**2. Previous surgical ablation**

## **2.1 The left atrial isolation procedure**

In 1980, Dr. James Cox developed the left atrial isolation at Duke University. This is the first surgical procedure designed specifically to eliminate AF. This procedure

confined AF to the left atrium, allowing the remainder of the heart to be in sinus rhythm [3–5].

#### **2.2 The Corridor procedure**

In 1985, Guiraudon et al. developed the corridor procedure to isolate a strip of atrial septum including both the sinoatrial and atrioventricular nodes to allow the sinoatrial node to pace both right and left ventricles [6]. The shortcomings of the corridor procedure included failure to prevent thromboembolism as well as atrioventricular dyssynchrony. It did have the advantage of preserving atrioventricular conduction [6].

#### **2.3 The atrial transection procedure**

Cox et al. first described the atrial transection procedure in 1985. Using a canine model, they found that a single longitudinal incision around both atria and down into the septum would terminate AF [4, 7]. This procedure effectively prevents AF or atrial flutter in animals but not in humans. Although this procedure was abandoned, it represented a transitional step toward the Cox-Maze procedure.

#### **2.4 The Cox-Maze procedure**

After extensive animal studies, The Cox-Maze procedure was introduced clinically by James Cox in 1987 [2, 4]. This procedure was designed based on the theory that macro-reentrant circuits cause and propagate AF. The Cox-Maze procedure restored sinus rhythm as well as AV synchrony, reducing the risk of stroke and thromboembolism [8]. The original of Cox-Maze procedure, The Cox-Maze I, consisted of multiple surgical incisions across both atria that allowed for a pathway for the sinus impulse to reach the AV node. It permitted depolarization of most of the atrial myocardium resulting in preservation of most of the atrial contractile function [9].

The Cox-Maze II was formulated because the Cox-Maze I had problems with late chronotropic incompetence with a high incidence of pacemaker implantation [10].

The Cox-Maze III proved to be effective and became the gold standard for surgical treatment of AF [1, 2]. The procedure is often called the cut-and-sew maze, and the surgical results of the Cox-Maze III were excellent, with over 90% of patients free from symptomatic AF at late follow up [11–14]. Despite its efficacy, the cutand-sew maze was technically difficult and required a lengthy period of aortic cross clamp time, which limited its widespread adoption. Over the last two decades, modern ablation devices transformed the Cox-Maze III into an easier, shorter, and less invasive procedure, which has been termed the Cox-Maze IV. These have allowed for more widespread adoption [15]. These modern technologies have been used to replace the surgical incisions and have allowed the development of less invasive approaches.

### **3. Surgical ablation technology**

When ablation technology was introduced, the goal was to replace the incision lines of the Cox-Maze III as much as possible. An ablation technology had to have

#### *Concomitant Atrial Fibrillation Surgery DOI: http://dx.doi.org/10.5772/intechopen.106066*

3 characteristics in order to replicate a surgical incision. First, a device had to create a line of bidirectional conduction block. A pattern of lesions with these properties can prevent AF, either through blocking macro or micro-reentrant circuits or by isolating focal triggers. Only transmural lesions produce reliable conduction block, as even small gaps in ablation lines retain the ability to conduct both sinus and fibrillatory impulses [16, 17]. Second, the ablation device had to be safe. Safety requires that the device delivers a precise dose of energy to minimize both inadequate ablation and potential injury to nearby vital structures by excessive ablation. Lastly, the ablation device had to make AF surgery simpler and require less operative time compared to the original technique.

Several ablation technologies have been developed, and each has its relative advantages and disadvantages. Cryoablation and bipolar radiofrequency (RF) devices have been shown to be the most effective and are the ablation technologies used for the Cox-Maze IV [18].

#### **3.1 Cryoablation**

Cryoablation technology creates ablation lines by freezing myocardial issue. Cryoablation preserves the myocardial fibrous skeleton and collagen structure, making it one of the safest energy sources available. These devices work by pumping a liquid refrigerant to the tip of a device where it undergoes evaporation, and in the process absorbing heat from the tissue in contact with the tip. This causes intracellular and extracellular water to freeze. The resulting ice crystals disrupt the plasma membrane and cause early cell death via cell lysis. Lesions also expand due to induced apoptosis. The size of the lesion produced depends on the thermal conductivity and temperature of both the probe and the tissue [19].

