**4. Cryoballoon evolution**

RF ablation catheters have made advancements over the years but they still rely on a "point-by-point" technique to achieve PVI which can be challenging and timeconsuming. This is due to the fact that RF ablation utilizes focal catheters as opposed to a balloon system that can produce circumferential continuous lesions resulting in shorter TTI and durable PVI.

The Arctic Front™ is the first cryoballoon catheter system introduced in the United States, and was used in the North American STOP AF trial. The study found that the first generation CB was a safe and effective alternative to antiarrhythmic therapy. Procedure times were sped up to about one third when compared to spot ablation techniques.

Evolution of CB from first to the second-generation included the addition of 4 jets, increased refrigerant flow, and moving the cooling zone more distally. These changes made the CB more efficacious. The second generation CB was used in the FIRE and ICE trial that demonstrated Cryoablation to be noninferior to RF ablation.

The latest technological advances in the family of CB include improved visualization of TTI and maneuverability of the catheter. Further modifications are inevitable and will surely provide even safer and more efficient catheters [31, 32].

### **5. Stereotaxis**

Guiding the catheter to the intended sites and maintaining adequate contact is a critical part of a successful procedure. The ability to see left atrium anatomy reduces complications and ensures that lesions are made at intended target sites.

#### *Frozen Hearts: The Emerging Role of Cryoablation for Pulmonary Vein Isolation DOI: http://dx.doi.org/10.5772/intechopen.105885*

Fluoroscopy was the main imaging technique used by electrophysiologists to target the ablation site however it had several drawbacks including 2-dimensional (2-D) representation, inability to visualize soft tissue, and a long learning curve. Other modalities to facilitate accessing the left atrium anatomy include intracardiac echocardiogram, computed tomography (CT) and magnetic resonance imaging (MRI).

Remote magnetic navigation (Stereotaxis) entered clinical use for electrophysiology interventional procedures several years ago. Using stereotaxis may help reduce the risk of complications and increase the patient's safety. The system creates a weak magnetic field around the patient that can be manipulated by an integrated computer and three-dimensional mapping system to drive flexible catheters within the heart with extreme precision.

Over the past 10 years, AF ablation has become the predominant indication in centers of excellence, possibly representing up to 60% of interventions. The main difficulties during these procedures are the duration, which may exceed 4 hours, and the length of time that both the operator and patient are exposed to radiation. The advantages of the technique were underlined by different authors, who highlighted that there was no risk of perforation, the catheter had excellent stability, and it was possible to navigate in complex anatomies, as has been described in patients with congenital heart defects. Although AF ablation was noticeably effective in 80% of cases, with a mean of 1.3–1.7 procedures per patient, the rate of major complications reported was 4.5% of cases, including 1% vascular accidents and 1.3% tamponade [33].

Several clinical trials have now been undertaken to evaluate RMNS in AF. The initial phase evaluated the feasibility of RMNS in 40 AF patients who required treatment by RFA. The authors demonstrated the feasibility and very good efficacy of the robotic technique. Application time was significantly reduced compared with the control group, although the trial was a case-control study.9. The operator highlighted the extreme stability of the magnetic catheter, which was especially useful for approaching the right veins. In the study, success was achieved in 38 of the 40 patients tested (95% of cases) [34].

## **6. Other ablation strategies**

Beyond minimally invasive strategies, there are surgical ablation techniques most well known of which is the COX-MAZE (CM) procedure. Surgical approaches to AF ablation vary in the technique and level of published research investigating outcomes. With changes in the goals of the procedure the CM has been revised multiple times with each interaction being assigned a roman numeral. The CM IV procedure had significantly shorter mean aortic cross-clamp time for a lone CM from 93 ± 34 min for the CM III to 47 ± 26min for the CM IV (P < 0.001). A propensity analysis performed by Lall et al. showed no significant difference in freedom from AF at 3, 6 and 12months postoperatively between appropriately matched patients undergoing either the CM III or the CM IV [34]. A report of over 2 decades by Weimar et al. demonstrated both the CM III and CM IV showed no difference in freedom from AF and a significantly decreased major complication rate. This was despite the fact that the recent cohort had more patients with long-standing persistent AF and much more intensive follow-up with the majority of patients having at least 24-h Holter monitoring [34].

A more recent CM IV study reviewed 576 consecutive patients who underwent the CM IV between January 2002 and September 2014. Most patients were followed up with prolonged Holter monitoring. Twelve-month freedom from AF was 93%, with 85% of patients free from all AADs, while 5-year freedom from AF was 78%, with 66% of patients also free from all AADs. When comparing patients with PAF to patients with persistent AF, freedom from AF on and off AADs was not significantly different at any time point [35].

The CM has been successful in reducing the incidence of stroke. In a report by Pet et al., 13% of the patients had experienced a preoperative neurological event out of the 433 studied. However, there were only 6 postoperative neurological events during long-term follow-up in this cohort (mean 6.6 ± 5.0years). The long-term stroke rate after the CM has been 0.2% per year, despite the fact that the great majority of patients had discontinued AADs [36].

Other cardiac diseases are often seen along with AF, and the CM is commonly used as an associated procedure. In patients who underwent mitral valve surgery, studies have demonstrated similar arrhythmia recurrence rates in patients with lone AF who have undergone stand-alone surgical ablation compared to those with AF and mitral regurgitation who underwent concomitant mitral procedures. Specifically, freedom from AF and AADs at 12 and 24months were nearly the same between the 2 groups (73% vs. 76% at 12months, 77% vs. 78% at 24months) [37]. Another prospective, randomized control trial which was performed at the Cardiothoracic Surgical Trials Network (CTSN) compared patients with persistent or long -standing AF with patients who had mitral valve disease that required surgical intervention. The experimental groups either underwent CA or no ablation. The results demonstrated that the patients that remained free from AF at both 6 and 12 months belonged to that of the CA group with P < 0.001. It is important to note that those patients that underwent CA did not significantly affect morbidity or mortality.

A comparison between patients undergoing stand-alone CM-IV to those undergoing CA with aortic valve replacement was just as effective as stone-alone CM IV in the treatment of AF among all ages and all comorbidities [38]. Outcomes of patients with AF that were planning on having left or biatrial CM IV and coronary artery bypass grafting (CABG) in the years of 2002 to 2015 demonstrated significantly low operative mortality rates. Freedom from AF at 1 year in the CM-IV group was upwards of 98% with 88% free of AADs at the 5 year follow up period [35–38].

Minimally invasive right minithoracotomy (RMT) is an alternate approach to standard surgical sternotomy approach. RMT has been associated with reduced operative morbidity and decreased intensive care unit stays. Major surgical complications were also found to be significantly lower in the RMT groups in composition to standard surgical approach [39].

In the last 3 decades, the development of ablation technologies has positively impacted the field of AF surgery and patient outcomes. Minimally invasive technologies have decreased the need for CABG procedure time, and with minimally invasive technologies come improved morbidity and mortality for patients. The number of patients undergoing surgical ablation procedures has been vastly increasing in the past 2–3 decades; however, there are still a significant number of patients with AF that are undergoing other cardiac interventions without treatment for their AF. With increased research and knowledge, increased education can encourage more aggressive treatment of AF in these patients. As continued learning of AF and the mechanisms of which it can develop evolves, improved diagnostic technologies can be implemented to a larger volume of patients [40].
