Left atrial electrophysiologic feature specific for the genesis of complex fractionated atrial electrogram during atrial fibrillation

The relationship between atrial fibrillation and coronary artery disease: Understanding common denominators

Atrial fibrillation (AF) and coronary artery disease (CAD) are highly prevalent cardiovascular conditions. The coexistence of both diseases is common as they share similar risk factors and common pathophysiological characteristics. Systemic inflammatory conditions are associated with an increased incidence of both AF and CAD. The presence of both entities increases the incidence of complications and adverse outcomes. Furthermore, their coexistence poses challenges for the management of patients, particularly with respect to anticoagulation and rhythm management. In this review, we aim to better understand the relationship between AF and CAD by detailing basic molecular pathophysiology, assessing therapeutic guidelines, and describing interactions between the two conditions.

Simultaneous Whole-Chamber Non-contact Mapping of Highest Dominant Frequency Sites During Persistent Atrial Fibrillation: A Prospective Ablation Study

Purpose

Sites of highest dominant frequency (HDF) are implicated by many proposed mechanisms underlying persistent atrial fibrillation (persAF). We hypothesized that prospectively identifying and ablating dynamic left atrial HDF sites would favorably impact the electrophysiological substrate of persAF. We aim to assess the feasibility of prospectively identifying HDF sites by global simultaneous left atrial mapping.

Methods

PersAF patients with no prior ablation history underwent global simultaneous left atrial non-contact mapping. 30 s of electrograms recorded during AF were exported into a bespoke MATLAB interface to identify HDF regions, which were then targeted for ablation, prior to pulmonary vein isolation. Following ablation of each region, change in AF cycle length (AFCL) was documented (≥ 10 ms considered significant). Baseline isopotential maps of ablated regions were retrospectively analyzed looking for rotors and focal activation or extinction events.

Results

A total of 51 HDF regions were identified and ablated in 10 patients (median DF 5.8Hz, range 4.4-7.1Hz). An increase in AFCL of was seen in 20 of the 51 regions (39%), including AF termination in 4 patients. 5 out of 10 patients (including the 4 patients where AF termination occurred with HDF-guided ablation) were free from AF recurrence at 1 year. The proportion of HDF occurrences in an ablated region was not associated with change in AFCL (τ = 0.11, p = 0.24). Regions where AFCL decreased by 10 ms or more (i.e., AF disorganization) after ablation also showed lowest baseline spectral organization (p < 0.033 for any comparison). Considering all ablated regions, the average proportion of HDF events which were also HRI events was 8.0 ± 13%. Focal activations predominated (537/1253 events) in the ablated regions on isopotential maps, were modestly associated with the proportion of HDF occurrences represented by the ablated region (Kendall's τ = 0.40, p < 0.0001), and very strongly associated with focal extinction events (τ = 0.79, p < 0.0001). Rotors were rare (4/1253 events).

Conclusion

Targeting dynamic HDF sites is feasible and can be efficacious, but lacks specificity in identifying relevant human persAF substrate. Spectral organization may have an adjunctive role in preventing unnecessary substrate ablation. Dynamic HDF sites are not associated with observable rotational activity on isopotential mapping, but epi-endocardial breakthroughs could be contributory.

MicroRNA-30c suppresses the pro-fibrogenic effects of cardiac fibroblasts induced by TGF-β1 and prevents atrial fibrosis by targeting TGFβRII

Atrial fibrosis serves as an important contributor to atrial fibrillation (AF). Recent data have suggested that microRNA-30c (miR-30c) is involved in fibrotic remodelling and cancer development, but the specific role of miR-30c in atrial fibrosis remains unclear. The purpose of this study was to investigate the role of miR-30c in atrial fibrosis and its underlying mechanisms through in vivo and in vitro experiments. Our results indicate that miR-30c is significantly down-regulated in the rat abdominal aortic constriction (AAC) model and in the cellular model of fibrosis induced by transforming growth factor-β1 (TGF-β1). Overexpression of miR-30c in cardiac fibroblasts (CFs) markedly inhibits CF proliferation, differentiation, migration and collagen production, whereas decrease in miR-30c leads to the opposite results. Moreover, we identified TGFβRII as a target of miR-30c. Finally, transferring adeno-associated virus 9 (AAV9)-miR-30c into the inferior vena cava of rats attenuated fibrosis in the left atrium following AAC. These data indicate that miR-30c attenuates atrial fibrosis via inhibition of CF proliferation, differentiation, migration and collagen production by targeting TGFβRII, suggesting that miR-30c might be a novel potential therapeutic target for preventing atrial fibrosis.

Persistent tachycardia within isolated pulmonary veins during atrial fibrillation ablation

During circumferential pulmonary vein (PV) isolation for ongoing atrial fibrillation (AF), distinguishing passive conduction to the pulmonary vein (PV) from rapid PV arrhythmia in the isolated PV is difficult. Hence, the purpose of this study is to investigate both the feasibility of distinguishing the PV tachycardia after circumferential PV isolation and the electrophysiological characteristics of these tachycardia. Among 178 consecutive patients who underwent circumferential PV isolation during ongoing AF, fibrillatory PV converted to a regular cycle length PV tachycardia independent of the atrial rhythm (=independent PV tachycardia) in 13 PVs among 12 (7%) patients. We classified independent PV tachycardia according to 3 different atrial rhythms: sinus rhythm (type 1, n = 2), atrial tachycardia (type 2, n = 4), and AF (type 3, n = 6). independent PV tachycardia was observed in 3 right PV and 10 left PV (P = 0.0864). There were 10 mappable independent PV tachycardia, in which 8 were focal and 2 were macroreentrant tachycardia. i-PVT can be diagnosed in a small number of patients who underwent circumferential PV isolation during AF. The main mechanism or independent PV tachycardia was focal tachycardia mainly in the left PV.

