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Ann Thorac Surg 2006;82:1362-1368
© 2006 The Society of Thoracic Surgeons

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Original Articles: Cardiovascular

Effects of Annular Size, Transmitral Pressure, and Mitral Flow Rate on the Edge-To-Edge Repair: An In Vitro Study

^a Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, Georgia
^b University of Texas Southwestern Medical Center, Lubbock, Texas
^c Texas Tech University, Lubbock, Texas

Accepted for publication May 4, 2006.

^_* Address correspondence to Dr Yoganathan, Wallace H. Coulter School of Biomedical Engineering, Georgia Institute of Technology and Emory University, Room 2119, U.A. Whitaker Bldg, 313 Ferst Dr, Atlanta, GA 30332-0535 (Email: ajit.yoganathan{at}bme.gatech.edu).

BACKGROUND: Although edge-to-edge repair is an established adjunctive procedure, there is still debate on its long-term durability and efficacy.

METHODS: Fifteen porcine mitral valves were studied in a physiologic left heart simulator with a variable size annulus (dilated = 8.22 cm², normal = 6.86 cm², contracted = 5.5 cm²). Mitral valves were tested under steady and physiologic pulsatile flow conditions (cardiac outputs: 4 to 6 L/min), at peak transmitral pressures between 100 mm Hg and 140 mm Hg. A miniature force transducer was used to measure the Alfieri stitch force (F_A). Mitral flow rate (MFR), transmitral pressure, effective orifice area, mitral regurgitation, and F_A were monitored.

RESULTS: The edge-to-edge repair led to a decrease in effective orifice area of 16.55% ± 8.22%; further reduction in effective orifice area was attained with annular contraction. Mitral regurgitation after the edge-to-edge repair was significantly higher (p <0.05) with annular dilation. In the pulsatile experiments, two peaks in F_A were observed: one during systole (F_A = 0.059 ± 0.024 N) and a second during diastole (F_A = 0.072 ± 0.021 N). Multivariate analysis of variance analysis showed that during systole, transmitral pressure and mitral annular area (MAA) had significant effects on F_A [F_A = (4.40 x 10^–4) transmitral pressure (mm Hg) + (5.0 x 10^–3) MAA (cm²) – 0.05 (R²= 0.80)], whereas during diastole MFR and MAA had significant effects on F_A [F_A = (1.03 x 10^–4) MFR² (L/min) – (1.60 x 10^–3) MAA (cm²) + 0.02 (R² = 0.90)].

CONCLUSIONS: With annular dilation, mitral regurgitation persisted even after the edge-to-edge repair. The edge-to-edge repair does not cause clinically relevant mitral valve stenosis in a normal size mitral valve. Mitral flow rate and transmitral pressure are the main determinants of F_A during the cardiac cycle. Increasing annular area increases F_A during systole but decreases F_A during diastole. Systolic F_A may become dominant with increases in MAA or peak transmitral pressure, or both.

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