Pathogenesis of acute ischemic mitral regurgitation in three dimensions

Abstract

Changes in the geometric and intravalvular relationships between subunits of the ovine mitral valve were measured before and after acute posterior wall myocardial infarction in three dimensions by means of sonomicrometry array localization. In 13 sheep, nine sonomicrometer transducers were attached around the mitral anulus and to the tip and base of each papillary muscle. Five additional transducers were placed on the epicardium. Snares were placed around three branches of the circumflex coronary artery. One to 2 weeks later, echocardiograms, dimension measurements, and left ventricular pressures were obtained before and after the coronary arteries were occluded. Data were obtained from seven sheep. Coronary occlusion infarcted 32% of the posterior left ventricle and produced 2 to 3+ mitral regurgitation by Doppler color flow mapping. Multidimensional scaling of dimension measurements obtained from sonomicrometry transducers produced three-dimensional spatial coordinates of each transducer location throughout the cardiac cycle before and after infarction and onset of mitral regurgitation. After posterior infarction, the mitral anulus enlarges asymmetrically along the posterior anulus, and the tip of the posterior papillary muscle moves 1.5 +/- 0.3 mm closer to the posterior commissure at end-systole. The posterior papillary muscle also elongates 1.9 +/- 0.3 mm at end-systole. The left ventricle enlarges asymmetrically and ventricular torsion along the long axis changes. The development of postinfarction mitral regurgitation appears to be the consequence of multiple small changes in ventricular shape and contractile deformation and in the spatial relationship of mitral valvular subunits.

Coordinate-Free Analysis of Mitral Valve Dynamics in Normal and Ischemic Hearts

“…Prior analyses used a coordinate system representation of mitral valve structures. 11,12 To eliminate rigid-body rotation and translation artifacts, these coordinate systems must be fixed to a mitral valve structure, such as the mitral annulus. Different choices of coordinate system result in different geometry and dynamics that may mask important findings; this dilemma has precluded gaining more mechanistic insight into the coordinated function of the valvular and subvalvular structures.…”

“…The proposed mechanisms range from theories of ischemia-induced deformation of the mitral annulus, 1,2 disturbances in papillary muscle dynamics, 3,4 and primary changes in LV shape and contractility [5][6][7][8] to theories that develop an integrated mechanism of LV contractility and mitral valve function 9,10 or of regional LV geometry and mitral valve function. [11][12][13] These disparate findings attest to our ignorance of this vexing problem.…”

“…11,12 Measurements of the 3D dynamic geometry of the mitral valve complex, however, depend on the choice of coordinate system. Subjectivity in the choice of coordinate system and the huge complexity inherent in processing and unifying the 3D coordinates of the mitral valve structures throughout the cardiac cycle may obfuscate salient findings and actually hinder our attempts to reach a mechanistic understanding of mitral valve function.…”

Geometric Differences of the Mitral Apparatus Between Ischemic and Dilated Cardiomyopathy With Significant Mitral Regurgitation

“…6 -11 With recent advances in 3D imaging techniques, geometric changes of the mitral apparatus accompanied by distortion of the LV chamber from which the PMs arise have been explored. [12][13][14][15][16][17] In these studies, leaflet tethering by the displaced PMs due to regional or global LV dysfunction has been suggested as a main mechanism of functional MR. However, the geometry of the mitral apparatus accompanied by regional or global LV dilatation has not been clarified differentially.…”

Echocardiographic evaluation of systolic heart failure

“…Leaflet motion is restricted with apical displacement of the coaptation zone, causing incomplete systolic closure of the mitral valve or “systolic tenting” 22 . Ischaemic MR results from complex alterations of spatial relationships between the LV and mitral apparatus 23 and a recent study confirmed that MR severity is related to systolic tenting and not LV dysfunction 24 . Ischaemic MR occurring early or late after AMI is associated with increased mortality 25 , 26 , and severe MR portends poor prognosis 27 , 28 .…”