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Introduction of transesophageal electrocardiography to surgery for continuous atrial fibrillation
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     Department of Surgery, Kurume University School of Medicine, 67 Asahi-machi, Kurume 830-0011, Japan

    Abstract

    The purpose of this study was to assess esophageal electrocardiographic characteristics of atrial fibrillation, and compare these results with outcomes of surgical interventions. We analyzed 158 patients, who were operated on for valvular heart disease and continuous atrial fibrillation. Recently, 57 patients were examined by transesophageal electrocardiography. The results of surgery and the relation between transesophageal electrocardiography and restoration to a sinus rhythm were analyzed. One-hundred and twenty-three patients (77.8%) had been restored to a sinus rhythm in the early stage and 116 patients (73.9%) in the late stage after operation. The restoration rate to a sinus rhythm was 77.0% in the maze procedure and 81.3% in pulmonary vein isolation. According to the form of f-waves obtained from the transesophageal electrocardiography, in patients with a regular f-wave pattern, the sinus rhythm was completely restored after maze or pulmonary vein isolation. By using transesophageal electrocardiography preoperatively, it may be possible to decide before surgery which operative procedure should be used, maze or pulmonary vein isolation.

    Key Words: Arrhythmia surgery; Atrial fibrillation; Transesophageal electrocardiography

    1. Introduction

    Surgical treatment for continuous atrial fibrillation (AF) associated with valvular heart disease is now widely accepted [1,2]. Various procedures such as Cox-maze, Kosakai-maze, left atrial maze or pulmonary vein isolation (PVI), have been reported [3], but the indications for each procedure are still unclear.

    Recent advances in the endocardial or intraoperative mapping system have allowed the origin of AF to be found. However, the mapping system cannot be easily introduced, because the system is expensive and time consuming. To more easily obtain electrical information on the atrium, we employed transesophageal electrocardiography (TE-ECG) as a direct detector of f-waves. The purpose of this study was to assess esophageal electrocardiographic characteristics of AF, and compare these results with outcomes of surgical interventions.

    2. Patients and method

    2.1. Patients

    From September 1994 to October 2005, 158 patients underwent surgical treatment for continuous AF concomitant with valvular heart disease. There were 69 men and 89 women with a mean age of 59.6 years (range 28 to 80 years). Preoperative patient characteristics are given in Table 1. All patients gave their informed consent to the examinations and surgical procedures.

    2.2. Transesophageal electrocardiography

    TE-ECG was performed from 5 to 2 days before the operation. The patients lay down in a supine position and were measured with the usual 12-lead ECG. Afterwards, an electrode catheter was passed through nares into the distal esophagus under surface anesthesia. An electrode catheter (Fukuda-Denshi, Tokyo) containing 4 poles (E1 to E4) spaced 10 mm apart was constructed, with pole E1 being the most cranial one. The exploring electrode was withdrawn centimeter by centimeter with simultaneous recording of the V1 lead. Four unipolar transesophageal leads were recorded until the tracings obtained with E1, E2, E3 and E4 showed the highest potentials of f-waves, when the catheter was fixed in place.

    2.3. Surgical indications and techniques for AF surgery

    Our indications for AF surgery concomitant with valvular heart disease were as follows: (1) a history of AF <20 years, (2) a cardiothoracic ratio <70%, (3) left atrial dimension <70 mm, and (4) voltage of f-waves at the V1 lead more than 0.1 mV. As a surgical procedure for AF, the maze procedure modified by Kosakai [4] was employed. Since 1999, pulmonary vein isolation or left atrial reduction [5] was introduced in patients without severe tricuspid regurgitation as a simplified left atrial procedure [3]. For selecting surgical procedure, we considered that tricuspid regurgitation was an important factor, because it was reported that patients with tricuspid regurgitation who require a tricuspid annuloplasty had a higher recurrence rate of AF after left atrial isolation [6]. According to the above indications, 126 patients underwent maze procedure and 32 patients underwent left atrial procedure.

    The surgical technique for AF was as follows. In all patients, standard cardiopulmonary bypass with bicaval cannulation was used. Incision and cryoablation lines were created as Kosakai's modification [4]. Briefly, a temporary transection of the superior vena cava was done for good exposure of the left atrium. Cryoablation was used to avoid cutting the sinus node artery which may result in sick sinus syndrome. Excess left atrial tissues were trimmed to approximately 4 cm. All of the right atrial appendage and part of the left atrial appendage were preserved.

    In candidates for the left atrial procedure, all four pulmonary veins were isolated as a box formation with the cut and saw technique. The left atrial appendage was closed from the left atrial side, or resected with surrounding left atrial tissue [5] in patients whose left atrial dimension was more than 55 mm. No additional cutting line or cryoablation was done in these patients.

    2.4. Evaluations

    The surgical results and restoration rate to the sinus rhythm were evaluated. Preoperative and perioperative factors were collected for statistical analysis. Physicians (K.T, K.A), who were blind to the study protocol, analyzed the f-waves obtained from TE-ECG. Follow-up data were collected from the records of our outpatient clinic or correspondence with referring physicians.

    2.5. Statistical methods

    Continuous variables were expressed as mean ± standard deviation. Freedom from AF was estimated by the Kaplan–Meier method. The unpaired t-test for continuous variables and chi-square analysis for categorical variables were used to examine the relationship between factors and the elimination of AF. P<0.05 was considered statistically significant.

    3. Results

    3.1. Operative results

    There was one (0.6%) early death because of pneumonia, which was not related specifically to the AF surgery. One-hundred and twenty-three patients (77.8%) had their sinus rhythm restored by the time they were discharged from hospital. According to the procedures, the restoration rate to sinus rhythm was 77.0% in the maze procedure and 81.3% in the left atrial procedure. No patients received pacemaker implantation during their hospital stay.

