Spatiotemporal electrophysiological changes in a murine ablation model.

AIMS: High recurrence rates after complex radiofrequency ablation procedures, such as for atrial fibrillation, remain a major clinical problem. Local electrophysiological changes that occur following cardiac ablation therapy are incompletely described in the literature. The purpose of this study was to determine whether alterations in conduction velocity, action potential duration (APD), and effective refractory period resolve dynamically following cardiac ablation. METHODS AND RESULTS: Lesions were delivered to the right ventricle of mice using a subxiphoid approach. The sham-operated control group (SHAM) received the same procedure without energy delivery. Hearts were isolated at 0, 1, 7, 30, and 60 days following the procedure and electrophysiological parameters were obtained using high-resolution optical mapping with a voltage-sensitive dye. Conduction velocity was significantly decreased at the lesion border in the 0, 7, and 30 day groups compared to SHAM. APD(70) at the lesion border was significantly increased at all time points compared to SHAM. Effective refractory period was significantly increased at the lesion border at 0, 1, 7, and 30 days but not at 60 days post-ablation. This study demonstrated that post-ablation electrophysiological changes take place immediately following energy delivery and resolve within 60 days. CONCLUSIONS: Cardiac ablation causes significant electrophysiological changes both within the lesion and beyond the border zone. Late recovery of electrical conduction in individual lesions is consistent with clinical data demonstrating that arrhythmia recurrence is associated with failure to maintain bi-directional conduction block.

Spinal cord stimulation protects against atrial fibrillation induced by tachypacing.

BACKGROUND: Spinal cord stimulation (SCS) has been shown to modulate atrial electrophysiology and confer protection against ischemia and ventricular arrhythmias in animal models. OBJECTIVE: To determine whether SCS reduces the susceptibility to atrial fibrillation (AF) induced by tachypacing (TP). METHODS: In 21 canines, upper thoracic SCS systems and custom cardiac pacing systems were implanted. Right atrial and left atrial effective refractory periods were measured at baseline and after 15 minutes of SCS. Following recovery in a subset of canines, pacemakers were turned on to induce AF by alternately delivering TP and searching for AF. Canines were randomized to no SCS therapy (CTL) or intermittent SCS therapy on the initiation of TP (EARLY) or after 8 weeks of TP (LATE). AF burden (percent AF relative to total sense time) and AF inducibility (percentage of TP periods resulting in AF) were monitored weekly. After 15 weeks, echocardiography and histology were performed. RESULTS: Effective refractory periods increased by 21 ± 14 ms (P = .001) in the left atrium and 29 ± 12 ms (P = .002) in the right atrium after acute SCS. AF burden was reduced for 11 weeks in EARLY compared with CTL (P <.05) animals. AF inducibility remained lower by week 15 in EARLY compared with CTL animals (32% ± 10% vs 91% ± 6%; P <.05). AF burden and inducibility were not significantly different between LATE and CTL animals. There were no structural differences among any groups. CONCLUSIONS: SCS prolonged atrial effective refractory periods and reduced AF burden and inducibility in a canine AF model induced by TP. These data suggest that SCS may represent a treatment option for AF.