One More Magnetic Resonance Imaging
Condition: Atrial Fibrillation
MeSH terms: Atrial Fibrillation
Study type: Interventional

Summary: 
      The objective of this study is to utilize delayed enhanced cardiac magnetic resonance imaging
      to assess the success of pulmonary vein isolation after cryoablation of paroxysmal atrial
      fibrillation. The primary hypothesis is that cardiac magnetic resonance imaging will be able
      to visualize changes in left atrial tissue characteristics caused by cryoablation used to
      treat paroxysmal atrial fibrillation.
    

Detailed description: 
      Atrial fibrillation (AF) is the most common arrhythmia in the world, affecting 1-2% of the
      general population and 10% of people older than 80 years old. Medical therapy is only
      partially effective at treatment of symptoms of atrial fibrillation and ablation procedures
      have been developed that offer a potential curative approach to treatment of the symptoms of
      atrial fibrillation. Prior to an ablation procedure, it is standard of care to perform
      imaging (either contrast cardiac computed tomography or cardiac magnetic resonance (CMR)
      imaging) to determine the size and orientation of the pulmonary veins, the presence or
      absence of left atrial thrombus and the size and volume of the left atrium. Cardiac magnetic
      resonance imaging has the advantage of high spatial resolution without additional radiation
      exposure. There are some additional features of CMR that make it potentially even more useful
      for patients undergoing an ablation procedure for treatment of atrial fibrillation. One main
      advantage involves the use of delayed-enhancement MRI (DE-MRI) to characterize the tissue of
      the left atrium to visualize the presence of absence of scars. Prior studies have
      demonstrated the ability of CMR to visualize radiofrequency-induced scar in the left atrial
      wall after atrial fibrillation ablation. These studies have postulated that CMR could be
      utilized to determine the success rates of atrial fibrillation ablation. However, there has
      been significant variability between published studies looking at CMR post radiofrequency
      ablation, which for many years was the only type of ablation procedure available to treat
      atrial fibrillation. Some studies demonstrate a correlation between DE-MRI and ablation
      lesions, while others do not report such a correlation. Furthermore, no study to date has
      been designed to examine cryoablation specifically. Cryoablation is alternative method of
      performing an ablation procedure that utilizes a freezing balloon to make a circumferential
      lesion around the atrum of the pulmonary vein, as opposed to radiofrequency ablation which
      uses a catheter to create the same pattern of lesions around the pulmonary vein utilizing a
      4mm catheter that generates heat as a byproduct of radiofrequency energy. Using DE-MRI to
      analyze injury and scar after cryoablation would be a novel application of this imaging
      modality.

      There are several reasons why lesions produced with cryoablation procedures may offer better
      visualization on DE-MRI as compared to radiofrequency ablation. First, the circumferential
      lesion generated by cryoablation is created utilizing a uniform distribution of energy in a
      simultaneous fashion to the entire pulmonary vein antrum. In contrast, lesions created by
      radiofrequency ablation are produced sequentially and each lesion has variable contact with
      the myocardium and therefore variable energy delivery. As a consequence, lesions created with
      radiofrequency ablation may not uniformly penetrate the myocardium, creating a situation
      whereby contiguous lesions have variable depth. This may explain the heterogeneity of scar
      visualization on DE-MRI in earlier studies. Furthermore, despite the advantages and accuracy
      of electroanatomical mapping, due to variations in tissue architecture in the pulmonary vein
      antrum, there may be technical challenges in ensuring truly contiguous lesions.
      Unfortunately, the non-contiguous nature of radiofrequency ablation lesions may not be become
      evident until localized tissue edema has subsided and clinical evidence of recurrent atrial
      fibrillation is observed several months after the procedure. Cryoablation offers a
      theoretical advantage in this regard by producing near uniform tissue contact as well as an
      ability to assess for gaps in tissue contact by injecting contrast dye under fluoroscopic
      visualization during the period of pulmonary vein occlusion to demonstrate areas of poor
      tissue contact where contrast dye escapes from the occluded pulmonary vein. Another advantage
      is that the cryoballoon is in contact with a greater amount of myocardium in the pulmonary
      vein antrum than the radiofrequency ablation catheter due to the larger surface area of the
      23 or 28mm diameter cryoballoon as compared to the 3.5 or 4mm diameter radiofrequency
      ablation catheter. The smaller surface area of the radiofrequency ablation lesions may be
      missed in the delayed enhancement sequences on MRI, which are acquired at a greater slice
      thickness as compared with standard acquisition. Therefore, the cryoablation lesions may be
      more likely to be visualized, as there is a greater probability that some portion of the
      ablated myocardium will be present in a given imaging slice of delayed enhanced atrial
      myocardium. Finally, the nature of cryoablation itself may cause less inflammation in the
      short term in the atrial myocardium as compared to radiofrequency ablation due to the fact
      that the tissue is frozen and not heated. The effect of this on ability to visualize ablated
      tissue on DE-MRI is unknown, as none of the published studies have examined cryoablation
      specifically.
    

Intervention name(s): Delayed Enhanced Cardiac Magnetic Resonance Imaging; Cryoablation
Intervention type(s): Other; Procedure
Intervention description(s): Subjects in this study get a Delayed Enhanced Cardiac Magnetic Resonance Imaging 2-6 weeks after they undergo cryoablation for atrial fibrillation. This MRI is compared to the pre-procedure cardiac MRI to determine if it possible to visualize the cryoablation lesions.; All subjects in this study undergo a cryoballoon ablation procedure to achieve pulmonary vein isolation for the purposes of treatment of atrial fibrillation
Other intervention name(s): Delayed Enhanced Cardiac MRI; Cryoballoon Ablation
Intervention model: Single Group Assignment
Masking: None (Open Label)
Primary purpose: Treatment