Atrial fibrillation surgery with a focus on patients with reduced left ventricular function and heart failure

Abstract

Introduction

Atrial fibrillation (AF), the most common sustained arrhythmia is associated with symptoms such as fatigue, reduced exercise tolerance, and impaired quality of life.^1,2 Assessment of AF symptoms in patients with concomitant valvular or ischaemic heart disease might be difficult, since both, AF as well as the underlying disease might cause similar symptoms. Atrial fibrillation accompanied by a reduced left ventricular ejection fraction (LVEF), leads to progressive heart failure with an increased mortality.³ An increasing knowledge about mechanisms of AF and the possible impact of specific structural heart diseases on the rhythm outcome led to an increased surgical treatment of AF.⁴ Surgical AF ablation is most often performed concomitant to other cardiac surgical procedures. Atrial fibrillation ablation surgery can be performed during primary open [e.g. mitral valve surgery (MVS)] as well as primary closed atrial procedures [e.g. coronary artery bypass grafting (CABG) or aortic valve replacement (AVR)]. Furthermore, surgical treatment of AF can also be performed in patients without structural or ischaemic heart diseases. The so-called surgical stand-alone AF ablation is today routinely performed via a lateral thoracotomy or through videoscopic port-access.

This review article aims to give an overview on the different surgical treatment options for AF and outlines the main issues in patients with heart failure and reduced LVEF.

Concomitant atrial fibrillation ablation surgery

The prevalence of AF in patients undergoing cardiac surgery varies between 30% in MVS, 14% for AVR, and 6% in patients presenting for CABG.¹ A recently published meta-analysis of the Society of Thoracic Surgery database with >86 000 patients showed an increase of surgical AF ablation concomitant to cardiac surgical procedures accompanied by a reduction in 30-day mortality and stroke.⁴ In concomitant surgical AF ablation, the guideline recommendations are depending on atrial access of the concomitant procedure.

If an atriotomy is performed (e.g. MVS), concomitant surgery has a Class I recommendation in 2017 the Heart Rhythm Society (HRS)/European Heart Rhythm Association (EHRA) guidelines.¹ Especially due to the increasing number of repairs in MVS, the establishment of a sinus rhythm is essential in order to renounce lifelong anticoagulation. In this patient cohort, the freedom of AF until 1 year post-operatively can be achieved in 60–90% of the patients.^5–14 A stable sinus rhythm can even be restored for 10 years after the concomitant Cox-Maze procedure, resulting in a significant increased long-term survival.¹⁵ A recently published study from a Polish registry was able to illustrate an improved survival if surgical ablation is performed concomitant to MVS.¹⁶ Those studies outlined large left atrial diameters, AF duration, advanced age, and failure to isolate the entire posterior left atrial wall as common predictors for AF recurrence.

If, in the presence of AF, the primary cardiac surgery does not require incision of the atria (e.g. AVR or CABG), there is a Class IIA recommendation for AF surgery in the 2017 HRS/EHRA guidelines.¹ Untreated AF is associated with increased risk of early and late mortality in cardiac surgery.

The gold-standard for surgical AF ablation is the Cox-Maze procedure, which necessitates opening of both atria, but resulted in 90% of freedom of AF at 5 years post-operatively.¹⁷ A less invasive approach is only to open the left atrium to perform the left-sided lesions of the Cox-Maze lesion set. The most simple approach, which is often performed in patients without necessity of opening of the atria for the surgical procedure (CABG or AVR), is an epicardial pulmonary vein isolation (PVI).^18,19 The limited approach of isolated PVI has nevertheless been associated with impaired rhythm outcomes, in comparison to an extended left atrial lesion set or a complete Cox-Maze procedure. Especially in patients with persistent- or long-standing persistent AF, a more extended lesion set has been shown to be associated with improved freedom from AF rates.

