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Atrial Fibrillation: Current Management and Best Practices

Atrial Fibrillation: Current Management and Best Practices

Open-heart surgical ablation to treat AF was introduced in the late 1980s by James Cox, MD. His initial procedure utilized a set of complicated incisions resembling a maze on the left and right atria.28 These incisions form scars that cause electrical impulses to move from the sinus node to the AV node, and prevents the formation of micro-reentry circuits that are needed to maintain AF.13 While this procedure has evolved since its debut, it remains a very complex technique that few surgeons perform.

The current iteration of the Maze procedure now uses surgical ablation instead of actual incisions and is sometimes called Cox Maze IV.28 The Cox Maze IV procedure, also referred to as the “cut-and-sew Maze,” is the gold standard for patients with AF needing surgical intervention to restore normal sinus rhythm.13 The Maze IV procedure successfully restores both rate and rhythm while decreasing the incidence of stroke.28 The surgical Maze procedure may be used in selected patients undergoing cardiac surgery for other indications (class IIa recommendation) or as a stand-alone procedure in patients with highly symptomatic AF not well managed with other treatment approaches.2

Catheter Ablation
Another increasingly popular option for AF patients is catheter ablation (CA) to normalize sinus rhythm, for those who do not respond to or are not good candidates for antiarrhythmic drug therapy.29 Technological advances have spurred its more frequent use. During CA, a minimally invasive procedure, a catheter is inserted into the heart via large blood vessels. Once the physician has identified where the abnormal electrical impulses are originating, radiofrequency or cryogenic energy is delivered to those tiny areas of the heart muscle to stop the irregular pulses.30,31 In radiofrequency ablation, current is applied in a point-by-point fashion, leading to cellular necrosis when the tissue is heated. In ablation utilizing cryogenic energy, a balloon is utilized to deliver cryogenic energy that, in one step, freezes the tissue, causes necrosis, and stops the pulses.31

Due to its complexity, the radiofrequency approach was performed in only a few specialized US centers; however, cryoablation is a much simpler approach. The FIRE AND ICE trial was a randomized, open-label study comparing the 2 techniques in patients with paroxysmal AF. Each treatment group had more than 300 patients assigned to it, and results demonstrated that cryoablation was noninferior to radiofrequency ablation.31

Practice guidelines suggest that CA is useful as a rhythm control strategy for patients with symptomatic paroxysmal AF refractory and who may be intolerant to at least 1 class I or III antiarrhythmic drug, once benefits and risks have been evaluated (class I recommendation).2 CA may be considered as a first-line therapy for patients with recurrent symptomatic paroxysmal AF for rhythm control before pharmacologic therapy is tried, after comparing risks and benefits of drug and ablation therapies (class IIa recommendation).2 Despite increasing popularity of CA for rhythm control in AF patients, the procedure does come with certain risks, including thromboembolism and hemorrhagic complications.32 Before a patient undergoes CA, the clinician may choose to continue the patient’s current anticoagulant therapy, or to hold their current anticoagulant and bridge the anticoagulant therapy with a low-molecular-weight heparin (LMWH). Evidence suggests that the continuation of warfarin in a patient undergoing CA is associated with decreased thromboembolic events and a lower rate of minor bleeding when compared with bridging VKA therapy with an LMWH.32 Finlay and colleagues evaluated safety and cost of conversion to LMWH before catheter ablation of atrial flutter versus uninterrupted warfarin in a nonrandomized, case-control study, and determined that the uninterrupted warfarin strategy was safer and more cost-effective than periprocedural conversion with LMWH. The mean cost per patient using anticoagulation with LMWH was approximately $150 per patient compared with $15 per patient for uninterrupted warfarin.33

Uninterrupted Anticoagulation
VKA versus NOAC

Previous evidence has suggested that, for AF patients undergoing CA, uninterrupted anticoagulation with a VKA may be safer and more effective than bridging. However, the ActiVe-controlled multi-cENTer stUdy with blind adjudication designed to evaluate the safety of uninterrupted Rivaroxaban and uninterrupted VKA in subjects undergoing cathEter ablation for nonvalvular Atrial Fibrillation (VENTURE-AF) trial was the first randomized trial to investigate uninterrupted anticoagulation with a VKA compared with a NOAC.34 Rivaroxaban selectively inhibits factor Xa to decrease thrombin generation.35 In a study of NVAF patients who were at a moderate to high risk for stroke, rivaroxaban was found to be noninferior to warfarin for the prevention of stroke or systemic embolism. There was also no significant difference in the risk of major bleeding when comparing rivaroxaban with warfarin; however, intracranial and fatal bleeding occurred less often with rivaroxaban. Rivaroxaban may be preferred in certain patients due to the lack of food-drug/drug-drug interactions associated with rivaroxaban, and due to the necessity of frequent coagulation monitoring associated with warfarin.22

