TRANSESOPHAGEAL ECHOCARDIOGRAPHIC ASSESSMENT OF THE CONTRIBUTION OF INTRINSIC TISSUE THICKNESS TO THE APPEARANCE OF A THICK MITRAL-VALVE INPATIENTS WITH MITRAL-VALVE PROLAPSE

Objectives. This prospective, blinded transesophageal echocardiographi c study was performed to determine the relative contributions of leafl et redundancy and overlap versus intrinsic tissue thickening as mechan isms for the apparent increase in diastolic thickness of the mitral va lve. Background. Increased diastolic thickness of the mitral valve has been identified as an echocardiographic feature that predicts subsequ ent adverse sequelae in patients with mitral valve pro lapse (MVP). Me thods. Eleven patients with clinical and transthoracic echo cardiograp hic evidence of MVP and 11 age-matched control subjects underwent prot ocol transesophageal echocardiography to image the mitral valve in two orthogonal planes and to measure its thickness in systole and diastol e. Results. Maximal diastolic width of the slack, unloaded anterior le aflet was significantly greater in patients with MW than in control su bjects (mean +/- SD: 0.64 +/- 0.20 cm vs. 0.30 +/- 0.04 cm, p < 0.001) . Similarly, diastolic posterior leaflet width was greater in patients with MW (0.67 +/- 0.39 cm vs. 0.31 +/- 0.06 cm, p < 0.01). In contras t, minimal systolic width of the distended pressure loaded mitral valv e was not significantly different between patients with MVP and contro l subjects for either the anterior (0.22 +/- 0.05 cm vs. 0.20 +/- 0.04 cm, p = NS) or the posterior (0.25 +/- 0.07 cm vs. 0.24 + 0.05 cm, p = NS) leaflets. The percent change in leaflet width from diastole to s ystole (%Delta W), an index of the contribution of dynamic factors (e. g., leaflet redundancy and overlap) to the apparent increase in diasto lic leaflet thickness, was significantly greater in patients with MW t han in control subjects for both the anterior (%Delta W 62 +/- 13% vs. 34 +/- 16%, p < 0.001) and the posterior (%Delta W54 +/- 19% vs. 22 /- 21%, p < 0.005) leaflets. Conclusions. The apparent increase in dia stolic mitral leaflet thickness in patients with MW versus control sub jects is largely attributable to dynamic factors such as leaflet redun dancy, over lap and deformation. During diastole, when the mitral leaf lets are slack and unstressed, the leaflets appear markedly thickened in patients with MVP. In contrast, during systole, when developed intr aventricular pressure distends the leaflets, causing them to stretch a nd balloon into the left atrium, the intrinsic tissue thickness is muc h less than that measured in diastole. These findings have important i mplications for the morphologic criteria used to diagnose MVP and the potential pathophysiologic mechanisms for adverse sequelae in this syn drome.