Past experience with both the catheter and surgical ablation of atrial fibrillation (AF) has provided several observations that should be considered when designing an off-pump hybrid procedure:
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The Maze procedure is the most effective intervention for AF.
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The Maze procedure is too invasive to be feasible as first-line therapy for AF.
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A Maze procedure cannot be performed by thoracoscopic surgery alone.
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A Maze procedure cannot be performed by catheter ablation alone.
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Interventional electrophysiologists (EPs) are excellent at closing the “gaps” of failed surgical lesions.
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Interventional EPs are excellent at ablating focal areas of the atrium.
These observations suggest that if the ultimate goal of a hybrid procedure is to attain the best possible outcomes by the least invasive technique, the ideal hybrid procedure would be one that combines surgical lesions and catheter lesions to create a complete biatrial Maze procedure. Thus, although current hybrid procedures are more successful for long-standing persistent AF (LSpAF) than catheter ablation, , they cannot attain the success of the open-heart Maze procedures because none of current hybrid procedures reproduce all of the lesions of a complete biatrial Maze procedure.
The success rates of hybrid procedures for the treatment of AF fall between those for the open surgical Maze-III and Maze-IV procedures and those for catheter ablation (see Chapter 39 , Fig. 39.1 ). The major advantage of hybrid procedures is that virtually all of the gaps in lesions that remain after the initial epicardial thoracoscopic lesions occur at the subendocardial level. This is because of the difficulty in creating complete and permanent transmural lesions with unipolar devices applied only to the epicardium in off-pump patients (see Chapter 20 , Fig. 20.6 ). Fortunately, the residual lesion gaps in the subendocardium can be closed with a high degree of success during the follow-up endocardial catheter ablation portion of most hybrid procedures. Therefore, the primary reason that hybrid procedures are less successful than open on-pump surgical Maze procedures is that several critical lesions of the on-pump Maze procedures are routinely not included as a part of off-pump hybrid procedures. Thus, even when the thoracoscopic epicardial lesions are combined with the endocardial catheter lesions, they still do not create the complete pattern of a biatrial Maze procedure.
Following the growing popularity and acceptance of off-pump hybrid procedures, it occurred to us that it should be possible to create all of the lesions of a biatrial Maze procedure with the combination of epicardial thoracoscopic surgery and endocardial catheter ablation in which case the results of such an off-pump “hybrid Maze procedure” would be identical to those of an on-pump surgical biatrial Maze procedure. The conduct and technique of such an off-pump complete hybrid Maze procedure is described in this chapter.
Technical Objectives in Current Non-Maze Hybrid Procedures
Initial Thoracoscopic Surgery
There is a fundamental difference in the goal of a surgical procedure when it is performed as sole therapy for AF and a surgical procedure when it is performed as the first step in a hybrid procedure for AF. When surgery is used as sole therapy for AF and performed on cardiopulmonary bypass, it is essential to create all of the lesions of a Maze procedure because it is the only chance the surgeon will have to cure the arrhythmia. However, when thoracoscopic surgery is performed as the initial step in a hybrid procedure, it is not only impossible but also unnecessary to create a complete maze pattern because it will always be followed by an obligatory catheter ablation. The objective of the initial thoracoscopic surgery in a hybrid Maze procedure is to create as many of the linear lesions of the Maze procedure as possible to limit the complexity of the subsequent catheter lesions required to ablate the AF.
Follow-Up Catheter Ablation
A primary objective of the catheter ablation in all hybrid procedures is to “touch up” any gaps in the thoracoscopic lesions. Because the follow-up catheter ablation is performed endocardially, it is usually simple to close any gaps in the thoracoscopic lesions as mentioned earlier. It seems more logical to us to perform staged hybrid procedures rather than joint procedures because the former allow the thoracoscopic lesions to heal and the gaps to declare themselves before the follow-up catheter ablation. However, experienced teams who have performed both staged and joint hybrid procedures have found no significant differences in the results. , This observation speaks well for the ability to create permanent transmural lesions by combining epicardial surgical and endocardial catheter lesions in one setting. However, as currently practiced, neither staged nor joint hybrid procedures overcome the problem of misplaced and/or arbitrarily deleted lesions in critical areas of the atria.
