Atrial Fibrillation Inducibility Research Articles

Abstract EC.02: Myosin Light Chain Dephosphorylation By Ppp1r12c Promotes Atria Hypocontractility In Atrial Fibrillation

Background: Atrial fibrillation (AF), the most common sustained cardiac arrhythmia, increases thromboembolic stroke risk five-fold. Although atrial hypocontractility contributes to stroke risk in AF, the molecular mechanisms reducing myofilament contractile function remain unknown. We tested the hypothesis that increased expression of PPP1R12C, the PP1 regulatory subunit targeting atrial myosin light chain 2 (MLC2a), causes hypophosphorylation of MLC2a and results in atrial hypocontractility. Methods: Right atrial appendage tissues were isolated from human AF patients versus sinus rhythm (SR) controls. Western blots, co-immunoprecipitation, and phosphorylation studies were performed to examine how the PP1c-PPP1R12C interaction causes MLC2a de-phosphorylation. In vitro studies of pharmacologic MRCK inhibitor (BDP5290) in atrial HL-1 cells were performed to evaluate PP1 holoenzyme activity on MLC2a. Cardiac-specific lentiviral PPP1R12C overexpression was performed in mice to evaluate atrial remodeling with atrial cell shortening assays, echocardiography, and AF inducibility with EP studies. Results: In human patients with AF, PPP1R12C expression was increased two-fold versus SR controls with > 40% reduction in MLC2a phosphorylation. 12C-PP1c binding and PPP1R12C-MLC2a binding were significantly increased in AF. In vitro studies utilizing drug BDP5290, which inhibits T560-PPP1R12C phosphorylation, demonstrated increased PPP1R12C binding with both PP1c and MLC2a, and dephosphorylation of MLC2a. Lenti-12C mice demonstrated a 150% increase in LA size versus controls, with reduced atrial strain and atrial ejection fraction. Pacing-induced AF in Lenti-12C mice was significantly higher than controls. Conclusions: AF patients exhibit increased levels of PPP1R12C protein compared to controls. PPP1R12C overexpression in mice increases PP1c targeting to MLC2a and causes MLC2a dephosphorylation, which reduces atrial contractility and increases AF inducibility. These findings suggest that PP1 regulation of sarcomere function at MLC2a is a key regulator of atrial contractility in AF.

Abstract P3126: Atrial Fibrillation Is Associated With Decreased Claudin-5 In Cardiomyocyte

Background: Although it is critically important to understand the underlying molecular and electrophysiological changes that predispose to the induction and maintenance of atrial fibrillation (Af), the underlying mechanism of Af is still poorly defined. Af is characterized as the electrophysiological and membrane integrity abnormality of the atrial cells, and claudin-5, a tight junction protein, may be involved in the pathophysiology of Af, however, the role of claudin-5 in Af is unknown. Methods and Results: Cardiac tissues from the left atrial appendage were obtained from AF patients with rheumatic valvular heart disease undergoing modified radiofrequency ablation maze procedure with approval from local human research ethic review and normal left atrial appendages were obtained from non-AF donors. Western blot, immunofluorescence and transmission electron microscope showed the expression of claudin-5 significantly decreased in cardiomyocytes from left atrium of AF patients compared to non-AF donors. Then proteomics analysis was performed to screen the specific protein expression and signal pathway changed in AF heart tissue vs. non-AF heart tissue, and showed that 83 proteins were downregulated and 102 proteins were upregulated in the left atrial appendage of AF patients. Among them, DAG, CACNA2D2, MYL2 were downregulated and MCU was upregulated. KEGG pathway analysis showed these changes would lead to hypertrophic and dilated cardiomyopathy. Finally, claudin-5 shRNA AAV was injected in mouse left ventricle to knockdown claudin-5 in cardiomyocytes to observe whether change of claudin-5 affects the protein expression in KEGG pathway analysis. We found claudin-5 deficiency caused severe ventricular dilation, ST elevation and arrythmia, and the protein level of DAG, CACNA2D2 and MYL2 were downregulated and MCU was upregulated. Co-immunoprecipitation also confirmed the specific protein-protein interaction between these targeted proteins and claudin-5. Conclusion: We demonstrated that the decrease of claudin-5 in the left atrium of AF patients with rheumatic valvular heart disease. The mechanism of AF might be associated with claudin-5 downregulation-induced decrease of DAG, CACNA2D2, MYL2 and increase of MCU in cardiomyocytes.

Intermittent ventricular pre-excitation in symptomatic adults: Always a marker of low risk?

Intermittent ventricular pre-excitation was considered a low-risk marker for sudden death. However, to date, some studies do not exclude the existence of accessory pathways (APs) with high-risk intermittent antegrade conductive properties. According to current European Guidelines, high-risk features of APs are antegrade pathway conduction ≤250 ms in baseline or during the adrenergic stimulus, inducibility of atrioventricular reciprocating tachycardias (AVRT), inducibility of pre-excited atrial fibrillation (AF), and presence of multiple APs. For all of these transcatheter ablation is recommended. The aim of our study was to evaluate the existence of differences in risk characteristics between patients with intermittent pre-excitation (IPX) and those with persistent pre-excitation (PPX), from a sample of adults with ventricular pre-excitation and symptoms like palpitations. 293 adults [IPX: 51 (17.4%); PPX: 242 (82.6%)] underwent electrophysiological study and then catheter ablation of their APs if arrhythmia inducibility (AVRT/AF) was noted, or, conversely, if it was appreciated a fast AP antegrade conduction, in baseline or during intravenous isoproterenol infusion, or if multiple APs were detected. There were no statistically significant differences in demographic characteristics (age and gender), AVRT/AF inducibility, antegrade conductive properties, the prevalence of multiple APs, and APs locations between IPX and PPX patients. In our study, patients with IPX did not show significant differences in clinical and electrophysiological features versus PPX patients.

