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Ann Thorac Surg 2007;84:1978-1983. doi:10.1016/j.athoracsur.2007.06.081
© 2007 The Society of Thoracic Surgeons
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Mark A. Groh
Oliver A. Binns
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Alan M. Johnson
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Right arrow Electrophysiology - arrhythmias

Original Articles: Cardiovascular

Ultrasonic Cardiac Ablation for Atrial Fibrillation During Concomitant Cardiac Surgery: Long-Term Clinical Outcomes

Mark A. Groh, MD*, Oliver A. Binns, MD, Harry G. Burton, III, MD, Stephen W. Ely, MD, PhD, Alan M. Johnson, MD

Mission Saint Joseph Hospital, Asheville, North Carolina

Accepted for publication June 27, 2007.

* Address correspondence to Dr Groh, Asheville Cardiovascular and Thoracic Surgeons PA, 257 McDowell St, Asheville, NC 28803 (Email: mgroh{at}avlcvsurgeons.com).


Dr Groh discloses that he has a financial relationship with St. Jude Medical.

 

   Abstract
Top
 Abstract
Introduction
 Material and Methods
 Results
 Comment
 References
 
Background: Therapeutic ultrasound as an alternative to the maze procedure was evaluated in this large US experience. Safety and efficacy were assessed at 6-, 12-, and 18-month visits with systematic 24-hour Holter monitoring.

Methods: From February 2005 to February 2007, 220 patients were prospectively enrolled in a single center study, and among them 129 patients with concomitant cardiac surgery and at least 6-month follow-up were reviewed. Primary procedures were mitral surgery in 50% of the cases, coronary bypass in 32%, and aortic surgery in 16%. Atrial fibrillation was permanent in 66 (51.1%), paroxysmal in 43 (33.3%), and persistent in 20 (15.5%) patients. An epicardial and circumferential left atrial encircling line was created on the beating heart. Routinely a mitral isthmus line was also created from the left atrium epicardium using an ultrasonic handheld device.

Results: No morbidity or mortality was device-related. There were four (2.33%) early deaths and six late extra-cardiac deaths. Follow-up ranged from 6 to 670 days with a mean follow-up of 358.5 days, median 340 days with two patients lost to follow-up. Freedom from atrial fibrillation or left-sided flutter was 83.2%, 84.4%, and 86.2% at 6, 12, and 18 months, respectively. A pacemaker was implanted in seven patients (5.4%). Male gender and left atrial dimension were significant risk factors for failure.

Conclusions: The study confirms the excellent safety record of the technology, and the efficacy at the level reported in a previous European multicenter study. Efficacy is also maintained at longer (12 and 18 months) follow-up.

In 1998, the seminal publication by Haissaguerre and colleagues [1] directed the attention of clinicians and researchers toward the pulmonary vein orifices as a main site for triggers initiating atrial fibrillation (AF), particularly in patients with the paroxysmal form of the disorder.

In the years after this discovery surgeons and cardiologists worked to create lines of conduction block in the left atrial (LA) wall around the pulmonary vein orifices. The resulting line of scar tissue would prevent the propagation of chaotic electrical activation originating around the pulmonary veins to the rest of the LA wall.

Different sources of energy, including radiofrequency [2], microwave [3], laser [4], and cryotherapy [5], have been developed and used to create intraatrial lesion lines from both an endocardial or epicardial approach. Independent of the energy source, the lesion set became a pulmonary vein encircling lesion, as described in a variety of feasibility and descriptive studies [2–5]. In most reports from the surgical literature, the lesion sets described were also attempting to replicate and simplify some of the original patterns developed by Cox in his pioneering "maze" procedure [6]. The Cox-maze procedure has not been widely adopted by the surgical community due to its relative complexity and invasiveness while addressing a nonstructural heart disease.

A technology, Epicor (now owned by St. Jude Medical, Inc, Minneapolis, MN), using therapeutic ultrasound in the form of high intensity focused ultrasound (HIFU; consisting of an array of ultrasonic transducers applied on the epicardial side of the LA and activated during an average ten-minute off-pump, beating heart algorithm) was developed. Safety and efficacy of the technology was later evaluated during a European multicenter study published in 2005 with six-month follow-up data [7].

Recently, large published series show a growing interest in understanding the correlation between the presence of preoperative AF and late outcomes in patients operated on for structural heart disease, be it mitral, aortic, or ischemic heart disease [8–11]. The conclusions of these reports point toward a strong justification to treat AF at the time of concomitant cardiac surgery in an attempt to improve significant long-term morbidity and mortality.

