Both mitral regurgitation and mitral stenosis are associated with left atrial pressure and volume overload, and both cause significant left atrial dilatation. Therefore, these patients are more prone to develop AF as the mitral valve disease progresses. For many years, if AF and mitral valve disease were clinically well tolerated, surgery was deferred until symptoms developed. In these patients, it was difficult to discern whether the dyspnea and fatigue were related to the AF or to the underlying mitral valve disease. Patients were often prescribed long-term diuretics and anticoagulants for AF until surgery was finally considered. In the interval, left ventricular dysfunction, pulmonary hypertension, and secondary (functional) tricuspid regurgitation associated with significant right atrial dilatation frequently developed. Preoperative sinus node dysfunction was not tested because the patient was in continuous AF but after surgery, sinus node dysfunction was often evident, requiring a permanent pacemaker implantation. MV surgery, with or without AF ablation, was considered high risk, and cardiac dysfunction may already have become irreversible. In a “Catch-22” mind-set, cardiologists were reluctant to refer patients for high-risk surgery, and the cycle continued with late referrals. Today, decades later, with more routine MV repair with concomitant AF surgery, the pattern has been broken, and asymptomatic patients with or without AF are commonly referred for surgery before left ventricular dysfunction and right heart changes occur. Many patients now undergo surgery before they have developed AF, but practices vary considerably across the world and depend on the patient’s comorbidities and age.

In a study of Medicare-age patients, we found the prevalence of AF before cardiac surgery to be higher than previously reported. In our study, up to 62% of patients in some subsets of MV surgery were found to have preoperative AF, and it varied by procedure between 45% and 62% of all MV operations ( Fig. 23.1 ). This study may be the most accurate accounting of preoperative AF because it investigated Medicare records for 3 years in advance of surgery. The primary study evaluating this issue that was based on the STS database showed a lower occurrence of preoperative AF in MV operations (34.4%; 30,011 of 87,214 patients). However, the STS database includes younger patients who are at a lower risk for AF, and it does not always capture paroxysmal AF (PAF) or AF that was not present on preoperative admission. However, all database studies show that the prevalence of preoperative AF is higher in MV operations than in non-MV operations ( Table 23.2 ).

Prevalence of preoperative atrial fibrillation (AF) in patients undergoing different cardiac procedures using a Medicare database. These numbers reflect an older population than Society of Thoracic Surgeons database reports and therefore, a higher prevalence of preoperative AF than previously reported. Preoperative AF was twice as common in mitral procedures as in non-mitral operations. AVR, Aortic valve replacement; CAB, coronary artery bypass; MV, mitral valve; MVR, mitral valve replacement; MVrep, mitral valve repair.

(Reproduced from McCarthy PM, Davidson CJ, Kruse J, et al. Prevalence of atrial fibrillation before cardiac surgery and factors associated with concomitant ablation. J Thorac Cardiovasc Surg . 2020;159(6):2245–2253.)

Left atrial pressure, volume, and enlargement are generally much lower in patients undergoing coronary artery bypass grafting (CABG) and aortic valve replacement (AVR) than in mitral valve (MV) patients. The cause-and-effect relationship of AF to coronary artery disease or aortic valve disease may not be as apparent in non-MV structural heart disease except in patients with heart failure and reduced left ventricular function who often have a dilated left atrium (LA). Also, patients with coronary artery disease and aortic valve stenosis may be older, which is another risk factor for AF. In the Medicare study mentioned earlier, using 3 years of medical record searches before surgery, the prevalence of preoperative AF was almost twice as high as it was in the STS studies ( Fig 23.1 ). CABG patients had a 20.1% prevalence of preoperative AF and AVR patients had a 33.4% prevalence in the Medicare study. In the STS database, preoperative AF was recorded in 10.3% of 361,138 patients undergoing CABG and in 17.8% of 87,426 patients undergoing AVR. These reports showed the prevalence of preoperative AF recorded in the STS database to be approximately one-half of the prevalence recorded in the older Medicare patients.

