Cover Story

Hybrid Ablation for Atrial Fibrillation

Eric S. Williams, MD, FHRS
Cardiac Electrophysiology, Swedish Heart and Vascular Institute, Swedish Medical Center, Seattle, Washington

Eric S. Williams, MD, FHRS
Cardiac Electrophysiology, Swedish Heart and Vascular Institute, Swedish Medical Center, Seattle, Washington

Catheter ablation for drug-refractory paroxysmal atrial fibrillation (AF) can be performed safely and effectively; however, efficacy is reduced in catheter ablation for persistent forms of AF.1-3 This is believed to be related to the more advanced left atrial disease substrate in patients with persistent AF, including the development of atrial chamber enlargement, atrial fibrosis, rotor activity, and non-pulmonary vein triggers of atrial fibrillation.4 Surgical ablation of AF has been described as more effective in these cases,5-7 though the potential for atrial tachycardia and flutter circuits from proarrhythmic linear ablation and surgical ablation gaps in the atrium have been reported.8 Here we describe a case of a staged hybrid AF ablation procedure in a patient with valvular heart disease.

Case Description

A 61-year-old man with a history of mitral valve prolapse was referred for surgical evaluation after he developed a three-month history of progressive exertional dyspnea and fatigue. Echocardiography demonstrated severe mitral regurgitation with a flail posterior leaflet. Left ventricular function was normal, with mild chamber enlargement (end-diastolic dimension of 6.1 cm). The left atrium was moderately to severely enlarged with a left atrial dimension of 5.4 cm. Additionally, he had developed atrial fibrillation with associated rapid ventricular response, controlled with digoxin, beta-blockers, and oral anticoagulation, two months prior.

He was taken by cardiothoracic surgery for a mitral valve repair, which included placement of a 40 mm annuloplasty ring, a left atrial appendage (LAA) occlusion device (AtriClip, AtriCure), and a left-sided Maze procedure for his comorbid persistent atrial fibrillation. The Maze consisted of cryoablation of his bilateral pulmonary veins, a box lesion, and a mitral lesion. His postoperative course was complicated by some early postoperative bradycardia, followed by development of a persistent atrial tachycardia on postoperative day #3. He was cardioverted on postoperative day #5 and discharged on warfarin anticoagulation. Beta-blockers were initially held due to his early postoperative bradycardia and a prolonged PR interval in sinus rhythm post cardioversion. 

At his three-month postoperative visit, he was referred to electrophysiology for evaluation of atrial tachycardia noted during cardiac rehabilitation. A resting 12-lead ECG is shown (Figure 1) as well as rhythm strips during his exercise routine, which show atrial tachycardia abruptly transition from 2:1 to 1:1 AV conduction (Figure 2). 

He was taken to the electrophysiology laboratory for three-dimensional electroanatomic mapping with intracardiac echocardiography guidance (CARTOSOUND, Biosense Webster, Inc., a Johnson & Johnson company). He presented in an incessant 2:1 atrial tachycardia with a 380 msec cycle length in the atrium. Biatrial activation and voltage mapping were performed using a continuous multi-electrode mapping module (CONFIDENSE, Biosense Webster, Inc., Inc., a Johnson & Johnson company). Right atrial mapping was performed with a contact force-sensing irrigated-tip radiofrequency (RF) ablation catheter (THERMOCOOL SMARTTOUCH, Biosense Webster, Inc., a Johnson & Johnson company), and left atrial mapping was performed with a 20-pole high-density mapping catheter (PENTARAY NAV, Biosense Webster, Inc., a Johnson & Johnson company). We did note an area of apparent slow conduction on the posterior wall, with an “early-meets-late” activation pattern between the right-sided pulmonary veins, suggestive of a reentrant tachycardia circuit (Figure 3). Bipolar voltage mapping revealed “gaps” from his index surgical ablation procedure that corresponded to this region (Figure 4). Touch-up endocardial RF ablation to this area terminated the tachycardia. Additional RF ablation was then performed to electrically isolate all four pulmonary veins, with entrance and exit block verified in sinus rhythm. An electrophysiology study was performed using intravenous adenosine to test for pulmonary vein reconnection, and with high-dose isoproterenol to look for non-pulmonary vein triggers and any other inducible atrial tachycardias. Typical atrial flutter was induced with programmed atrial stimulation and terminated with ablation to the cavotricuspid isthmus and verification of bidirectional block.

