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Eur J Cardiothorac Surg 2002;21:249-254
© 2002 Elsevier Science NL
Division of Cardiovascular Surgery, Cardiovascular Disease Institute of Xijing Hospital, The 4th Military Medical University, Xi'an 710032, People's Republic of China
Received 9 July 2001; received in revised form 15 November 2001; accepted 20 November 2001.
* Corresponding author. Tel.: +86-29-3373475; fax: +86-29-3373475
e-mail: liying{at}fmmu.edu.cn
| Abstract |
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Key Words: Radiofrequency ablation Atrial fibrillation Mitral valve Maze procedure
| 1. Introduction |
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| 2. Materials and methods |
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2.2. Control patients
Eighty-seven similar patients (in age, AF duration, cardiomegaly, LA size, preoperative NYHA functional class) to the study group were selected from the same period. The control patients received mitral valve replacement without RAMP. The information related to preoperative clinical parameters in the two groups as well as the statistical analysis of the comparison between the two groups are presented on Table 1.
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2.3. Surgical technique
All the patients were operated upon by median sternotomy with cardiopulmonary bypass. Moderate hypothermia (2528 °C) was used during cardiopulmonary bypass and myocardial protection was performed with cold blood cardioplegia repeated every 30 min. In the study group, radiofrequency ablation was conducted under direct vision with an EPT2000 radiofrequency machine and ablation probe. The probe was modified from a radiofrequency catheter ablation wire, the probe was made of a stainless wire of 2 mm diameter into the shape of L with length of 20 cm and width of 2.5 cm, so ablation was made in the form of a line instead of a point in catheter ablation. When one part of atrial tissue which was being radiofrequency-ablated was burnt from red to grayish white, we stopped ablation and another part of the atrium went on to be ablated. The energy used in radiofrequency ablation was 30 W/s. The temperature was estimated to be between 90 and 100 °C. Cox III maze procedure incision routes [5] were used as our basic method. The right atrial incisions were the same as the original Cox maze III procedure and were made on beating hearts without aortic crossclamping. After crossclamping, an atrial septal incision posterior to the orifice of the superior vena cava was made to provide excellent exposure of the left atrium, and the left atrial isolation was performed. Our major modification was in the isolation of the left atrium (Fig. 1)
, which included the following: (1), the base of the left atrial appendage was ablated from inside with radiofrequency, and the appendage was ligated to prevent thrombus formation; (2), the encircling isolation of the orifices of pulmonary veins was performed by radiofrequency ablation from inside; (3), the encircling radiofrequency ablation of the base of left atrial appendage and that of the orifices of pulmonary veins were joined by a radiofrequency ablation line. The method to interrupt conduction across the posteroinferior left atrium was the same as the original Cox III maze: a vertical posterior left atriotomy was placed from the inferior rim of the encircling radiofrequency ablation of the orifices of pulmonary veins down to the level of the posterior mitral valve annulus, and the fibers were dissected away from the coronary sinus and cryoablation was made around the coronary sinus. After left atrial isolation, mitral valve replacement was performed (St. Jude mechanical valves were used), then we closed the left atrial incision and atrial septal incision. After closure of the left heart and deairing from the aortic root, the crossclamp was released and tricuspid valvoplasty was performed in patients with more than moderate tricuspid insufficiency, then we closed the right atrium.
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| 3. Results |
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3.3. Heart rhythm
Immediately after operation, AF disappeared in 92 patients (95.8%) in the study group compared with 65 patients (74.7%) in the control group. These patients experienced various kinds of superventricular heart rhythms within the first week after the operation: sinus rhythm in 85 patients (88.5%); junctional rhythm in 60 patients (62.5%); atrial flutter in five patients (5.2%); atrial tachycardia in eight patients (8.3%); and atrial extrasystole in 14 patients (14.6%). No patients had postoperative conduction problems. As shown in Table 3, at the time of hospital dismissal, 76 patients (79.2%) in the study group had sinus rhythm compared with 29 patients (33.3%) in the control group (P<0.01), nine patients (9.4%) in the study group and seven patients (8%) in the control group had junctional rhythm, two patients in the control group had atrial flutter, 11 patients (11.5%) in the study group and 46 patients (52.9%) in the control group had AF (P<0.01). Table 4 presents the heart rhythm 3 years after operation: 74 patients (77%) in the study group had sinus rhythm compared with 22 patients (25.3%) in the control group (P<0.01); 22 patients (22.9%) in the study group had AF compared with 65 patients (74.7%) in the control group. Freedom from AF in the study group was 77% 3 years after operation compared with 25% in the control group (P<0.01; Fig. 2)
. From Fig. 2, the patients who remained at risk of AF were represented. In the study group, the number of the patients that remained at risk of AF was 11, 11, 16, 18 and 22 at 1, 3, 6, 12 and 36 months after operation, respectively, and in the control group, the number of the patients that remained at risk of AF was 47, 49, 57, 63 and 65 at 1, 3, 6, 12 and 36 months after operation, respectively.