Finally, because HIFU had not been evaluated outside of the constraints of a controlled clinical trial, the primary endpoint of this study was to evaluate clinical outcomes after HIFU ablation during concomitant surgery in a consecutive series of patients operated on in a single US center with long-term follow-up.


   Material and Methods
Top
 Abstract
 Introduction
 Material and Methods
Results
 Comment
 References
 
Patients
Out of a total of 220 consecutive patients who underwent an LA ablation procedure using the Epicor technology at Mission Hospital, Asheville, NC, from February 2, 2005 to February 2, 2007, a group of 129 consecutive patients who had a concomitant ablation and a minimum follow-up time of six months will represent the population under analysis for this study. Preoperative data, intraoperative procedural details, and postoperative follow-up data were collected systematically and prospectively in a confidential database. The study was approved by the Institutional Review Board and individual patient consents were obtained.

Detailed demographic data are summarized in Table 1, with 50 female and 79 male patients of a mean age of 71.32 years; 56% of the population under study being older than 70 years and 16% older than 80 years. Left ventricular ejection fraction (LVEF) was lower than 0.30 in 21% of the cases. Mean LA diameter measured at preoperative echocardiography was 48.8 mm, and was over 50 mm in 40% of the cases.


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  		Table 1 Patient Demographic Information (n = 129)
 
The type and distribution of preoperative AF, according to the American Heart Association/American College of Cardiology/European Society of Cardiology classification [12], were as follows: permanent, n = 66 (51.1%); paroxysmal, n = 43 (33.3%); persistent, n = 20 (15.5%). According to the more recent Cox classification [13], the types were continuous in 66 patients (51%) and intermittent in 3 (49%). When compared with permanent AF patients for demographic variables, paroxysmal AF patients were significantly younger, shorter, with a shorter AF duration, and smaller LA diameter (Table 2).


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  		Table 2 Comparison Between Permanent and Paroxysmal AF Patient’s Demographics
 
The detailed primary concomitant procedures are summarized in Table 3, with three main subgroups according to the primary procedure; namely, mitral valve surgery in 50%, coronary artery bypass grafting (CABG) in 32%, and aortic valve surgery in 16%. In this difficult patient population, CABG was performed in 75% of the patients who had primary aortic valve surgery and in 51% of the patients who had primary mitral surgery. Over 50% of the primary mitral valve surgery population had additional valvular surgery.


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  		Table 3 List of Concomitant Cardiac Procedures in 129 Patients
 
System Description and Surgical Technique
The system has been described in detail elsewhere [7] and consists of an array of transducers (UltraCinch; Epicor) positioned after proper sizing around the LA wall over the antrum of the pulmonary vein orifices. Once connected to a generator, the device creates a circumferential lesion from the LA epicardium. This primary lesion pattern can be completed by also making a linear lesion extending from the left lower vein orifice to the mitral valve annulus, to create the "mitral line" component of the Cox-maze procedure using an UltraWand (St Jude Medical) employing the same ultrasonic acoustic energy. The importance of the mitral isthmus line aiding further compartmentalization of the LA as well as the coronary sinus wall ablation has been stressed elsewhere [14].

The operative technique is performed while the normally perfused heart is fully beating before the intracardiac part of the operation is carried out for the concomitant surgery. The surgical dissection is limited to freeing the pericardial reflections around both vena cavae so that a proper sizer can allow for a precise measurement of the LA circumference. Once the sizing is done, the UltraCinch is introduced in the proper position by following the lead of the sizer and is secured in place with the aid of two tourniquets. The average ten-minute algorithm is fully automated and this time can be used to prepare for the following intracardiac part of the concomitant procedure. After the pulmonary vein isolation is completed the mitral isthmus line is created. Our practice is to place the patient in steep Trendelenburg position and place a deep pericardial suture to assist in visualization. The apex of the heart is lifted and the handheld UltraWand is placed into position to create the linear lesion. The ablation does not add any bypass or cardiac exclusion time to the concomitant procedure and will prolong the overall total operative time by no more than three minutes [7]. Although the device may be placed readily, performance of the procedure needs to be meticulous with proper attention to details (proper sizing requires special attention), and knowledge of this new energy source.

Previous cardiac surgery had been done in 14 patients (14%), requiring a more extensive dissection to free the intrapericardial adhesions. No major difficulties were seen for the UltraCinch placement and positioning. All patients in this series were treated with a circumferential pulmonary vein ablation combined with a mitral isthmus line. Both lesions were performed epicardially on the beating heart. Finally, the left atrial appendage was not routinely excluded.