Either way, multiple randomized and matched cohort studies showed that the addition of surgical AF ablation concomitant to AVR^20,21 or CABG²² does not increase the mortality. If a PVI is performed with a bipolar radiofrequency (RF) clamp concomitant to AVR or CABG the 1-year freedom of AF varies between 50% and 89% which is superior to treatment with antiarrhythmic drugs (AADs) alone.^23–27

Based on the literature which proved the efficacy and safety of concomitant surgical AF ablation recent HRS/EHRA guidelines adopted the recommendation of concomitant AF ablation. There is a Class I indication for surgical AF ablation in patients with symptomatic AF undergoing cardiac surgery with opening of the atria (e.g. MVS) and a Class IIa indication in procedures without opening of the atria (e.g. AVR, CABG).¹

Concomitant surgical occlusion of left atrial appendage

The left atrial appendage (LAA) can be an origin of thrombus formation and is accounted for up to 90% of strokes in AF patients.²⁸ Consequently, closure and/or removal of the LAA should be one of the main targets during every AF surgery. Previous analysis from the Cox-Maze procedure showed a decreased stroke rate after LAA excision.²⁹ Furthermore, small retrospective studies suggested fewer neurological events after surgical LAA occlusion.³⁰ Besides reduction of stroke risk, electrical isolation of the LAA also seems to be mandatory in order to maintain sinus rhythm after surgical AF ablation since the LAA can be accountable for up to 27% of atrial arrhythmias.³¹ However, at the moment, no prospective data are available which evaluated the success after surgical LAA occlusion. On the other hand, evidence is available from two randomized trials (PROTECT AF and PREVAIL) which compared the percutaneous closure of the LAA with the WATCHMAN device to anticoagulation, showing a non-inferiority compared with oral anticoagulation in protecting against stroke in case of LAA closure.^32,33 In regards of surgical AF ablation, there are different techniques available while complete excision of the LAA or external closure with an AtriClip seems to be the most efficient techniques to avoid a remaining stump with residual flow.^34–36 Alternative techniques (e.g. external or internal ligation, stapled excision) resulting in insufficient closure of the LAA led to a higher annual rate of neurological events (approximately 1%)³⁷ and therefore should be avoided. A recently published randomized multicentre study (LAACS) addressed the role of prophylactic surgical LAA occlusion in patients regardless of their preoperative AF status. In this study, a significant lower rate of post-operative ischaemic brain injury was found in the group of patients with LAA closure (16% vs. 5%; P = 0.02).³⁸ Overall, concomitant surgical LAA closure is, when performed correctly, reasonable without additional risks and seems to reduce the burden of stroke in AF patients undergoing cardiac surgery. However, closure of the LAA needs to be performed meticulously by using the right techniques and success of complete closure needs to be evaluated post-operatively. Although there is a lack of prospective randomized data of the surgical LAA occlusion, the results of the epicardial LAA closure with an AtriClip are promising. Furthermore, the randomized data from the endovascular closure of the LAA show that cessation of anticoagulation after successful LAA closure is justifiable and might probably be adopted by the surgical community. However, due to the lack of prospective randomized data, at the moment, there is no recommendation for cessation of anticoagulation after surgical LAA closure and anticoagulation should be maintained according to CHA₂DS₂-VASc score. Nevertheless, there is an urgent need for prospective randomized studies addressing the important questions of the benefits of the surgical LAA closure.

Stand-alone atrial fibrillation surgery and hybrid ablation

Stand-alone surgical ablation in patients with paroxysmal AF can be considered in AAD-refractory AF for patients who have failed one or more attempts of catheter ablation. For patients with persistent- or long-standing persistent AF surgical stand-alone ablation can also be considered after failed catheter ablation or in patients not suitable for catheter ablation. Furthermore, a hybrid concept consisting of a surgical ablation with simultaneous- or staged catheter ablation can be useful.¹

