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J Thorac Cardiovasc Surg 2003;125:315-324
© 2003 The American Association for Thoracic Surgery

Surgery for Acquired Cardiovascular Disease (ACD)

Tachycardia-induced cardiomyopathy in the ovine heart: Mitral annular dynamic three-dimensional geometry

From the Department of Cardiothoracic Surgery,^a Division of Cardiovascular Medicine,^b Stanford University School of Medicine, Stanford, Calif, and Laboratory of Cardiovascular Physiology and Biophysics,^c Research Institute of the Palo Alto Medical Foundation, Palo Alto, Calif.

Supported by grants HL-29589 and HL-67025 from the National Heart, Lung, and Blood Institute. Drs Timek, Tibayan, and Dagum were also supported by NHLBI INRSA grants HL-10452, HL-67563, and HL-10000, respectively. Drs Timek, Lai, Dagum, and Tibayan are Carl and Leah McConnell l Cardiovascular Surgical Research Fellows. Dr Timek was also a recipient of the Thoracic Surgery Foundation Research Fellowship Award. Dr Lai was supported by a fellowship from the American Heart Association, Western States Affiliate.

Received for publication April 8, 2002. Revisions requested June 12, 2002; revisions received July 15, 2002. Accepted for publication July 18, 2002. Address for reprints: D. Craig Miller, MD, Department of Cardiothoracic Surgery, Falk Cardiovascular Research Center, Stanford University School of Medicine, Stanford, CA 94305-5247 (E-mail: dcm{at}leland.stanford.edu).

Background: Ring annuloplasty has been used to correct annular dilatation and mitral regurgitation in dilated cardiomyopathy, but little is known about the dynamic precise 3-dimensional geometry of the mitral annulus in this condition.
Methods: Nine sheep had radiopaque markers sewn to the mitral annulus, creating 8 distinct segments beginning at the posterior commissure (segments 1-4, septal mitral annulus; segments 5-8, lateral mitral annulus). Biplane videofluoroscopy and transesophageal echocardiography were performed before and after rapid pacing (180-230 min^-1 for 15 ± 6 days) sufficient to develop tachycardia-induced cardiomyopathy and mitral regurgitation. Mitral annular segment contraction was defined as the percentage difference between maximum and minimum lengths. Mitral annular area and mitral annular septal-lateral and commissure-commissure diameters and 3-dimensional shape were determined from marker coordinates.
Results: With tachycardia-induced cardiomyopathy, end-diastolic mitral annular area, septal-lateral diameter, and commissure-commissure diameter increased by 36% ± 14%, 25% ± 12%, and 9% ± 5%, respectively (P < .01), whereas mitral regurgitation increased from 0.3 ± 0.2 to 2.2 ± 0.9 (P < .0001). All annular segments dilated at end-diastole with tachycardia-induced cardiomyopathy, except the segment between the midseptal annulus and the left fibrous trigone. Annular segment contraction was significantly decreased with tachycardia-induced cardiomyopathy in the lateral, but not in the septal, regions. Three-dimensional reconstruction of annular shape revealed a saddle shape of the annulus at baseline; this shape was also measured with tachycardia-induced cardiomyopathy, but there was some flattening of the septal annulus.
Conclusions: With tachycardia-induced cardiomyopathy, the mitral annulus dilated substantially, being more in the septal-lateral than in the commissure-commissure dimension. Greater annular segmental dilatation and decreased contraction occurred in the lateral annulus. The saddle shape of the annulus was retained but flattened.

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