Postoperative Protocol
Postoperative management of anticoagulation and antiarrhythmic drugs was considered as a critical part of the surgical management of AF. Started in the immediate postoperative period, anticoagulant therapy (Coumadin; DuPont, Wilmington, DE) was maintained for a minimum of one year [15]. On the basis of previous studies, a prophylactic antiarrhythmic drug (generally amiodarone) was started at the completion of the procedure and maintained orally for at least three months after surgery [15]. External cardioversion was not encouraged in the early postoperative period and contemplated whenever necessary at the three-month visit time.

A physical examination, standard 12-lead electrocardiogram, and 24-hour Holter monitoring, were performed at the 3-, 6-, 12-, and 18-month follow-up visits. Patients also had electrocardiogram and physical examinations at two and eight weeks postoperatively.

Statistical Analysis
Data were entered into a computerized database and analyzed with a statistical package (STATISTICA; StatSoft, Inc, Tulsa, OK). The descriptive summary of data included mean ± standard deviation and 95% confidence intervals for continuous variables and proportions for categoric variables. Between-group differences were assessed with t tests and analysis of variance in more than two groups for continuous variables and {chi}2 tests for nominal variables. Logistic regression analyses were performed to assess the significance of certain variables on the odds of developing AF. All reported p values are two-sided. Estimates of percentage of patients surviving over time were computed using the Kaplan-Meier technique.


   Results
Top
 Abstract
 Introduction
 Material and Methods
 Results
Comment
 References
 
Evaluation of Safety
Complication
There were no device or ablative procedure-related adverse events. An important point was the absence of esophageal, coronary, or phrenic nerve damage. Complications observed within the first 30 days but not leading to death included the following: ventilation greater than 24 hours in 23 patients (17.8%), pneumonia in ten patients (7.8%), renal dysfunction in six patients (4.7%), reexploration for bleeding or tamponade in three patients (2.3%), and stroke in one patient. A pacemaker had to be implanted for atrioventricular conduction block or sinus node dysfunction in seven patients (5.43%) ranging in age from 67 to 81, mean 74.14 ± 5.6 years, after the following concomitant procedures: two mitral valve replacements, two aortic valve replacements, two mitroaortic valve replacements, and one CABG.

Mortality
There were four early deaths, deemed unrelated to the device or the ablative procedure (2.33%) and occurring within 30 days of surgery in patients aged 69, 78, 81, and 82 years of age, and due to respiratory failure and stroke, acute respiratory distress syndrome, and septicemia; in a patient with myeloproliferative disorder, pneumonia and multiorgan failure.

There were a total of six late deaths occurring more than 30 days after surgery; none of them being "late" in-hospital deaths, and due to multiorgan failure in a patient on hemodialysis, sepsis associated with a chronic indwelling venous port, persistent severe pulmonary hypertension with seizures, pneumonia with sepsis, complications of renal failure, and esophageal cancer.

Evaluation of Efficacy
Patient accountability
While 129 patients had been enrolled in the study, two patients were lost to follow-up. These two patients are known to be alive and well but did not present for the physical and 24-hour Holter monitoring. Follow-up ranged from 6 to 670 days with a mean follow-up of 358.53 days (median, 340 days). Given the additional early and late mortality, there were 119 patients available for follow-up at 6 months, 64 patients available at 12 months, and 29 available at 18 months. All patients with pacemakers underwent pacemaker interrogation in search of a silent arrhythmia.

Freedom from AF
The definition of "freedom" from AF was intentionally restrictive and failure included not only presence of AF over time but also presence of any form of "left atrial reentry tachycardia," represented by any left-sided flutter or focal tachycardia. Right-sided flutter, which we have found to be occasionally unknown or "hidden" behind AF at the time of surgery, was not considered a failure because neither the device nor the procedure were designed to treat it. Patients with a pacemaker had to show a sinus or atrially paced rhythm and no evidence of mode switching.

Three patients went to the electrophysiology lab for postoperative study. One patient underwent successful right-sided flutter ablation. Two patients had mixed right-sided and left-sided flutter. One of these patients had a previous septal defect repair and could be treated with only a right-sided isthmus ablation that cured his flutter. The second patient underwent left and right isthmus ablation that was also successful. Freedom from AF was 83.19% at 6 months, 84.38% at 12 months, and 86.21% at 18 months, when 29 patients were still under observation (Fig 1). Categorized by AF type and concomitant procedure type, the results are displayed in Table 4. These results indicate that efficacy is significantly higher for paroxysmal than permanent (or continuous) AF at six months, and that there is no significant difference in freedom from AF between primary mitral and coronary patients. The aortic subset was too small for a valid comparison.