After the initial thoracoscopic lesions have been created, three options remain for the catheter ablation portion of a hybrid procedure. The first option is to perform catheter mapping to localize and ablate extrapulmonary vein sites such as complex fragmented atrial electrogram spots, focal “rotors,” and so on or to map-guide the placement of additional linear lesions in the atrium. An example of this approach is described in Chapter 34 . This effort to “tailor” the treatment of each individual patient results in variations of the final lesion pattern of the hybrid procedure from one patient to another. The desire to tailor AF therapy based on the patient’s specific intraprocedure maps is a laudable goal, but it disregards the futility of previous efforts to map-guide both surgical and catheter procedures for AF. Optimal long-term results are difficult to attain with map-guided interventional procedures primarily because of the changing nature of AF drivers with time as discussed in Chapter 6 (see Fig. 6.12) and Chapter 12 . The second option for the catheter ablation portion of a hybrid procedure is to create the same predetermined hybrid lesion pattern in all patients. Examples of this approach are described in Chapters 35 and 36 . , The third option is to create additional lesions during the catheter ablation that result in the final combined lesion set to be that of a Maze procedure. However, the ability to complete a biatrial Maze procedure during the follow-up catheter ablation depends on the lesion pattern that was created during the initial thoracoscopic surgery.
Hybrid Maze Procedure
As discussed in Chapter 19 , use of the term “Maze procedure” as a generic term for anything done surgically to the atrium to treat AF can be misleading. Unfortunately, this practice has been especially common during the development of hybrid procedures over the past decade. The catchy phrase “totally thoracoscopic Maze procedure” has made it even easier to be misled into thinking that actual Maze procedures are being performed when that is not the case. For example, articles specifically including the term “Maze procedure” in their titles , lead one to believe that a technique for performing a complete Maze procedure had already been described. However, none of the patients reported in these articles received a Maze procedure. In fact, most of them had no right atrial lesions at all, and a significant number had no left atrial appendage (LAA) closure, both of which are critical elements of a Maze procedure.
The Maze procedure was designed to interrupt all of the potential macro-reentrant drivers that sustain AF while leaving the atria capable of being activated by a sinus-generated impulse after surgery. Although the macro-reentrant drivers may be stable or fleeting in nature, the regions in both atria that are capable of sustaining them have been well-defined ( Fig. 37.1 ). This has allowed the concept of the Maze procedure to remain the same for the Maze-I, Maze-II, Maze-III (both the cut-and-sew and cryosurgical techniques), and Maze-IV iterations as well as for the off-pump hybrid Maze procedure described later.
Potential locations of atrial drivers in non-paroxysmal atrial fibrillation (AF). The red circles represent the actual macro-reentrant circuits that have been documented during AF. Note that they can and do occur in both the right atrium (RA) and left atrium. The long reentrant circuit in the RA, which may travel either anterior or posterior to the superior vena cava orifice, and the reentrant circuit around the tricuspid valve are the ones responsible for typical atrial flutter. The long circuits crossing the inferior left atrial isthmus between the inferior pulmonary veins and the mitral annulus, one of which is passing through the coronary sinus, are the pathways of postintervention atypical left atrial flutter, also known as perimitral flutter.
Thoracoscopic Surgery via the Right Chest
Right Atrial Lesions
As discussed in Chapter 13 , the possible locations of macro-reentrant drivers in the right atrium (RA) have been identified, and they are present in up to 30% of patients with AF ( Fig. 37.2 ). Therefore, the RA should not be ignored in any surgical procedure designed to ablate AF.
Right atrial drivers of atrial fibrillation (AF). The red circles represent the locations of the macro-reentrant circuits that can occur in the right atrium and serve as drivers of AF.
The first right atrial lesion to perform is the superior vena cava (SVC) lesion, which precludes the development of macro-reentry around the orifice of the SVC and interrupts one of the three macro-reentrant circuits that can cause classic atrial flutter ( Fig. 37.3 ). As opposed to when the on-pump Maze-III or Maze-IV procedure is performed, the SVC lesion is specifically not extended into the inferior vena cava (IVC) in the off-pump hybrid Maze procedure . The IVC lesion is unnecessary because a CTI lesion will be performed later during the follow-up catheter ablation procedure. However, following the creation of the SVC lesion, there are still several potential right atrial sites where macro-reentrant drivers can form ( Fig. 37.4 ).