Spatial correlation of left atrial low voltage substrate in sinus rhythm versus atrial fibrillation: The rhythm specificity of atrial low voltage substrate.

Improved sinus rhythm (SR) maintenance rates have been achieved in patients with persistent atrial fibrillation (AF) undergoing pulmonary vein isolation plus additional ablation of low voltage substrate (LVS) during SR. However, voltage mapping during SR may be hindered in persistent and long-persistent AF patients by immediate AF recurrence after electrical cardioversion. We assess correlations between LVS extent and location during SR and AF, aiming to identify regional voltage thresholds for rhythm-independent delineation/detection of LVS areas. (1) Identification of voltage dissimilarities between mapping in SR and AF. (2) Identification of regional voltage thresholds that improve cross-rhythm substrate detection. (3) Comparison of LVS between SR and native versus induced AF. Forty-one ablation-naive persistent AF patients underwent high-definition (1 mm electrodes; >1200 left atrial (LA) mapping sites per rhythm) voltage mapping in SR and AF. Global and regional voltage thresholds in AF were identified which best match LVS < 0.5 mV and <1.0 mV in SR. Additionally, the correlation between SR-LVS with induced versus native AF-LVS was assessed. Substantial voltage differences (median: 0.52, interquartile range: 0.33-0.69, maximum: 1.19 mV) with a predominance of the posterior/inferior LA wall exist between the rhythms. An AF threshold of 0.34 mV for the entire left atrium provides an accuracy, sensitivity and specificity of 69%, 67%, and 69% to identify SR-LVS < 0.5 mV, respectively. Lower thresholds for the posterior wall (0.27 mV) and inferior wall (0.3 mV) result in higher spatial concordance to SR-LVS (4% and 7% increase). Concordance with SR-LVS was higher for induced AF compared to native AF (area under the curve[AUC]: 0.80 vs. 0.73). AF-LVS < 0.5 mV corresponds to SR-LVS < 0.97 mV (AUC: 0.73). Although the proposed region-specific voltage thresholds during AF improve the consistency of LVS identification as determined during SR, the concordance in LVS between SR and AF remains moderate, with larger LVS detection during AF. Voltage-based substrate ablation should preferentially be performed during SR to limit the amount of ablated atrial myocardium.

Additional left atrial lesions improve the effect of cryoballoon pulmonary vein isolation in paroxysmal atrial fibrillation patients

Aim. Cryoballoon ablation (CBA) is one of the methods for catheter pulmonary vein isolation (PVI) for paroxysmal atrial fibrillation (AF). Left atrial additional lesion (LAAL) to PVI were proposed to eliminate extrapulmonary AF triggers. Nonetheless whether the additional lesions improve CBA effectiveness is not clear.Methods. Primary CBA procedures performed for paroxysmal AF during 2017-2021 were analyzed. The study group (Algorithm group, n=82) was recruited prospectively in 2019-2021. As the first step CBA PVI were performed in all pts. In those who were on sinus rhythm (SR) after the PVI, AF induction attempts with burst atrial pacing were performed. Pts with induced AF and those who stayed on AF after PVI underwent LAAL at the left ganglionated plexus area. In case of stable SR (non-inducible AF) the procedure finished. If AF was inducible or did not terminate during CBA, the second LAAL set were performed - LA posterior wall lesions. If AF was still inducible or did not terminate, the SR was restored by electrical cardioversion. The control group (Control group, n=94) was formed retrospectively from patients with routinely performed only CBA PVI with achievement of isolation criteria in 2017-2019. If AF continued, sinus rhythm was restored by cardioversion. There were no attempts of induction AF during the procedure.Results. The Algorithm and Control groups were comparable in terms of clinical, demographic and electrophysiological characteristics. At 12 months postoperatively, the effectiveness was higher in the Algorithm group than in the Control group (78.0% vs. 62.8%, p = 0.044). No adverse effects were found.Conclusion. Thus, the stepwise approach with LAAL increases the effectiveness of CBA in the long-term period and does not affect the risk of complications.

Light transmittance in human atrial tissue and transthoracic illumination in rats support translatability of optogenetic cardioversion of atrial fibrillation.

Optogenetics could offer a solution to the current lack of an ambulatory method for the rapid automated cardioversion of atrial fibrillation (AF), but key translational aspects remain to be studied. To investigate whether optogenetic cardioversion of AF is effective in the aged heart and whether sufficient light penetrates the human atrial wall. Atria of adult and aged rats were optogenetically modified to express light-gated ion channels (i.e., red-activatable channelrhodopsin), followed by AF induction and atrial illumination to determine the effectivity of optogenetic cardioversion. The irradiance level was determined by light transmittance measurements on human atrial tissue. AF could be effectively terminated in the remodeled atria of aged rats (97%, n=6). Subsequently, ex vivo experiments using human atrial auricles demonstrated that 565-nm light pulses at an intensity of 25mW/mm2 achieved the complete penetration of the atrial wall. Applying such irradiation onto the chest of adult rats resulted in transthoracic atrial illumination as evidenced by the optogenetic cardioversion of AF (90%, n=4). Transthoracic optogenetic cardioversion of AF is effective in the aged rat heart using irradiation levels compatible with human atrial transmural light penetration.

