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Interact CardioVasc Thorac Surg 2009;9:609-612. doi:10.1510/icvts.2009.208173 © 2009 European Association of Cardio-Thoracic Surgery
Restoration of atrial contractility after surgical cryoablation: clinical, electrical and mechanical results
a Department of Cardiovascular Surgery, Hospital Universitario La Princesa, C/Diego de León 62, 28006 Madrid, Spain Received 23 March 2009; received in revised form 21 May 2009; accepted 25 May 2009
*Corresponding author. Hospital Universitario La Princesa, Servicio de Cirugía Cardiovascular, 5a planta, C/Diego de León 62, 28006 Madrid, España.
To assess the electrical sinus rhythm (SR) recovery and the mechanical effectiveness of the atrial contraction by echocardiography is essential in patients undergoing atrial fibrillation (AF) surgery. Between September 2006 and May 2008, patients with chronic AF (n=33; permanent=23 or paroxysmal=10) underwent mitral surgery and surgical cryoablation for AF. Exclusion criteria were: AF that has persisted for 10 years and left atrium (LA) >65 mm. Echocardiography study was performed at six months after surgery. Mean age was 62 years (22 female, 11 male). Mean AF duration was three years (range 0.5–7.4). Mean atria size was 52.4±5.6 mm. Mitral valve surgery involved 32 prosthetic replacements and one mitral valve repair. There was no surgical mortality. Success rate for SR at three and six months was 90% and 82%, respectively. The only predictor of conversion to SR at six months was being at SR when discharge from the hospital. In patients in SR, echocardiographic study provided mechanical effectiveness of the atria in 100% of right atrium and 70% of the LA. Cryoablation for AF is an effective technique to recover electrocardiographic SR while being able to recover atrial contraction effectiveness.
Key Words: Atrial fibrillation; Cox-Maze III; Atrial mechanical function; Cryoablation; Mitral valve disease
Atrial fibrillation (AF) is one of the most common arrhythmias, affecting 1% of the general population and 10% of people over 80 years. Patients with AF have an increased risk of peripheral embolism, cardiac failure development and higher limitations due to dyspnea and fatigue on exercise. In the same way, some studies have demonstrated a lower survival rate and worse outcomes on those patients with AF when comparing with patients with sinus rhythm (SR). Cox-Maze technique for surgical AF treatment started being used in 1987 and it has suffered lots of modifications since then. Nowadays, most centers have replaced the ‘cut and sew’ technique by other methods that use several power sources to achieve the same results in a much easier way [1–3]. One of the methods used today for AF surgical treatment is cryoablation which has demonstrated to be a safe, simple reproducible procedure with a success rate comparable to any other procedure [4, 5]. Some predictor factors of AF into SR conversion described in literature are: AF duration, left atrium (LA) size and type of associated mitral pathology [6–8]. However, organized atrial activity [SR on surface electrocardiogram (ECG)] is not always accompanied by an effective mechanical atrial contraction [9–11]. Atrial contraction is effective when we find A waves in tricuspid and/or mitral transvalvular flow using Doppler echocardiography [9, 12]. The A wave may not appear despite of finding mechanical activity areas (tissue A wave) on the late diastole during the tissue Doppler (TDI) study of the atrial wall. When that happens, the patient may not profit from hemodynamics advantages of an organized atrial contraction. For the time being, echocardiographic data on atrial activity after AF surgical correction by cryoablation are scarce. In the present study, we describe mid-term results for AF treated by cryoablation, under an echocardiographic and clinical point of view, performing a detailed study of the atrial contraction by assessing transvalvular Doppler and atrium wall TDI.
Between September 2006 and May 2008, all patients undergoing mitral valve surgery and AF treatment by cryoablation system were selected (n=33). Inclusion criteria were: patients requiring mitral valve surgery with or without related procedures and having documented paroxysmal, persistent or permanent AF during six months at least. Exclusion criteria included: presence of AF for >10 years and a transversal LA diameter >65 mm measured with echocardiogram on the parasternal long axis. Table 1 shows patients demography.
