Introduction

The Cox-Maze III procedure described a lesion pattern that divided the atria into appropriate segments to eliminate the reentrant circuits responsible for maintaining atrial fibrillation (AF). The principles of segmentation, specifically pulmonary vein isolation (PVI) and posterior left atrial isolation, remain the cornerstone of all ablative interventions for AF ( Fig. 20.1 ).

Posterior view of open chest Cox-Maze III lesion pattern

blue: incision; aqua: cryothermal lesions; red: appendage excision; black dots: tricuspid or mitral valve annulus

Radiofrequency (RF) and cryothermal energy sources have replaced surgical incision, and transvenous catheters have supplanted sternotomy and cardiopulmonary bypass in treating AF. Endocardial catheter ablation, mainly PVI, and surgical Maze-like patterns have become mainstays of interventional treatment AF. Although catheter and minimally invasive surgical therapies have reduced the invasiveness of ablative AF therapies, independently they fail to meet the superior outcomes of the original cut-and-sew procedure. Epicardial surgical ablation in conjunction with endocardial catheter ablation, a hybrid ablation procedure, offers the potential advantage for robust lesion formation, left atrial debulking, and endocardial mapping/ablation of residual arrhythmia circuits. Hybrid AF procedures suggest improving procedural success over isolated epicardial surgical or endocardial catheter ablation procedure for AF, particularly in those with persistent or long-standing persistent AF, and those with significant structural heart disease. However, the ideal patient populations who may benefit from hybrid AF ablation and the ideal tools and techniques for a hybrid approach have yet to be determined. This chapter reviews the hybrid ablation procedure including methods of hybrid ablation, available tools, and reported efficacy of the procedure.

Catheter Approaches

Since the classical paper of Haissaguerre and coworkers, interventional therapies for atrial fibrillation have dominated numerically by endocardial catheter-based approaches. Techniques have evolved, with a movement away from focal elimination of pulmonary vein tachycardia foci to segmental PVI, and ultimately with the realization that the pulmonary vein antra were critical to the maintenance of atrial fibrillation, to wide area circumferential ablation. These approaches work well in paroxysmal atrial fibrillation , especially in the absence of important structural heart disease. But for patients with structural heart disease and those with persistent and long-standing persistent atrial fibrillation, endocardial lesion patterns have become more complex. Catheter-based approaches to these more complex patients have included creation of long linear ablation lesions, with or without an attempt to debulk the left atrium with a posterior wall isolation similar to the Cox maze procedure. More recently others have moved away from posterior wall isolation rather focusing on ablation targeted at low-voltage areas of the left atrium wherever they occur. Alternative approaches have included ablation of ganglionic plexi (GP) and attempts to identify critical driver activity in the atria, either by ablation of complex fractionated atrial electrograms, or through software signal analysis to identify critical rotor drivers.

Significant technical advances in catheter ablation technology have paralleled this lesion pattern strategy. High-density automated mapping systems guide lesion placement and map complex tachycardia circuits. Also, with the development of high flow externally irrigated catheters and force sensing technology, consistent catheter contact during lesion placement now makes much larger and more consistent lesions.

Even with the rapid progress made in catheter ablation technology and techniques, success rates remain disappointing to date, especially in the most complex patients who benefit the most from sinus rhythm. Studies with longer than 2-year follow-up report success rates after multiple catheter ablations between 57% and 63% for patients with persistent AF. Success rates are sure to increase as our understanding of the mechanisms of AF develops, along with continuing technological improvements. However, endocardial catheter ablation remains limited by the inadequacy of adequate linear lesion formation, which is particularly necessary to effectively treat complex patients with nonparoxysmal AF.

Surgical Approaches

Approaches to the surgical interventional management of AF emerged from two distinct schools of thought. Surgical approaches to the management of AF in patients undergoing concomitant cardiac surgery, or as a stand-alone procedure, drew from the belief that AF could be managed through atrial debulking and modification of the underlying substrate to minimize the chances of sustained atrial reentry circuits. However, open surgical procedures for AF management, although quite effective, were not broadly adopted due to their associated morbidity ( Table 20.1 ).

Alternative minimally invasive surgical procedures have been developed for patients not requiring concomitant cardiac surgery. Some minimally invasive approaches replicated the Maze procedure better than others, with some compromising procedural completeness for less invasive techniques. However, the guiding principles of a surgical therapy for AF remain the same: complete isolation of the four pulmonary veins, electrical isolation of the posterior left atrium, management of the left atrial appendage (LAA), and debulking ablation of the right atrium.

