Slow Pathway Ablation Decreases Vulnerability to Pacing-Induced Atrial Fibrillation: Possible Role of Vagal Denervation

Low-Voltage Zones as the Atrial Fibrillation Substrates: Relationship With Initiation, Perpetuation, and Termination

Background: Low-voltage zones (LVZs) were usually targeted for ablation in atrial fibrillation (AF). However, its relationship with AF initiation, perpetuation, and termination remains to be studied. This study aimed to explore such relationships.

Methods: A total of 126 consecutive AF patients were enrolled, including 71 patients for AF induction protocol and 55 patients for AF termination protocol. Inducible and sustainable AF were defined as induced AF lasting over 30 and 300 s, respectively. Terminable AF was defined as those that could be terminated into sinus rhythm within 1 h after ibutilide administration. Voltage mapping was performed in sinus rhythm for all patients. LVZ was quantified as the percentage of the LVZ area (LVZ%) to the left atrium surface area.

Results: The rates of inducible, sustainable, and terminable AF were 29.6, 18.3, and 38.2%, respectively. Inducible AF patients had no significant difference in overall LVZ% compared with uninducible AF patients (10.2 ± 11.8 vs. 8.5 ± 12.6, p = 0.606), while sustainable and interminable AF patients had larger overall LVZ% than unsustainable (16.2 ± 11.5 vs. 0.5 ± 0.7, p < 0.001) and terminable AF patients (44.6 ± 26.4 vs. 26.3 ± 22.3, p < 0.05), respectively. The segmental LVZ distribution pattern was diverse in the different stages of AF. Segmental LVZ% difference was initially observed in the anterior wall for patients with inducible AF, and the septum was further affected in those with sustainable AF, and the roof, posterior wall, and floor were finally affected in those with interminable AF.

Conclusions: The associations between LVZ with AF initiation, perpetuation, and termination were different depending on its size and distribution.

Atrioventricular Node Slow-Pathway Ablation Reduces Atrial Fibrillation Inducibility: A Neuronal Mechanism

BACKGROUND

Radiofrequency ablation (RFA) for atrioventricular nodal reentrant tachycardia appears to reduce atrial tachycardia, which might relate to parasympathetic denervation at cardiac ganglionated plexuses.

METHODS AND RESULTS

Compared to 7 control canines without RFA, in 14 canines, RFA at the bottom of Koch's triangle attenuated vagal stimulation-induced effective refractory periods prolongation in atrioventricular nodal and discontinuous atrioventricular conduction curves but had no effect on the sinoatrial node. RFA attenuated vagal stimulation-induced atrial effective refractory periods shortening and vulnerability window of atrial fibrillation widening in the inferior right atrium and proximal coronary sinus but not in the high right atrium and distal coronary sinus. Moreover, RFA anatomically impaired the epicardial ganglionated plexuses at the inferior vena cava‒inferior left atrial junction. This method was also investigated in 42 patients who had undergone ablation of atrioventricular nodal reentrant tachycardia, or 12 with an accessory pathway (AP) at the posterior septum (AP-PS), and 34 patients who had an AP at the free wall as control. In patients with atrioventricular nodal reentrant tachycardia and AP-PS, RFA at the bottom of Koch's triangle prolonged atrial effective refractory periods and reduced vulnerability windows of atrial fibrillation widening at the inferior right atrium, distal coronary sinus and proximal coronary sinus but not the high right atrium. In patients with AP-free wall, RFA had no significant atrial effects.

CONCLUSIONS

RFA at the bottom of Koch's triangle attenuated local autonomic innervation in the atrioventricular node and atria, decreased vagal stimulation-induced discontinuous atrioventricular nodal conduction, and reduced atrial fibrillation inducibility due to impaired ganglionated plexuses. In patients with atrioventricular nodal reentrant tachycardia or AP-PS, RFA prolonged atrial effective refractory periods, and narrowed vulnerability windows of atrial fibrillation.

Clinical and electrophysiological characteristics of the patients with relatively slow atrioventricular nodal reentrant tachycardia

OBJECTIVE

The aim of this study is to retrospectively investigate clinical and electrophysiologic characteristics of typical AVNRT with relatively slow tachycardia rates below the average value compared to faster ones, in patients without structural heart disease.

METHODS

The present study retrospectively included a total of 1,150 patients receiving successful slow-pathway radio frequency ablation for typical slow-fast AVNRT. Patients were divided into two groups according to their tachycardia cycle length: group I included 1,018 patients with tachycardia cycle length < 400 msn and group II included 132 patients with cycle length > 400 msn. Patients with another form of arrhythmia other than typical AVNRT, the existence of structural heart disease, preexisting prolonged PR interval, history of clinically documented AF, and reasons capable of causing AF were accepted as exclusion criterias.

RESULTS

The patients in group II were older than those in group 1 (p=0.039), and male ratio was significantly higher in group II compared to group I (p=0.02). Wenckebach cycle length and AV node antegrade effective refractory period values before the RF ablation were significantly higher in group II compared to group I (p=0.0001 and 0.01, respectively). Right atrium effective refractory period values in both pre- and post-ablation period were significantly higher in group I compared to group II (p=0.0001 and 0.004, respectively). The existence of atrial vulnerability before ablation was significantly higher in group II compared to group I (p=0.007); however, there was no difference between the two groups in terms of atrial vulnerability after the ablation. In addition, while the ratio of anterior location as an ablation site near the His-bundle region was significantly higher in group II, the ratio of posterior location was significantly higher in group I (p=0.0001 for both).