Unfortunately, any type of concomitant surgical ablation for AF, including the least complex pulmonary vein isolation, was not common. In Medicare patients, surgical ablation was performed in only 22.2% overall and was highest for MV surgery patients (37.6%) compared with non-MV surgery patients (16.2%) ( Fig. 23.2 ). In comparison, MV surgery was performed in 25% of the STS population with AF ( n = 86,941) and in these patients AF was ablated in 68.4%. In 34,600 CABG patients with preoperative AF in the STS database, concomitant AF ablation was performed in 30.5%. For AVR patients, concomitant ablation was performed in 33.1% of 15,596 patients.

Overall, concomitant surgical atrial fibrillation (AF) ablation was performed in 22.2% of patients with preoperative AF. Patients with mitral valve surgery had the highest AF treatment (37.6%) compared with nonmitral valve surgery (16.2%). MV, Mitral valve.

(Reproduced from McCarthy PM, Davidson CJ, Kruse J, et al. Prevalence of atrial fibrillation before cardiac surgery and factors associated with concomitant ablation. J Thorac Cardiovasc Surg . 2020;159(6):2245–2253.)

The STS published guidelines supporting concomitant surgical AF ablation in 2017. Following a study of concomitant surgical ablation in Florida and Maryland from 2016 to 2017, there was an increase in surgical ablation, but it was only from 2.1% to 17.4% ( P <.001). Concomitant surgical ablation for mitral surgery, and non-mitral surgery, now have Class I indications in the 2023 STS guidelines, and the benefits of surgical ablation are made clear. Our hope is that with the new guidelines, wider education of surgeons and cardiologists regarding the data supporting safety and effectiveness, and publications such as this textbook, concomitant AF ablation will increase significantly.

There have been multiple studies over the past several years demonstrating the safety of adding a Cox-Maze procedure to ablate AF concomitantly in patients undergoing coronary artery bypass graft (CABG) and/or valve surgery. Ad et al. first showed in 2012 that adding a Cox-Maze-III procedure to isolated CABG or AVR procedures did not increase major morbidity or operative mortality rates. Al-Atassi et al. confirmed in 2017 that “patients undergoing isolated CABG, AVR, or combined CABG and AVR with a history of AF can undergo concomitant AF ablation without increased surgical risk.” These were particularly interesting studies because the LA had to be opened to perform the Cox-Maze-III procedure, which obviously is not normally required for either CABG or AVR. Damiano’s group in St. Louis first showed in 2013 that adding a Cox-Maze-IV procedure to MV surgery “ did not significantly affect the procedural mortality.”

A propensity score-matched STS study by Badhwar et al. in 2017 demonstrated that concomitant surgical ablation by a variety of ablation techniques resulted in an actual reduction in 30-day mortality rate (by 8%) and perioperative stroke rate (by 16%). In addition, a study by the Nationwide Inpatient Database also showed a reduction in operative mortality rate when concomitant AF was surgically ablated (3.6% treated vs 4.2% untreated; P <.001) and stroke (2.0% vs. 2.8%; P <.001). Both of the latter were large studies of approximately 50,000 patients each. The STS CABG and AVR studies did not show any 30-day differences except for an increase in postoperative pacemaker requirements in the AF ablated AVR patients (6.8% vs 5.0; P <.001). Finally, these studies provided a major stimulus for the 2017 STS Guideline Committee to grant Class 1 recommendations for the concomitant surgical ablation of AF during MV surgery, CABG, AVR, and CABG plus AVR.

The Cox-Maze procedure gradually evolved from “cut and sew” in the 1990s to the use of cryoablation, unipolar radiofrequency (RF) ablation, and eventually bipolar RF ablation beginning about 2000. With the advent of these new ablation tools, more surgeons adopted concomitant surgical ablation of AF, so more studies were performed to demonstrate the reduction in AF after surgical ablation (see Table 23.1 ). By current standards, the trials were not robust but nevertheless, using a variety of technologies and lesion sets and with variable types and duration of AF monitoring after the procedure, all of the initial RCTs demonstrated a higher freedom from AF in the surgical ablation groups. Also, there were no increased perioperative complications in these smaller series, until the cardiothoracic surgery network (CTS Net) trial published in 2015 showed a much higher requirement for new pacemakers in ablated patients than in nonablated patients (21.5% vs. 8.1% per 100 patient years; P =.01) (see Chapter 21 ). It is well recognized and universally accepted that surgical ablation effectively treats patients with AF, but it took more time and larger studies with longer follow-up periods to demonstrate a clinical benefit. Also, there were various technologies, lesion sets, and patient populations used in the RCTs, which confounded the ability to judge clinical benefits.