Figure 1
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  		Fig 1. Freedom from atrial fibrillation (AF) at three different visit times: 6, 12, and 18 months after surgery. Within parentheses, number of patients exposed at a given time interval.

 

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  		Table 4 Freedom From AF as a Function of Types of AF and of Concomitant Surgery
 
When compared with the previously published European experience [7], where the follow-up time was limited to six months, there were no significant differences in the rate of freedom from AF at this timeline in every subgroup: in the total group of 119 patients, 83.19% (Asheville) versus 85.11% (Europe), p = 0.70; in the continuous AF group of 60 patients, 77% (Asheville) versus 80% (Europe), p = 0.64; in the intermittent AF group of 59 patents, 90% (Asheville) versus 100% (Europe), p = 0.08.

Univariately, two variables were risk factors for failure: male gender (p = 0.017), and LA size expressed in number of ultrasonic units (p = 0.007), which is an indicator of the LA diameter with less variability than echocardiographic measurement due to the proper sizing, as proven by the good correlation between UltraCinch and LA diameter (p = 0.003) (Fig 2). At logistic regression analysis only male gender and increased UltraCinch size are significant at the two-sided 5% significance level. Regarding the type of AF, only patients entering with paroxysmal AF have decreased odds of failure compared with other patients (odds ratio [OR] 0.309). The most significant predictor proved to be size of the UltraCinch used for the ablation. Interestingly, for every one unit increase in UltraCinch size, the odds of a patient failing treatment increases by 66.2% (OR 1.662). The actuarial survival, including early mortality, was 93.79 ± 0.02% at 6 months and 91.74 ± 0.02%, at 12 and 18 months, at which time 29 patients were still at risk (Fig 3).


Figure 2
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  		Fig 2. UltraCinch (U-Cinch) size as a function of left atrium (LA) preoperative diameter measured at echography, with 95% confidence limits. (Pre-op = preoperative.)

 

Figure 3
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  		Fig 3. Global actuarial survival, including early mortality. Within parentheses, number of patients exposed at a given time interval. (AF = atrial fibrillation.)

 

   Comment
Top
 Abstract
 Introduction
 Material and Methods
 Results
 Comment
References
 
Surgical ablation for AF in patients undergoing cardiac surgery has been amply justified by recent publications [8–11], all concluding that uncorrected preoperative AF is generally associated with increased late cardiac morbidity and mortality and poor long-term survival in the three main categories (mitral, aortic, and coronary) of structural heart disease. Analysis of clinical outcomes after the use of HIFU during concomitant cardiac surgery in a typical US center, has led to a number of conclusions.

As in the previously published data, the device has continued to demonstrate an excellent safety record in our experience as well. We observed no complications of any type related to the device or the ablation procedure. The epicardial origin of energy delivery certainly plays an important role in this regard. The ultrasonic beam is directed toward the blood pool, avoiding potential damage to the surrounding structures like the esophagus or the phrenic nerves.

The prevalence of AF in patients referred for the concomitant therapy of structural heart disease has been reported to range from 8% in coronary patients, 10% in aortic patients, to up to 46% in mitral patients [9–11]. Since HIFU became available to us, the experience of Mission St Joseph Hospital, performing approximately 1,100 open-heart surgeries per year, has been to perform an ablation at the time of surgery in 198 patients over the past two years, or in 9% of the global surgical population referred to our institution. This "index" of prevalence of AF in patients undergoing cardiac surgery may have been underestimated until now and the relatively older age (mean 71.3 years) of our patients compared with that observed in other publications [16, 17] may account for the difference. Nevertheless, as surgical patients are becoming older, the increased trend in AF prevalence, reaching 10% of the population near the age of 80 [18], will lead to a significant increase in patients in AF at the time of surgery, as previously anticipated in other publications [8].

Given our patients population advanced age and complexity of structural heart disease it has become mandatory for us to address AF at the time of surgery in the least invasive fashion that does not add incremental risk to the patient. Conversely, intracardiac ablation procedures all add cardiac exclusion and bypass times. Some of these intracardiac procedures attempt to create the full maze III lesion patterns with alternative energy sources rather than division and suture in an attempt to mitigate operative risk [19]. The Epicor system is easily and rapidly inserted around the LA on the beating heart before cardiopulmonary bypass or cardiac exclusion. This off-pump ablation has been shown in our population of complicated patients not to increase operative risk. Patients with AF and structural heart disease not requiring a left atriotomy (ie, aortic valve replacement or coronary artery bypass grafting) have thus become, in our experience, ideal candidates for a short and no risk Epicor epicardial ablation prior to going on bypass.

