THE RELATIONSHIP BETWEEN THE MITRAL ANNULUS AND LEFT-VENTRICULAR OUTFLOW TRACT

Mitral annular inflexibility due to rigid prostheses (ring or valve) h as long been considered to contribute to the mechanism of dynamic left ventricular outflow tract (LVOT) obstruction after mitral repair or r eplacement. In clarifying the geometric relationship between LVOT orif ice and mitral valve annulus (MVA) in eight normal subjects, the autho rs have endeavored to show how that a rigid mitral prosthesis might ob struct the LVOT based on the assumption that any rigid prosthesis nece ssarily follows the motion of the posterior half of the MVA (MVApost) in the course of every heart beat. During systole, the relationship be tween the MVApost and the approximated plane of the LVOT orifice was c onstant. However, with the respect to the relationship between the LVO T orifice and the approximated plane of the MVApost (PI-MVApost), the intersection between the two shifted toward the apex during systole. A ssuming the prosthesis is aligned on the MVApost with the same orienta tion as the PI-MvApost, this shift implies a reduction in the effectiv e size of the LVOT orifice due to the prosthesis. The calculated obstr uction rate was 24.9% (0 ms), 30.9% (100 ms), 35.5% (200 ms), and 45.4 % (300 ms). These results indicate the importance of maintaining the f lexibility of the MVA after mitral valve surgery.