Feasibility of myxomatous mitral valve repair using direct leaflet and chordal radiofrequency ablation

Abstract

Objective: Minimally invasive repair of mitral valve prolapse (MVP) causing severe mitral regurgitation (MR) should reduce MR and have chronic durability. Our ex vivo, acute in vivo, and chronic in vivo studies suggest that direct application of radiofrequency ablation (RFA) to mitral leaflets and chordae can effect these repair goals to decrease MR.

Methods: A total of seven canines were studied to assess the effects of RFA on mitral valve structure and function. RFA was applied ex vivo (n = 1), acutely in vivo using a right lateral thoracotomy and cardiopulmonary bypass (n = 3), and chronically in vivo using percutaneous access to the heart (n = 3). RFA was applied to the mitral valve and its associated chordae. Mitral valve structure and function (in vivo preparations) were then assessed.

Results: Ex vivo application of RFA resulted in qualitative reduction in mitral leaflet surface area and chordal length. Acute in vivo application of RFA to canines found to have MVP causing severe MR demonstrated a 43.7-60.7% statistically significant (P = 0.039) reduction in postablation MR. Chronic, in vivo, percutaneous application of RFA was found to be feasible and the engendered alterations durable.

Conclusion: These data suggest that myxomatous mitral valve repair using radiofrequency energy delivered via catheter is feasible.

Figure 1. Pre- and Post-Radiofrequency Ablation of Ex-Vivo Canine Anterior Mitral Leaflet

The top image depicts a native canine anterior mitral leaflet and chordae. The bottom left image is status-post the application of 15sec irrigated RFA (20Watts) to the leaflet only. The bottom right image is status-post the application of an additional 5sec irrigated RFA (20Watts) to the chordae associated with the anterior leaflet.

Figure 2. Pre- and Post-Ablation Morphology and Structure of Myxomatous Mitral Valve

Transthoracic echocardiograms performed before (2A) and after RFA (2B) demonstrated a reduction in the degree of MVP, MR, and chordal length (see insets). This animal underwent 3 applications of RFA at an average power of 12.2±1.4W for an average of 50±10sec each.

Figure 3. ICE-Guided Percutaneous Ablation of Mitral Valve Anterior Leaflet

To guide mitral valve ablation, ICE catheter was placed in the right atrium and positioned to give a modified three chamber view. The left atrium is a 12 o’clock, the left ventricle is directly inferior to the left atrium, and the ablation catheter is advanced retrograde across the aortic valve and positioned adjacent to the anterior leaflet of the mitral valve. The top image depicts the mitral valve prior to RFA and the bottom image depicts the mitral valve following RFA. One notes the obvious thickening found post-RFA.

Figure 4. Chronic Echocardiographic Changes after Percutaneous Anterior Mitral Leaflet Ablation

The transthoracic apical 4 chamber echocardiogram still frames were taken at baseline and weekly thereafter for 5 weeks. The baseline echo demonstrates a typical baseline mitral valve morphology. The subsequent echocardiograms depict the typical changes found after RFA. One can see thickening of the entire anterior leaflet, pronounced at the base and tip of the leaflet that persists throughout the entire follow-up.

Figure 5. Histopathologic Changes In Mitral Leaflets after Radiofrequency Ablation

Affected valves show small areas of coagulation necrosis (consistent with RFA injury), labeled by arrows A, and surrounding fibroblastic proliferation, labeled by arrows B, as a feature of tissue repair.