CONCLUSION

Our experience demonstrates that clinical and electrophysiologic characteristics of AVNRT patients with relatively slower tachycardia rates were quite different compared to the faster AVNRT cases.

Lone atrial fibrillation in the young - perhaps not so "lone"?

OBJECTIVE

To determine if pediatric patients with a history of lone atrial fibrillation (AF) have other forms of supraventricular tachycardia (SVT) that may potentially trigger AF.

STUDY DESIGN

A multicenter review of patients with lone AF who underwent electrophysiology (EP) study from 2006-2011 was performed.

INCLUSION CRITERIA

age ≤21 years, normal ventricular function, structurally normal heart, history of AF, and EP study and/or ablation performed.

EXCLUSION CRITERIA

congenital heart disease or cardiomyopathy. Patient demographics, findings at EP study and follow-up data were recorded.

RESULTS

Eighteen patients met inclusion criteria. The mean age was 17.9 ± 2.2 years, weight was 82 ± 21 kg, body mass index was 27 ± 6, and 15 (83%) were males. Eleven (61%) were overweight or obese. Seven (39%) had inducible SVT during EP study: 5 atrioventricular nodal re-entry tachycardia (71%) and 2 concealed accessory pathways with inducible atrioventricular re-entry tachycardia (29%). All 7 patients with inducible SVT underwent radiofrequency ablation. There were no complications during EP study and/or ablation for all 18 patients. The mean follow-up was 1.7 ± 1.5 years and there were no recurrences in the 7 patients who underwent ablation. There were 2 recurrences of AF in patients with no other form of SVT during EP study.

CONCLUSIONS

Inducible SVT was found in 39% of pediatric patients undergoing EP study for lone AF. EP study should be considered for pediatric patients presenting with lone AF.

Inducibility of atrial fibrillation in the absence of atrial fibrillation: what does it mean to be normal?

BACKGROUND

While inducibility of atrial fibrillation (AF) is often used as an endpoint for radiofrequency ablation of AF, little is known regarding inducibility among normals. We therefore evaluated the inducibility of AF with rapid atrial pacing in patients without a clinical history of AF after catheter ablation of supraventricular tachycardia (SVT).

METHODS

We prospectively evaluated 86 patients with no history of AF who were referred for catheter ablation of SVT. After successful ablation, two different rapid atrial pacing protocols for induction of AF were tested. First, AF induction was attempted by 5-second bursts of atrial pacing from the coronary sinus ostium (CSO) at three different cycle lengths (CLs). Next, decremental pacing was performed from the CSO starting at a CL of 250 ms to the loss of 1:1 atrial capture. This protocol was repeated 3 times for each subject.

RESULTS

Three of the subjects (3.5%) enrolled had inducible AF with the first pacing protocol. However, with the second protocol, AF was inducible in 22 patients (25.6%), including sustained AF in 16 patients (18.6%). There were significant differences in the inducibility of AF between the two atrial pacing protocols. Additionally, with the second pacing protocol, patients with a loss of 1:1 atrial capture at CL <180 ms were more easily inducible for AF (21/63 vs. 1/23; P = .006).

CONCLUSION

Using a specific, decremental pacing protocol, 26% of patients without a history of AF had inducible AF. These findings suggest that significant further investigation is needed to optimize the specificity of using AF induction as an endpoint for AF ablation.

Coexisting sustained tachyarrthymia in patients with atrial fibrillation undergoing catheter ablation

Background and Objectives

During the index procedure of catheter ablation (CA) for atrial fibrillation (AF), it is important to assess whether other atrial or ventricular tachyarrhythmia coexist. Their symptoms are often attributed to residual tachycardia after successful elimination of AF by CA. This tachycardia could also be non-pulmonary vein (PV) foci initiated AF. This study examined the coexistence of other sustained tachyarrhythmia of patients who underwent radiofrequency CA (RFCA) for AF.

Subjects and Methods

Four hundred fifty-nine consecutive patients (375 males, aged 53.4±11.4 years) who underwent RFCA for AF were investigated. Atrial and ventricular programmed stimulation (PS) with or without isoproterenol infusion were performed, and spontaneously developed tachycardias were analyzed.

Results

Fifteen patients (3.3% of total) were diagnosed to have other sustained arrhythmias that included slow-fast type atrioventricular nodal reentrant tachycardia (AVNRT, n=6), atrioventricular reentrant tachycardia (AVRT, n=5) that utilized left posteroseptal (n=4) and parahisian bypass tract (n=1), atrial tachycardia (AT, n=2) originating from the foramen ovale (n=1) and the ostium of coronary sinus (n=1), sustained ventricular tachycardia (VT, n=2) involving one from the apical posterolateral wall of left ventricule in a normal heart and one from an anterolateral wall in an underlying myocardial infarction (MI). These sustained tachycardias were neither clinically documented nor had structural heart diseases, with the exception of one patient with MI associated VT. Two patients had the triple tachycardia; one involved AVNRT, AVRT, and AF, and the other involved VT, AT, and AF. All associated tachycardias were successfully eliminated by RFCA.

Conclusion

Fifteen (3.3%) patients with AF had coexisting sustained tachycardia. RFCA was successful in these patients. Identification of tachycardia by PS before RFCA for AF should be done to maximize the efficacy of the first ablation session.