The ablation of atrial fibrillation with the loop catheter design: what we have learned from the animal model

Epigallocatechin-3-Gallate Inhibits Atrial Fibrosis and Reduces the Occurrence and Maintenance of Atrial Fibrillation and its Possible Mechanisms

BACKGROUND

Atrial fibrosis is one of the main causes of the onset and recurrence of atrial fibrillation (AF), for which there is no effective treatment. The aim of this study was to investigate the effect and mechanism of epigallocatechin-3-gallate (EGCG) on AF in rats.

METHODS

The rat model of AF was established by rapid pacing induction after angiotensin-II (Ang-II) induced atrial fibrosis to verify the relationship between atrial fibrosis and the AF. The expression levels of TGF-β/Smad3 pathway molecules and lysyl oxidase (LOX) in AF were detected. Subsequently, EGCG was used to intervene Ang-II-induced atrial fibrosis to explore the role of EGCG in the treatment of AF and its inhibitory mechanism on fibrosis. It was further verified that EGCG inhibited the production of collagen and the expression of LOX through the TGF-β/Smad3 pathway at the cellular level.

RESULTS

The results showed that the induction rate and maintenance time of AF in rats increased with the increase of the degree of atrial fibrosis. Meanwhile, the expressions of Col I, Col III, molecules related to TGF-β/Smad3 pathway, and LOX increased significantly in the atrial tissues of rats in the Ang-II induced group. EGCG could reduce the occurrence and maintenance time of AF by inhibiting the degree of Ang-induced rat atrial fibrosis. Cell experiments confirmed that EGCG could reduce the synthesis of collagen and the expression of LOX in cardiac fibroblast induced by Ang-II. The possible mechanism is to down-regulate the expression of genes and proteins related to the TGF-β/Smad3 pathway.

CONCLUSION

EGCG could downregulate the expression levels of collagen and LOX by inhibiting the TGF-β/Smad3 signaling pathway, alleviating Ang-II-induced atrial fibrosis, which in turn inhibited the occurrence and curtailed the duration of AF.

Relationship between lesion formation and electrophysiological responses using catheters equipped with mini-electrodes in chronic atrial fibrillation

BACKGROUND

The study focuses on the electrophysiological changes associated with lesion formation using 4.5-mm irrigated and 8-mm standard catheters equipped with mini-electrodes (MEs) positioned circumferentially on the tip.

OBJECTIVE

The aim of the study was to test the relationship between the maximal electrogram (EGM) reduction, frequency spectrum shift, and their impact on atrial lesion formation in the atrial fibrillation (AF) model. Furthermore, we hypothesize that the high fidelity recording from the MEs allows improved discrimination of ablated tissues from nonablated tissues.

METHODS

Under fluoroscopic and NavX guidance, atrial ablation lesions were placed in 4 canines in chronic AF (>12 months in AF) to achieve intercaval, cavotricuspid isthmus, and left atrial contiguous lesions. Lesion times were titrated to the maximal loss of EGM amplitude as recorded from the MEs. Radiofrequency (RF) lesions were sequentially connected on the basis of the ME recordings of tissue viability.

RESULTS

In lesions formed using a 4.5-mm irrigated catheter (172 lesions) and in those formed using an 8-mm catheter (155 lesions), the time to nadir of the EGM reduction was 22 ± 12 and 22 ± 9 seconds (NS:p>0.05). Contiguous transmural lesions were successfully placed and guided by the ME EGMs and confirmed by frequency spectra.

CONCLUSION

In the chronic AF model, EGM reduction and frequency spectrum shift recorded from the MEs are twice the reduction recorded using the 4.5mm and 8mm tip to ring electrodes. RF titration based on the maximal EGM diminution is an effective approach to monitor lesion formation and may improve safety by preventing unnecessarily prolonged RF application. The ME EGM recording greatly facilitates placement of contiguous transmural linear lesions.