Idiopathic isolated fibrotic atrial cardiomyopathy underlies unexplained scar-related atrial tachycardia in younger patients.

Aims: Unexplained scar-related atrial tachycardia (AT) has been frequently encountered in clinical practice. We hypothesized that idiopathic, isolated fibrotic atrial cardiomyopathy (ACM) underlies this rhythm disorder. This study was aimed to characterize the underlying substrate and to explore the aetiology of this unexplained scar-related AT. Methods and results: Twenty-six (11 men, aged 46 ± 13 years) of 52 non-surgical scar-related AT patients identified by three-dimensional voltage mapping were enrolled in this prospective observational study. Multimodality image examinations (echocardiography, cardiac magnetic resonance, 99Tc single-photon emission computed tomography), ventricular voltage mapping, and intracardiac pressure curve recording ruled out ventricular involvement. Catheter ablation was acutely successful for all the patients, and pacemaker implantation was performed in seven patients who presented sinus node dysfunction or atrial standstill after termination of the AT. In three patients with multiple AT recurrences, the diseased areas of the right atrium were resected and dechannelled via mini-invasive surgical interventions. Histological examinations revealed profound fibrosis without amyloidosis or adipose deposition. Viral and familial investigations yielded negative results. Fibrosis progression over a median of 45 (5-109) months of follow-up manifested as atrial arrhythmia recurrence in seven patients and atrial lead non-capture due to newly developed atrial standstill in two patients. Two patients suffered four ischaemic stroke events before receiving anticoagulation treatment. Conclusion: Isolated, fibrotic ACM may underlie the idiopathic scar-related ATs. This novel cardiomyopathy has unique clinical characteristics with high morbidity including stroke and warrants specific therapeutic strategies. Further investigations are required to determine the aetiology and mechanism.

Prevention of postsurgical atrial tachycardia with a modified right atrial free wall incision.

BACKGROUND: Most postsurgical macroreentry atrial tachycardias (PS-MATs) are atriotomy related; however, underlying mechanisms and prevention remain undefined. OBJECTIVE: The purpose of the present study was to investigate the electrophysiological and histologic bases of right atriotomy incision arrhythmogenicity and whether a modified atriotomy that extends the incisional line to the tricuspid annulus (TA) and inferior vena cava (IVC) prevents PS-MAT. METHODS: Atrial arrhythmia induction and electrophysiological and histologic characteristics were studied 8 weeks after right atriotomy in 30 adult swine according to incision distance to TA or IVC (groups A, B, and C: broad, narrow, and closed corridors, respectively; group D, no-incision sham; n = 6 per group, except n = 12 for group B). RESULTS: Sustained PS-MATs were induced and mapped in the broad- and narrow-corridor groups (A, 1 of 6 [16.7%] vs B, 5 of 12 [41.7%]) but not in the closed-corridor (C) or sham (D) groups (P = .087). With 20-ms pacing cycle-length decrements (from 350 to 270 ms), mean conduction time over 20 mm at the atriotomy-to-TA corridor was 29.2 ± 2.2, 31.0 ± 4.2, 26.0 ± 1.9, and 17.0 ± 1.4 ms for 5 and 10 mm (both group B), 15 mm (group A), and sham incision (P = .017), respectively. Conduction properties correlated with histologic findings: the wider the corridor, the healthier its tissue. In group C (modified atriotomy), both corridors were replaced by dense scar with complete conduction block. CONCLUSION: Atriotomy corridor width determines conduction properties and contributes to arrhythmogenicity. A modified right atriotomy that extends to the TA and IVC prevents PS-MAT.

Down-regulation of ATBF1 activates STAT3 signaling via PIAS3 in pacing-induced HL-1 atrial myocytes.

Atrial fibrillation (AF) is progressive and is the most common clinical arrhythmia. It is associated with inflammatory changes characterized by signal transducer and activator of transcription 3 (STAT3) signaling. A zinc finger homeobox 3 (ZFHX3, also named AT-motif binding factor 1, ATBF1) gene variant has been found in patients with AF. However, the mechanism by which the ATBF1 leads to inflammation in AF remains unknown. The aim of this study was to investigate whether tachypacing induces a decrease in ATBF1 expression and then activates STAT3 signaling via protein inhibitor of activated STAT3 (PIAS3). Atrial (HL-1 myocytes) cells were cultured in the presence of rapid electrical stimulations. In tachypaced HL-1 cells, we found that ATBF1 and PIAS3 protein levels were decreased, while the level of phosphorylated STAT3 (p-STAT3) was highly up-regulated compared with that of total STAT3. Knockdown of ATBF1 enhanced this trend, while the overexpression of ATBF1 had the opposite effect. A binary complex of ATBF1 and PIAS3 was formed and then the DNA-binding ability of activated STAT3 was enhanced in tachypaced HL-1 cells. These data indicate that tachypacing decreased ATBF1, leading to enhanced STAT3 DNA-binding activity due to the reduced formation of a binary complex of ATBF1 and PIAS3.