title: Pathogenesis of mitral regurgitation in tachycardia-induced cardiomyopathy.
abstract: BACKGROUND
  Dilated cardiomyopathy is often associated with mitral regurgitation (MR), or so-called functional MR, the mechanism of which continues to be debated. We studied the valvular and ventricular 3D geometric perturbations associated with MR in an ovine model of tachycardia-induced cardiomyopathy (TIC).
  
  
  RESULTS
  Nine sheep underwent myocardial marker implantation in the left ventricle (LV), mitral annulus, and mitral leaflets. After 5 to 8 days, the animals were studied with biplane videofluoroscopy (baseline), and mitral competence was assessed by transesophageal echocardiography. Rapid ventricular pacing (180 to 230 bpm) was subsequently initiated for 15+/-6 days until the development of TIC and MR, whereupon biplane videofluoroscopy and transesophageal echocardiography studies were repeated. LV volume was calculated from the epicardial marker array. Valve closure time was defined as the time after end diastole when the distance between leaflet edge markers reached its minimal plateau. TIC resulted in increased LV end-diastolic volume (P=0.001) and LV end-systolic volume (P=0.0001) and greater LV sphericity (P=0.02). MR increased significantly (grade 0.2+/-0.3 versus 2.2+/-0.9, P=0.0001), as did mitral annulus area (817+/-146 versus 1100+/-161 mm(2), P=0.0001) and mitral annulus septal-lateral diameter (28.2+/-3.5 versus 35.1+/-2.6 mm, P=0.0001). Time of valve closure (70+/-18 versus 87+/-14 ms, P=0.23) and angular displacement of both the anterior (29+/-5 degrees versus 27+/-3 degrees, P=0.3) and posterior (55+/-15 degrees versus 44+/-11 degrees, P=0.13) leaflet edges relative to the mitral annulus after valve closure did not change, but leaflet edge separation after closure increased (5.2+/-0.9 versus 6.8+/-1.2 mm, P=0.019).
  
  
  CONCLUSIONS
  MR in TIC resulted from decreased leaflet coaptation secondary to annular dilatation in the septal-lateral direction. These data support the use of annular reduction procedures, such as rigid, complete ring annuloplasty, to address functional MR in patients with dilated cardiomyopathy.
authors.affiliation: Department of Cardiovascular and Thoracic Surgery, Division of Cardiovascular Medicine, Stanford University School of Medicine, Stanford, CA, USA.
authors.forename: T A
authors.initials: TA
authors.lastname: Timek
authors.forename: P
authors.initials: P
authors.lastname: Dagum
authors.forename: D T
authors.initials: DT
authors.lastname: Lai
authors.forename: D
authors.initials: D
authors.lastname: Liang
authors.forename: G T
authors.initials: GT
authors.lastname: Daughters
authors.forename: N B
authors.initials: NB
authors.lastname: Ingels
authors.forename: D C
authors.initials: DC
authors.lastname: Miller
mesh_terms: D000818:Animals; D002304:Cardiac Pacing, Artificial; D002311:Cardiomyopathy, Dilated / Q000209:etiology / Q000503:physiopathology*; D004195:Disease Models, Animal; D017548:Echocardiography, Transesophageal; D006352:Heart Ventricles / Q000000981:diagnostic imaging / Q000503:physiopathology; D006439:Hemodynamics; D008943:Mitral Valve / Q000000981:diagnostic imaging / Q000503:physiopathology; D008944:Mitral Valve Insufficiency / Q000175:diagnosis / Q000209:etiology / Q000503:physiopathology*; D013610:Tachycardia / Q000150:complications / Q000503:physiopathology*; D018487:Ventricular Dysfunction, Left / Q000000981:diagnostic imaging / Q000503:physiopathology