Summary
Background
Epicardial ganglionated plexi (GP) ablation can prevent atrial fibrillation inducibility. However, the long-term effects of GP ablation on atrial fibrillation have not been elucidated.
Methods
Thirteen adult dogs of either sex, weighing 13–17 kg, were randomly assigned to a sham-operated group ( n = 6) or a GP ablation group ( n = 7). After right thoracotomy, the atrial effective refractory period (AERP) was measured and atrial fibrillation was induced by right atrial rapid burst pacing. Atrial fibrillation and AERP were remeasured after anterior right and inferior right GP ablation in the GP ablation group. The animals were allowed to recover for 8 weeks, after which atrial fibrillation and AERP were measured again. Concentrations of C-reactive protein, tumour necrosis factor-alpha (TNF-α) and interleukin-6 were measured in the blood and atrial tissues.
Results
After 8 weeks, atrial fibrillation was induced in all animals in the GP ablation group. AERP and dispersion of AERP (dAERP; maximum AERP minus minimum AERP) were increased after GP ablation but AERP recovered after 8 weeks. There were no significant differences in the concentrations of C-reactive protein, TNF-α or interleukin-6 in venous blood between the two groups and the concentration of C-reactive protein in the atrium did not change before and after GP ablation. However, the concentrations of TNF-α and interleukin-6 in the atrium increased significantly 8 weeks after GP ablation ( P < 0.05).
Conclusion
Increased concentrations of TNF-α and interleukin-6 in the atrium after GP ablation provide a new causative factor in terms of atrial fibrillation vulnerability.
Résumé
Justification
L’ablation épicardique des plexus ganglionnaires peut prévenir l’induction d’une fibrillation atriale. Cependant, les effets à long terme de l’ablation des plexus ganglionnaires sur la fibrillation atriale n’ont pas été étudiés.
Méthode
Treize chiens adultes, de sexe male ou femelle, d’un poids de 13 à 17 kilos ont été randomisés en un groupe témoin ( n = 6) et un groupe bénéficiant d’une ablation du plexus ganglionnaire ( n = 7). Après thoracotomie droite, la période réfractaire effective (AERP) a été mesurée et la fibrillation atriale induite par un pacing auriculaire rapide. La fibrillation atriale et AERP ont été mesurées après une ablation ganglionnaire antérieure droite et inférieure droite, dans le groupe ablation du plexus ganglionnaire. Un suivi de huit semaines a été assuré, au terme duquel la fibrillation atriale et l’AERP ont été à nouveau déterminés. Les concentrations de CRP, de TNF-α, d’interleukine 6 ont été mesurées sur des échantillons sanguins et atriaux.
Résultats
Au terme de ces huit semaines, la fibrillation atriale a été induite chez tous les animaux dans le groupe ablation. L’AERP et la dispersion de l’AERP (dAERP, maximum AERP moins minimum AERP) était significativement augmentée après ablation, mais l’AERP est récupérée au terme des huit semaines de suivi. Il n’y avait pas de différence significative dans la concentration de CRP, de TNF-α ou d’interleukine 6 dans le sang veineux entre les deux groupes et la concentration de CRP dans l’oreillette n’était pas modifiée de façon significative après ablation des plexus ganglionnaire. Cependant, la concentration de TNF-α et d’interleukine 6 dans l’oreillette augmentait significativement à huit semaines après ablation des plexus ganglionnaire ( p < 0,05).
Conclusion
L’augmentation des concentrations de TNF-α et interleukine 6 dans l’oreillette après ablation des plexus ganglionnaires suggère un mécanisme causal nouveau dans la vulnérabilité à la fibrillation atriale.
Background
The autonomic nervous system plays an important role in the pathogenesis of AF, with increased sympathetic and parasympathetic activity and a decreased AERP . Recent reports have demonstrated that stimulation of the epicardial fat pads containing clusters of GP can initiate spontaneous AF . Radiofrequency GP ablation can prevent AF inducibility . Although long-term vagal denervation of the atria can be achieved by radiofrequency catheter ablation of epicardial fat pads , the long-term effects of GP ablation on AF are yet to be clarified. One study reported that radiofrequency fat pad ablation may not achieve long-term suppression of AF induction in a canine model. In humans, a high AF recurrence rate was observed during follow-up after selective vagal denervation alone , and GP ablation shows inferior clinical outcome compared with circumferential ablation .