The patient returned to clinic one-month post ablation, and a repeat 12-lead ECG and ambulatory cardiac event monitor showed maintenance of sinus rhythm. He will wean off of beta-blockers and warfarin after repeat cardiac monitoring at the six-month mark.

Discussion

We described a case of a patient with persistent AF and mitral valve disease that was successfully treated with a staged hybrid AF ablation approach. In the setting of moderate to severe left atrial enlargement and severe mitral regurgitation, the long-term success rates of antiarrhythmic medications and endocardial catheter ablation are low.4 At the time of operative intervention for his mitral valve disease, a concomitant limited Maze procedure was performed. Atrial tachycardia detected in follow-up was subsequently addressed with an endocardial catheter ablation procedure.

Surgical treatment for AF has evolved since the original Cox Maze procedure, which consisted of a cut-and-sew approach with biatrial incisions, performed using a median sternotomy and cardiopulmonary bypass. The goal of Cox Maze surgery is to interrupt potential macroreentrant circuits in the atria that can perpetuate atrial tachyarrhythmias. Although this technique has been proven to be highly effective in several prospective studies, the surgical complexity and potential for morbidity limited its initial widespread adoption.5,6,9,10 The Cox-Maze IV replaced the cut-and-sew incisions with linear lesions from other energy sources, such as bipolar RF and cryoablation, with an associated significant reduction in perioperative complications.11 More recently, the lesion set has been simplified and techniques refined to allow for a minimally invasive approach, either though a thoracotomy, mini-thoracotomy, or totally thoracoscopic video-assisted approach,12 and can be performed without the need for cardiopulmonary bypass in many cases.13 The disadvantage of these less invasive surgical approaches is that the epicardial ablation techniques used in the left atrium may not provide the transmural lesions necessary for durable pulmonary vein isolation, and endocardial “touch-up” ablation may be required for long-term atrial arrhythmia control.8,14

In the case of our patient, who was taken for primary mitral valve surgery and underwent a concomitant surgical AF procedure, the Cox-Maze IV lesion set was not performed in favor of a more limited surgical ablation in the left atrium.13 For cases of persistent AF, biatrial surgical ablation has generally been shown to be more effective at controlling atrial arrhythmias than ablation limited to the left atrium, for the reasons previously mentioned.9,11 Although the patient did not have recurrent atrial fibrillation in follow-up, he did develop an incessant organized atrial tachycardia, which was suspected to be related to a “gap” of electrically active left atrial tissue from his index surgical ablation procedure.

During the endocardial mapping and ablation procedure for this patient, although the pulmonary veins did require some touch-up RF ablation, the posterior wall and LAA were well covered (with dense scar) by the index surgical ablation procedure. The appendage is known to be responsible for greater than 90% of all cardioembolic strokes related to AF. It has been suggested that ligation of the LAA in patients with AF could reduce the risk of cardioembolism.4 Additionally, the LAA is increasingly thought to be an important non-pulmonary vein ectopic trigger in patients with persistent AF, and its electrical isolation or exclusion may be critical to ensuring long-term AF control.15,16 The advantages of a hybrid AF ablation approach in these situations are clear: to use the endocardial approach to achieve durable pulmonary vein isolation and verify lines of conduction block, and to use the surgical intervention to consolidate areas in the left atrium often poorly addressed endocardially, such as the posterior wall (due to the concern of causing esophageal injury with RF ablation) and the LAA (with the ability to surgically achieve both electrical isolation and mechanical exclusion from the left atrium). 

Conclusion

There has been a growth in hybrid approaches to AF ablation for the treatment of persistent and longstanding persistent AF, in which the results of catheter ablation alone have been suboptimal.1-3 The goals of such techniques are to provide improved long-term, arrhythmia-free success, with a reasonably low risk of complications and a reasonable postoperative recovery. As the less invasive surgical ablation approaches may result in non-transmural lesion formation, high-density three-dimensional electroanatomic mapping techniques to assess bipolar voltage in the atrium for endocardial “gaps” and activation patterns for areas of slow conduction will be increasingly important in the post-surgical evaluation of AF ablation patients with residual atrial arrhythmias.

Disclosure: Dr. Williams has no conflicts of interest to report regarding the content herein.   

References

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