Potential mechanism of left ventricular outflow tract obstruction after mitral ring annuloplasty

Objectives: The purpose of this study was to explore whether geometric chan ges that predispose to left ventricular outflow tract obstruction after mit ral ring annuloplasty are coupled to subvalvular apparatus disturbances. Me thods: Radiopaque markers were implanted in sheep: 9 in the ventricle, 1 in the high interventricular septum, 1 on each papillary muscle tip, 8 around the mitral anulus, 4 on the anterior mitral leaflet, and 2 on the posterio r leaflet. One group served as control (n = 5); the others were randomized to undergo annuloplasty with the Duran ring (n = 6; Medtronic, Inc, Minneap olis, Minn) or Carpentier-Edwards Physio ring (n = 6; Baxter Healthcare Cor p, Irvine, Calif), After a 7- to 10-day recovery period, 3-dimensional mark er coordinates were measured with biplane videofluoroscopy. Results: At the beginning of ejection, (1) the anterior leaflet was displaced toward the l eft ventricular outflow tract; (2) the normal atrially flexed anterior anul us was flattened into the left ventricular outflow tract; (3) the posterior anulus was displaced toward the left ventricular outflow tract; (4) the an terior papillary muscle was displaced septally; and (5) the posterior papil lary muscle was dislocated inwardly toward the anterior papillary muscle in the Physio ring group compared with the control group, During ejection, al l these structures moved septally, encroaching further on the left ventricu lar outflow tract. In the Duran ring group, only the posterior anulus was d isplaced toward the left ventricular outflow tract; the anterior leaflet wa s not displaced toward the left ventricular outflow tract, and it did not m ove septally during ejection. Conclusions: The semirigid Physio ring was as sociated with perturbations in annular dynamics that caused changes in papi llary muscle geometry. We propose an integrated valvular-subvalvular mechan ism to explain displacement of the anterior leaflet into the left ventricul ar outflow tract after mitral ring annuloplasty.