Effect of Structural Remodeling on Scar Formation as Assessed by DE-MRI of the Left Atrium
Condition: Atrial Fibrillation
MeSH terms: Atrial Fibrillation
Study type: Observational

Summary: 
      The purpose of this study is to evaluate the impact of pre-ablation fibrosis on scar
      formation in the left atrium of the heart. This will be assessed by delayed enhancement
      magnetic resonance imaging and will be looked at in patients who have undergone successful
      open irrigated cooled-tipped radio-frequency ablation of paroxysmal atrial fibrillation.
      Follow-up after ablation will be for 12 months.
    

Detailed description: 
      Atrial fibrillation (AF) is an electrophysiological condition characterized by disorganized
      electrical activity that involves the entire atria. AF manifests initially as paroxysms of
      arrhythmia that later progress into persistent and permanent forms. It is a progressive
      disease associated with structural, electrical and contractile changes in the left atrium
      (LA). A major determinant of the progression of AF is structural remodeling or fibrosis that
      occurs in the left atrium. A more extensively remodeled atrium presents the substrate needed
      for the arrhythmia to persist. Structural remodeling is also a major determinant for success
      of rhythm control strategies in AF. While catheter ablation has reproducibly been shown to be
      superior to anti-arrhythmic drug (AAD) therapy for rhythm control in AF, the success of this
      procedure is significantly affected by the extent of structural remodeling present at the
      time of catheter ablation.

      Delayed-Enhancement Magnetic Resonance Imaging (DE-MRI) has been demonstrated to be a very
      effective modality in identifying fibrotic and scarred cardiac tissue with excellent
      correlation to electro-anatomical mapping. This is related to the characteristics of
      Gadolinium, an extracellular contrast agent that is very effective in identifying regions of
      fibrotic non-viable myocardium. DE-MRI technology can be a very powerful, non-invasive
      method, of identifying the extent and the distribution of structural remodeling or fibrosis
      associated with AF. Specific image acquisition sequences have allowed for reproducible
      identification of high pixel intensity regions within the 2-dimensional images of the atrial
      wall. 3-Dimensional reconstruction of the entire left atrium then provides a quantification
      of the overall volume occupied by these hyper-enhanced regions relative to the entire left
      atrial wall volume. Used prior to catheter ablation, DE-MRI can therefore identify regions of
      significant structural remodeling or fibrosis. The same technology has also been shown to be
      very useful in examining the amount and distribution of ablation-induced scarring.

      Catheter ablation has emerged as an effective interventional therapeutic modality for AF
      patients. Current ablation techniques, including pulmonary vein antrum isolation (PVAI), use
      radiofrequency (RF) energy to induce thermal damage to the LA substrate in an attempt to
      electrically disconnect and isolate arrhythmogenic foci originating from the pulmonary veins
      (PVs). Multiple catheter technologies for RF have been developed. Catheters may be either
      cooled or not. Cooling allows for higher and deeper energy delivery with larger lesion
      formation. Open irrigation cooled-tip RF ablation of AF is associated with less impedance
      rise, microbubble formation, and esophageal injury when compared with traditional non-cooled
      ablation catheters. It is also associated with shorter RF delivery time, fluoroscopy, and
      procedural time.

      Understanding the temporal sequence of events of LA structural remodeling (preceding AF
      ablation) to scar formation (following AF ablation) can prove valuable in determining whether
      certain patients are more susceptible to recovery of electrical conduction and recurrence of
      AF. DE-MRI recently has been introduced as a means to visualize this RF-induced scarring
      post-ablation. These scans can be reconstructed into three-dimensional (3D) recreations of
      the LA allowing for further analysis and quantification of the LA scar formation following RF
      ablation.

      Objectives:

      Primary Objective

      • To evaluate the impact of pre-ablation structural remodeling (fibrosis) on scar formation
      and progression in the LA as assessed by DE-MRI in patients who have undergone successful
      open irrigated cooled-tipped RF ablation of paroxysmal atrial fibrillation (PAF), using
      observational, longitudinal data from the University of Utah Comprehensive Arrhythmia
      Research & Management (CARMA) Center supported AFIB database (approved IRB #20347) over a
      12-month follow up period.

      Secondary Objectives

        -  To determine if secondary variables, such as total ablation time, number of lesions,
           power delivered, and impedance, may play a significant role in catheter induced scar
           formation.

        -  To promulgate future research opportunities in the field of AF, particularly with
           regards to possible early intervention measures that may impact its progression.

        -  To adapt treatments aimed at patients with AF who are diagnosed at earlier stages.

        -  To use DE-MRI to further the knowledge and understanding of RF ablation therapy and to
           better understand the benefits and longitudinal effects of using scar formation to
           eliminate the fibrotic tissue that conducts the impulses which leads to AF.
    

Observational model: Cohort
Time perspective: Retrospective
Sampling method: Non-Probability Sample
Study population: 
        Forty patients ages 18-89 years, who have had an open irrigation cooled-tipped RF ablation
        procedure for PAF. Patients must participate in 3-, 6-, and 12-months follow-up post
        ablation. PAF is defined by >2 documented episodes of AF that terminate spontaneously
        within 7 days. AF has to be documented by means of electrocardiography, holter monitor,
        loop recorder, or echocardiography.
      
Keywords: Paroxysmal Atrial Fibrillation; Radio-frequency Ablation; Ablation; Open irrigation cooled-tip