Catheter ablation for ventricular tachycardia

Stent-based electrode for radiofrequency ablation in the rat esophagus: a preliminary study

Endoluminal radiofrequency (RF) ablation has been widely used as a safe and effective treatment for Barrett's esophagus. However, inadequate RF ablation may occur due to insufficient contact between the electrode and target tissues. Herein, a stent-based monopolar RF electrode (SE) was developed to evenly deliver RF energy to the inner wall of the rat esophagus. The optimal RF parameters were evaluated in the exposed rat esophagus. The temperature in the rat esophagus reached 70 ℃ in 89 s at 30 W, 59 s at 40 W, and 34 s at 50 W. The technical feasibility and efficacy of RF ablation using SE were evaluated based on changes in histological transformation and immunohistochemical parameters of tissues compared at immediately, 1 and 2 weeks after the procedure. The degrees of inflammatory cell infiltration, fibrotic changes, TUNEL, and HSP70 in the RF-ablated rat esophagus were significantly higher than compared with sham control (all p < 0.05). TUNEL-positive deposition gradually decreased, but HSP 70-positive deposition maintained a similar level for 2 weeks. The stent-based RF ablation was technically feasible and effective in evenly inducing thermal damages to the rat esophagus. The RF ablation system using the SE may represent a promising treatment for endoluminal malignancies.

Combined Therapeutic and Monitoring Ultrasonic Catheter for Cardiac Ablation Therapies

This study evaluated the feasibility of a combined therapeutic and diagnostic ultrasonic catheter for cardiac ablation therapies. Ultrasound can be used to determine when diseased cardiac tissues have become fully coagulated through a method known as local harmonic motion imaging (LHMI). LHMI is an imaging modality for treatment monitoring that uses acoustic radiation force, displacement tracking and the different mechanical properties of viable and ablated tissues. In this study, we developed catheters that are capable of LHMI measurements. Experiments were conducted in phantoms, ex vivo cardiac samples and the in vivo beating hearts of healthy porcine subjects. In vivo experiments revealed that four of four epicardial sonications revealed a decrease in measured displacements from LHMI experiments and that when lower power was used, no lesions formed and there was no corresponding decrease in measured displacement amplitudes. In addition, two of three endocardial lesions were confirmed and corresponded to a decrease in the measured displacement amplitude.

The evaluation of steerable ultrasonic catheters for minimally invasive MRI-guided cardiac ablation

PURPOSE

The purpose of this study was to develop steerable MR-compatible ultrasound catheters suitable for minimally invasive MRI-guided cardiac ablation therapies.

METHODS

MRI-compatible ultrasound steerable catheters were developed and tested for their overall tissue heating performance and safety. Ultrasound transducers were mounted on a monodirectional deflectable catheter tip that was made to be MRI-compatible. Catheter safety was assessed on the potential to form hot spots at the distal end of the catheter throughout fast spin echo and thermometry scans. Heating experiments were performed on phantoms and ex vivo porcine cardiac samples.

RESULTS

During catheter safety experiments, a maximum temperature increase of 11.35 ± 0.83°C was evident after a 12-min, 40-s fast spin echo scan with a whole body specific absorption rate (SAR) of 1.9 W/kg and 1.07 ± 0.22°C during thermometry scans (flip angle = 90°; scan time = 12 min, 41 s; whole body SAR = 0.34 W/kg). Temperature elevations induced by the sonication were shown to be on the order of 38.1 ± 5.2°C for phantom experiments and 49.3 ± 9.7°C for ex vivo cardiac samples.

CONCLUSION

Steerable ultrasound catheters have the potential to be safely placed in an MR system with little concern of catheter self-heating and driven to heat surrounding structures to cause ablations. In addition, these catheters have the added benefit of a deflectable tip that allows the treatment of multiple targets from within the bore of the MR scanner.