Previous studies have demonstrated that inflammation might be an independent risk factor for AF and the nervous system reflexively regulates the inflammatory response, just as it controls heart rate and other vital functions . Recently, a study showed that selective vagal denervation of the sinus and atria decreased heart rate variability and eliminated baroreflex sensitivity . We hypothesized that long-term atrial denervation might induce changes in inflammatory factors, which could be the mechanism of recurrence of AF.
Methods
Preparation of animal model
All animal studies were reviewed and approved by the ethical committee of Wuhan University. Animal handling was carried out according to the Wuhan Directive for Animal Research. Thirteen adult dogs of either sex, weighing 13–17 kg, were used in the present study. The animals were abdominally anaesthetized with pentobarbital sodium (30 mg/kg) and ventilated with room air. Continuous electrocardiogram monitoring was done using lead II and aVF. Dogs in the sham-operated group (group 1; n = 6) underwent right thoracotomy at the fourth intercostal space without fat pad ablation, while dogs in the GP ablation group (group 2; n = 7) underwent fat pad ablation after the right thoracotomy.
After surgery, the fat pad containing the anterior right GP and the inferior right GP were exposed in the GP ablation group . Complete ablation of each GP was achieved as previously described .
Electrophysiological measurements
AERP was determined by a LEAD-2000B instrument (Sichuan, P. R. China). The S 1 –S 2 intervals were decreased from 150 ms to refractoriness, initially by decrements of 10 ms (S 1 :S 2 = 8:1). As the S 1 –S 2 intervals approached the AERP, decrements were reduced to 5 ms. An extra stimulus (S 2 ) was added in atrial late diastole and the interval between S 1 and S 2 was reduced in 5 ms steps until there was no propagated atrial response. The longest S 1 –S 2 coupling interval that failed to result in a propagated atrial response was taken as the local AERP. AERP was determined at each electrode pair along the catheters positioned at the right atrial appendage, right atrium, left atrial appendage and left atrium.
An S 1 S 1 (120 ms cycle length, 5 s) programmed stimulus method was adopted to induce AF. AF was defined as irregular atrial rates faster than 500 beats per minute associated with irregular atrioventricular conduction lasting > 5 s. Induction of AF was assessed three times in each dog. In the sham-operated group, AERP and AF were measured immediately after thoracotomy and after 8 weeks. In the GP ablation group, AERP and AF were measured before GP ablation, immediately after GP ablation and 8 weeks after GP ablation.
Radioimmunoassay
For radioimmunoassay, 4 mL of venous blood were collected in ethylene diamine tetra-acetic acid vacutainers and centrifuged at 3000 rpm for 10 min at 4 degrees (Avanti J-E, Beckman Coulter, Inc., Brea, CA, USA), before surgery and after 8 weeks. The serum was separated and kept in microtubes and stored at −80 °C until assay. After 8 weeks, the hearts were immediately excised and 100 mg of myocardial tissue were taken from the posterior wall of the left and right atria, about 1 cm from the ablation site. Tissue samples were homogenized in phosphate-buffered saline buffer and centrifuged at 3000 g for 20 min at 4 °C. After centrifugation, supernatants were collected. The proinflammatory markers CRP, TNF-α and IL-6 were measured using commercially available enzyme linked immunosorbent assay kits (eBioscience, San Diego, CA, USA).
Statistical analysis
Values are shown as means ± standard deviations. Statistical comparisons were made using analysis of variance. Paired and unpaired comparisons were made using Student’s t test. Unpaired t tests were used to compare the means of nerve densities. Statistical significance was assumed if p values were less than 0.05.
Results
AERP and induction of AF
Immediately after anterior right and inferior right GP ablation in the GP ablation group, AERP and dispersion of AERP (dAERP) were significantly longer than before GP ablation. For instance, the AERP at right atrial sites increased from 132 ± 4 ms at baseline to 139 ± 6 ms ( P < 0.05). After 8 weeks, however, AERP was shorter than immediately after GP ablation, with no statistical significance compared with baseline. There were also no significant differences in AERP and dAERP between baseline and after 8 weeks in the sham-operated group ( Fig. 1 A–C).