The advancement of minimally invasive approaches, with and without the use of cardiopulmonary bypass, has reduced the trauma of the surgical procedure, thereby expanding the number of patients experiencing this therapy. The minimally invasive Cox-Maze III/IV is perhaps most similar to the original Cox-Maze procedure. Performed with cardiopulmonary bypass, the minimally invasive Cox-Maze procedure creates a lesion pattern that closely mimics the original Maze III pattern ( Fig. 20.2 ) via a right minithoracotomy. https://www.youtube.com/watch?v=XHOR4RxO_4c

Posterior view of minimally invasive Cox-Maze IV lesion pattern as performed via right thoracotomy on cardiopulmonary bypass

black: incision; blue: radiofrequency lesions; aqua: cryothermal lesions; red: appendage excision; black dots: tricuspid or mitral valve annulus

Of 104 patients reported, at 3 years 92% of the patients were in sinus rhythm and 80% in sinus rhythm without antiarrhythmic drugs (AADs). Complications included only one stroke and no operative mortality. This minimally invasive Cox-Maze procedure eliminates the sternotomy and reduces the hospital stay to four days. However, the surgery requires cardiopulmonary bypass with or without cardiac arrest.

Alternative minimally invasive techniques do not require the use of cardiopulmonary bypass and use energy sources and devices that consistently create transmural lesions similar to those achieved with an incision. Epicardial off-pump PVI has become important since the1998 report by Haissaguerre, which identified the pulmonary veins as an important source of triggers to initiate AF. Saltman initially described a bilateral thoracoscopic approach using microwave energy to create a box lesion around the pulmonary veins. With ablation of the pulmonary veins, 62% patients failed to return to AF at 8 months. Pruitt et al. soon followed with a report of 50 patients who were treated using microwave energy via bilateral thoracoscopy to create a box lesion around the pulmonary veins, a right atrial lesion to the atrial appendage, and another from the superior to the inferior vena cava ( Fig. 20.3 ). These patients had a rapid return to normal activity and an average hospital stay of 3.7 days. However, late follow-up revealed failure of the procedure to electrically isolate the pulmonary veins, with more than 50% returning to AF. Devices using microwave energy have since been removed from the market.

Posterior view of radiofrequency box lesion around the pulmonary veins (dark blue) and lesions across right atrium and superior to inferior vena cava (light blue).

In the mid-2000s, the bipolar RF clamp was introduced ( Fig. 20.4 ), and in 2005, Wolf described an epicardial off-pump PVI procedure performed via thoracoscopy or minithoracotomy ( Fig. 20.5 ). The initial 27 patients demonstrated promising results, with 91% free from AF at 3-month follow-up. LAA removal contributed to a reduced stroke risk. This minimally invasive beating heart procedure opened the door for a less invasive surgical approach but avoided many of the lesions initially described by Cox, specifically lesions connecting to the annulus of the mitral and tricuspid valve.

Atricure Isolator bipolar clamp (A) and magnified view (B) of bipolar electrodes

Posterior view of Wolf mini -maze lesion pattern

blue: radiofrequency lesions; red: appendage excision

As the role of GP in the initiation and maintenance of AF became apparent, GP ablation emerged as a potential ancillary strategy for surgical AF ablation. Several studies evaluated the benefit of stand-alone epicardial PVI with GP ablation on the maintenance of sinus rhythm. Edgerton et al. reported outcomes in 52 patients with symptomatic paroxysmal AF. Patients underwent bilateral minithoracotomies with GPs identified by vagal response to high-frequency stimulation. Bipolar RF clamps were used to isolate the pulmonary vein antrums, and GP ablation was performed. LAA was excised or stapled in 88%. Patients were followed with 24-hour Holter or two-week monitoring at 6 and 12 months. Average hospital length of stay was 5 days. Three patients required postoperative pacemaker implantation. At 12-months follow-up, 80% of patients were in sinus rhythm. Edgerton et al. reported their outcomes based upon long-term follow-up with at least 24-hour electrocardiogram (ECG) measurement.

However, the majority of patients in these initial minimally invasive surgical studies had paroxysmal AF. Because endocardial catheter ablation can be highly effective for paroxysmal AF and is a much less invasive procedure, stand-alone epicardial ablation for paroxysmal AF has not gained widespread acceptance. Additionally, some literature suggests that catheter-based GP ablation may provide marginal benefit, but this remains controversial. Follow-up studies have demonstrated that PVI alone is insufficient for the treatment of persistent AF.