Mechanisms of Atrial Fibrillation in Obstructive Sleep Apnoea.

Obstructive sleep apnoea (OSA) is a strong independent risk factor for atrial fibrillation (AF). Emerging clinical data cite adverse effects of OSA on AF induction, maintenance, disease severity, and responsiveness to treatment. Prevention using continuous positive airway pressure (CPAP) is effective in some groups but is limited by its poor compliance. Thus, an improved understanding of the underlying arrhythmogenic mechanisms will facilitate the development of novel therapies and/or better selection of those currently available to complement CPAP in alleviating the burden of AF in OSA. Arrhythmogenesis in OSA is a multifactorial process characterised by a combination of acute atrial stimulation on a background of chronic electrical, structural, and autonomic remodelling. Chronic intermittent hypoxia (CIH), a key feature of OSA, is associated with long-term adaptive changes in myocyte ion channel currents, sensitising the atria to episodic bursts of autonomic reflex activity. CIH is also a potent driver of inflammatory and hypoxic stress, leading to fibrosis, connexin downregulation, and conduction slowing. Atrial stretch is brought about by negative thoracic pressure (NTP) swings during apnoea, promoting further chronic structural remodelling, as well as acutely dysregulating calcium handling and electrical function. Here, we provide an up-to-date review of these topical mechanistic insights and their roles in arrhythmia.

Assessing the utility of atrial fibrillation induction to risk stratify children with Wolff-Parkinson-White syndrome.

Wolff-Parkinson-White syndrome is associated with sudden cardiac death from rapid conduction through the accessory pathway in atrial fibrillation. Adult patients are at higher risk for sudden cardiac death if the shortest-pre-excited-RR-interval in atrial fibrillation (SPERRI) is ≤250 milliseconds (msec) during electrophysiologic study. Exclusive conduction through the atrioventricular node in atrial fibrillation is presumed to convey lower risk. The shortest-pre-excited-paced-cycle-length with atrial pacing has also served as a marker for risk stratification. To determine accessory pathway characteristic of patients undergoing induction of atrial fibrillation during electrophysiologic study. We reviewed 321 pediatric patients that underwent electrophysiologic study between 2010 and 2019. Induction of atrial fibrillation was attempted on patients while on isoproterenol and SPERRI was measured if atrial fibrillation was induced. Shortest-pre-excited-paced-cycle-length (SPPCL) was determined while on isoproterenol. Atrial fibrillation was induced in 233 (73%) patients. Of those, 104 (45%) patients conducted exclusively through the atrioventricular node during atrial fibrillation (Group A). The remaining 129 (55%) patients had some conduction through the accessory pathway (Group B). In Group A, SPPCLwas 260 msec with 48 (46%) conducting through the accessory pathway at ≤250 msec. In Group B, SPPCL was 240 msec with 92 patients (71%) conducting at ≤250 msec (p < 0.05). In Group B, SPERRI was 250 msec and had a positive correlation with SPPCL (p < 0.001, R2 = 0.28). Almost half (46%) of those with exclusive conduction through the atrioventricular node in atrial fibrillation had rapid accessory pathway conduction with atrial pacing. Conduction in atrial fibrillation during electrophysiologic study on isoproterenol via the atrioventricular node may not exclude high-risk accessory pathways in pediatric patients.

Atrial stimulation protocols to test inducibility of atrial fibrillation

Abstract Funding Acknowledgements Type of funding sources: None. Background The electrophysiological inducibility of atrial fibrillation (AF) after pulmonary vein isolation (PVI) has been identified as a predictor of future AF recurrence. Stimulation protocols have not been sufficiently studied prospectively with respect to their reliability for inducing AF. Methods and results We conducted a prospective monocentric randomized clinical trial to evaluate different standardized electrical stimulation protocols on their potential to induce AF. Patients with symptomatic AF presenting in sinus rhythm scheduled for PVI were enrolled. The primary outcome was induction of AF. A total of 30 patients (age=62±2 years, 17% female, 13% persistent AF, left atrial systolic volume (LASV) 93±5 ml) were enrolled and randomized. To one of three different stimulation protocols performed at the beginning of PVI. Atrial fibrillation was induced in 4 out of 10 patients (40%) with fixed cycle length stimulation followed by up to 3 extrastimuli (protocol A), 6 out of 10 patients (60%) with burst stimulation (protocol B) and 9 out of 10 patients (90%) with fixed stimulation using the shortest cycle length with 1:1 atrial capture (protocol C), respectively. Time from start of stimulation to inducibility of AF was significantly lower in protocol C vs. protocol B and A (29±10 sec vs 40±14 sec vs 366±71 sec; p&amp;lt;0.0001). Isoprenaline was used in 10% in protocol A, 40% in protocol B and 80% protocol C. Overall, there were no significant differences concerning age (61±3 vs. 63±4 years; p=0.74), LASV (93±6 vs. 94±8 ml; p=0.98) or other parameters between patients with inducible and non-inducible AF. Conclusion With systematic stimulation protocols AF can be induced in up to 90%. Further studies are warranted to assess the specifity of these stimulations.

