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Interact CardioVasc Thorac Surg 2007;6:319-322. doi:10.1510/icvts.2007.151787 © 2007 European Association of Cardio-Thoracic Surgery
Long-term follow-up after endocardial radiofrequency modified Nitta procedure for concomitant atrial fibrillation treatmentDepartment of Cardiac Surgery, Erasme University Hospital, Route de Lennik 808, 1070 Brussels, Belgium Received 8 January 2007; received in revised form 10 February 2007; accepted 12 February 2007
*Corresponding author. Moorselbaan 164, 9300 Aalst, Belgium. Tel.: +32-477-485546; fax: +32-53-724552.
In atrial fibrillation (AF) patients, the surgical restoration of sinus rhythm aims at restoring atrial contraction, hence to decrease thromboembolic events. We investigated the long-term outcome of radiofrequency (RF) ablation by a modified Nitta procedure, in patients with AF associated with operative structural heart diseases. Between September 2000 and April 2004, a total of 20 patients (63.7±13.34 years) with structural heart diseases due to surgery and chronic AF underwent endocardial RF ablation. Evaluation was achieved at discharge, at 6 months, 12 months and in November 2005. Echocardiography, 12-derivations electrocardiogram and 24-h electrocardiogram were obtained. At the mean follow-up of 43.25±13.4 months, 14 out of 20 patients (70%) were in sinus rhythm. Actuarial freedom from AF recurrence was 85% after 6 months, 75% after 12 months and 70% at the follow-up completion. Effective atrial contraction was present in 78.5% of patients with sinus rhythm. No hemodynamic pulmonary edema has been reported during the hospital stay, and no thromboembolic event has been reported during the follow-up period. The Nitta procedure, modified for RF ablation, is an easy procedure when performed in the setting of structural heart disease surgery. Further studies are warranted to evaluate this technique on a larger scale basis.
Key Words: Atrial fibrillation; Mitral valve disease; Radiofrequency
Atrial fibrillation (AF) is the most frequent cardiac arrhythmia. AF can be resistant to a medical treatment. In the past decade we have seen the emergence of several non-pharmacological techniques for the treatmemt of AF. The Cox maze procedure, described in 1991, became the gold standard for the surgical treatment of AF [1], with success percentages between 75% and 97% being reported [2, 3], The goal of this treatment is the permanent ablation of AF, restoration of the atrio-ventricular synchronicity and the preservation of the mechanics of atrial function. However, this procedure reduced the left atrial contribution to ventricular filling [4], hence the development of the radial procedure by Nitta [5], the goal being the preservation of blood supply to most atrial segments and improving atrial transport function. However, in spite of good results, these surgical procedures remain complex and increase the length of aortic clamping, cardiopulmonary bypass and increase the risk of bleeding. In this study, we performed a radiofrequency (RF) modified Nitta procedure in patients with AF associated with structural heart disease.
2.1. Patients Between September 2000 and April 2004, twenty consecutive patients with AF associated to a structural heart disease underwent an RF modified Nitta procedure combined with structural heart disease surgery. The group consisted of nine men (45%) and 11 women (55%), whose age ranged from 32 to 81 years with an average of 63.7±13.34 years (mean±S.D.). AF was chronic in 14 patients (70%), paroxystic in five patients (25%) and one patient (5%) with atrial flutter (Table 1).
