Hong-Wei Tan

Beneficial effect of pioglitazone on the outcome of catheter ablation in patients with paroxysmal atrial fibrillation and type 2 diabetes mellitus

AIMS Pioglitazone, one of the peroxisome proliferator-activated receptor-gamma activators, possesses anti-inflammatory and antioxidant properties. In the present study, we sought to identify the impact of pioglitazone on the outcome of catheter ablation for paroxysmal atrial fibrillation (PAF). METHODS AND RESULTS We conducted a prospective observational cohort study of 150 consecutive patients undergoing catheter ablation of drug-refractory PAF. All patients had a history of type 2 diabetes mellitus (T2DM) and were divided based on whether they received pioglitazone before ablation or not. After grouping, 51 patients treated with pioglitazone and 99 control subjects were followed up at least 15 months after ablation. After a single ablation, sinus rhythm was maintained in 44 patients (86.3%) of the pioglitazone group vs. 70 patients (70.7%) of the control group (P = 0.034) without antiarrhythmic drug during a mean follow-up of 22.9 ± 5.1 months. The second ablation was performed in 5 patients (9.8%) from the pioglitazone group and in 24 patients (24.2%) from the control group (P = 0.034). Multivariate logistic analysis showed left atrium diameter was associated with a high risk of atrial tachyarrhythmias recurrence, and treatment with renin-angiotensin system inhibitor as well as pioglitazone was associated with a reduced atrial tachyarrhythmias recurrence rate. CONCLUSION Pioglitazone improved the preservation of sinus rhythm and reduced the reablation rate in patients with PAF and T2DM after catheter ablation.

Novel connexin40 missense mutations in patients with familial atrial fibrillation.

AIMS This research was aimed at screening connexin40, a cardiac gap junction protein alpha 5, for genetic defects in patients with familial atrial fibrillation (AF). METHODS The subjects included 218 unrelated families with lone AF and 200 ethnically matched unrelated healthy individuals as controls. The entire coding region of the connexin40 gene was sequenced initially in 218 unrelated probands with familial AF. The relatives of mutation carriers and 200 controls were subsequently genotyped for the presence of mutations identified in probands. RESULTS Three novel connexin40 mutations, p.V85I, p.L221I, and p.L229M, were identified in 3 of 218 unrelated AF families, respectively. These heterozygous missense mutations co-segregated with AF in the families and were absent in the 200 unrelated control subjects. A cross-species alignment of connexin40 protein sequences revealed that the altered amino acids were completely conserved evolutionarily. CONCLUSION The findings expand the spectrum of mutations in connexin40 linked to AF and provide new insight into the molecular aetiology involved in the pathogenesis of AF.

Angiotensin II increases CTGF expression via MAPKs/TGF-β1/TRAF6 pathway in atrial fibroblasts.

The activation of transforming growth factor-β1(TGF-β1)/Smad signaling pathway and increased expression of connective tissue growth factor (CTGF) induced by angiotensin II (AngII) have been proposed as a mechanism for atrial fibrosis. However, whether TGFβ1/non-Smad signaling pathways involved in AngII-induced fibrogenetic factor expression remained unknown. Recently tumor necrosis factor receptor associated factor 6 (TRAF6)/TGFβ-associated kinase 1 (TAK1) has been shown to be crucial for the activation of TGF-β1/non-Smad signaling pathways. In the present study, we explored the role of TGF-β1/TRAF6 pathway in AngII-induced CTGF expression in cultured adult atrial fibroblasts. AngII (1 μM) provoked the activation of P38 mitogen activated protein kinase (P38 MAPK), extracellular signal-regulated kinase 1/2(ERK1/2) and c-Jun NH(2)-terminal kinase (JNK). AngII (1 μM) also promoted TGFβ1, TRAF6, CTGF expression and TAK1 phosphorylation, which were suppressed by angiotensin type I receptor antagonist (Losartan) as well as p38 MAPK inhibitor (SB202190), ERK1/2 inhibitor (PD98059) and JNK inhibitor (SP600125). Meanwhile, both TGFβ1 antibody and TRAF6 siRNA decreased the stimulatory effect of AngII on TRAF6, CTGF expression and TAK1 phosphorylation, which also attenuated AngII-induced atrial fibroblasts proliferation. In summary, the MAPKs/TGFβ1/TRAF6 pathway is an important signaling pathway in AngII-induced CTGF expression, and inhibition of TRAF6 may therefore represent a new target for reversing Ang II-induced atrial fibrosis.