JK07 prevents atrial fibrosis and atrial fibrillation inducibility in a porcine DOCA model

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Geconcerteerde Onderzoeksactie (GOA) grant 499 of the University of Antwerp Industrieel OnderzoeksFonds/Strategisch Basisonderzoek 498 (IOF/SBO) research grant of the University of Antwerp Background Atrial fibrosis is a substrate of atrial fibrillation (AF), and higher burdens of fibrosis are associated with resistance to therapy and worse prognosis. Currently, no therapies exist that target atrial fibrosis. JK07 is a long-acting neuregulin-fusion protein that has been shown to decrease ventricular fibrosis in models of heart failure through selective stimulation of the ErbB4 receptor. Purpose To test the ability of JK07 to reduce atrial fibrosis and AF inducibility in minipig model of deoxycorticosterone acetate (DOCA, an aldosterone agonist) induced hypertension. Methods 18 Aachener minipigs were randomized into 3 groups: control (CTRL), DOCA + Vehicle (DOCA+VEH) and DOCA+JK07. The control group did not undergo a therapeutic intervention. To induce hypertension and atrial fibrosis, pellets releasing 10 mg/kg DOCA over a period of 60 days were implanted in minipigs in the DOCA+VEH and DOCA+JK07 groups. The DOCA-implanted animals underwent weekly treatment with JK07 (0.3 mg/kg; DOCA + JK07) or its vehicle (DOCA + VEH), starting at the day of implantation (total of 9 administrations). After 60 days, arterial blood pressure was measured invasively and a decapolar catheter was placed in the right atrium. AF inducibility was tested by performing 50 burst pacing episodes and quantified as the percentage of successful episodes where an AF run ≥ 5 sec could be induced after the burst, out of the 50 attempts. Atrial fibrosis was quantified using ImageJ software on Masson trichrome staining of left atrial specimens, isolated after euthanizing the animals. Results Mean arterial pressure was significantly higher in the DOCA+VEH (142 ± 10 mmHg) and DOCA+JK07 (132 ± 15 mmHg) groups than in the CTRL group (105 ± 8 mmHg, p&amp;lt;0.01), without an effect of JK07. AF inducibility in the DOCA+VEH group was significantly higher than in the CTRL group (66/250 vs. 9/300, p&amp;lt;0.001), and the DOCA + JK07 group (66/250 vs. 8/300, p&amp;lt;0.001). Likewise, the degree of atrial fibrosis was significantly higher in the DOCA+VEH group compared to CTRL (14.18 ± 1.81 vs. 8.30 ± 2.52, p&amp;lt;0.001) and compared to DOCA+JK07 (14.18 ± 1.81 vs. 10.65 ± 1.59, p=0.0049). Conclusions JK07 prevents atrial fibrosis and AF inducibility in a porcine DOCA model. The effect of JK07 is unrelated to effects on blood pressure, but probably related to reduced atrial fibrogenesis.

Impact of effective refractory period personalization on prediction of atrial fibrillation vulnerability

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – EU funding. Main funding source(s): European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska- Curie grant agreement Introduction Although the effective refractory period (ERP) is one of the main electrophysiological properties governing atrial tachycardia (AT) maintenance, ERP personalization is rarely performed when creating patient-specific computer models of the atria to inform clinical decision making. State-of-the-art models usually do not consider physiological ERP gradients but assume a homogeneous ERP distribution. This assumption might have an influence on the ability to induce reentries in the model. Aim To evaluate the impact of incorporating clinical ERP measurements when creating in silico personalized models to predict vulnerability to atrial fibrillation (AF). Methods Clinical ERP measurements were obtained from three patients from multiple locations in the atria. The protocol for ERP identification consisted of trains of 7 S1 stimuli with a basic cycle length of 500ms followed by an S2 stimulus with a coupling interval between 300 and 200ms in decrements of 10ms until loss of capture. The atrial geometries from the electroanatomical mapping system were used to generate personalized atrial models. To reproduce patient-specific ERP, the established Courtemanche cellular model was gradually reparameterized from control conditions to a setup representing AF-induced remodeling. Three different approaches were studied: 1) a control scenario with no ERP personalization 2) a discrete split where each region had a single ERP value and 3) a continuous ERP distribution by interpolation of measured ERP data (Fig. 1). Arrhythmia vulnerability was assessed by virtual S1S2 pacing from different locations separated by 3cm. The number and location of inducing points and type of arrhythmia were determined for the three approaches. The mean conduction velocity was set to 0.7 m/s and the electrical propagation in the atria was modeled by the monodomain equation and solved with openCARP. Results Incorporating patient-specific ERP as a continuous distribution did not induce any reentrant activity. A summary of induced ATs is shown in Table 1. For patient A, AF was induced from 3 different locations with the control setup, whereas 9 ATs were induced with the regional method, of which 4 were AF and 5 macro reentries. For patient B, AF was induced from 1 point with the control setup; whereas with the regional approach, AF was induced at 4 points. For patient C, only one macro reentry was induced with the regional method. Conclusion Incorporation of patient-specific ERP values has an impact on the assessment of AF vulnerability. Furthermore, the type of personalization affects the likelihood of AF inducibility. The incorporation of more detailed ERP distributions may lead to a more accurate prediction of AF trigger points and could in the future inform patient-specific therapy planning. Larger cohorts need to follow to demonstrate the role of incorporating clinical patient-specific ERP values into personalized models for predicting AF vulnerability.