Two commercially available sources of cryothermal energy are in clinical use in cardiac surgery. Nitrous oxide-based devices are manufactured by AtriCure (Cincinnati, OH). Devices using Argon have been developed and are currently distributed by Medtronic (Minneapolis, MN). The minimum temperature that can be produced by an ablation device is limited by the thermodynamic properties of the refrigerant used. At 1 atmosphere of pressure, nitrous oxide is capable of cooling tissue to −89.5°C, whereas argon can cool tissue to −185.7°C. Nitrous oxide based cryoablation has a long history of clinical use with a well-defined efficacy and is safe except around the coronary arteries [20, 21]. Experimental and clinical studies have shown intimal hyperplasia and coronary artery stenosis after cryoablation [21–23]. The disadvantage of cryoablation is the relatively longer time required to create transmural lesion (usually 2–3 minutes). There is also difficulty in creating lesions on beating heart from an epicardial approach due to the circulating blood acts as a heat sink effect [24]. Moreover, freezing of intra-atrial blood poses a potential risk of thromboembolism.

The nitrous oxide technology can be used with both the rigid, reusable, and the flexible, disposable probes. The argon technology is available only as a flexible, disposable ablation device.

#### **3.2 Radiofrequency energy**

Radiofrequency (RF) has been used for many years by cardiac electrophysiologists and surgeons to ablate cardiac tissue. RF energy can be delivered using unipolar or bipolar electrodes.

#### **3.3 Unipolar RF**

Energy is delivered between the tip of electrode and a grounding pad attached to the patient. Unlike bipolar RF energy, an alternating amount is delivered between 2 jaws of a clamp. Several factors contributed to lesion size such as tissue contact area, interface temperature, the amount of power applied and duration of energy delivery. Several factors can limit the depth of the lesion, potentially preventing successful creation of a transmural lesion with conduction block. These include char formation, epicardial fat, myocardial and endovascular blood flow, and tissue thickness. Several unipolar RF ablation devices have been developed. These include dry, irrigated and suction assisted devices. These devices have had limited applicability in cardiac surgery. Transmural lesions can be created with dry unipolar RF on the arrested heart in animal studies. Unfortunately, this has not been reproducible in clinical practices [25]. There is one study that confirmed that only 20% of transmural lesions achieved after 2 minutes of ablation time during mitral valve surgery. Moreover, the results of epicardial unipolar RF ablation on the beating heart were found to be even less successful. Another animal study has demonstrated the epicardial unipolar RF failed to create transmural lesions on the beating heart [26]. One clinical study has shown only 10% success rate of transmural lesions achieved after epicardial RF ablation [27]. Convection caused by circulating blood that explained the failure of epicardial unipolar RF ablation on the beating heart [28, 29]. No unipolar RF device has been shown by independent laboratories to be capable of reliably creating transmural lesions on the beating heart [30]. The recent expert consensus guidelines mentioned that the use of epicardial unipolar RF ablation outside of clinical trials is not recommended because its efficacy remains questionable [31].

#### **3.4 Bipolar RF**

The electrodes are embedded in the jaws of a clamp to focus the delivery of energy. Multiple studies have shown bipolar RF ablation to be able to create transmural lesions on the beating heart in animals and humans with short ablation times [32–34]. Bipolar RF devices are currently sold by two companies in United States (AtriCure, West Chester, OH and Medtronic, Minneapolis, MN). Both devices have shown similar experimental and clinical efficacy. Bipolar RF energy also has a more favorable safety profile compared to unipolar RF. Some clinical complications of unipolar RF devices have been reported including coronary vessel injuries, stroke and esophageal perforation leading to atrioesophageal fistula [35–39]. There have been no collateral injuries reported after bipolar RF technology despite its widespread clinical use. Innovation continues within the field of RF ablation technology, including the development of unipolar-bipolar hybrid devices. The Cobra Fusion (AtriCure, West Chester, OH) a suction-assisted device that combines bipolar and unipolar RF, has been shown in early experimental reports to have improved efficacy in creating transmural epicardial lesions on the beating heart [40].

The recent expert consensus guidelines state that the best evidence exists for the use of bipolar radiofrequency (RF) clamps and cryoablation devices, which have become integral parts of many procedures, including pulmonary vein isolation and the Cox-Maze IV procedure.

Bipolar RF clamps or cryoprobes (both reusable and/or disposable) are recommended to be used for PVI in both empty arrested and beating heart with exit block confirmation testing. For beating heart, endocardial cryoablation is recommended for free wall linear ablation instead of epicardial cryoablation due to higher success rate of transmurality. The guidelines also suggest to identify and avoid injury to coronary vessels while doing ablation with any devices [31].

Other energy delivery devices including microwave, laser, and ultrasound have been used clinically but limitations of these technologies have led to limited use and withdrawal of these devices from the market [28, 41–45].