This study also represents data on the long-term analysis of the use of HIFU ablation. It shows that the original six-month follow-up data in the European study remains stable and comparable with our experience with a freedom from AF maintained at over 85% throughout the first 18 months of follow-up in the 29 patients still at risk at that timeline (Fig 3).

Postoperative management of these patients is, in our opinion, a full part of the therapy. As such it is significantly more intensive than standard postoperative care. Precise timelines for visits and medication adjustments are best established and scheduled as a standing order set. The follow-up can be performed by the surgical or the medical cardiology group, but in the latter case the group should also be educated in the characteristics of the technology, the timeline of the visits, as well as the reasons for the postoperative management strategy and protocols.

In patients with AF concomitant with structural heart disease, structural and electrophysiological changes take place over time within the LA wall. Over months and years of mitral stenosis or regurgitation, aortic stenosis or regurgitation, or ischemic heart disease the LA wall undergoes changes due to pressure and volume overload of the LA. Primarily this is a consequence of left ventricular systolic and (or) diastolic dysfunction of various intensity and duration. Those changes are structural (dilatation of the LA cavity, some degree of hypertrophy, fibrosis formation, overstretching of the myocardial fibers [20]), and provide an electrophysiological "substrate," which increases the likelihood of AF by causing heterogeneity in intraatrial and interatrial conduction [21]. The reverse remodeling taking place after correction of the structural heart defect will take time and the mere isolation of triggers around the pulmonary veins will not be sufficient to suppress all causes and effects of AF within the early postoperative period [22]. It is then important to explain to the patient, the family, and the referring cardiologist that persistence of AF is common during the first three months. Moreover, ablation lesions leave an inflammatory and hence arrhythmogenic scar during the first few postoperative weeks. During the time taken by reverse remodeling changes to take place it is then justified to keep the patients on both anticoagulant and antiarrhythmic drugs to protect them from the risk of thromboembolic complications, as currently accepted for the same reasons by electrophysiologists after catheter ablation for both paroxysmal and permanent forms of AF [15]. We feel this approach is supported in our series by the observation that no patient suffered thromboembolic event through late follow-up.

Among the limitations of the study we see the lack of rigorous control of the postoperative rhythm in patients with paroxysmal forms of AF, knowing that some of them might have asymptomatic paroxysms. Longer terms of monitoring may be helpful in the future, including the potential for implantable device monitors, which will make more precise determinations possible.

Another limitation of the study could be the lack of postablation testing for electrical isolation in the operating room. However, we consider immediate postablation block a poor predictor of late clinical success. The presence of immediate electrical isolation after catheter and surgical ablation does not always correlate with histologic transmurality and has been shown to not predictably result in patients being free from AF at later follow-up [23–25]. It is therefore possible that, despite a fully automated algorithm and a consistent procedure eliminating operator-dependent variables, human or procedural error might have resulted in some patients having received suboptimal ablation.

In conclusion, the Epicor HIFU-based system is an easy to use, beating heart off-pump technology to safely ablate cardiac tissue during concomitant cardiac surgery, with a success rate of 80% to 85% at up to 18 months after surgery in a difficult group of patients suffering from long-lasting structural heart disease. Continuous improvements on this still early-stage and developing technology should allow for still better outcomes and expansion to other indications.


   References
Top
 Abstract
 Introduction
 Material and Methods
 Results
 Comment
 References
 

  1. Haissaguerre M, Jais P, Shah DC, et al. Spontaneous initiation of atrial fibrillation by ectopic beats originating in the pulmonary veins N Engl J Med 1998;339:659-666.[Abstract/Free Full Text]
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  8. Quader MA, McCarthy PM, Gillinov AM, et al. Does preoperative atrial fibrillation reduce survival after coronary artery bypass grafting? Ann Thorac Surg 2004;77:1514-1524.[Abstract/Free Full Text]
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  12. Fuster V, Rydén LE, Asinger RW, et al. ACC/AHA/ESC guidelines for the management of patients with atrial fibrillation: executive summary: a Report of the American College of Cardiology/ American Heart Association Task Force on Practice Guidelines and the European Society of Cardiology Committee for Practice Guidelines and Policy Conferences (Committee to Develop Guidelines for the Management of Patients With Atrial Fibrillation) Developed in Collaboration With the North American Society of Pacing and Electrophysiology J Am Coll Cardiol 2001;38:1231-1265.[Free Full Text]
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