title: Paradoxic decrease in ischemic mitral regurgitation with papillary muscle dysfunction: insights from three-dimensional and contrast echocardiography with strain rate measurement.
abstract: BACKGROUND
  Ischemic mitral regurgitation (MR) was first ascribed to papillary muscle (PM) contractile dysfunction. Current theories include apical leaflet tethering caused by left ventricular (LV) distortion, but PM dysfunction is still postulated and commonly diagnosed. PM contraction, however, parallels apical tethering, suggesting the hypothesis that PM contractile dysfunction can actually diminish MR due to ischemic distortion of the inferior base alone.
  
  
  RESULTS
  We therefore occluded the proximal circumflex circulation in 7 sheep while maintaining PM perfusion, confirmed by contrast echocardiography. By 3D echocardiography, we measured the tethering distance between the ischemic medial PM tip and anterior annulus and LV ejection volume to give MR (by subtracting flowmeter LV outflow). In 6 sheep without initial MR, inferior ischemia alone produced PM tip retraction with restricted leaflet closure and mild-to-moderate MR (regurgitant fraction, 25.2+/-2.8%). Adding PM ischemia consistently decreased MR and tethering distance (5.2+/-0.3 to 1.4+/-0.3 mL; +3.8+/-0.5 mm to -2.2+/-0.7 mm axially relative to baseline; P<0.001) as PM strain rate decreased from +0.78+/-0.07 per second (contraction) to -0.42+/-0.06 per second (elongation, P<0.001) and leaflet tenting decreased. In one sheep, prolapse and MR resolved with inferior ischemia and recurred with PM ischemia.
  
  
  CONCLUSIONS
  PM contractile dysfunction can paradoxically decrease MR from inferobasal ischemia by reducing leaflet tethering to improve coaptation. This emphasizes the role of geometric factors in ischemic MR mechanism and potential therapy.
authors.affiliation: Cardiac Ultrasound Laboratory, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: E
authors.initials: E
authors.lastname: Messas
authors.forename: J L
authors.initials: JL
authors.lastname: Guerrero
authors.forename: M D
authors.initials: MD
authors.lastname: Handschumacher
authors.forename: C M
authors.initials: CM
authors.lastname: Chow
authors.forename: S
authors.initials: S
authors.lastname: Sullivan
authors.forename: E
authors.initials: E
authors.lastname: Schwammenthal
authors.forename: R A
authors.initials: RA
authors.lastname: Levine
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D004452:Echocardiography / Q000379:methods*; D015150:Echocardiography, Doppler; D019560:Echocardiography, Three-Dimensional; D006329:Heart Conduction System / Q000503:physiopathology; D006439:Hemodynamics; D020407:Internet; D008944:Mitral Valve Insufficiency / Q000150:complications / Q000503:physiopathology*; D009200:Myocardial Contraction / Q000502:physiology; D017202:Myocardial Ischemia / Q000150:complications / Q000503:physiopathology*; D010210:Papillary Muscles / Q000503:physiopathology*; D012756:Sheep; D013314:Stress, Mechanical