All patients had documented AF for at least 6 months duration before the operation. The average size of the left atrium, as measured on an M-mode tracing taken from a two-dimensional parasternal long axis view (Sonos 5500. Hewlett Packard), was 51.6±14.07 mm (range 30–95). Left ventricular ejection fraction (LVEF) was 60.05±12.11% (range 40–75). No patients had previously undergone heart surgery. In all patients ventricular rate control medications, calcium blockers and/or digoxin was allowed until the day before surgery. ß-Adrenergic blockers were continued. Oral anticoagulant therapy for the prevention of thromboembolism, secondary to chronic AF, was discontinued two days before surgery. Eighty percent of patients were in AF at the time of surgery. Radiofrequency energy was used to create long continuous endocardial lesions under direct vision with a hand-held tip probe. The RF energy was administrated using a continuous sinusoidal unmodulated waveform of 500 kHz (HAT 200S, Sulzer-Osypka GmbH, Grenzach-Wyhlen, Germany) and delivered in a unipolar mode between the 4-mm tip electrode of a specially designed probe and a 10x16-cm external backplate electrode that was underneath the back of the patient. The ablation probe had a thermistor embedded centrally in the distal part of the tip electrode for continuous monitoring of catheter tip temperature.The ablation procedure was done in a bloodless operating field and temperature guided energy applications were performed with a preselected catheter tip temperature of 60 °C. The heart was exposed through a median sternotomy and suspended in a pericardial cradle. Cardiopulmonary bypass was instituted using aortic and bicaval cannulation and moderate hypothermia (28 °C). The operative procedure was based on the radial procedure as described by Nitta et al. [5]. In our RF, all right atrial incisions currently used in the maze III were replaced by endocardial ablation linear lines, except for the excision of the right atrial appendage. In the left atrium, after the exclusion of the left atrial appendage by an interior continuous suture line, endocardial ablation lines were applicated around the pulmonary vein orifices separately; an ablation line beginning at the left superior pulmonary vein toward the left atrial appendage and another ablation beginning at the inferior left pulmonary vein extending downward to the mitral valve annulus at the anterolateral commisure. In two patients the procedure was limited to the left atrium, and in one patient atrial reduction plasty was performed because the left atrial diameter was 95 mm. The surgical treatment of the concomitant structural heart disease was performed after aorta cross-clamp, before or after left atrial ablation, and the right-sided procedure was performed on the beating heart without cross-clamp. Atrioventricular pacing was put in all the patients. Concomitant cardiac procedures are summarized in Table 2.
2.3. Follow-up Early postoperative care was similar to that for routine open-heart surgery. Patients were seen in the outpatient clinic within four weeks, or earlier when necessary. At 6 months, 12 months and after patient status was determined by records of outpatient visits and correspondence with referring cardiologist, Doppler echocardiography, electrocardiogram 12-derivations and 24-h holter monitoring were obtained. Antiarrhythmic drugs were tapered gradually after cardiac rhythm was considered stable. Follow-up for thromboembolic complications was achieved by phone contact with referring cardiologist. No specific study was performed. Based on the clinical observations, there were no deaths during the follow-up. Descriptive statistics are the mean±S.D. or median (range) for continuous variables and counts with percentages for categorical variables. Survival analysis was performed according to Kaplan–Meier (percent of patients free of AF recurrence). Analyses were performed using the statistical package SPSS 11.0 (SPSS, Chicago, IL).
3.1. In-hospital mortality and morbidity There were no perioperative and postoperative deaths. Postoperative atrial arrhythmias were treated with sotalol (80–120 mg) or amiodarone (200 mg). Two patients were successfully rescued without sequelae, one for ventricular fibrillation and the other for asystole. There were no acute pulmonary edemas in hospital stay. Studying daily weight was performed in all the patients. Diuretics were routinely administrated in patients with mitral valve disease (14 patients, 70%) and hemodynamic assessments were performed in all the patients during the first 48 h. The in-hospital complications are summarized in Table 3.
3.2. Cardiac rhythm and atrial contractility At 6 months follow-up, 18 patients were free of atrial tachyarrhythmias, and at 12 months 15 patients were free of atrial tachyarrhythmias. At 8 months, one patient received a DDD pacemaker because of AF paroxystic with junction exhaust rhythm, while a second patient underwent a heart transplantation one year after surgery because of ischemic cardiomyopathy. At the end of follow-up 14 patients (70%) were in sinus rhythm (Fig.1). In these patients transthoracic Doppler echocardiography was performed at 6 months, 12 months and finally at the last visit to the cardiologist and demonstrated right atrial contractility in 11 patients (78.5%) and left atrial transport in 11 patients (78.5%). In three patients the echocardiography report did not specify the presence or the absence of atrial contractility.
