Atrial fibrillation (AF) is the most common sustained arrhythmia in humans. It is well documented that there are currently about 2.4 million patients with AF in the United States and about 6 million patients with AF in Western Europe and Japan. The number of patients with AF in China is at least 8 million, and will continue to increase as the population ages [1].
In order to achieve a radical cure for AF, Williams et al. proposed the left atrial isolation procedure (isolation procedure) in 1980 and Guiraudon proposed the corridor procedure (corridor procedure) for the treatment of AF in 1985, but it was not until 1989, when Cox et al. reported the atrial maze procedure (maze procedure), that the surgical treatment of AF was made possible. However, it was not until 1989, when Cox et al. reported the maze procedure, that the surgical treatment of atrial fibrillation achieved a more satisfactory result [2], namely: (i) permanent elimination of atrial fibrillation; (ii) preservation of atrial synchronous excitation; and (iii) preservation of atrial transmission function. The surgical treatment of atrial fibrillation has been studied in a series of researches on the improvement of the surgical procedure, the selection of indications, and the evaluation of the efficacy. The efficacy of Dr. Cox’s maze procedure is the most prominent, and it has gradually been widely promoted and recognized. In the past 10 years, the surgical treatment of atrial fibrillation has gained wide recognition, and the improvement of various surgical procedures and the evaluation of long-term efficacy have received positive attention.
I. Classic Cox maze surgery (Maze surgery) and modified maze energy ablation
The basic principle of the Maze procedure is to create a pathway that allows the impulse from the sinus node to reach the atrioventricular node to drive the ventricle. The procedure avoids atrial folding, preserves atrioventricular synchronization and postoperative atrial transmission, and eliminates the risk of thrombosis. The classic maze procedure has undergone continuous improvement from type I to type III. The surgical approach is shown in Figure 1: the left and right auricles are resected and four incisions are made along the peripulmonary vein, the right atrial wall (from the root of the superior vena cava posteriorly to the sulcus sulcus), the atrial septum (from the top of the atrium to the fossa ovalis) and the top of the atrium between the right and left auricles (the incision is made anteriorly through the root of the superior vena cava and around the pulmonary vein), and the boundary ridge is cut [3]. The labyrinth type III procedure was modified from the type I procedure in two ways: not making an incision at the top of the right atrium; and making a cup-shaped incision around the four pulmonary vein ports. The modification reduces the extent of the surgical incision, avoids damage to the sinus node artery and reduces the extent of left atrial isolation, achieves a better time-varying heart rate response and recovery of atrial function, and requires less permanent pacemakers [3].
Cox et al. performed the maze procedure in 306 patients with atrial fibrillation from 1989 to 1999, with a mortality rate of 3.3% for the entire group. 265 patients completed 3 to 11.5 years of follow-up (mean 3.7 ± 2.9 years), and 95% of them had complete resolution of atrial fibrillation, and another 5% could control atrial fibrillation with antiarrhythmic drugs without recurrence [4]. Krishna pooled the data of long-term follow-up of 1,553 patients from 18 classic Maze III surgery study groups in recent years (1995-2004) [5], with a mean follow-up time of 5.5 years and an atrial fibrillation elimination rate of 84.9% at follow-up, which was significantly lower than the long-term results of the Cox group. However, the percentage of paroxysmal AF in this group was 22.4% (61% in the Cox group) and the percentage of isolated AF was 19.3% (65.4% in the Cox group), and the preoperative patient composition was obviously different from that of the Cox group, and the results better reflect the long-term efficacy of classical Maze III surgery in the treatment of surgical atrial fibrillation.
Due to the high surgical technique requirements of classical Maze surgery, the long operation time, the existence of left atrial incision on left atrial function, and the occurrence of complications such as bleeding, energy ablation surgery came into being. Energy ablation surgery is the physical means to achieve tissue degeneration, necrosis, and conduction blockage, the first reported is cryoablation, radiofrequency ablation is currently the most widely used clinical means, and in recent years the development of microwave, ultrasound and laser atrial fibrillation ablation.
