on September 22, 2009
Published online before print September 22, 2009, doi: 10.1161/CIRCIMAGING.108.823732
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Original Article |
Mechanism of Decrease in Mitral Regurgitation Following Cardiac Resynchronization Therapy: Optimization of the Force Balance Relationship
1 Massachusetts General Hospital, Boston, MA;
2 Hospital Clínic, University of Barcelona, Barcelona, Spain
* Corresponding author; email: jhung{at}partners.org
Background—Cardiac resynchronization therapy (CRT) has been shown to reduce functional mitral regurgitation (FMR). It has been proposed that the mechanism of MR reduction relates to geometric change or, alternatively, changes in left ventricular (LV) contractile function. Normal mitral valve (MV) function relies on a balance between tethering and closing forces on the MV leaflets. FMR results from a derangement of this force-balance relationship and CRT may be an important modulator of MV function by its ability to enhance the force-balance relationship on the MV. We hypothesized that CRT improves the comprehensive force balance acting on the valve, including favorable changes in both geometry and LV contractile function.
Methods and Results—We examined the effect of CRT on FMR in 34 patients pre and post CRT (209 ± 81 days). MR Regurgitant volume (RV), closing forces on MV (derived from Doppler transmitral pressure gradients), including dP/dt and a factor (closing pressure ratio) expressing how long the peak closing gradient is maintained over systole (Closing pressure ratio = velocity time integral (VTI)/MR peak velocity x mitral regurgitation time), and dyssynchrony by tissue Doppler were measured. End-diastolic (EDV), end-systolic (ESV) volumes, mitral valve annular area (MAA) and contraction (% change in MAA from end-diastole to mid-systole), leaflet closing area (leaflet area during valve closure), tenting volume (volume under leaflets to annular plane) were measured by 3D echo. Post CRT, EDV (253 ± 111 vs. 221 ± 110 ml, p<0.001), ESV (206 ± 97 vs 167 ± 91 ml, p<0.001) decreased and EF (19 ± 6 vs 27 ± 9 %, p<0.001) increased. MR RV decreased from 35 ± 17 to 23 ± 14 ml (p <0.001), MAA (11.6 ± 3.5 to 10.5 ± 3.1 cm2 p<0.001), leaflet closing area (15.4 ± 5 to 13.7 ± 3.8 cm2, p<0.001) and tenting volume (5.7 ± 2.6 to 4.6 ± 2.2 ml, p<0.001) decreased. Peak velocity (and therefore transmitral closing pressure) was more sustained throughout systole, as reflected by the increase in the closing pressure ratio (0.77 ± 0.1 vs. 0.84 ± 0.1, pre CRT vs post CRT. p=0.01); dP/dt also improved post CRT. There was no change in dyssynchrony, or MAA contraction.
Conclusions—Reduction in MR post CRT is associated with favorable changes in MV geometry and closing forces on the MV. It does so by favorably affecting the force balance acting on the MV in two ways: reducing tethering through reversal of LV remodeling; and increasing the systolic duration of peak transmitral closing pressures.
Key Words: heart failure • valves • 3D echocardiography • Cardiac resynchronization therapy • Functional mitral regurgitation
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Circ Cardiovasc Imaging 2009 2: 427-428.
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  K. Eskesen, S. Kanagalingam, and T. P. Abraham Mitral Regurgitation in Cardiac Resynchronization: Solving Another Piece of the Puzzle Circ Cardiovasc Imaging, November 1, 2009; 2(6): 427 - 428. [Full Text] [PDF]
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