Atrial Fibrillation

• ◆
  

  Atrial fibrillation (AF) is a supraventricular tachyarrhythmia that is projected to affect 12 million patients in the United States by 2050; prevalence is increased in older people and in patients with hypertension, heart failure, coronary artery disease (CAD), valvular heart disease, obesity, diabetes mellitus, and chronic kidney disease (CKD). AF is present in up to 50% of patients undergoing mitral valve surgery and also in 1% to 6% of patients presenting for coronary artery bypass graft (CABG) surgery.

  
  
• ◆
  

  Hemodynamic consequences of AF result from uncoordinated atrial contraction, suboptimal ventricular filling, and sympathetic activation. The mechanisms of AF vary among affected individuals and so, too, do clinical presentations. In patients with mitral stenosis, hypertension, hypertrophic cardiomyopathy (HCM), or restrictive cardiomyopathy, diastolic ventricular filling is already impaired, and loss of atrial contraction caused by concomitant AF may markedly decrease cardiac output. AF is an independent risk factor for cardiac mortality and morbidity and is associated with reduced early and long-term survival and a fivefold increased risk of stroke.

  
  
• ◆
  

  Although left atrial enlargement, longer duration of AF, and advanced age have been associated with reduced success, they do not contraindicate surgical ablation. The 2012 Expert Consensus Statement on Catheter and Surgical Ablation of Atrial Fibrillation has recommended consideration of AF ablation in all patients with symptomatic AF undergoing other cardiac surgery (Class IIa, level of evidence C). The guidelines also suggest consideration of stand-alone AF surgery for symptomatic AF patients who prefer a surgical approach, who have failed one or more attempts at catheter ablation, or who are not candidates for catheter ablation (Class IIb, level of evidence C).

Step 1

Surgical Anatomy

• ◆
  

  The pulmonary veins and posterior left atrium are the critical anatomic sites in patients with isolated AF. However, some patients also manifest right atrial focal or reentrant activation. Around 60% of AF is paroxysmal AF, which is initiated by focal pulmonary vein or atrial triggers. The remaining 40% of AF is classified as persistent or long-standing persistent AF and is due to well-established, self-perpetuating, macroreentrant circuits that generally have little or nothing to do with these focal atrial or pulmonary vein triggers. Data from the Society of Thoracic Surgeons (STS) database have demonstrated that preoperative AF is present in 11% of patients presenting for nonemergent, first-time cardiac surgery. In patients with concomitant AF secondary to left heart pathology (e.g., mitral valve disease, aortic valve disease, CAD), the mechanism of concomitant persistent and long-standing persistent AF may not be due to pulmonary vein triggers alone, and simple pulmonary vein isolation may not be adequate. Although controversial, most authorities have agreed that persistent and long-standing persistent AF, whether stand-alone or concomitant, requires additional linear lesions to accompany pulmonary vein isolation to attain long-term freedom from AF.

  
  
• ◆
  

  Routine real-time intraoperative mapping is currently not available to guide AF ablation in cardiac surgery patients. Therefore, an anatomic approach is the foundation for the surgical ablation of AF.

Step 2

Preoperative Considerations

• ◆
  

  The two settings in which cardiac surgeons encounter patients seeking ablation of AF are AF in patients undergoing concomitant cardiac surgery and isolated AF as an indication for a stand-alone procedure.

  
  
• ◆
  

  In the concomitant setting, ablation is usually performed in patients with mitral valve disease and AF. Almost all such patients should have a combined procedure that includes correction of the mitral valve dysfunction and ablation of AF. An exception might be made in a very high-risk patient undergoing a complex and lengthy reoperative procedure; in that case, it might be prudent to close the left atrial appendage (LAA) but forgo ablation to minimize cross-clamp time.

  
  
• ◆
  

  Stand-alone surgical ablation is uncommon, and there are few data documenting long-term results of newer, less invasive procedures. Stand-alone surgical ablation is indicated in the following cases: (1) patients who fail medical therapy and catheter ablation; (2) patients who fail medical therapy and have contraindications to catheter ablation (e.g., left atrial thrombus, discontinuous inferior vena cava, contraindication to warfarin); and (3) selected highly symptomatic individuals who desire the procedure with the highest probability of success. Surgical approaches in these patients include the full Cox-Maze IV procedure performed on cardiopulmonary bypass or an off-pump procedure centered on bilateral pulmonary vein isolation, generally incorporating additional lesions. Long-term results of the Cox-Maze IV operation suggest 2-year freedom from AF of 65% to 85%. In patients with left atrial thrombus, the Cox-Maze IV procedure with cardiopulmonary bypass is indicated because less invasive, off-pump approaches may result in the dislodgment of thrombus.

Step 3

Operative Steps

• ◆
  

  The Maze procedure is the gold standard for the surgical treatment of AF and is the most effective curative therapy for AF yet devised. This procedure includes isolation of the pulmonary veins and multiple left and right lesions to interrupt the reentrant circuits of AF, as well as excision or exclusion of the LAA to reduce the risk of thromboembolism. A left atrium-based procedure that includes an encircling lesion around all four pulmonary veins with a lesion to the mitral annulus eliminates AF in 60% to 90% of mitral valve patients. The addition of right atrial lesions in these patients is simple and likely increases the rate of cure while simultaneously decreasing the risk of typical right atrial flutter. Therefore, AF ablation should probably entail treatment of both atria whenever feasible.