The principle of cryoablation is to apply low temperature to produce damage to the tissue. The process is to contact the atrial tissue with liquid nitrogen or carbon dioxide gas at -60°C for 2-3 minutes via a cryoprobe. The cryoprobe produces heat absorption after contact with the myocardium, resulting in intracellular icing and damage to the myocardial cells, which destroys the role of abnormal electrophysiological cells. 24 hours after the injury, the tissue freezes and dissolves, 48 hours after the inflammatory response, and 12 weeks after the tissue fibrosis and scarring occurs. The advantages are that the tissue structure is largely maintained, producing uniform tissue damage, no damage to the intima, and less likely to produce thrombus; while the disadvantages are that the injury sometimes does not penetrate the wall and tissue thawing can cause recurrence [6].Gaita reported that 105 patients with rheumatic mitral valve damage combined with atrial fibrillation treated by cryotherapy had a 90% atrial fibrillation elimination rate at 41±17 months follow-up [7].Baek reviewed a comparison of cryoablation and classical maze procedure for rheumatic mitral valve lesions combined with atrial fibrillation.At 4 years of follow-up, the survival rate was 98.8% in the cryo group and 100% in the classical maze group.The atrial fibrillation elimination rate was 77.9% in the cryo group and 84.6% in the classical maze group.Statistical analysis showed no significant difference in complication occurrence, atrial fibrillation elimination and survival between the two groups [8].Gammie et al. reported the use of the newly available argon cryoablation probe in 38 patients with atrial fibrillation, 36 of whom underwent simultaneous coronary, heart valve and aortic surgery. The device used argon gas to rapidly cool the atrial tissue to -120 to 160°C. Each ablation took 1 to 2 minutes and took a total of l5 to 20 minutes. The average postoperative follow-up was 12 months, and 95% of patients were in sinus rhythm [9]. Mack reported 63 cases of atrial fibrillation ablated by argon cryoablation with -40°C and a 1-minute ablation time, with a postoperative follow-up of l2 months, and 88.5% were in sinus rhythm [10].
Radiofrequency ablation is the use of high temperature to produce tissue burns, myocardial coagulation, the formation of scarring, clinical use is difficult to determine whether the cautery reaches the transmural, excessive cautery is prone to side damage, insufficient cautery postoperative atrial fibrillation recurrence ratio increased, and then invented the flushing radiofrequency. Flushing radiofrequency can use saline to lower the atrial surface temperature while allowing heat conduction to the deeper part of the heart about 4 mm, basically achieving wall penetration without perforation [11]. sie completed 200 cases of simultaneous cardiac radiofrequency ablation between 1995 and 2001, with an average follow-up time of 40 months, an overall mortality rate of 13.5%, a loss of follow-up rate of 4%, and a sinus rhythm or atrial rhythm of 73.4%. 6.3% in permanent pacemaker atrial paced rhythm, and 20.3% in atrial fibrillation or atrial flutter rhythm [12]. In a randomized controlled prospective study designed by Deneke et al, concurrent radiofrequency atrial fibrillation ablation with mitral valve surgery was compared with mitral valve surgery alone. At long term follow-up, there was a significant difference in the rate of recovery of sinus rhythm (80.0% versus 26.7%), and 66.7% of patients in the concurrent RF surgery group had recovery of biventricular pump function after surgery as evaluated by ultrasound, which was significantly higher than that of the surgery alone group [13].Sie was the first to successfully apply washout radiofrequency for concurrent surgical ablation of atrial fibrillation in 108 patients treated with a survival rate of 90% at 39 months of follow-up. Atrial fibrillation elimination rate was 78.5%, and atrial function was restored in 77% of patients evaluated by Doppler ultrasound [14].
With the improvement of technology, bipolar RF pens began to be used in clinical applications. The low temperature and low damage to surrounding tissues produced by bipolar RF pen ablation can better maintain the atrial transmission function and thus reduce the incidence of intraoperative and postoperative thrombus, ventricular and pulmonary vein stenosis [15].Gaynor et al. reported 30 cases of a modified maze III procedure using bipolar RF ablation, namely the maze IV procedure. The ablation route of the Maze IV procedure differs from the Maze III procedure in that the former isolates both pulmonary veins separately, maintaining electrical continuity between the majority of the posterior wall of the left atrium and the rest of the atrium. In 67% of the patients in the group who underwent mitral valve surgery and coronary artery bypass grafting for atrial fibrillation at the same time, 93.1% maintained sinus rhythm at 6 months of follow-up [16]. Stephan et al. performed surgical simultaneous radiofrequency ablation with a monopolar radiofrequency and bipolar radiofrequency knife for 106 patients, respectively, and maintained sinus rhythm at 66.6% at 36 months of follow-up [17]. However, the grouping ratio of this study varied widely, and the long-term follow-up results were not sufficient to illustrate the efficacy of monopolar and bipolar RF pens, and further comparisons between the two will require a series of prospective randomized trials to reveal.
