or cryo energy in symptomatic patients with atrial fibrillation (AF) has shown to be effective as compared to anti-arrhythmic drugs. However, all the techniques used during AF ablation are not free of complication. There are several well-known peri-procedural complications in which operators should be informed of the possible risks, cautious during the procedure and able to manage them when occurred. Herein, we aimed to review possible complications of AF cryoablation.