3.3. Thromboembolic events There was no thromboembolic event during follow-up. Oral anticoagulation therapy was prescribed for at least three months postoperatively, unless there was another reason to continue. At end of follow-up, 10 patients (50%) still were using oral anticoagulation because of the presence of mechanical valves or the recurrence of AF.
The Cox's maze procedure [2] has apparently remained a universally applicable and potentially effective treatment to restore sinus rhythm in patients with AF and concomitant structural heart disease. Nitta [5] in 1999 developed the radial approach to allow a more physiologic atrial activation sequence. However, these surgical procedures involve extensive incision, extend the cardiac arrest, CBP time and increase the risk of bleeding. During the past decade, ablation devices, pecutaneous procedure, and the combination of surgery with ablation devices have been developed [6]. This study shows a good outcome of RF modified Nitta procedure for the treatment of AF associated with structural heart disease, despite this, underlying disease can have an impact on ablative procedure to AF. After a median follow-up of 48.5 months, 70% of patients were free of AF, without any patients being on antiarrhythmic drugs. Postoperative complication rate was acceptable without surgery-related mortality. 4.1. Comparison with other surgical procedures The outcome of our study, despite the limited number of patients, compares favorably with other studies investigating the outcome of radiofrequency modified maze procedure or radial procedure for AF [7, 8]. Sie et al. showed a 73% complete success rate after mean follow-up of 41 months [7]. In our study, there were no preoperative or postoperative deaths and to our knowledge there were no device-related complications in the follow-up, but a life-threatening complication of esophageal perforation has been reported with the unipolar radiofrequency device [9].The right atrial appendage has been shown to secrete atrial natriuretic peptides [10]. This reduced secretion of atrial natriuretic peptides could be one of the mechanisms responsible for the postoperative complication of fluid retention frequently seen in patients after the maze procedure [5]. The absence of fluid retention in our patients postoperatively and in-hospital stay could be related to the preservation of the right atrial appendage. 4.2. Cardiac rhythm and atrial contractility Chronic AF for longer than 6 months, low amplitude fibrillatory waves of <1 mm, large left atrial size of 60 mm, mitral valve diseases, and reduced left ventricular function, are associated with failure to restore sinus rhythm after a maze procedure [11]. In four patients with AF at the end of follow-up, one patient has an enlarged left atria of 60 mm, this is known to be a determining factor in the development and maintenance of AF, two patients have a reduced left ventricular function (<50%), and three of the four patients have a mitral valve disease.The studies report an atrial contraction in 90–100% of patients in sinus rhythm after RF procedure [12], which appears higher than after the maze procedure [13]: in our study atrial contraction was present in 78.5% of patients in sinus rhythm. This result, which is lower than after the RF modified maze procedure, is probably related to the lack of information in three patients' echocardiography reports. The incidence of stroke associated with atrial fibrillation can be reduced significantly by adequate anticoagulation, however, anticoagulation does not abolish the stroke rate. The ability of the maze procedure to decrease the risk of stroke associated with AF is due to the restoring of sinus rhythm and atrial transport function in combination with surgical removal or obliteration of the left atrial appendage, where most thrombi associated with AF develop [14]. Even if the remaining atria were in sinus rhythm after the maze procedure, the isolated posterior left atrium would still be fibrillating or inexcitable and flaccid. Therefore, the isolated portion of the left atrium would provide a nidus for the development of mural thrombus and continue to expose patients to the risk of thromboembolism [15].The Nitta RF modified procedure does not create regional isolation in any part of the atrium. The absence of thromboembolic events in our study during the follow-up could be promoted by the procedure. In conclusion, the Nitta procedure modified for RF ablation is an easy and safe procedure when performed in the setting of structural heart disease surgery. It is effective to achieve long-term sinus rhythm and atrial contraction is restored in 70% of the cases. Further studies are warranted to evaluate this technique on a larger scale basis.
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Abstract
1. Introduction