Microwave energy ablation for atrial fibrillation is a new technique in recent years, which uses microwave energy to generate a high temperature of 50°C to cauterize the atrial tissue, producing pathological changes of central necrosis surrounded by hemorrhage and a solid scar after 6 months, producing linear conduction block, with a different mechanism of thermal damage than radiofrequency ablation. Microwave causes water molecules in the tissue to vibrate through high frequency electromagnetic radiation, converting electromagnetic energy into heat. Its heat conduction is slower than radiofrequency ablation but it heats the tissue more deeply, does not scorch the endocardium when used extracardially, and reduces the possibility of thromboembolism. Knaut in Germany followed 105 patients with microwave surgical ablation of atrial fibrillation, and 1 year after the procedure, 62.2% maintained sinus rhythm [18]. Molloy reported 29 cases of microwave ablation of chronic and paroxysmal atrial fibrillation, 13 of which were performed without extracorporeal circulation. The ablation routes included isolation of bilateral pulmonary veins, linear ablation connecting both pulmonary veins, and ablation of the left pulmonary vein to the left auricle. Based on the knowledge that Marshall’s ligament contains adrenergic fibers, the Marshall’s ligament was isolated and cauterized. Linear ablation of the left atrial isthmus was not performed to avoid damage to the rotating branches of the coronary artery. At 4 months of follow-up, 86% (23/28) of patients maintained sinus rhythm [19].
Ultrasound ablation is used to affect myocardial cell conduction function by causing cells to oscillate and be damaged by the thermal energy generated by friction. Its main advantages are the ability to rapidly establish reproducible continuity and transmural damage around the pulmonary veins without the use of extracorporeal circulation and the ability to establish linear ablation of the mitral isthmus without fear of damaging the coronary arteries. Ultrasound ablation for atrial fibrillation is currently undergoing clinical trials in Europe, with only a few reports. Laser ablation is also in the experimental phase, and results from large group clinical trial studies are not yet available.
Long-term outcomes of the left atrial labyrinth alone and bilateral labyrinth procedures
The electrophysiological study found that patients with mitral valve lesions combined with atrial fibrillation had most of their atrial fibrillation originated from the folding of the left auricle and the opening of the left pulmonary vein, which led some scholars to believe that atrial fibrillation could be treated by performing left-sided maze surgery in patients with mitral valve lesions combined with atrial fibrillation. In a review by Krishna, the clinical outcomes of the left-sided maze alone and the bilateral maze were analyzed and differed in univariate analysis (77.5% versus 83.2%), but using multivariate analysis, Krishna found that the clinical outcomes of the left-sided maze alone and the bilateral maze were similar [21].
In Barnett’s study of 69 clinical studies including 5885 patients who underwent surgical maze surgery for atrial fibrillation, there was no significant difference in survival rates between bilateral and left-sided maze surgery in the long term (1-3 years) (94.9%-92.8% versus 93.9%-89.4%), while the atrial fibrillation elimination rate was better in the bilateral maze surgery group than in the left-sided maze group (92.0%-87.1% versus 86.1%-73.4%). Nair observed the presence of refractory channels near the coronary sinus orifice in patients with rheumatic heart disease [23], and Waldo also believed that intervening venous sinus lines are necessary to completely interrupt the refraction of atrial fibrillation and atrial flutter [24].
III. Minimally invasive surgical treatment of atrial fibrillation
The traditional concept is that catheter ablation is mostly chosen for patients with paroxysmal and isolated atrial fibrillation of non-severe organic heart disease, while surgical ablation is indicated for atrial fibrillation complicated by organic heart disease such as valvular disease, coronary artery disease, and precordial disease. However, with the development of minimally invasive cardiac surgical techniques, surgical treatment of AF is being extended beyond the original indications to isolated and paroxysmal AF. The earliest small-incision ablation was reported by Cox et al [25], and treatment was performed using subcardiac beating epicardial cryoablation. In the last 5 years, minimally invasive ablation techniques have used thoracoscopic or small incisions and applied advanced ablation equipment to perform epicardial ablation under the beating heart, with the advantages of minimal patient injury, rapid and accurate operation, few complications, and good outcomes. These include, Wolf Mini-maze ablation procedure, and robot-assisted flushing radiofrequency ablation.
The Wolf Mini-maze procedure was proposed by Dr. Randall Wolf in 2002 and is indicated for isolated and paroxysmal atrial fibrillation. The procedure performs four key steps, including bilateral pulmonary vein isolation, linear ablation of the left atrium, partial denervation of the epicardium, and excision of the left auricle. The procedure avoids the traditional median chest opening, which is less invasive and safer; the heart beats without extracorporeal circulation, the procedure is performed under direct vision, the ablation line is clear and accurate, and complications such as pulmonary vein stenosis are avoided; the radiation damage from prolonged X-ray exposure is also avoided. and anticoagulants. The overall cure rate at 2 years after the procedure was 80%, with no postoperative strokes [26].