In those with persistent AF, adding linear ablation to PVI, specifically isolating the posterior left atrium, has proven to be beneficial. However, the creation of epicardial ablations deep enough, connect to the cytoskeleton of the heart, thus closing electrical gaps that may persist near the mitral and tricuspid valve, remains difficult, if not impossible, with existing energy sources on the beating heart ( Table 20.2 ). Edgerton et al. developed a beating heart procedure using minimally invasive techniques known as the Dallas lesion set ( Fig. 20.6 ).

Posterior view of the Dallas ablation lesion set

blue: radiofrequency lesions; red: appendage excision

This approach connected epicardial ablations to the left fibrous trigone at the aortic valve root. In 30 patients (10 persistent, 20 long-standing persistent), Edgerton et al. described the totally thoracoscopic isolation of bilateral pulmonary vein antrums using a bipolar RF clamp. Additionally, they interrogated and ablated the GP, excised the LAA, and added a connecting lesion between the pulmonary veins at the left atrial (LA) roof, which was also extended to the fibrous aortic valve annulus and to the excised LAA base. Pacing techniques verified conduction block across the roof and anterior trigone lines. Patients were followed for 6 months with ECG and 14- to 21-day auto-triggered monitors. Three (10%) patients required pacemakers. At 6 months, overall success rate was 58% off AADs, and 80% with or without AADs, as assessed by long-term (14- to 21-day) event monitoring.

Weimer et al. reported a larger study of 89 patients with paroxysmal (35%), persistent (24%), or long-standing persistent (42%) AF undergoing the Dallas epicardial lesion set. Mean hospital length of stay was 8 days. One patient required conversion to extracorporeal circulation. Freedom from AF and AAD therapy was 71%, 82%, and 90% at 6, 12, and 24 months, respectively, with no difference in those with paroxysmal or persistent AF. However, 5% of patients required subsequent catheter ablation for recurrent AF or atrial flutter.

The minimally invasive, beating heart approach to AF treatment enables real-time interrogation of the surgical ablations, because the heart remains electrically active. It is therefore important to interrogate the integrity of the ablation lines to confirm transmurality and to eliminate gaps. There is ongoing dialogue concerning the validity of lesion interrogation acutely versus delayed lesion interrogation to allow any acute and temporally nonconductive injuries to recover. The Five-box thoracoscopic maze ( Fig. 20.7 ) procedure described by Sirak critically interrogates the ablation lines to confirm the epicardial electrical isolation of five segments of the left and right atrium. Patients fare well with the meticulous thoracoscopic dissection and lesion placement, with an average hospital stay of 3.9 days and 92% freedom from tachyarrhythmias and AADs at 24 months by 7-day event monitoring. Two of the 179 patients required conversion to sternotomy, and two patients had catheter ablation of the cavotricuspid isthmus at 13 months and remained in normal rhythm.

Posterior view of 5-box ablation lesion pattern

blue: radiofrequency lesions [solid in foreground/dotted in background]; red: appendage excision

Nasso et al. described the use of an alternative surgical technique for PVI through only a right minithoracotomy. In 104 patients, a linear vacuum-assisted unipolar RF ablation catheter was looped around the pulmonary veins by way of the transverse and oblique pericardial sinuses using a magnet tipped introducer. Patients were followed with 24-hour Holter monitoring. Periprocedural complications included one case of intraoperative LA rupture requiring sternotomy for repair, one case of hemorrhagic stroke four days postop, and one transient ischemic attack in the early postoperative period. At an average 17 months follow-up, 89% were free of AF (96% of paroxysmal AF and 80% of persistent AF). Whereas using only a right thoracic incision provides an advantage for Nasso’s approach, the LAA is not addressed.

To evaluate the differences in catheter and surgical ablation for AF, Boersma et al. compared the efficacy and safety of catheter ablation and minimally invasive surgical ablation in 124 patients with drug-refractory AF, left atrial dilatation (>4 cm), and hypertension in the FAST study. AF was paroxysmal (67%), persistent (33%), or long-standing persistent (8%). The surgical ablation pattern was consistent with the Dallas lesion set as described by Edgerton. Catheter ablation included wide-area linear antrum ablation with PV isolation guided by circular mapping catheter. Additional lines were made at the discretion of the electrophysiologist. Patients were followed with ECG and 7-day Holter monitoring at 6 and 12 months. Median length of stay was 5.5 days versus 2 days for surgical or catheter ablation, respectively. In the surgical group, complications included one patient requiring conversion to median sternotomy, one patient requiring pacemaker implantation, six patients with pneumothorax, one with hemothorax, one with stroke, one tamponade, and one rib fracture. In the catheter group, complications included one transient ischemic attack and four groin hematomas. However, at 12 months, freedom from AF longer than 30 seconds in the absence of AADs was 66% in the surgical group versus 37% in the catheter group (P = .0022).