The first series of stand-alone surgical ablation has been published by James Cox. He reported the outcomes of 112 patients undergoing Cox-Maze III procedure via sternotomy with cardiopulmonary bypass on the arrested heart. Although, showing excellent results with a rate sinus rhythm off AADs of 80%, this ‘cut- and sew’ procedure did not gain widespread application, due to its complexity and invasiveness.³⁹ When replacing the cut- and sew principle by creation of transmural lesions with different thermal energies such as RF or cryothermy, less invasive approaches were used. The full Cox-Maze procedure can nowadays be performed via a minimally invasive right lateral thoracotomy. In several cases, series and larger single-centre studies, excellent outcomes with freedom from AF between 72% and 88% have been shown for this procedure.^26,40,41 These results are in terms of efficacy comparable to the cut- and sew maze, with shorter cross-clamp times and less invasiveness. Nevertheless, to perform a complete Cox-Maze IV procedure, cardiopulmonary bypass, and cardioplegic arrest of the heart are necessary.

In recent years, other approaches limiting the lesions to those that can be applied from the epicardial surface of the heart have been developed. First surgical PVI and occlusion of the LAA via thoracoscopic, video-guided approach has been described by Wolf et al. in 2005.⁴² In their small series of 27 patients, treated by epicardial PVI on the beating heart, they had a success rate of 91% and 65% off AADs, respectively. In a larger study, using PVI in combination with partial autonomic denervation the rate of freedom of AF off AAD was 72%, 46.9%, and 32% in patients with paroxysmal, persistent-, and long-standing persistent AF.⁴³ While the results of an isolated PVI are satisfying in patients with paroxysmal AF, the data clearly indicates, that there is a necessity for a more extended lesion set for surgical treatment of patients with persistent- and long-standing persistent AF. A more extended lesion, which can be applied thoracoscopically on the beating heart without cardiopulmonary bypass, has been published by Weimar et al.⁴⁴ It consists of a left atrial box lesion and a trigonum line to the non-coronary aortic annulus performed with bipolar and linear unipolar RF devices. Furthermore, a resection of the LAA was conducted in their study. Results in a cohort of 89 patients have been promising with freedom from AF of 90% after 1 year and freedom from AF off AADs of 82%.

A European multicentre randomized trial including 475 patients treated by the above-mentioned totally thoracoscopic ablation has recently been published.⁴⁵ Using an epicardial left atrial box lesion as well as a trigonum line, the study has shown freedom from AF rates of 72.7% for paroxysmal, 68.9% for persistent, and 54.2% for long-standing persistent AF after a mean follow-up period of 20 ± 9 months. The overall freedom from 30-day complication rate was 92.4%. In this study, the recurrence of AF was significantly lower in patients treated with thoracoscopic stand-alone AF ablation compared with catheter-based ablation (56% vs. 87%) with similar long-term clinical event rates.⁴⁶ Another randomized clinical trial comparing catheter ablation with minimally invasive surgery in patients with drug-refractory AF with dilated atria or previously failed catheter ablation has shown a superior rate of freedom from AF in surgical patients (surgery: 66% vs. 37% catheter ablation).⁴⁷ However, this was accompanied by a higher complication rate in the surgical group (e.g. pneumothorax, major bleeding, and the need for pacemaker). Similar results were shown in a meta-analysis of seven studies, showing superior freedom from AF rate for surgical patients, however, also accompanied by a higher pacemaker implantation rate.⁴⁸

A strategy, which is nowadays used by many AF heart teams is a hybrid approach, consisting of surgical and catheter ablation, which can either be applied as a single- or staged procedure. In the HISTORIC-AF trial, it was shown, that a hybrid approach with AF surgery and catheter ablation resulted in improved rhythm outcomes, compared with surgery alone.⁴⁹ Similar results were shown in a meta-analysis comparing hybrid ablation with catheter ablation alone for patients with persistent- and long-standing-persistent AF. The hybrid approach has shown significantly higher rates of freedom from AF than catheter ablation alone (70.7% vs.49.9%).⁵⁰

Using the hybrid approach by combining the advantages of both techniques might be considered in the future as the treatment of choice in patients with persistent and especially in patients with long-standing persistent AF and dilated atria.

