Patent foramen ovale closure by radiofrequency thermal coaptation - First experience in the porcine model and healing mechanisms over time

Background - Percutaneous transcatheter patent foramen ovale (PFO) closure is now standard practice and may limit embolic complications for at least 10 years. Implantable PFO closure devices may be complicated by thrombosis, infection, device fracture, or embolization. A novel strategy uses radiofrequency- based thermal energy to seal PFO membranes, with no implanted device. We successfully used this method and examined histopathologic events in swine to characterize safety and efficacy. Methods and Results - Thirteen domestic swine were examined over time after thermal PFO closure. Three animals were euthanized within 1 hour of treatment, 5 after 7 days, and 5 at 28 days. Gross and histopathologic findings were examined. Radiofrequency energy was delivered successfully in all cases, and PFOs were closed in 12 of 13 cases. One case was not suitable for histological examination because of laceration at euthanasia, and the other PFO was clinically closed, with no shunt at 7 days, but was histologically open. All of the other PFOs were confirmed closed histologically. Acute histological results showed edema, hemorrhage, and myocyte necrosis. Minimal thrombus formation occurred on the left atrial endocardial surface. At day 7, transmural thermal effects occurred through the atrial wall that extended to the epicardial surface. At day 28, thermal effects showed excellent scar formation. Collagen, matrix, and neovascularization were present in all cases. No animal experienced adverse events. Conclusions - Thermal PFO closure is feasible, safe, and effective in swine. Thermal healing is nearly complete by 4 weeks and consists of collagen formation and tunnel closure. This technique may allow substantial reduction in PFO closure risk over current device-based therapy.