Impact of different energy sources on the cardiac autonomic nervous system in the setting of single-shot pulmonary vein isolation

Abstract Funding Acknowledgements Type of funding sources: None. Background The cardiac autonomic nervous system is an epicardial neural network composed of ganglionated plexi (GPs) and interconnecting neurons, which plays a significant role in the induction and maintenance of atrial fibrillation (AF). Targeted GPs ablation in addition to pulmonary vein isolation (PVI) has been associated with superior AF outcomes. Due to the anatomical proximity of the GPs with the pulmonary veins, PVI with cryoballoon catheter ablation (CBA) has shown to concomitantly affect the GPs, as documented by increased heart rates (HR) after ablation. Recently, pulsed-field ablation (PFA) has emerged as a safe and effective non-thermal alternative for single-shot PVI, with specific selectivity for the cardiac tissue. The impact of PFA on the cardiac autonomic nervous system is still to be elucidated. Purpose To assess the effect of PFA on the cardiac autonomic nervous system, evaluated with the variation in resting heart rate pre- and post-ablation. Methods We retrospectively included all consecutive patients with symptomatic paroxysmal AF undergoing first-time PVI with the multispline PFA catheter between January and September 2022. They were compared with consecutive patients undergoing PVI with CBA in the same study period. Patients not in sinus rhythm before ablation or with cardiac implantable electronic devices were excluded. All antiarrhythmic drugs were discontinued at least 3 days before ablation. Pre-ablation and 24-hour post-ablation ECGs in sinus rhythm were collected and analysed to assess HR. Results A total of 90 patients (PFA group, n=30 vs CBA group, n=60) were included in the analysis. Baseline patients’ characteristics were similar between the two groups (Figure 1). Pre-ablation HRs in the PFA and the CBA groups were 64.2 ± 10.3 bpm and 64.2 ± 12.8 bpm, respectively. Vagal reactions during ablation occurred more frequently with PFA than CBA (77% vs 38%, p=0.001). After 24h post-ablation, the HR increase in the PFA and CBA groups was 2.2 ± 5.4 bpm and 12.4 ± 11.9 bpm, respectively (p&amp;lt;0.001, Figure 2). Conclusion PVI with the novel multispline PFA catheter is associated with less increase in HR 24 hours after ablation compared to CBA. This effect may be the result of tissue selectivity of PFA for cardiomyocytes, which has minimal effect on extracardiac structures, including the cardiac autonomic nervous system.

Symptomatic intermittent ventricular pre-excitation in adult: a monocentric retrospective study

Abstract Funding Acknowledgements Type of funding sources: None. Backgorund: Intermittent ventricular pre-excitation was considered a low-risk marker for sudden death. However, to date some studies do not exclude the existence of accessory pathways (APs) with high-risk intermittent antegrade conductive properties. High-risk features of APs are: ERP/SPERRI ≤250 msec (in basal or during adrenergic stimulus), inducibility of atrioventricular reciprocating tachycardias (AVRT), inducibility of pre-excited atrial fibrillation (AF), multiple APs. For these catheter ablation is recommended. Purpose The aim of this retrospective study was to evaluate the existence of a statistically significant difference in the risk characteristics between patients with intermittent pre-excitation (IPX) and with persistent pre-excitation (PPX), from a sample of adults with symptomatic ventricular pre-excitation (Wolff-Parkinson-White Syndrome). Methods Between August 2005 and December 2015, 293 adults (age ≥18 years) [males: 183 (62.5%)], without structural heart disease, with signs of ventricular pre-excitation and symptomatic for palpitations underwent an EP study [IPX: 51 (17.4%), males: 31 (60.8%); PPX: 242 (82.6%), males: 152 (62.8%)]. The APs were submitted to catheter ablation if EP study showed inducibility of arrhythmias (AVRT/AF) and, in case of non-inducibility of arrhythmias, if ERP ≤250 msec, in basal or during intravenous infusion of isoproterenol. Additionally, the presence of multiple accessory pathways was assessed during the test. Results The 2 groups of patients did not show statistically significant differences in age at the time of EP study [IPX: mean age 37.23±16.89 years Vs PPX: mean age 39.03±16.19 (P-value&amp;gt;0.05)] and gender (IPX male: 60.8% Vs PPX male: 62.8%; P-value&amp;gt;0.05). When measured, there were no statistically significant differences regarding ERP [IPX: mean ERP 260±45.8msec Vs PPX: mean ERP 267.7±59.6msec; P-value&amp;gt;0.05]. The inducibility of arrhythmias (AVRT/AF) was 59.3% in the IPX group (27 patients) vs 38% in the PPX group (92 patients), showing statistically significant differences (P-value&amp;lt;0.05). Multiple accessory pathways were found in 2 patients of the IPX group (3.9%), both females (100%), and in 6 patients of the PPX group (2.5%), of which 2 females (33.3%), not showing statistically significant differences (P-value&amp;gt;0.05). Conclusion In our study, patients with IPX did not shown statical significant differences in clinical and electrophysiological features Vs PPX partients. Thus, intermittent ventricular pre-excitation could not absolutely be considered a marker of lower arrhythmic risk.

The novel left atrial anterior 'seatbelt' line reduces sustained atrial arrhythmia by 72% compared to pulmonary vein isolation alone in a cohort of 400 virtual atria models