VENTURE-AF was a multinational, randomized, open-label, parallel-group phase IIIb study. Researchers randomly and evenly assigned patients with planned CA to receive either an orally administered VKA, titrated to maintain an INR between 2.0 and 3.0, or an orally administered dose of rivaroxaban 20 mg daily. Inclusion criteria for the study included patients 18 years or older who had either paroxysmal, persistent, or long-standing persistent NVAF. Patients were excluded from the study if they were determined to have valvular AF, which is defined as the presence of a prosthetic heart valve (excluding annuloplasty, with or without prosthetic ring, commissurotomy, and/or valvuloplasty), hemodynamically significant mitral valve stenosis, or rheumatic heart disease. The number of patients needed to determine superiority or noninferiority between the 2 groups was determined to be too large to study; therefore, the investigators opted for a descriptive comparison by selecting the number of subjects they felt would yield clinically relevant results. Since patients enrolled in the study were scheduled in advance to receive CA, the study design allowed for 2 pathways. Patients either followed a delayed CA pathway and were required to take anticoagulation for 3 weeks prior to the procedure, or they were placed on an advanced schedule to receive anticoagulation for as little as 1 day, and up to 7 days, prior to the procedure if diagnostic criteria demonstrated the absence of a clot within the heart. Each treatment group received intravenous unfractionated heparin (UFH) during the procedure in order to achieve a target-activated clotting time (ACT) of 300 to 400 seconds. Anticoagulation was continued post procedure for approximately 30 days, with the post study treatment regimen determined by the patient’s provider. While the primary endpoint of the study was to examine the incidence of major bleeding events between the 2 treatment groups within the first 30 ± 5 days post CA, major secondary endpoints were also evaluated. These included composite and individual cases of ischemic stroke, noncentral nervous system systemic embolism, MI, and vascular death, as well as other bleeding events and AEs related to the procedure. A major bleeding event was judged to have occurred by an independent clinical endpoint committee based on it meeting at least 1 of following the definitions: an International Society on Thrombosis and Haemostasis (ISTH) major bleed, a Global Use of Strategies to Open Occluded Coronary Arteries (GUSTO) severe/life-threatening bleed, or a Thrombosis in Myocardial Infarction (TIMI) major bleed.34

Given that this study was exploratory in nature and not designed to determine statistical significance, the findings have limited value in determining a new standard of care. The authors of the study pointed to the combined retrospective evidence to conclude that there may be a higher complication rate with uninterrupted anticoagulation prior to CA, but stated that the results of the study should be viewed with caution. The open-label design of the study was of particular concern, as it allowed the provider to know the treatment regimen and thus introduced the potential for bias. Although limitations related to the size of the cohorts and already low numbers of observed bleeding events in patients treated by the highly skilled electrophysiologists in the study prohibit drawing definitive conclusions, the study was well designed and attempted to minimize the impact of confounders. The study employed a randomized international multicenter design coupled with blind adjudication of events in an effort to reduce reporting bias. This study adds to the growing evidence that the use of uninterrupted VKA or uninterrupted factor Xa inhibitors such as rivaroxaban may be safe, effective alternatives to bridging patients for CA procedures. However, more investigations in this area are warranted to achieve more confidence in this approach. As such, practitioners should continue to determine the best treatment strategy available utilizing their experience in practice and current treatment guidelines to develop a plan that is individualized to the patient to achieve the best outcome with minimal complications.34

A second study, RE-CIRCUIT, evaluated uninterrupted dabigatran compared with uninterrupted warfarin in patients undergoing AF ablation. This randomized, open-label, multicenter, controlled trial included patients aged ≥18 years with documented paroxysmal or persistent NVAF within the previous 24 months who were scheduled for AF ablation and were candidates for dabigatran 150-mg twice-daily treatment. Patients with valvular or irreversible AF, or AF secondary to a reversible cause, were excluded from the study. Treatment group assignments were carried out using a 1:1 ratio. Patients received either dabigatran 150 mg twice daily or warfarin with dose adjustments to maintain a target INR, with therapeutic range defined as 2.0-3.0. A combination of warfarin 1-, 3-, and 5-mg tablets were used to adjust warfarin dosing. If a patient had been treated with a VKA before the study, study treatment was not initiated until the individual’s INR was below 3 (for warfarin) or below 2 (for dabigatran). This study utilized 4 different treatment phases: 1) 0-2 weeks of screening; 2) 4-8 weeks of anticoagulation before ablation to ensure goal anticoagulation range was achieved; 3) 8 weeks of post CA anticoagulation; and 4) 1 week of follow-up.36

 
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