An issue of Seminars in Thoracic and Cardiovascular Surgery in 2000 convened a group of large-volume “cut-and-sew” Maze procedure patients reported from many centers, with a mix of concomitant and isolated Maze procedures. The late stroke rate was very low, and for instance, at Washington University in St. Louis, the freedom from stroke after the concomitant ablation of AF with a Cox-Maze-III procedure was 99.6% at 11.5 years ( Fig. 23.4 ). Left atrial appendage occlusion (LAAO), or excision or exclusion, is an integral part of all iterations of the Maze procedure. Subsequent database studies showed a reduction in late stroke for patients with LAAO and a history of AF compared with those with no treatment.

Patients in atrial fibrillation (AF) needing surgical ablation who presented to Washington University in St. Louis had known risks for a future stroke based on what is now called the CHA ₂ DS ₂ -VASc scores. The solid black line represents the 12-year risk of a thromboembolic stroke in those patients with a score greater than 3 who were not anticoagulated, and the dashed black line shows the stroke risk after anticoagulating those patients with warfarin for 12 years. The solid blue line represents the 12-year risk of a thromboembolic stroke in patients with a score greater than 2 who were not anticoagulated, and the dashed blue line shows the stroke risk after anticoagulating those patients with warfarin for 12 years. The solid gray line represents the 12-year risk of a thromboembolic stroke in patients with a score greater than 1 who were not anticoagulated. This curve is essentially the same for anticoagulated patients if hemorrhagic strokes are included. By observing these known risks and calculating the number of strokes to be projected over 12 years, the entire group of patients would be projected to have a total of 68 thromboembolic strokes over the next 12 years if they were not treated with a Maze procedure. The lower red line is the actual number of thromboembolic strokes (one mild stroke) that occurred in this entire group of patients over the 12 years after a Cox-Maze-III procedure for AF.

(Modified from Cox JL, Ad N, Palazzo T. Impact of the Maze procedure on the stroke rate in patients with atrial fibrillation. J Thorac Cardiovasc Surg . 1999;118(5):833–840.)

The definitive study proving that LAAO reduced the incidence of stroke in patients with preoperative AF was the LAAOS III trial. It showed that LAAO resulted in a 33% reduction in stroke over a mean follow-up period of 3.8 years in a study population of 2379 patients ( Fig. 23.5 ). More recently, a study by Mehaffey et al. has shown that ablation and LAAO are the ideal treatment for patients with concomitant AF in terms of stroke risk benefit with the highest survival rates identified in patients with both treatments ( Fig. 23.6 ).

Results of the left atrial appendage occlusion study (LAAOS) III trial show a lower risk of stroke or systemic embolism in patients who had cardiac surgery treated with ongoing antithrombic therapy and left atrial appendage closure compared to those without it. CI, Confidence interval; HR, hazard ratio.

(Reproduced from Whitlock RP, Belley-Cote EP, Paparella D, et al. Left atrial appendage occlusion during cardiac surgery to prevent stroke. N Eng J Med. 2021;384(22):2081–2091.)

Results of a study evaluating surgical ablation (SA) and left atrial appendage occlusion (LAAO) showed the highest survival compared with LAAO alone or no atrial fibrillation (AF) treatment. The curves steadily diverge over 3 years of follow-up. CI, Confidence interval.

(Reproduced from Mehaffey JH, Hayanga JWA, Wei L, Mascio C, Rankin JS, Badhwar V. Surgical ablation of atrial fibrillation is associated with improved survival compared with appendage obliteration alone: an analysis of 100,000 Medicare beneficiaries. J Thorac Cardiovasc Surg. 2024;168(1):104–116.)