2.1. Surgical technique All the procedures were carried out by full sternotomy and extracorporeal circulation. After aortic clamp, LA was opened and left auricular appendix was ligated from its inside using a 3/0 monofilament suture. The cryoablation probe was applied during 60 s with a temperature between –100 °C and –160 °C. Lines were created surrounding pulmonary veins and joining these circles among them. Two more lines were performed. One between the left pulmonary veins and the left appendage and another one between the left pulmonary veins and the P3 portion of the mitral annulus. Those patients suffering tricuspid pathology or having atrial flutter history underwent another lesion line between the tricuspid septal valve and the inferior cava. Afterwards, surgery was carried out on mitral valve as well as other procedures if necessary. Mitral valve lesion etiology was rheumatic for 22 patients, degenerative for seven, prolapse for three, and caused by endocarditis for one. Mitral valve surgery involved 32 prosthetic replacements (29 mechanical and 3 biological), and one mitral valve repair. There were 15 (46%) tricuspid annuloplasties made with Carpentier–Edwards ring, 12 (36%) aortic valve replacements and 1 aortocoronary bypass (3%). Those patients with intrahospitalary AF (solved or not) were discharged with oral amiodarone, 200 mg administrated every 12–24 h during three months. If patient still suffered from AF three months after surgery, an electrical cardioversion was scheduled. If not, amiodarone was retrieved.2.3. Echocardiographic study and follow-up All patients were scheduled followed at one, three and six months taking an ECG with strip rhythm. All patients with SR in the ECG were submitted to a control echocardiogram six months after surgery. All the studies were performed by the same operator. Mitral and tricuspid transvalvular flow registry with continuous and pulsed Doppler, and TDI registry, were both carried out on the side wall of both atria on the parasternal 4-chamber view, in order to study atrial contractility. The aim of the TDI study was to detect the low speed rates which originated from the atrial wall movement. An A wave on the TDI recording from any atrium is considered and an indication of mechanical activity (organized movement) during atrial contraction at least on the recorded area. An A wave corresponds with flow through the valves during atrial contraction and it means that there is an effective atria contraction from the mechanical and hemodynamical point of view. Continuous variables are expressed as mean and S.D. Categorical variables are expressed with their frequency and percentage. Analytical study of the differences among cohorts was stated using Mann–Whitney test for numerical variables and using Fisher's exact test for categorical ones. A paired test and a search for a predictor of transmitral flow was performed.Statistical analysis of the relation between SR reversion at discharge and at six months, and several predictor factors were made using univariant logistic regression models. Those variables involving statistical significance were analyzed again using a multivariate analysis if applicable. Kaplan–Meier method was used for studying AF freedom through time.
Patients mean age was 62.6±12.3 years. Beside mitral valve surgery, 78.8% (n=26) of patients underwent another kind of procedure. When leaving the operation room, 21 patients showed from low rate nodal rhythm (<50 lpm), nine patients were in SR, three patients in AF. There was no surgical mortality. Mean hospital stay was 15±12 days (range 5–71 days). Three patients required an endocavitary permanent pacemaker through the study. Six patients received electric cardiovertion at three months. In the postoperative period, 60.6% (n=20) of patients suffered at least one episode of AF and 9.1% (n=3) required an electrical cardioversion. The percentage of patients in SR at discharge was 67% (n=22). During the follow-up, 90% and 82% of patients presented electrical SR at three and six months, respectively. The only predictor of SR at three and six months was being in SR when discharged from the hospital (100% of patients in SR vs. 70% of patients in AF at three months; P=0.03 and 100% of patients in SR vs. 55.6% of patients in AF at six months; P=0.014). There were two deaths during follow-up, one due to cerebral bleeding caused by oral anticoagulation and one due to pulmonary infection. During the follow-up, freedom from death was 94% and freedom from AF was 84% using the Kaplan–Meier curve with a mean follow-up of 24 months. Figs. 1 and 2 show freedom from death and AF during the last follow-up period, respectively.
