Recognition of MRI’s Roles in Ablation
As catheter ablation has become an increasingly popular and accepted treatment for atrial fibrillation, the role of MR imaging to support the procedure has expanded to include guiding patient selection, pre-surgical planning, preacquired anatomical mapping used during the procedure itself, and post-surgical confirmation of the integrity of the procedure. These pre- and post-operative MRI assessments can improve ablation procedure outcomes in patients suffering from atrial fibrillation. These roles are recognized by reimbursement policies of major insurance companies.
Role of MRI in Guiding Ablation Procedures
In newer ablation techniques, accurately visualizing the lesions with respect to their extent and anatomic location is increasingly important. Techniques which rely on fluoroscopy and three-dimensional mapping to guide the catheter “are limited in their ability to confirm the presence, exact location, and extent of ablation lesions, parameters that serve as indicators of the procedural success.” MRI can provide this anatomical assessment in a systematic, repeatable manner. (Source: Dickfeld, et al)
Use of preacquired MR images with market-leading 3-D electroanatomical navigation systems provides superior support to visualize, diagnose, and guide treatment for arrhythmia. These navigation systems merge 2-D and 3-D MR images with electroanatomical data to facilitate catheter navigation, pre-procedure planning, and therapy delivery.
MRI and Ablation Preparation
MRI is an effective imaging tool for planning and roadmapping surgical interventions, including patient selection.
- Detailed anatomical visualization. MRI has been found to be “superior to TEE in displaying pulmonary veins” and navigating the complex structures in the area around the confluence of these veins. MRI is “particularly effective in the diagnosis of pulmonary venous abnormalities.” (Source: Yang, et al)
- One-stop shopping. A single CMR exam can provide left atrial appendage (LAA) anatomy, rule out thrombus, and display the pulmonary veins prior to a cardioversion or pulmonary vein isolation procedure. (Source: Balhan, et al: “CMR is Equally Effective…”)
- Assess disease state. Atrial fibrillation is associated with “diffuse left atrial (LA) fibrosis and a reduction in endocardial voltage.” These changes indicate the severity of the disease and appear to be predictors of treatment outcome. Since delayed-enhancement MRI (DE-MRI) can non-invasively assess myocardial tissue, pre-ablation DE-MRI can provide insight into the disease state. (Source: Oakes, et al: “Detection and Quantification…”)
MRI and Post-surgical Success Confirmation
MRI provides effective post-surgical confirmation of the integrity of electrophysiology procedures.
- Accurate evaluation of ablation lesions. Contrast-enhanced MRI (CE-MRI) has for years been employed successfully to evaluate tissue recoverability after myocardial infarction. In electrophysiology, DE-MRI supports accurate evaluation of ablation lesions to assess procedural success. (Source: Dickfeld, et al)
- Predicting recurrence. Delayed-enhancement MRI (DE-MRI) provides anatomic evidence of the scar created during ablation, and morphologic characteristics of the scar can be used to predict the potential recurrence of arrhythmia. (Source: Peters, et al: “Detection of Pulmonary Vein…”)
- Treating recurrence. The objective of pulmonary vein antrum (PVA) isolation is to “electrically isolate the left atrium from arrhythmogenic foci located in the pulmonary veins.” Though difficult to achieve, unbroken scars around the pulmonary veins are associated with better clinical outcomes. Resumption of fibrillation after the procedure is thought to be due to incomplete ablation lesion sets. DE-MRI can accurately define scar lesions after ablation procedures. During repeat ablation, DE-MRI can be used to find and close breaks in the ablation lesions. (Source: Badger, et al: “Evaluation of LA Lesions…”)
- Noninvasive assessment. Assessing the permanence of tissue damage non-invasively with MR is an important step toward improved success of ablation procedures in the treatment of atrial fibrilation. (Source: McGann, et al)
- Managing post-surgical complications. Noninvasive post-ablation assessment with MR can contribute significantly to “monitoring early complications, tracking lesion progression and initiating early intervention to avoid serious procedural consequences.” (Source: Badger, et al: “Initial Experience…”)
Use of MRI during preoperative planning and patient followup eliminates radiation exposure that would otherwise be introduced during these exams. MR imaging can also reduce radiation exposure during the procedure itself, insofar as quality images and effective surgical planning reduce procedure time.
Badger T, et al. “Evaluation of Left Atrial Lesions After Initial and Repeat Atrial Fibrillation Ablation: Lessons Learned From Delayed-Enhancement MRI in Repeat Ablation Procedures” Circ Arrhythm Electrophysiol 2010;3;249-2.
Badger T, et al. “Initial Experience of Assessing Esophageal Tissue Injury and Recovery Using Delayed-Enhancement MRI After Atrial Fibrillation Ablation” Circ Arrhythm Electrophysiol 2009;2;620-625
Balhan S, et al. “Cardiovascular MRI is equally effective as Transesophageal Echocardiogram in Evaluation of Left Atrial Appendage Thrombus in Atrial Fibrillation: A Strategy for Pulmonary Vein Isolation” Journal of the American College of Cardiology. 2010.
Dickfeld T, et al. “Characterization of Radiofrequency Ablation Lesions With Gadolinium-Enhanced Cardiovascular Magnetic Resonance Imaging” Journal of the American College of Cardiology. 2006 January 17; 47(2): 370–378.
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Oakes R, et al. “Detection and Quantification of Left Atrial Structural Remodeling Using Delayed Enhancement MRI in Patients with Atrial Fibrillation” Circulation. 2009 April 7; 119(13): 1758–1767.
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