CONTROVERSIES IN FELINE CARDIOMYOPATHY: SAM OF THE MITRAL VALVE - WHAT CAUSES THAT FLIPPING THING?

摘要

Dynamic left ventricular outflow tract (LVOT) obstruction (dynamic subaortic stenosis) due to the septal leaflet of the mitral valve (and/or the chordal structures associated with it) being dragged into the outflow tract is a common manifestation of hypertrophic cardiomyopathy (HCM) in cats. Although this phenomenon is called by several different names, systolic anterior motion (SAM) of the mitral valve is the generally accepted term.The mechanism by which SAM occurs has been and remains controversial. The Venturi effect was an early theory. The Venturi effect is the reduction in fluid pressure (suction) that results when a fluid flows through a narrowed (stenotic) region, increasingits velocity. It was thought that the LVOT was narrowed due to HCM and that the increased velocity of blood flow in this region "sucked" the mitral valve into the LVOT. In the 1980s, the realization that SAM can start prior to the ejection of blood through the LVOT effectively disproved this theory.1 However, one can occasionally still find this as a postulated mechanism in the literature.