Pre-ablation magnetic resonance imaging of the cavotricuspid isthmus

AIMS: In this prospective pilot study, pre-procedural MRI was performed on patients undergoing radiofrequency ablation of the cavotricuspid isthmus (CTI) to assess variation in isthmus anatomy and its impact on catheter ablation. METHODS: In 41 patients, 34 males, mean age 56 +/- 11.5 years, pre-procedural MRI was performed prior to ablation. On the basis of the magnetic resonance imaging (MRI), isthmus length and description of isthmus morphology was determined. Catheter ablation of the CTI was then performed using a standard technique by an experienced operator without prior knowledge of the MRI findings. RESULTS: The following morphological variants of isthmus morphology were demonstrated: long isthmus, concave isthmus shape, simple pouches, and eccentric septally directed pouches distinct from the coronary sinus. There was a trend towards longer RF times for long and concave shaped CTI. Eccentric septally directed pouches were associated with significantly longer radiofrequency energy delivery times (29.5 +/- 24.5 min RF versus 14.5 +/- 12.9 min RF; P = 0.037). CONCLUSION: The anatomy of the CTI is highly variable. Ablation difficulty can be predicted by the presence or absence of morphological variants and the length of CTI demonstrated by cardiac MRI.