    Follow-up was completed in 153 patients (97.5%) with a duration of 4.9±2.7 years (range 6 months to 11.4 years). There were 11 (7.0%) late deaths during follow-up. One patient died of cerebral infarction, whose cardiac rhythm was AF, and one patient died of cerebral bleeding, which was related to postoperative anticoagulant therapy. Two patients died suddenly because of unknown reasons and the remaining 7 patients died of non-cardiac reasons.

    Sinus rhythm was observed in 116 patients (73.9%) at follow-up. Freedom from AF was 80.3% at 1 year after operation, 76.9% at 3 years, and 73.4% at 5 years or more (Fig. 1). According to the procedures, sinus rhythm was observed as 71.2% in the maze procedure and 84.4% in the left atrial procedure. Eight patients (5.1%) underwent pacemaker implantation during follow-up because of sick sinus syndrome or AF with block.

    3.2. TE-ECG

    TE-ECG was performed recently in 57 patients. There were 27 men and 30 women with a mean age of 61.4 years (range 29–77 years). The etiologies of the heart valve disease were mitral valve disease in 47 patients and aortic valve disease in 10 patients. The mean duration of AF was 3.5 years (range 3 months to 20 years). In this subgroup, there was no operative death. Because these patients consisted of recent cases, there was no late death during 3.0 ±1.2 years follow-up.

    Almost all patients showed irregular f-wave in V1 lead, but two patients showed regular f-wave in V1 lead. Twenty-two patients showed low voltage (=0.1 mV) in V1 lead. The f-wave of TE-ECG was not the same as shown in V1 lead recorded at the same time (Fig. 2). According to the form of f-wave obtained from TE-ECG, we divided the patients into three types. Regular type: the f-wave showed a regular pattern and its voltage was more than 0.1 mV. Irregular type: the f-wave showed an irregular pattern and its voltage was more than 0.1 mV. Fine type: the f-wave was not observed or its voltage was <0.1 mV (Fig. 2B).

    Twenty patients (35.1%) were considered the regular type, 27 patients (47.4%) the irregular type, and 10 patients (17.5%) the fine type. The restoration rate to sinus rhythm according to the f-wave type was 100% in the regular type patients, 88.9% in the irregular type, and 50% in the fine type. In the irregular type group, 95.6% of the patients were restored to sinus rhythm by the maze procedure and 50% by the left atrial procedure (Table 2). The regular type patients were significantly (P=0.0271) restored to sinus rhythm compared to patients with the other patterns.

    4. Discussion

    Remaining atrial fibrillation (AF) or failure of surgical defibrillation after maze procedure increases the risk of late stroke [7], and thus stricter indications for the surgical treatment for AF should be considered. Various reports have pointed out that the duration of AF, voltage of f-waves at the V1 lead, cardiothoracic ratio, and left atrial dimension were strong predictors for restoring sinus rhythm [8,9]. Among them, we believe that the voltage of the f-waves at the V1 lead is an important factor, because, the voltage of the f-waves at the V1 lead may reveal the electrical activity of the atrium during AF [10]. However, the voltage of f-waves at the V1 lead may be affected by several factors, such as the thickness of the chest wall, respiration, and muscular noise. Furthermore, the V1 lead may not reflect the true left atrial activity, because of the distance between the left atrium and the lead. Thus, the certain potential of the atrium, especially the left atrium, must be measured and examined.

    Transesophageal electrocardiogram (TE-ECG) has been utilized for determining atrial conduction intervals and analyzing atrial rhythms [11]. It was considered that the esophageal electrocardiogram could record depolarizations arising from the left atrium because the esophageal electrode lies close to the posterior left atrium. Binkley and colleagues [12] reported that the esophageal electrocardiogram originated from the left atrium by a clinical study comparing esophageal electrocardiogram with direct left atrial mapping. This result is why we applied the esophageal electrocardiogram in patients with continuous AF to examine the true activity of the left atrium.

    The mechanism of continuous AF associated with organic heart disease has not been clarified. Recently, the electrical activity of the left atrium during continuous AF has been well studied. Harada and colleagues [13] reported that repetitive activation in the left atrium was observed by an intraoperative mapping system in patients with continuous AF and mitral valve disease. Sueda and colleagues [14] also reported that the left atrium showed a rapid atrial fibrillatory cycle at several points in patients with continuous AF associated with mitral valve disease. They considered this repetitive and regular wavelet to arise from the left atrium in sustained AF, and that the ablation of the left atrium could terminate AF. Their reports supported the simple left atrial procedure as a surgical treatment for continuous AF associated with mitral valve disease.

    As mentioned above, we believe that the TE-ECG reflects the electrical potential of the left atrium. The fact that all patients who showed a regular pattern with TE-ECG restored to sinus rhythm after the maze procedure or PVI demonstrates that the left atrial repetitive wavelet was successfully ablated. However, in patients with an irregular pattern, 50% of them did not have their sinus rhythm restored by PVI. From these results, patients whose f-wave on TE-ECG was regular are good candidates for a left atrial procedure such as PVI.

    We must state some limitations of this study. First, the obtained TE-ECG was recorded as unipolar electrical activity, in other words a sum of the total electrical activity of the left atrium, not the local activity. To obtain more accurate information, a bipolar recording system should be used, and a comparison of the findings between TE-ECG and local electrical mapping, especially that of the left atrium, should be performed. Second, we classified the f-wave form of TE-ECG into three patterns. This classification should also be examined and confirmed by direct mapping data in patients with continuous AF.

    In conclusion, this study is the first step for introducing TE-ECG into surgery for AF. By using TE-ECG preoperatively, it may be possible to decide before surgery which operative procedure should be used, maze or pulmonary vein isolation.

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