Impact of Septal Radiofrequency Ventricular Tachycardia Ablation
Insights From Magnetic Resonance Imaging
We present the case of a 38-year-old woman with no past medical history and structurally normal heart with recurrent drug-refractory septal ventricular tachycardia (VT). Despite treatment with flecainide, celiprolol, and sotalol, she experienced breakthrough episodes of VT (Figure 1B). She had undergone 5 failed attempts at VT ablation. She was therefore referred for a further attempt at ablation. Cardiac multidetector computed tomography and late gadolinium enhancement (LGE) MRI were performed before VT ablation. MRI demonstrated nontransmural subendocardial LGE on either side of the septum, which corresponded to previous ablation sites (Figure 2A, Movie I in the online-only Data Supplement).
Consecutive Unipolar Ablation Procedures
Given the multiple failed attempts of endocardial ablation, we used a simultaneous endocardial and epicardial approach. VT was not inducible despite the use of isoproterenol and atropine. The ablation site was then targeted based on substrate mapping and pacemapping. Epicardial mapping did not show any abnormal voltage areas, and pacemap did not match the VT morphology. Endocardial mapping was then performed and radiofrequency energy was delivered at sites with good pacemaps (40 W, Thermocool Smarttouch, Biosense Webster) on the left and right ventricular midseptum. Radiofrequency delivery (40 W, 15g of contact force) at the right ventricular septum resulted in a steam pop after 34 seconds. A postprocedural MRI demonstrated the presence of a septal intramural hematoma without transmural scar (Figure 2B).
Bipolar Ablation Procedure
Because of VT recurrence, she was referred for a seventh attempt at ablation. Preprocedural MRI demonstrated resolution of the intramural hematoma and persistence of the nontransmural lesions (Figure 2C). During the procedure, VT was not inducible. Bipolar ablation was then performed at the optimal pacemap site, between left and right ventricular septum (Figure 3). The 2 catheters (Thermocool) were connected to the dual-catheter ablation box (Stockert, not CE marked). We delivered up to 60 W between both distal tips with close monitoring of temperature and impedance for 120 seconds. On day 1 postablation, MRI demonstrated myocardial swelling and transmural heterogeneous midseptal LGE (Figure 4A). Three months later, she was free of VT without any antiarrhythmic therapy. MRI demonstrated septal wall thinning and transmural LGE (Figure 4B).
This case illustrates how MRI can offer new insights into scar formation after unipolar ablation, steam pop, and bipolar ablation. In the present case, before the first ablation, the transmurality of scar was minimal, despite repeated procedures. After steam pop, MRI demonstrated an intramural hematoma that disappeared at 3 months, with no significant impact on scar transmurality. After bipolar ablation, the acute LGE observed could also be related to an edematous response to ablation. However, MRI at 3 months clearly indicated a permanent septal lesion. First, LGE appears homogeneous and intense and is associated with wall thinning and akinesia (Movie II in the online-only Data Supplement), which indicates the absence of myocyte viability. Second, myocardial perfusion appears severely compromised, indicating microvascular necrosis (Figure 4B). Finally, a quantitative approach was applied by using T1 mapping before and after gadolinium administration. In the present case, the calculated extracellular volume fraction was 85% in the midseptum, indicating an extremely dense scar (Figure 4B). Further studies are desirable to better define the prognostic value of these structural and functional MRI measurements after VT ablation.
Sources of Funding
Dr Berte is supported by an educational European Heart Rhythm Association grant. The study is funded by an Equipex MUSIC ANR-11-EQPX-0030 and an IHU LIRYC ANR-10-IAHU-04 grant.
Drs Jaïs, Haïssaguerre, Hocini, and Sacher have received lecture fees from Biosense Webster and St. Jude Medical. The other authors report no conflicts.
The online-only Data Supplement is available with this article at http://circ.ahajournals.org/lookup/suppl/doi:10.1161/CIRCULATIONAHA.114.010175/-/DC1.
- © 2014 American Heart Association, Inc.