3.1. Echocardiographic data A significant reduction in LA diameter was found after surgery (52.4±6.0 mm vs. 48.9±4.8 mm; P=0.02). Postoperative echocardiographic using TDI technique showed an A wave in every patient on SR, both in LA and RA. Doppler study showed transtricuspid flow in 100% of patients on electrical SR with a mean A wave speed of 0.6 m/s (0.3–3.8 m/s). Transmitral flow was positive in 70% of patients in electrical SR with a mean A wave speed of 0.72 m/s (0.3–1.3 m/s). No transmitral flow predictor variable was found in the statistical analysis, however, it was found that those patients with severe pulmonary hypertension (>60 mmHg) were less likely to have a positive transmitral flow (86% vs. 40%: P=0.09).
In the present study, we have analyzed the reversion to electrical and mechanical SR in patients with chronic AF using Maze surgery by atrial cryoablation technique in conjunction with concomitant mitral surgery. Conversion to electrical SR was achieved at six months in 83% of patients. Six months after surgery all patients underwent an echocardiographic study that provided evidence of both atria contraction using the TDI study of all patients and presence of transvalvular flow on 100% of right atriums and 70% of LAs during late diastole. For more than 20 years, Cox-Maze procedure has been the gold standard for treating AF surgically [13, 14]. Cox-Maze surgery is intended to: create permanent AF ablation, atrial synchrony restoration and atrial contractility preservation [15]. Despite its high success rate, it is a complex technique that entails long surgery times and significant bleeding risks [15]. Cryoablation is a simple technique that does not increase surgical risks and has demonstrated its cost-effectivity [7]. Literature sets cryoablation success rate at 6–12 months between 65% and 85% [5–8]. In our series, success rate is at three and six months 90% and 82%, respectively. Like other authors, we believe that in order to obtain good results, it is essential to do a thorough patient's follow-up and to complete their treatment with antiarrythmic agents and electrical cardioversion when necessary. Literature describes some success predictors after atrial cryoablation such as: LA size, AF duration and mitral disease etiology. However, these results have not been reproduced by all groups [6–8]. We have found no relation between reversion to SR and atrial size or AF duration. Our only predictor of conversion to electrical SR at six months was the SR at discharge. Our percentage of patients in SR was higher at six months after the procedure than at discharge. This may reflect the need of following patients and treating them with medication and electric cardiovertion. This may complement the surgical ablation. This finding has been also reported by Manasse et al. [8]. We assessed atria mechanical activity at six months using an echocardiographic study. By the means of tissue study TDI, we have found that in all cases there is mechanical contraction in some atrial wall areas of both atria. However, it does not always involve an effective mechanical atrial contraction, i.e. transvalvular flow during late diastole or atrial contraction, that should be assessed by continuous or pulsed Doppler. In all cases, we found hemodynamic effective contraction in the right atrium, whereas the LA showed transmitral flow in 70% of patients with SR. We think these are very good results even if many of our patients were in paroxysmal AF and the preoperative mean duration of AF was not to long. We found in our study that severe pulmonary hypertension could be related to atrial mechanical activity. Recently, the mechanical function after Maze surgery without valve surgery has been described [15]. We want to remark that one of the main benefits of SR restoration is to improve those symptoms due to the loss of atrial contribution to ventricular filling. This contribution may be essential in the context of ventricular hypertrophy or diastolic dysfunction. Also, there is a patient population with biological prostheses or valve repair surgery, who can have an additional benefit. In this group, the AF abolition and the restoration of an effective atrial contraction could help to take the decision about withdrawing oral anticoagulation. To take this decision, we think that a standard ECG is not enough and mechanical atrial effectiveness must be addressed. Further follow-up is required in order to confirm whether electrical SR remains over time. We could not perform a 24-h Holter due to the fact that many patients are referred to our hospital from other regions. However, we performed a 24-h Holter in all patients in which oral anticoagulation could be interrupted if normal SR is restored (patients with no mechanical prosthesis).In conclusion, cryoablation is an effective system to recover both electrical and mechanical SR. Using TDI study, we have proved contraction in some points of both atria in all cases. LA showed effective atrial contraction measured by transvalvular Doppler in 70% of LA and in 100% of the RA. Rhythm at discharge was a success predictor six months after surgery, whereas pulmonary hypertension grade seems to be related to echocardiographic effective atrial contraction.
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Abstract
1. Introduction
