Epicardial and Endocardial Hybrid Ablation for Atrial Fibrillation

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 ).

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.