Rapid atrial pacing induces myocardial fibrosis by down-regulating Smad7 via microRNA-21 in rabbit

Tachycardia-induced atrial fibrosis is a hallmark of the structural remodeling of atrial fibrillation (AF). The mechanisms underlying tachycardia-induced atrial fibrosis remain unclear. In our previous study, we found that Smad7-downregulation promoted the development of atrial fibrosis in AF. Fibroblasts are enriched in microRNA-21 (miR-21), which contributes to the development of fibrosis and heart failure in the cardiovascular system. Our study was designed to test the hypothesis that miR-21 reinforces the TGF-β₁/Smad signaling pathway in AF-induced atrial fibrosis by down-regulating Smad7. Rapid atrial pacing (RAP, 1000 ppm) was applied to the left atrium of the rabbit heart to induce atrial fibrillation and fibrosis. qRT-PCR and northern blot analysis revealed that RAP caused a marked increase in the expression of miR-21. Transfection with a miR-21 inhibitor significantly increased the expression of Smad7, while the expression of collagen I/III significantly decreased. These changes were implicated in the AF-induced release of miR-21 and down-regulation of Smad7. Adult rat cardiac fibroblasts treated with TGF-β₁ showed increased miR-21 expression and decreased Smad7 expression. Pretreatment with a TGF-β₁ inhibitor reduced the TGF-β₁-induced up-regulation of miR-21. Pretreatment with pre-miR-21 and a miR-21 inhibitor significantly decreased and increased Smad7 expression, respectively. This result was negatively correlated with the expression of collagen I/III in fibroblasts. Moreover, the results of a luciferase activity assay suggest that Smad7 is a validated miR-21 target in CFs. Our results provide compelling evidence that the miR-21 specific degradation of Smad7 may decrease the inhibitory feedback regulation of TGF-β1/Smad signaling and serves as a new insight of the mechanism of atrial fibrosis in atrial fibrillation.

Use of antiarrhythmic drugs during ablation of persistent atrial fibrillation: observations from a large single-centre cohort

Catheter ablation of complex fractionated atrial electrograms (CFAE), also known as defragmentation ablation, may be considered for the treatment of persistent atrial fibrillation (AF) beyond pulmonary vein isolation (PVI). Concomitant antiarrhythmic drug (AAD) therapy is common, but the relevance of AAD administration and its optimal timing during ablation remain unclear. Therefore, we investigated the use and timing of AADs during defragmentation ablation and their possible implications for AF termination and ablation success in a large cohort of patients. Retrospectively, we included 200 consecutive patients (age: 61 ± 12 years, LA diameter: 47 ± 8 mm) with persistent AF (episode duration 47 ± 72 weeks) who underwent de novo ablation including CFAE ablation. In all patients, PVI was performed prior to CFAE ablation. The use and timing of AADs were registered. The follow-ups consisted of Holter ECGs and clinical visits. Termination of AF was achieved in 132 patients (66 %). Intraprocedural AADs were administered in 168/200 patients (84 %) 45 ± 27 min after completion of PVI. Amiodarone was used in the majority of the patients (160/168). The timing of AAD administration was predicted by the atrial fibrillation cycle length (AFCL). At follow-up, 88 patients (46 %) were free from atrial arrhythmia. Multivariate logistic regression analysis revealed that administration of AAD early after PVI, LA size, duration of AF history, sex and AFCL were predictors of AF termination. The administration of AAD and its timing were not predictive of outcome, and age was the sole independent predictor of AF recurrence. The administration of AAD during ablation was common in this large cohort of persistent AF patients. The choice to administer AAD therapy and the timing of the administration during ablation were influenced by AFCL, and these factors did not significantly influence the moderate single procedure success rate in this retrospective analysis.

Atrial rhythm influences catheter tissue contact during radiofrequency catheter ablation of atrial fibrillation: comparison of contact force between sinus rhythm and atrial fibrillation

Catheter tissue contact force (CF) is an important factor for durable lesion formation during radiofrequency catheter ablation (RFCA) of atrial fibrillation (AF). Since CF varies in the beating heart, atrial rhythm during RFCA may influence CF. A high-density map and RFCA points were obtained in 25 patients undergoing RFCA of AF using a CF-sensing catheter (Tacticath, St. Jude Medical). The operators were blinded to the CF information. Contact type was classified into three categories: constant, variable, and intermittent contact. Average CF and contact type were analyzed according to atrial rhythm (SR vs. AF) and anatomical location. A total of 1364 points (891 points during SR and 473 points during AF) were analyzed. Average CFs showed no significant difference between SR (17.2 ± 11.3 g) and AF (17.2 ± 13.3 g; p = 0.99). The distribution of points with an average CF of ≥20 and <10 g also showed no significant difference. However, the distribution of excessive CF (CF ≥40 g) was significantly higher during AF (7.4 %) in comparison with SR (4.2 %; p < 0.05). At the anterior area of the right inferior pulmonary vein (RIPV), the average CF during AF was significantly higher than during SR (p < 0.05). Constant contact was significantly higher during AF (32.2 %) when compared to SR (9.9 %; p < 0.01). Although the average CF was not different between atrial rhythms, constant contact was more often achievable during AF than it was during SR. However, excessive CF also seems to occur more frequently during AF especially at the anterior part of RIPV.