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – EU funding. Main funding source(s): European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No.860974. Background The success-rate of pulmonary vein isolation (PVI) is modest in persistent atrial fibrillation (AF), but additional empirical ablation, such as posterior wall isolation (PWI), has not been shown to reduce the rate of AF recurrence. The "seatbelt", an anterior linear ablation lesion connecting the right superior pulmonary vein to the mitral annulus, is a novel substrate modification approach that is yet to be tested in a large-scale randomised clinical trial. Purpose To use in-silico trials with human-based modelling and simulation to compare the efficacy of (i) PVI alone, (ii) PVI and PWI (PVI+PWI), or (iii) PVI and seatbelt (PVI+SB) for the prevention of atrial arrhythmia in large populations of virtual patient models. Methods AF was simulated in a cohort of 400 virtual atrial models with anatomical and electrophysiological variability, with AF persisting for &amp;gt;7 seconds defined as sustained. Models which sustained AF were each independently subjected to all three ablation approaches before repeating the AF induction protocol. Results Three hundred forty-four (86%) atrial models developed sustained AF at baseline. After applying the ablation lesions, substantially fewer models sustained atrial arrhythmias in the PVI+SB group (50 [14%] vs. 134 [39%] with PVI+PWI vs. 172 [50%] with PVI). PVI+SB was more effective than PVI and PVI+PWI in preventing both AF and atrial flutter (i.e., presence of a single rotor), since PVI and PVI+PWI led to the formation of anatomical re-entries around the rings of the pulmonary veins and the posterior wall of the left atrium, respectively (Figure). Therefore, PVI+SB restricted atrial flutter mainly to the right atrium (either anatomical, around the inferior cava vein, or functional, meandering throughout the venous portion of the right atrium, Figure). Importantly, in all three ablation strategies, the likelihood of AF recurrence was directly proportional to the surface area of the right atrium (AF probability increased 0.95%/cm², 0.88%/cm² and 0.56%/cm² after PVI+SB, PVI+PWI and PVI, respectively). The role of the right atrial size was less accentuated for PVI alone, since after the ablation the entire left atrial body was still available for rotor anchoring. Moreover, an enlarged left atrium enabled the appearance of micro-re-entries in the anterior and inferior wall of the left atrium, even after applying floor and roof lines. One atrial model additionally presented a rotor in the posterior wall of the left atrium after completely isolating it from the left atrial body. Conclusion(s) In a cohort of 400 virtual atrial models, PVI+SB reduced sustained atrial arrhythmias by 72% compared to PVI alone and by 64% to PVI+PWI, but AF could still originate in an enlarged right atrium.

P164 PERCUTANEOUS LEFT STELLATE GANGLION BLOCK IN REFRACTORY LEFT ATRIAL TACHYCARDIA

Abstract Percutaneous left stellate ganglion block (PLSGB) has been recently implemented for the acute treatment of refractory ventricular arrhythmias (VAs). The beneficial effect on supraventricular arrhythmias susceptibility and their ventricular response is well characterized in animal models, less so in humans. Available data suggest a significant prolongation of atrial refractory period, a reduction in inducibility and duration of atrial fibrillation and of all spontaneous intra– and postoperative atrial arrhythmias after thoracic and cardiac surgery. Here we describe a case of PLSGB for focal atrial tachycardia (AT). Case: we present a 68–year–old men with hypertension, obesity, OSAS and previous anterior myocardial infarction in the setting of a trivessel coronary disease, treated with PCI and complicated by apical aneurysm, with a LVEF of 38% and a moderate mitral and aortic regurgitation. He was on chronic antiarrhythmic therapy with bisoprolol 1.25 mg and ranolazine. He presented in the ED due to palpitations, pre–syncopal episodes, and worsening dyspnea. The ECG showed very frequent, self–limiting episodes of AT with a 1:1 atrioventricular (AV) conduction and a variable heart rate (HR) between 100 and 160 bpm, alternating with sinus rhythm at 45–50 bpm, sometimes conducted with aberrancy. Isolated and repetitive premature ventricular beats (PVB, maximum 8 beats) were also documented. Amiodarone, lidocaine, and intravenous unloading therapy were tried, without benefit. Coronary angiography was negative. PLSGB with an ultrasound–guided lateral approach (local bolus of lidocaine 100 mg+ropivacaine 20 mg) was performed, without complications, inducing palpebral ptosis. Over the next 15 hours we observed the disappearance of non–sustained VAs, the reduction of PVBs, and a progressive reduction of AT burden, of mean hourly HR (from 84 to 50 bpm, –40%) and of mean HR during AT (from 158 to 84 bpm, –47%, with AV 1:1 conduction). The patient subsequently underwent ablation of an extra systolic focus found near the ostium of the right inferior pulmonary vein, with no recurrences after 18 months. Conclusions This case highlights the potential efficacy of PLSGB in the acute treatment of supraventricular arrhythmias refractory to medical therapy. Prospective studies will help us to identify the extent, time of onset, and duration of its benefit depending on the type and mechanism of the underlying arrhythmia and the clinical characteristics of the patient.

Sacubitril/valsartan reduces susceptibility to atrial fibrillation by improving atrial remodeling in spontaneously hypertensive rats

AimSacubitril/valsartan (Sac/Val, LCZ696), the world's first angiotensin receptor-neprilysin inhibitor (ARNi), has been widely used in the treatment of heart failure. However, the use of Sac/Val in the treatment of atrial fibrillation (AF), especially AF with hypertension, has been less reported. We investigated the effect of Sac/Val on atrial remodeling and hypertension-related AF. MethodsThe AF induction rate and electrophysiological characteristics of spontaneously hypertensive rats (SHRs) treated with Sac/Val or Val were detected by rapid atrial pacing and electrical mapping/optical mapping. The whole-cell patch-clamp and Western blot were used to observe electrical/structural remodeling of atrial myocytes/tissue of rats and atrium-derived HL-1 cells cultured under 40 mmHg in vitro. ResultsSac/Val was superior to Val in reducing blood pressure, myocardial hypertrophy and susceptibility of AF in SHRs. The shorten action potentials duration (APD), decreased L type calcium channel current (ICa,L) and Cav1.2, increased ultrarapid delayed rectified potassium current (Ikur) and Kv1.5 in atrial myocytes/tissue of SHRs could be better improved by Sac/Val, as well as the levels of atrial fibrosis. While the protein expression of angiotensin-converting enzyme-1 (ACE-1), angiotensin, angiotensin II type I AT1 receptor (AT1R) and neprilysin (NEP) were increased, which could be more effective ameliorated by Sac/Val than Val. Furthermore, Val + Sacubitrilat (LBQ657) (an active NEP inhibitor) was also superior to LBQ657 or Val in improving the electrical and structural remodeling of HL-1 cells through inhibiting NEP. ConclusionSac/Val can improve atrial structural and electrical remodeling induced by hypertension and reduce the AF susceptibility by inhibiting RAS and NEP. The above effects of Sac/Val were superior to Val alone.