Robotic-assisted microwave atrial fibrillation ablation: In 2004, Didier first reported lumpectomy with robotic arm-assisted pulmonary vein isolation at a microwave energy of 65 w for 90 s. The procedure time was relatively long (4 h 15 min). MRI performed 3 months after surgery showed synchronized atrial systole and left atrial and left ventricular ejection fractions of 35 mm and 52%, respectively. The patient maintained sinus rhythm at 1 year postoperative follow-up [27].
IV. Use of postoperative antiarrhythmic drugs
It has been argued that the continued use of antiarrhythmic drugs in patients with successful AF ablation also seems to facilitate the reversal of atrial remodeling and the maintenance of sinus rhythm. In contrast, most centers routinely administer oral amiodarone for six months after surgical treatment of atrial fibrillation to maintain the surgical outcome. in a 6-year follow-up observation of 200 patients with radiofrequency ablation of atrial fibrillation, Hauw et al. 49% of patients relied on antiarrhythmic drugs to maintain sinus rhythm after surgery, and the commonly used drugs were sotalol (80 mg/day) or amiodarone (200 mg/day); of these, the proportion of patients with mitral valvuloplasty was 37%, 65% for mitral mechanical valve replacement, and 54% for mitral bioprosthetic valve replacement. More studies have shown that the percentage of complete elimination of distant atrial fibrillation (sinus or atrial rhythm with exemption of antiarrhythmic drugs) after maze surgery for isolated atrial fibrillation is about 70% to 80%, and the percentage of reliance on antiarrhythmic drugs to maintain sinus or atrial rhythm is about 10% to 20% [12].
V. How to evaluate the efficacy
The literature reports a long-term success rate of 79% to 99% for the maze procedure. How is success defined and how exactly should we calculate the atrial fibrillation waiver rate? Should we calculate the rhythm at the follow-up point, or should we calculate it using the Kaplan-Meier survival curve, or should we calculate it by the time of the onset of the atrial fibrillation interval. stulak analyzed the 10-year follow-up results of 335 patients who underwent the classic Maze procedure in three ways [28]: the atrial fibrillation elimination rate was calculated according to the rhythm at the follow-up point, and the atrial fibrillation waiver rate was 88% (64% sinus rhythm, 18% According to the Kaplan-Meier survival curve, the preoperative paroxysmal atrial fibrillation rate was 90% at 5 years and 64% at 10 years; the preoperative chronic persistent atrial fibrillation rate was 80% at 5 years and 62% at 10 years; according to the interruption time of atrial fibrillation, the atrial fibrillation rate was 80% at 3 years, 78% at 6 years, and 62% at 9 years. The waiver rates were 78% at 3 years, 78% at 6 years, and 76% at 9 years. The reason for the results of the multi-method analysis is the limitation of the current clinical evaluation tools. Most of us rely on a single ECG to determine the rhythm, whereas a 24-hour ECG would be more accurate, but there are many difficulties in applying a 24-hour ECG to a large sample for long-term follow-up. A single ECG evaluation may underestimate the recurrence of atrial fibrillation and thus overestimate the efficacy of the procedure; conversely, it is unreasonable to judge the procedure as a failure when there is any single recurrence of arrhythmia. Therefore, the vast majority of centers determine outcomes by a combination of patient self-report, ECG, and ambulatory ECG. Although there is no uniform success rate regulation and no uniform follow-up procedure, the results of surgical treatment of atrial fibrillation are positive, both the classical maze surgery and the modified energy ablation maze surgery bring longer life span and higher quality of life to the majority of patients.
VI. Prospects for the surgical treatment of atrial fibrillation
Surgical treatment of atrial fibrillation has quietly undergone many profound changes. These profound changes have made the surgical treatment of atrial fibrillation easier, safer and more effective, and have also expanded the indications for surgical procedures, from traditional median opening to transthoracoscopic epicardial ablation, from traditional maze surgery to energy ablation, and from direct vision surgery to robotic assistance.
After years of technical precipitation, energy ablation has become the routine of surgical treatment of atrial fibrillation, and the accumulation of minimally invasive techniques is leading the new trend of surgical treatment of atrial fibrillation and will achieve impressive achievements, which will certainly promote the improvement and development of comprehensive treatment of atrial fibrillation.
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