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Radiofrequency ablation came up short for preventing left ventricular outflow tract (LVOT) obstruction, a feared complication of transcatheter mitral valve implantation (TMVI), researchers reported.

In five TMVI candidates considered at risk of LVOT obstruction, a SCORPION ablation planned months in advance was technically successful, but associated with complete heart block and implantation of a permanent pacemaker in all five cases, reported Vasilis Babaliaros, MD, of Emory Structural Heart & Valve Center in Atlanta, and colleagues.

One person underwent urgent TMVI within 24 hours of SCORPION because of decompensated heart failure. Despite the ablation and subsequent anterior mitral leaflet modification, TMVI still increased the LVOT gradient and the patient died days later from shock and multi-organ failure, they noted in a research letter in .

Of the four remaining patients, three had successful TMVI with intentional laceration of the anterior mitral leaflet (another technique to prevent LVOT obstruction) at 51 to 334 days post-SCORPION -- one still showing an increase in LVOT gradient despite the operators' efforts. One person was lost to follow-up.

LVOT obstruction is a stubborn, life-threatening complication of TMVI, a percutaneous technique that goes beyond the mere clipping of transcatheter edge-to-edge repair to treat severe mitral valve regurgitation or stenosis in people ill-suited for surgery. The complication occurs when the valve implant intrudes on the LVOT or pushes the anterior mitral leaflet into the outflow. LVOT obstruction is especially common in valve-in-mitral annular calcification implants and is associated with high mortality.

Babaliaros and colleagues had hoped that SCORPION -- the technique of septal bipolar ablation of a noncoronary segment of ventricular myocardium to prevent outflow obstruction -- could selectively ablate the region of the interventricular septum enough to increase the predicted neo-LVOT area and avoid intentional leaflet laceration.

The technique is a standalone radiofrequency ablation procedure with the active ablation electrode inserted into the LVOT and a return electrode placed against the opposing right ventricular septum, a configuration that ensures "high current density on the septum," according to the investigators.

Yet based on the available CT scans in this report, SCORPION increased predicted neo-LVOT from a median 0 mm² to 30 mm² and the skirt neo-LVOT from a median 188 mm² to 224 mm² -- not enough to do the trick, Babaliaros and colleagues suggested. "SCORPION failed to change predicted neo-LVOT area enough to avoid adjunctive intentional laceration of the anterior mitral leaflet to prevent left ventricular outflow tract obstruction at the time of TMVI," they wrote.

Then there was the problem of the 100% permanent pacemaker implant rate.

"Pacemaker implantation following radiofrequency ablation is likely related to the required transmural ablation of the high basal interventricular septum near the conduction system and apparently remains an inevitable consequence. It is unlikely that technical refinement in mapping or ablation would reduce this risk or significantly increase debulking. There is need for other approaches that might overcome these limitations," the authors wrote.

Their study also has implications for adjunctive intentional laceration of the anterior mitral leaflet, which was performed in three out of four patients as a TMVI adjunct for reducing LVOT obstruction.

In the of this technique, leaflet laceration is performed using radiofrequency energy splitting the anterior mitral valve leaflet down the midline. LAMPOON continues to be refined as a bailout and a preventive technique after a successful early feasibility study in 2019.

For the present report, Babaliaros and colleagues included five patients deemed at risk for LVOT obstruction based on CT criteria of neo-LVOT <200 mm² and skirt neo-LVOT <180 mm². All were women with multiple comorbidities and a median 12.0% Society of Thoracic Surgeons predicted risk of 30-day mortality.

Three out of the five patients already had baseline LVOT gradients. Three patients also had unsuccessful attempts at prophylactic alcohol septal ablation due to unfavorable coronary anatomy.

SCORPION ablation lesion counts ranged from nine to 30 per person, and the average ablation took 22 minutes.

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