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| 4. Discussion |
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Adding the Cox maze procedure may increase the operation risk because of extensive atrial incisions and reanastomosis requiring longer cardiac arrest and cardiopulmonary bypass time. For this reason, we developed this RAMP to shorten the operation time. To identify the advantages of RAMP in the treatment of AF in patients undergoing mitral valve replacement, we retrospectively compared 96 patients of rheumatic mitral disease undergoing ARMP plus mitral valve replacement with 87 similar patients undergoing isolated mitral valve replacement. The risk associated with the combined RAMP included the procedure itself, the prolonged cardiac arrest and cardiopulmonary bypass. All the patients undergoing the combined procedures needed no circulatory assistance device. The times required for the combined procedure were 24 and 46 min longer than the isolated mitral valve replacement for cardiac arrest and cardiopulmonary bypass, respectively, which were much shorter than those reported by Kawaguchi and Ki-Bong Kim [2,9]. All those above suggested the simplicity and safety of this RAMP. AF was ablated by radiofrequency in 77% of patients of this group after the combined RAMP. This number is much higher than that in the control group (25%), while AF was reported to be abolished in only 28% of patients after operation with aggressive treatment using cardioversion after repair of underlying lesions alone [14]. Three years after operation, 77% of patients remained AF free late after the combined modified procedure, although the addition of the modified Cox maze may not be solely responsible for the result alone. Compared with the result of AF treatment with the isolated maze procedure, the rate of retaining atrial rhythm after the combined modified operations was still lower. When compared with the results reported by Kawaguchi et al. and Nobuhiro Handa [2,10], there was not much difference between those groups in the rate of regaining atrial rhythm and of AF free. Kawaguchi and Koskai's analysis suggested that the difference of the rate of regaining atrial rhythm between the isolated maze procedure and combined modified method appeared to result from the duration of the arrhythmia and left atrium diameter (LAD) rather than the technical modification itself [8,19], so the difference in the kind of patients, the duration of the arrhythmia and LAD might account for the lower rate of regaining atrial rhythm than the Cox III maze procedure in isolated AF.
About 20% of the patients after the Cox Maze procedure needed permanent pacemaker implantation [5]. Permanent pacemaker implantation after the Cox Maze procedure can be due to several reasons: (1), preoperative sick sinus syndrome; (2), iatrogenic injury of the sinus node and its blood supply; (3), preoperative pacemaker implantation. We did not have permanent pacemaker implantation in the patients of our study. The following are the possible reasons: (1), there was no presence of coronary artery disease and preoperative sick sinus syndrome; (2), during operation, before the decision was made to do the modified maze procedure, cardioversion was performed to test the sinus function of the patients. If the patient did not resume sinus rhythm or if the sinus rhythm was too slow after cardioversion, the patient would not receive the modified Maze procedure; (3), in the Cox III procedure, the left atrial dome incision is moved more posteriorly. This causes the atrial septotomy to be moved more posteriorly as well. The Cox III procedure thus addresses the chronotropic incompetence of the sinus node; (4), in our modified method, we did not perform left atrial incisions, so the possibility of injury of the sinus blood supply from the left coronary artery is much decreased and sinus node function was preserved; (5), there was a difference in age between Cox's patients and our patients.
Prospective studies have shown that the risk of stroke in patients with AF is 58% per year [2022]. The reduction in risk of stroke by anticoagulation with warfarin was from 37 to 86% [23,24]. Addition of the maze procedure is effective in the reduction of the risk of postoperative stroke. Preoperatively, nine patients (9.4%) in our study group and seven patients (8%) in the control group had stroke history. We have not encountered postoperative stroke events in either the study group or the control group. The possible reason is that the patients in this study received anticoagulation treatment routinely after mitral valve replacement. Literature shows hospital mortality ranging from 0 to 5.8% in the patients treated with the Cox III maze procedure in association with other surgical procedures, such as mitral valve treatment [8,17,18]. We did not have hospital and late deaths in the 96 patients of study group, for three probable reasons: (1), we carried out strict selection of patients with relatively good cardiac function as candidates of this treatment, in which most patients were in NYHA class II or III, 57.3% in the study group and 67.8% in the control group were in NYHA class III, and no patients was in class IV; (2), the addition of RAMP made the crossclamp time and cardiopulmonary bypass time only 24 and 46 min longer than those in the control group, which made operation safer; (3), no patients in the study was older than 60 years old and the patients were of good general physical condition. Postoperative bleeding is one complication related with the Cox maze procedure because of extensive incisions and it was reported with an incidence of 78% reoperation in literature [5,7,8,25]. In our study, we performed two cases of reoperation in the study group and one case in the control group because of postoperative bleeding. The was no significant difference in terms of postoperative bleeding between the study group and control group, which suggested that our modified method may decrease the possibility of bleeding from the LA of the heart.
The results of this study suggested that this RAMP is an effective method in the treatment of AF associated with mitral valve disease, and substantial benefits from regained atrial rhythm outweigh the risk of adding the modified maze procedure. We recommend that RAMP be performed on the patients with a possibility of recovering sinus rhythm. Since adding this RAMP needs a much shorter time than the standard Cox III maze procedure and other modified maze procedures, this method may not be restricted to patients with good ventricular function.
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