Downregulation of FKBP5 Promotes Atrial Arrhythmogenesis.

Atrial fibrillation (AF), the most common arrhythmia, is associated with the downregulation of FKBP5 (encoding FKBP5 [FK506 binding protein 5]). However, the function of FKBP5 in the heart remains unknown. Here, we elucidate the consequences of cardiomyocyte-restricted loss of FKBP5 on cardiac function and AF development and study the underlying mechanisms. Right atrial samples from patients with AF were used to assess the protein levels of FKBP5. A cardiomyocyte-specific FKBP5 knockdown mouse model was established by crossbreeding Fkbp5flox/flox mice with Myh6MerCreMer/+ mice. Cardiac function and AF inducibility were assessed by echocardiography and programmed intracardiac stimulation. Histology, optical mapping, cellular electrophysiology, and biochemistry were employed to elucidate the proarrhythmic mechanisms due to loss of cardiomyocyte FKBP5. FKBP5 protein levels were lower in the atrial lysates of patients with paroxysmal AF or long-lasting persistent (chronic) AF. Cardiomyocyte-specific knockdown mice exhibited increased AF inducibility and duration compared with control mice. Enhanced AF susceptibility in cardiomyocyte-specific knockdown mice was associated with the development of action potential alternans and spontaneous Ca2+ waves, and increased protein levels and activity of the NCX1 (Na+/Ca2+-exchanger 1), mimicking the cellular phenotype of chronic AF patients. FKBP5-deficiency enhanced transcription of Slc8a1 (encoding NCX1) via transcription factor hypoxia-inducible factor 1α. In vitro studies revealed that FKBP5 negatively modulated the protein levels of hypoxia-inducible factor 1α by competitively interacting with heat-shock protein 90. Injections of the heat-shock protein 90 inhibitor 17-AAG normalized protein levels of hypoxia-inducible factor 1α and NCX1 and reduced AF susceptibility in cardiomyocyte-specific knockdown mice. Furthermore, the atrial cardiomyocyte-selective knockdown of FKBP5 was sufficient to enhance AF arrhythmogenesis. This is the first study to demonstrate a role for the FKBP5-deficiency in atrial arrhythmogenesis and to establish FKBP5 as a negative regulator of hypoxia-inducible factor 1α in cardiomyocytes. Our results identify a potential molecular mechanism for the proarrhythmic NCX1 upregulation in chronic AF patients.

PO-01-151 DEGREE OF FIBROSIS REMODELING ALTERS ATRIAL FIBRILLATION INDUCIBILITY

Mechanistically, the role of remodeled substrate in atrial fibrillation (AF) inducibility is not well understood. Here we assess the changes in AF reentrant-drivers (RDs) based on different levels of fibrotic remodeling – as visualized by degree of enhancement in late gadolinium enhancement (LGE) MRI. We compare the inducibility of the native fibrotic substrates in patients undergoing first-time ablation (FtA) and in those of repeat ablation (ReA) and characterize the regions most involved in RD maintenance. To investigate how different levels of fibrotic remodeling (enhancement in LGE MRI) affect AF inducibility. Ten LGE MRIs were obtained from AF patients undergoing FtA (n=5) or ReA (n=5). Fibrotic tissue was differentiated using personalized image intensity ratio (IIR) threshold; for scar, we used IIR=1.61; and the IIR for dense fibrosis was the midpoint between the two (Fig. 1B). For each patient, two personalized bi-atrial models were constructed: baseline and multi-level fibrosis. The baseline model includes only two tissue types – normal myocardium and fibrotic tissue; the multi-level fibrosis model for FtA has the addition of dense fibrosis, and for ReA, dense fibrosis and scar (Fig. 1C). Each model was tested for AF inducibility by rapid pacing from 40 uniformly distributed bi-atrial sites (Fig. 1D). RD-harboring regions were “cut out” (Fig. 1E) and the volumetric fraction of each substrate in each region was calculated (Fig. 1F). The ReA group had on average more remodeled tissue (29.11%) than the FtA group (20.05%). While the ReA group did not have more RDs than the FtA group, their RDs were more frequently inducible (from different pacing sites) compared to the RDs in the FtA group (usually inducible from just one pacing site). In general, one model was not found to be more arrhythmogenic than the other. For 7/10 patients, the model-pair produced at least one common RD. In all models, RDs required at least 30% of remodeled tissue within the local RD region. In ReA multi-level fibrosis models, RD-harboring regions had tissue significantly more remodeled (72.34%) than RD-harboring regions in baseline models (36.59%; p<0.0001). Different levels of fibrotic remodeling result in different levels of AF inducibility. These insights might be important in predicting ablation targets in AF patients.

