Pathophysiology and Impact of Atrial Fibrillation
Atrial fibrillation (AF) is common in patients requiring aortic valve surgery. Although age is a risk factor for both AF and aortic valve disease, , there is a direct relationship between the severity of aortic stenosis (AS) and the presence of AF, with up to one-third of AS patients having concomitant AF. , It is thought that the increased incidence of AF in patients with AS is due to increased left ventricular pressure overload that can result in a cascade of left ventricular diastolic dysfunction leading to left atrial enlargement that in turn promotes the development of AF. Laenens et al. reported in a prospective multicenter registry that patients with both AS and AF had a worse 10-year survival rate than AS patients in sinus rhythm. However, in patients with no echocardiography markers of left ventricular diastolic dysfunction, AF was not an independent predictor of death. Kubala and colleagues reported the results of a retrospective single-center study of 1838 patients who underwent aortic valve replacement for severe AS. In those who underwent surgical or transcatheter aortic valve replacement, the 5-year survival rate was 86% in patients who were in sinus rhythm compared with only 77% in patients who were in AF. Furthermore, the 2023 Society of Thoracic Surgeons guidelines gave a Class I recommendation for concomitant surgical AF ablation in patients undergoing non–mitral valve surgery. Therefore, all cardiac surgeons should be facile in concomitant surgical AF ablation and left atrial appendage occlusion (LAAO) and excision.
Several studies have demonstrated that there is a relationship between AF and thoracic aortic aneurysms, though the pathologic relationship is unclear. A 2020 study of 1000 consecutive patients with AF showed by cross-section chest computed tomography scanning that 20% had previously undetected thoracic aortic dilatation. The authors suggested that a surveillance strategy for thoracic aortic disease should be considered in all patients with AF, particularly in those with other risk factors for aortic disease. A 2021 Danish study of 14,989 patients identified AF as an independent risk factor for ascending and descending thoracic aortic aneurysms, and the presence of these two localized aneurysms increased the incidence of aortic arch aneurysms by a factor of 6–8.
Choice of Atrial Fibrillation Ablation Procedure in Patients Undergoing Aortic Valve Surgery and/or Thoracic Aneurysm Surgery
In patients undergoing surgery for aortic valve disease and/or thoracic aortic aneurysms who have concomitant AF, the specific AF ablation technique of choice depends primarily on whether the patient has paroxysmal AF (PAF) or nonparoxysmal AF (non-PAF). The choice of surgical ablation technique in these patients is further affected by the fact that the Maze procedure requires opening the left atrium (LA), which is not necessary in either aortic valve or thoracic aneurysm surgery. Fortunately, other surgical ablation approaches can yield satisfactory results without opening the LA, though they are not as successful as Maze procedures. The optimal treatment objectives in concomitant PAF and non-PAF are discussed in detail in Chapter 25 .
Paroxysmal Atrial Fibrillation and Aortic Valve Surgery
The objective of treating PAF in patients requiring aortic valve surgery is to isolate as many atrial triggers as possible to decrease the likelihood of AF episodes being induced. Because 70% of the triggers in patients with concomitant PAF are located in, around, and between the pulmonary veins (PVs) ( Fig. 29.1 ), a box lesion around all four PVs and the intervening left atrial posterior wall will isolate these atrial triggers, thereby reducing the likelihood of future AF episodes by 70%. In addition, approximately 10% of concomitant PAF triggers are located in the left atrial appendage (LAA), so if it is either amputated or electrically isolated with an epicardial LAA clip, the overall result will be isolation of 80% of the atrial triggers. Thus in patients with AS and/or thoracic aneurysm with concomitant PAF, the surgical options are as follows: (1) ignore the concomitant AF, resulting in the same level of AF as the patient experienced preoperatively; (2) amputate or clip the LAA, resulting in 10% less AF postoperatively; (3) perform a box lesion and apply an LAA clip, resulting in 80% less AF postoperatively; or (4) open the LA and perform a Maze procedure, resulting in over 90% less AF postoperatively.
Locations of atrial triggers in concomitant paroxysmal atrial fibrillation (PAF). Atrial triggers are responsible for the induction of atrial fibrillation (AF) and therefore for each of the individual recurrent AF episodes in patients with PAF. The objective of surgical intervention for PAF in patients with aortic valve disease and/or thoracic aortic aneurysms is the isolation of as many of these AF triggers as possible in hopes of decreasing the likelihood of another AF episode occurring. Seventy percent of these AF triggers reside in or near the pulmonary veins (PVs) and the posterior left atrial wall between the two pairs of PVs. Approximately 10% of them are in the left atrial appendage (LAA), and the other 20% are widely scattered throughout the two atria.
The creation of a box lesion without opening the LA has traditionally been performed by external isolation of the PVs with a bipolar radiofrequency (RF) clamp and then creating roof and floor lesions with a dual-electrode unipolar Coolrail device ( Fig. 29.2 ). However, the creation of a box lesion has recently become much easier and promises to be more effective using an Encompass clamp (Atricure, Inc.) ( Fig. 29.3 ). The Encompass clamp is a bipolar RF clamp designed so that one arm can be placed above the superior PVs and one arm below the inferior PVs to create a complete box lesion in one step ( Fig. 29.4 ). In patients with PAF who require aortic valve and/or thoracic aneurysm surgery, we prefer to open the LA and perform a CryoMaze-III procedure when possible, but we consider performing a box lesion plus LAAO to be a satisfactory alternative.
Box lesion plus left atrial appendage occlusion for concomitant paroxysmal atrial fibrillation (PAF). A box lesion encompassing all four pulmonary veins (PVs) and the intervening posterior left atrial wall isolates 70% of the atrial fibrillation (AF) triggers, and an epicardial left atrial appendage (LAA) clip isolates another 10%. Therefore, the creation of a box lesion plus clipping the LAA results in 80% less PAF afterward. One way that a box lesion can be created is by isolating the PVs in pairs and then creating roof and floor lines with a Coolrail device (inset) to complete the box lesion as is done in the Maze-IV procedure. The PVs are isolated using bipolar radiofreqency (RF) clamps while the roof and floor lesions are created using less reliable unipolar RF devices. If successful, this technique isolates the 20% of AF triggers in the posterior left atrial wall plus the 50% of AF triggers in and around the PVs themselves. It is assumed that this latter 50% of PV triggers are distributed roughly equally between the left and right pairs of PVs.
Bipolar radiofrequency (RF) Encompass clamp. This clamp is designed to encompass the entire “box” in the left atrium (LA) that includes all four pulmonary veins and the intervening posterior wall of the LA. Therefore, in patients with concomitant atrial fibrillation (AF), this clamp should isolate 70% of all the AF triggers in the LA. Because this is a bipolar RF clamp, it eliminates the problem of having to create the roof and floor lines of the box lesion with unipolar RF devices that are known to be less reliable than bipolar RF devices.
