The initial observations of arrhythmogenic activity in the pulmonary veins (PVs) with the potential for triggering atrial fibrillation accounted for extensive investigation for more than a decade. Electrical isolation of the PVs has emerged as the mainstay strategy during percutaneous transcatheter and surgical ablation procedures for atrial fibrillation.
Extensive investigations have been conducted on different ablation strategies, catheters, and energy sources to improve the efficacy and safety of PV isolation in patients with atrial fibrillation. Radiofrequency (RF) energy is widely used and is the only U.S. Food and Drug Administration–approved energy for ablation of atrial fibrillation. In an effort to overcome the shortcomings of drawing a continuous line around the PV ostia by point-by-point focal RF catheter ablation, novel catheter designs have been evaluated aimed at circumferential ablation to achieve PV isolation with a single or only a few energy deliveries. Current investigational devices deliver RF, ultrasound, laser, and cryothermal energy. Safety remains a critical aspect of ablation procedures.
Cryothermal energy is thought to have advantages over other energy sources because experimental and clinical studies have demonstrated that cryolesions exhibited preserved endocardial and myocardial structural integrity and were free of overlying thrombus. Likewise with RF, cryoablation of PVs was initially described using a point-by-point ablation strategy. This approach was limited because of long freezing time, 4 minutes for each application.
We have performed the initial preclinical feasibility and safety studies using a novel curvilinear catheter for PV isolation in a canine closed chest model. This chapter details our initial experience with cryoablation. Other additional outstanding experimental and clinical investigations on cryoablation are listed as well for further review.
Study Design
The study catheter, Arctic Circler (CryoCath, Montreal, Quebec, Canada), was used to create circumferential PV electrical isolation by delivering cryothermal energy to its distal spiral components (7 French; 20-mm outer diameter; refrigerated by N 2 O at temperature −75°C to −89°C; Figures 5–1 to 5–3 ). A total of 21 mongrel dogs weighing 22 to 28 kg were studied under general anesthesia for acute and survival experiments. Transeptal puncture/catheterization was guided by fluoroscopy and intracardiac echo; both intracardiac echo and PV angiography were used to assess PV dimensions before and after cryoablation and at follow-up studies (see Figure 5–3 ). After PV angiography, a detailed sinus rhythm mapping of the right superior PV was obtained with a closely spaced octapolar linear or a circular multielectrode catheter. PV isolation (entrance conduction block) was assessed by analysis of bipolar recording obtained immediately after cryoablation, at follow-up studies, and before death ( Figure 5–4 ). Gross and microscopic examination was performed to examine the characteristics of acute and chronic PV cryolesions; detailed dissection of the heart and lungs and the surrounding structures was also done ( Figures 5–5 to 5–10 ).
