Impact of simulated MitraClip on forward flow obstruction in the setting of mitral leaflet tethering: An in vitro investigation

OBJECTIVES: We aimed to evaluate diastolic leaflet tethering as a factor that may cause mitral stenosis (MS) after simulated MitraClip implantation, using an in vitro left heart simulator. BACKGROUND: Leaflet tethering commonly seen in functional mitral regurgitation may be a significant factor affecting the severity of MS after MitraClip implantation. METHODS: A left heart simulator with excised ovine mitral valves (N = 6), and custom edge-to-edge clip devices (GTclip) was used to mimic implantation of MitraClip in a variety of positions. Anterior mitral leaflet (AML) tethering severity was varied for each case (leaflet excursion of 75°, 60°, and 45°, consistent with mild, moderate and severe tethering), and the baseline mitral annular area (MAA) was varied across samples (3.6-4.8 cm2 ). The resulting mitral valve area (MVA), and peak/mean mitral valve gradient (MVG) were measured in each case. RESULTS: AML tethering severity was a highly significant factor increasing MVG and decreasing MVA (P  5 mmHg resulted more frequently than with GTclip placement alone (46% vs. 4%, respectively). However, severe AML tethering alone significantly reduced baseline MVA to 3.6 ± 0.2 cm2 , and increased baseline MVG to 3.0 ± 0.4 mmHg. At MAA above 4.7 cm2 , severe AML tethering did not cause moderate MS, even with placement of two GTclips (95% confidence). CONCLUSIONS: Our results show that diastolic AML tethering may predispose to MS after clip placement, however, MS was not observed when baseline MVA was above 4.0 cm2 . Severity of AML tethering may be an important criterion in selecting patients for edge-to-edge repair.