Superior vena cava (SVC) lesion. The SVC lesion (blue line) extends from the SVC two-thirds of the way down to the inferior vena cava (IVC), but it is not extended into the IVC . It is positioned parallel and immediately anterior to the edge of the crista terminalis, where the right atrial wall is thin.
Potential right atrial drivers after the superior vena cava (SVC) lesion completed. The SVC lesion prevents macro-reentry around the orifice of the SVC, and it also interrupts the macro-reentrant circuit passing posterior to the SVC orifice that is one of the three right atrial circuits than can drive atrial flutter.
In an off-pump complete surgical Maze procedure, the distal end of the “T” lesion terminates at the tricuspid valve annulus (see Chapter 13 , Figs. 13.8 and 13.13 ). However, the “T” lesion cannot be extended to the tricuspid annulus thoracoscopically. Instead, when the right atrioventricular groove is reached, the lesion is curved up along the anterior edge of the RA and extended to the tip of the right atrial appendage (RAA; Fig. 37.5 ). This lesion is a combination of the proximal free-wall portion of the “T” lesion and the RAA lesion described in Chapter 13 , and it interrupts another of the three potential drivers of atrial flutter and prevents macro-reentry around the base of the RAA.
Modified “T” lesion combined with right atrial appendage (RAA) lesion. The “T” lesion of an open on-pump Maze procedure is modified in the off-pump hybrid Maze procedure in which it purposely is not extended to the tricuspid valve annulus. Instead, when it reaches the anterior edge of the right atrium, the lesion is curved upward and is extended to the tip of the RAA. The IVC lesion in the open Maze procedure is created to prevent reentry around the orifice of the IVC. However, a CTI lesion performed during the follow-up catheter ablation in a hybrid procedure prevents reentry around the IVC orifice, so the surgical IVC lesion is unnecessary.
After these RA lesions have been created, the only sites in the RA where macro-reentry can occur are around the tricuspid valve annulus and around the orifice of the IVC ( Fig. 37.6 ). Fortunately, both of these potential RA drivers use the cavotricuspid isthmus (CTI) and can easily be blocked by the creation of a CTI lesion during the follow-up catheter ablation (see later).
Potential right atrial drivers after completion of all thorascopic right atrial lesions. After completion of the thoracoscopic right atrial lesions, the only remaining potential right atrial reentrant drivers are one around the tricuspid annulus and one around the inferior vena cava orifice. Both of these potential drivers use the cavotricuspid isthmus (CTI) and can be easily interrupted during the follow-up catheter ablation by performing a CTI lesion.
All of the thoracoscopic right atrial lesions in the hybrid Maze procedure are created using a dual-electrode, unipolar Coolrail device (AtriCure, Inc.) ( Fig. 37.7 , right inset ). As mentioned, because these lesions are created epicardially, they are most likely to fail endocardially, so any gaps are quite amenable to being closed during the follow-up endocardial catheter ablation.
Complete right atrial thoracoscopic lesion set. Operative photo of the thoracoscopic right atrial lesions of the hybrid Maze procedure (dashed white lines). Left inset, Diagrammatic sketch of the corresponding right atrial lesions. Right inset, Photo of the dual-electrode, unipolar Coolrail device used to create the right atrial lesions epicardially. IVC, Inferior vena cava; RAA, right Atrial appendage; SVC, superior vena cava.
Left Atrial Lesions
Waterston’s groove is developed to expose the medial portion of the posterior left atrial septum ( Fig. 37.8 ). At the upper end of Waterston’s groove, dissection is continued between the top of the left atrium (LA) and the right pulmonary artery to open the transverse sinus that extends to the posterior pericardial space ( Fig. 37.9 ). At the lower end of Waterston’s groove, the thin pericardial reflection off the posterior wall of the IVC is divided to expose the oblique sinus ( Fig. 37.10 ). Opening both the transverse sinus above and the oblique sinus below allows a guiding device to be passed around the posterior LA medial to the orifices of the right pulmonary veins (PVs; Fig. 37.11 ). One arm of a bipolar radiofrequency (RF) clamp is then placed around the posterior LA using a rubber drain guide, and the right PVs are isolated ( Fig. 37.12 ).