GATA4 loss-of-function mutations in familial atrial fibrillation

BACKGROUND Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia and a major source of the substantially increased morbidity and mortality. Growing studies demonstrate that genetic defects play pivotal roles in a subgroup of AF. However, AF is a genetically heterogeneous disorder and the molecular basis of AF in a majority of cases remains unknown. METHODS The whole coding region of the GATA4 gene, which encodes a zinc-finger transcription factor essential for cardiogenesis, was analyzed in 130 unrelated probands with AF in contrast to 200 unrelated ethnically matched healthy individuals used as controls. The available family members of the probands harboring the identified mutations were genotyped. The functional effect of the mutant GATA4 was characterized using a luciferase reporter assay system. RESULTS Two novel heterozygous GATA4 mutations, p.S70T and p.S160T, were identified in 2 unrelated families with AF inherited as an autosomal dominant trait, respectively, which co-segregated with AF in each family with complete penetrance. Functional analysis showed that the mutations of GATA4 were associated with a significantly decreased transcriptional activity. CONCLUSION The findings provide new insight into the molecular mechanism involved in the pathogenesis of AF, suggesting the potential implications in the genetic diagnosis and gene-specific therapy of this common arrhythmia.

Mutational spectrum of the GATA5 gene associated with familial atrial fibrillation

Atrial fibrillation (AF) is the most common cardiac arrhythmia seen in clinical practice, with an estimated prevalence of 1-2% in the general population. The incidence of AF increases dramatically with age, ranging from less than 1% in patients under 60 years of age to almost 10% in those aged 80 and over (1). AF is associated with substantial morbidity, mortality and health care burden. AF confers a five-fold increased risk of stroke, and about 15-20% of all strokes result from this tachycardia. AF also accounts for an approximately two-fold increase in risk of death, and a third of all hospitalizations for cardiac rhythm disturbances (1-3). AF frequently arises from diverse cardiac and systemic disorders, including hypertension, coronary artery disease, valvular heart disease, and hyperthyroidism (1). However, in 30% to 45% of AF cases, an underlying cause cannot be detected by routine methods, a condition usually defined as idiopathic or lone AF, of which at least 15% have a positive family history, hence termed familial AF (1). There is now growing evidence demonstrating that genetic defects play an important role in the pathogenesis of AF and multiple genes involved in AF have been identified (4). Nevertheless, AF is genetically heterogeneous and the genetic determinants of AF remain largely unclear. Recent studies highlight a key role for several cardiac transcrip- tion factors, including NKX2-5, GATA4, GATA5 and GATA6, in the cardiogenesis (5,6), and mutations in NKX2-5, GATA4 and GATA6 have been causally implicated in congenital heart diseases and AF (7-12). GATA5 is another member of the GATA family, and its expression and functions overlap with those of GATA4 and GATA6 during cardiovascular development, especially in regulation of target gene expression synergistically with NKX2-5, which points to the likely association of functionally impaired GATA5 with AF (5,6). To assess the prevalence and spectrum of GATA5 mutations in patients with familial AF, 130 unrelated index patients with familial AF identified among the Chinese Han population were included in this study. The control population comprised 200 unrelated ethnically matched healthy individuals. All subjects were appraised by medical history, physical examination, electrocardiography, and echocardiogra- phy. The study subjects were clinically classified using a consistently applied set of definitions (10). The baseline demographic and clinical characteristics of the study population are summarized in Table 1 .T he study protocol was reviewed and approved by the local institutional ethics committee and written informed consent was obtained from all participants prior to study. Peripheral venous blood specimens were taken from all subjects and genomic DNA was extracted as described previously (10). According to the genomic DNA sequence of GATA5 (GenBank accession no. NT_011362), the primer sequences were designed as shown in Table 2. The coding exons (exons 2-7) and their flanking splice junction sites of GATA5 were screened for genetic variations by means of polymerase chain reaction, followed by DNA sequencing with Big Dye chemistry under an ABI 3130 XL DNA Analyzer.

Efficacy of catheter ablation and surgical CryoMaze procedure in patients with long-lasting persistent atrial fibrillation and rheumatic heart disease: a randomized trial

AIMS Catheter ablation and surgical Maze procedure are effective in treating atrial fibrillation (AF) patients. However, there is no study that compares the effect of circumferential pulmonary vein isolation (CPVI) combined with substrate ablation after valvular surgery and the concomitant Maze procedure for the treatment of AF in patients with rheumatic heart disease (RHD). The aim of this study was to compare the effectiveness of CPVI combined with substrate modification and surgical Maze procedure using Saline-Irrigated Cooled-tip Radiofrequency Ablation (SICTRA) system for the treatment of long-lasting persistent AF in patients with RHD. METHODS AND RESULTS Between January 2006 and June 2008, 99 patients with long-lasting persistent AF and RHD were randomly assigned to undergo valvular operation and CPVI combined with substrate modification 6 months after the surgery (Group A, 49 patients) or valvualr operation and concomitant Maze procedure (Group B, 50 patients). The mean follow-up periods were 15 ± 5 and 20 ± 8 months in Groups A and B, respectively. After one procedure, Group B had a significantly higher freedom from artial arrhythmias compared with Group A (82% in Group B vs. 55.2% in Group A, P < 0.001). Fifteen patients in Group A underwent a redo procedure. Six patients in Group B underwent catheter ablation and four were treated successfully. The cumulative rates of sinus rhythm were 71% in Group A and 88% in Group B (P < 0.001). CONCLUSION The concomitant Cox Maze procedure using SICTRA is more effective than subsequent CPVI combined with substrate modification in treating patients with long-lasting persistent AF and RHD.

