**Histopathological Change Following Cox-Maze IV Procedure for Atrial Fibrillation Procedure for Atrial Fibrillation**

**Histopathological Change Following Cox-Maze IV** 

DOI: 10.5772/intechopen.72786

Takashi Murashita Takashi Murashita Additional information is available at the end of the chapter

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62 Cardiac Arrhythmias

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Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.72786

#### **Abstract**

The prevalence of atrial fibrillation and the likelihood of undergoing concomitant surgical ablation at the time of open heart surgery are increasing. Currently, the conventional cutand-sew Maze procedure has been predominantly replaced by Cox-Maze IV procedure, in which new energy sources such as radiofrequency energy and/or cryoablation are applied. Cox-Maze IV procedure has been associated with lower rate of complications than a cutand-sew procedure. However, some previous studies reported the lower success rate of Cox-Maze IV procedure, possibly because radiofrequency ablation or cryoablation cannot always achieve transmurality. For the success of surgical ablation, achieving transmurality, defined as complete atrial wall thickness of fibrotic changes, is of paramount importance. A review of previous articles regarding histopathological changes of the atrial tissue following surgical ablation is performed. The effectiveness of new energy sources such as radiofrequency and cryoablation in terms of histological transmurality is discussed.

**Keywords:** atrial fibrillation, Maze procedure, radiofrequency, cryoablation

#### **1. Introduction**

Surgical ablation for atrial fibrillation (AF) has been under continuous development for over two decades. The most recent guidelines for the surgical treatment of AF reported by the Society of Thoracic Surgeons (STS) state that surgical ablation for persistent AF can be performed without adding operative risk and is recommended at the time of concomitant mitral valve operations, isolated aortic valve operations, isolated coronary artery bypass grafting, and combined aortic valve and coronary artery bypass surgery (class I strength of recommendation) [1]. Surgical ablation is also recommended to symptomatic AF refractory to medical or catheter-based therapy in the absence of structural heart disease (class II strength of recommendation) [1].

Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons

around the orifices of the pulmonary veins and the remaining are located in other sites such as right atrium, left atrium, crista terminalis, and left atrial appendage. The findings of their paper, which reported that the triggers were successfully treated with radiofrequency ablation, led to an explosion of efforts by a number of cardiologists and cardiac surgeons to treat AF with catheter ablation and surgical techniques, respectively. The concept of treating AF was originally focused on isolating the pulmonary veins, either by catheters or surgical devices.

Histopathological Change Following Cox-Maze IV Procedure for Atrial Fibrillation

http://dx.doi.org/10.5772/intechopen.72786

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However, AF produces unfavourable changes in atrial function and structure, which is called remodeling [21]. After many years of paroxysmal AF, the macroreentrant circuits of AF can become self-perpetuating. At this point, paroxysmal AF can become long-standing or persistent AF, and the underlying electrophysiologic culprit is no longer the focal triggers, but rather the macroreentrant circuits themselves. Therefore, for long-standing or persistent AF, simple isolation of pulmonary veins is not an effective treatment because the focal triggers do not account for onset of AF for this type of AF. In these patients, it is necessary to interrupt the macroreentrant circuits by placing additional linear lesions in the atria. This concept has led

The era of cryosurgery began with the development of automated cryosurgical equipment in the 1960s. Cooper et al. described cryosurgical resection of parenchymal organs using liquid nitrogen-refrigerated clamp in 1966 [22]. Cryosurgery has been an integral part of the surgical treatment of cardiac arrhythmias since the 1970s. With the recent technological development of cryoablation devices, the use of cryothermy in the treatment of cardiac arrhythmias

Cryoablation is effective in producing electrical silent ablation lines, and can be used judiciously safely without injuring surrounding structures such as coronary arteries and valve

Gage et al. described the mechanisms of tissue injury in cryosurgery [23]. The adverse effect of low temperature on cells begins as temperature falls into the hypothermic range. The function and structure of cells are stressed, and cell metabolism progressively fails. As the temperature goes further down and falls into the freezing range, water is crystallized, which causes more serious consequences than the earlier cooling. Ice crystal formation first occurs in the extracellular spaces, and with further cooling, it occurs within the cell. Intracellular ice formation requires temperatures colder than −40°C. Once intracellular ice is formed, it disrupts organ-

The progress to a stable lesion can be divided into three phases: (1) freeze/thaw phase, (2)

haemorrhagic and inflammatory phase, and (3) replacement fibrosis phase [24].

to a surgical ablation technique called Cox-Maze procedure.

**3. Cryoablation**

is increasing.

tissue.

**3.1. Introduction of cryoablation**

**3.2. Mechanisms of tissue injury in cryoablation**

elles and cell membranes, and cell death is practically certain.

**Figure 1.** Scheme of the bi-atrial Cox-Maze procedure IV utilizing radiofrequency (RF) or cryoablation energy sources.

The first clinical surgical ablation for AF was introduced by Dr. James Cox in 1987, and was termed the Cox-Maze I. The successful 22 cases were reported in 1991 [2]. Over the subsequent years, the operation evolved into the Cox-Maze III or the cut-and-sew Maze [3], which has been applied extensively in clinical practice [4]. In the meantime, the introduction of ablation technology has significantly changed the attitude. Damiano et al. employed a combination of radiofrequency energy and cryoablation to replace several of the Cox-Maze III cut and sew lesions and termed this procedure as the Cox-Maze IV [5, 6]. Finally, the lesion sets of the Cox-Maze IV have evolved to its current form [7, 8] (**Figure 1**).

Khargi et al. reported that conventional cut-and-sew Cox-Maze III procedure is getting less frequently performed, and alternative sources of energy were predominantly used in all surgical ablation cases (92.0%), and almost always (98.4%) in concomitant procedures [9]. Cryoablation is employed as an alternative source of energy [10–12]. As compared to radiofrequency and cryoablation, other energy sources such as microwave, laser, and high-frequency ultrasound have proven less effective, and are not commercially available now [13–18].