PO-02-214 JK07 PREVENTS HYPERTENSION-INDUCED ATRIAL FIBROSIS AND ATRIAL FIBRILLATION INDUCIBILITY IN A PIG MODEL

An important substrate of atrial fibrillation (AF) is atrial fibrosis, and a higher burden of fibrosis correlates with worse prognosis and therapy resistance. Currently, no therapies exist that target atrial fibrosis. JK07 is a long-acting neuregulin-fusion protein that activates the ERBB4 receptor, which mitigates ventricular fibrosis in models of heart failure. To test the ability of JK07 to reduce atrial fibrosis and AF inducibility in the minipig model of deoxycorticosterone acetate (DOCA, an aldosterone agonist) induced hypertension. Eighteen Aachener minipigs were randomized into three groups: control (CTRL), DOCA + Vehicle (DOCA+VEH) and DOCA+JK07. The control group did not undergo disease induction or therapeutic intervention. To induce hypertension and atrial fibrosis in minipigs in the DOCA+VEH and DOCA+JK07 groups, DOCA pellets were implanted releasing 10 mg/kg DOCA over a period of 60 days. The DOCA-implanted animals underwent weekly treatment with JK07 (0.3 mg/kg; DOCA + JK07) or vehicle control (DOCA + VEH), starting on the day of implantation (total of 9 administrations). After 60 days, arterial blood pressure was measured invasively and a decapolar catheter was placed in the right atrium. AF inducibility was tested by performing 50 burst pacing episodes and quantified as the percentage of “successful” episodes where an AF run ≥ 5 sec could be induced after the burst, out of the 50 attempts. Atrial fibrosis was quantified using AFAT software on Masson trichrome staining of left atrial appendage specimens, isolated after euthanizing the animals. Mean arterial pressure was significantly higher in the DOCA+VEH (142 ± 10 mmHg) and DOCA+JK07 (132 ± 15 mmHg) groups than in the CTRL group (105 ± 8 mmHg, p<0.01), without an effect of JK07. AF inducibility in the DOCA+VEH group was significantly higher than in the CTRL group (66/250 vs. 9/300, p<0.001), and the DOCA + JK07 group (66/250 vs. 8/300, p<0.001). Likewise, the degree of atrial fibrosis was significantly higher in the DOCA+VEH group compared to CTRL (10.32% ± 4.74% surface area vs. 5.28% ± 3.06%, p<0.001) and compared to DOCA+JK07 (10.32% ± 4.74% vs. 3.82% ± 2.68%, p<0.001). JK07 prevents atrial fibrosis and AF inducibility in a porcine DOCA model. The effect of JK07 is unrelated to effects on blood pressure, but probably related to reduced atrial fibrogenesis.

PO-455617-18 SHORT COUPLED PREMATURE ATRIAL COMPLEXES LEAD TO ADVERSE ATRIAL REMODELING AND ATRIAL FIBRILLATION IN A SWINE MODEL

Frequent premature atrial complexes (PACs) are associated with left atrial (LA) myopathy and atrial fibrillation (AF), however, the effect of coupling interval and irregularity on the ensuing atrial myopathy has not been tested. To explore the impact of coupling interval and regularity of atrial ectopics on the development of atrial remodeling and AF in a swine model. Thirty-five swine underwent baseline electrophysiologic study followed by pacemaker implantation and pacing from the lateral LA via the coronary sinus for 16 weeks in 4 groups: 1) controls without PACs (CTRL, n=10); 2) 50% paced PACs at a short coupling interval (CI) of 250ms (Short-PAC, n=10); 3) 50% PACs at a long CI of 400ms (Long-PAC, n=5); and 4) regular pacing at a faster mean atrial rate (130 beats/min) than during PACs (Reg-130, n=10). At the terminal study, a repeat electrophysiologic study was performed followed by sacrifice and histologic analysis. Structural changes: The Short-PAC group had the greater degree of LA dilation (terminal - baseline: Short-PAC 5.9±1.2cm2 vs. Long-PAC 3.9±0.5cm2 vs. Reg-130 3.0±1.0cm2 vs. CTRL 0.9±0.3cm2, p<0.001) and decrease in peak LA strain (terminal - baseline: Short-PAC -17.3±3.2% vs. Long-PAC -12.7±2.9% vs. Reg-130 -8.2±2.9% vs. CTRL -0.7±4.2%, p<0.001). Electrophysiologic changes: The Short-PAC group had slower LA conduction velocity than the Reg-130 and CTRL groups (Short-PAC 1.1±0.2m/s vs. Long-PAC 1.2±0.1m/s vs. Reg-130 1.3±0.1m/s vs. CTRL 1.5±0.2m/s, p<0.001); atrial effective refractory period (ERP) was only decreased in the Reg-130 group (terminal - baseline: Short-PAC -4.0±23.6ms vs. Long-PAC -8.7±17.9ms vs. Reg-130 -23.7±14.3ms vs. CTRL -3.2±23.7ms, p=0.09). Fibrosis: percent LA fibrosis was highest in the Short-PAC group followed by Long-PAC, Reg-130, and then CTRL groups (Figure, Panel A). AF induction: The Short-PAC group had the longest duration of induced AF (Panel B). In a swine model, frequent PACs can cause structural and electrical atrial remodeling with a heightened propensity for AF. PACs led to slow conduction and fibrosis without change in atrial ERP, suggesting a process distinct from tachy-pacing induced atrial remodeling. Moreover, PACs with short CIs resulted in a greater degree of LA remodeling and induced AF duration compared to PACs with long CIs. These findings suggest that frequent, short coupled PACs pose the highest risk for developing atrial remodeling and AF.