Novel Germline GJA5/Connexin40 Mutations Associated with Lone Atrial Fibrillation Impair Gap Junctional Intercellular Communication

Atrial fibrillation (AF) is the most common form of sustained cardiac arrhythmia worldwide. Here, we investigate the molecular and cellular mechanisms of lone AF‐linked germline mutations in the connexin40 (Cx40) gene, GJA5. The entire coding region of GJA5 was sequenced in 68 unrelated patients with lone AF. A novel germline heterozygous missense mutation in Cx40 (p.I75F) was identified in one index patient. The mutation was also present in the probands father with lone AF but was not found in the unaffected family members who were examined and 200 unrelated healthy control individuals. Electrophysiological studies revealed no electrical coupling of the cell pairs expressing the mutant alone and a significant reduction in gap junction coupling conductance when the mutant was coexpressed with wild‐type (wt) Cx40 or Cx43. Interestingly, another lone AF‐linked Cx40 mutant p.L229M did not show any apparent coupling defect when expressed alone or together with wt Cx40 but specifically reduced the gap junction coupling when coexpressed with wt Cx43. This study is the first to demonstrate that the germline familial mutations in Cx40 impair the gap junctions through different mechanisms, which may predispose the mutant carriers to AF.

GATA6 loss-of-function mutation in atrial fibrillation

Atrial fibrillation (AF) is the most common type of sustained cardiac arrhythmia and is associated with substantial morbidity and mortality. Increasing evidence demonstrates that hereditary defects are involved in the pathogenesis of AF. However, AF is of remarkable genetic heterogeneity, and the heritable components responsible for AF in the majority of patients remain unclear. In this study, the entire coding region of the GATA6 gene, which encodes a zinc-finger transcription factor crucial for cardiogenesis, was sequenced in 138 unrelated patients with lone AF, and a novel heterozygous GATA6 mutation, c.704A > C equivalent to p.Y235S, was identified in a patient. The detected substitution, which altered the amino acid highly conserved evolutionarily across species, was absent in 200 unrelated ethnically matched healthy individuals, and was predicted to be disease-causing by MutationTaster. Genetic analysis of the available relatives of the mutation carrier showed that in the family the variation co-segregated with the disease transmitted as an autosomal dominant trait, with complete penetrance. The functional analysis performed using a luciferase reporter assay system revealed that the mutant GATA6 protein resulted in significantly decreased transcriptional activity compared with its wild-type counterpart. These findings provide novel insight into the molecular pathophysiology implicated in AF, suggesting the potential implications in the prophylactic strategy and effective therapy for this common arrhythmia.

Decreased Connexin 43 and Increased Fibrosis in Atrial Regions Susceptible to Complex Fractionated Atrial Electrograms

Background and Objectives: Complex fractionated atrial electrograms (CFAE) is distributed at preferential sites of atrium, and the mechanism underlying CFAE is not fully understood. We hypothesized that preexisting atrial abnormalities may be involved in the formation of CFAE. Methods: Twelve pigs were subjected to acetylcholine infusion and right atrial pacing to induce sustained atrial fibrillation. The shortest complex interval map was used to visualize CFAE on three-dimensional anatomic structure of left atrium, and the CFAE sites were labeled by ablation. The expression of connexin 43 (Cx43) and myocardial fibrosis were examined. Results: The expression of Cx43 at CFAE sites was significantly decreased when compared with non-CFAE sites, while myocardial fibrosis was enhanced in CFAE sites compared with non-CFAE sites. Conclusions: These results suggested that the decreased expression of Cx43 and enhanced myocardial fibrosis at CFAE sites of the left atrium may be the structure abnormalities underlying CFAE.

Efficacy, safety and outcome of catheter ablation for atrial fibrillation in octogenarians

BACKGROUND AND OBJECTIVES Catheter ablation is effective in treating patients with atrial fibrillation (AF). The aim of the study was to evaluate the safety, efficacy and outcome of catheter ablation for AF in octogenarians. METHODS AND RESULTS 377 consecutive patients were divided into three groups based on age: ≥80 years (group 1; n=49), 70-79 years (group 2; n=151), 60-69 years (group 3; n=177). The efficacy and safety for those three groups were determined. The success rate after one procedure was similar in three groups (70% in group 1, 72% in group2 and 74% in group 3, P=NS) during a mean follow-up of 18 months. Major complication rates were comparable between the three groups. However, the octogenarians were less likely to undergo a repeated procedure than other groups (8% in group 1, 15% in group 2 and 18% in group 3, P<0.05), and were more likely to remain on antiarrhythmic drugs. CONCLUSION Catheter ablation for AF attempted in octogenarians appears to be effective and with low risk. Ablation results are comparable with those noted in younger patients.