A 32-year-old woman with atypical atrial flutter was referred for a first-ever ablation. A preprocedural delayed-enhancement cardiac magnetic resonance (DE-CMR) was performed; the three-dimensional reconstruction of left atrium depicting the healthy (purple) and scarred myocardium (red) was imported into the navigation system to guide the ablation. A counterclockwise perimitral activation sequence was identified (panel A).
The substrate characterization provided by DE-CMR facilitated the identification of an anatomical isthmus at the inferior aspect of the left atrium (panels B and C), between a large, scarred area at the posterior wall (asterisk) and the inferior mitral annulus (black arrowheads). The integrated DE-CMR reconstruction allowed catheter positioning and limited mapping at this site; a continuous, fractionated signal—highly suggestive of a protected, slow-conducting isthmus—was identified. Radiofrequency application at this site terminated the arrhythmia. No further arrhythmias could be induced.
The standard ablation approach of a perimitral flutter includes extensive ablation at the mitral isthmus to create a line of block; in patients without prior AF ablation, additional encircling lesions around the left-sided pulmonary veins are required. In this case, DE-CMR was crucial in identifying the critical isthmus of the circuit; this allowed limited mapping to the area of interest and limited energy delivery.
The full-length version of this report can be viewed at: http://www.escardio.org/communities/EHRA/publications/ep-case-reports/Documents/Simplified-mapping-and-ablation.pdf.