Surgical ablation in patients with reduced left ventricular function and heart failure

In patients with heart failure, there is a high prevalence of AF.^51,52 Presence of AF contributes to an increased mortality and morbidity in those patients.^3,53 There is an ongoing debate on ideal treatment strategy in heart failure patients with AF. It has been shown that a rhythm control strategy with antiarrhythmic medication is not superior compared with rate control in patients with AF and heart failure.⁵⁴ In recent years, several studies have shown improved outcomes of catheter ablation in heart failure patients, compared with rate control- or AV node ablation and biventricular pacing.^55,56 The CASTLE-AF study, a large randomized multicentre trial, investigating catheter ablation vs. best medical therapy (either rate or rhythm control) in patients with heart failure and AF has been recently published.⁵⁷ In patients undergoing catheter ablation, a significant reduction of all-cause mortality, cardiovascular mortality, as well as heart failure hospitalizations has been shown.

Less data are available for surgical ablation in patients with AF and heart failure. There is one study of stand-alone ablation in patients with reduced LVEF by Stulak et al.⁵⁸ In their investigation including 37 patients with reduced LVEF undergoing isolated Maze procedure, they found the greatest improvement of LVEF in patients with preoperative severely reduced LVEF (33% to 53%) and in patients with chronic AF. Those improvements were seen immediately post-operative and sustained during follow-up period of up to 48 months.

Furthermore, only few studies are available in heart failure patients undergoing concomitant surgical ablation. In a prospective study by Ad et al.,⁵⁹ 42 patients with heart failure and severely reduced LVEF were treated with concomitant surgical ablation. In those patients, an improved LVEF accompanied by an improved health-related quality of life status was present 12 months post-operatively. However, most of these patients received a concomitant surgical procedure such as CABG or valve repair. The lack of a control group makes it difficult, to distinguish between beneficial effects of the ablation or the surgical procedure itself. In line with those findings was a retrospective analysis by Pecha et al.⁶⁰ which investigated the safety and efficacy of concomitant surgical ablation in heart failure patients with severely reduced LVEF. In this study, patients with successful ablation had a significantly higher improvement of LVEF, compared to patients without successful ablation. Furthermore, New York Heart Association functional class was only improved in patients with restoration of sinus rhythm. Besides those small studies, there are no prospective randomized trials investigating concomitant surgical ablation in the setting of heart failure and its impact on survival. However, regarding this data, as well as data from large registries, showing that surgical ablation does not increase perioperative risk, AF ablation should be considered in heart failure patients with AF. Especially in patients with severely reduced LVEF, the AV synchrony, and atrial contraction plays an important role in terms of cardiac output and therefore should be addressed during concomitant surgery. In order to provide the best possible care and generate excellent post-operative outcome, surgical ablation in patients with an ejection fraction <30% should be referred to a high-volume cardiovascular institution with a team of rhythm and heart failure specialists (cardiology and cardiac surgery). Nevertheless, to validate the results from the above-mentioned retrospective studies, there is a need for larger prospective trials to confirm the safety and determine the effects of surgical AF ablation in the context of heart failure.

Conclusion

Concomitant surgical ablation is an established procedure in patients with AF undergoing cardiac surgery, with a clear recommendation in guidelines. An important part of surgical AF therapy is LAA closure. Here, it is essential to use adequate techniques such as surgical excision or AtriClip placement to ensure complete closure of the LAA without remaining stump or perfusion. Stand-alone surgical AF ablation and hybrid procedures have become an important adjunct to surgical armamentarium of AF treatment. Especially in patients with persistent- or long-standing persistent AF and patients with previously unsuccessful catheter ablation, surgical stand-alone ablation is a useful option. Little data are available on surgical ablation in patients with heart failure and reduced LVEF. However, in line with data from catheter ablation in patients with heart failure, some surgical AF ablation studies have shown beneficial effects, with improvement of LVEF and heart failure symptoms in those patients. Most importantly, as it has been established in interventional valve treatment, a heart-team approach (consisting of an electrophysiologist and cardiac surgeon) will be of increasing importance in the future treatment of AF patients.

Conflict of interest: none declared.

References