Hemodynamic Study On Systolic Anterior Motion Of The Mitral Valve In Hypertrophic Obstructive Cardiomyopathy

Part Ⅰ Numerical simulation study on systolic anterior motion of themitral valve in hypertrophic obstructive cardiomyopathyObjective:To investigate the hydrodynamic mechanisms of systolic anterior motion(SAM)of the mitral valve in hypertrophic obstructive cardiomyopathy(HOCM).Methods:Based on computed tomography(CT)images and clinical data,pre-and post-operative computational models of the left ventricle were constructed for 6 HOCM patients receiving septal myectomy.SAM was abolished in 5 patients and persisted in one after septal myectomy surgery.The obtained simulation results including flow field of the left ventricle and mechanical behaviors of the mitral valve(MV)between pre-and post-operative FSI models were compared.Results:The pressure difference and shear stress on the mitral valve leaflets(MVL)were relatively high pre-operatively,and decreased significantly after satisfactory surgery,but remained high following failed surgery.The significant increase in coaptation-to-septal distance was found when SAM was abolished.Conclusions:Our results indicated that high pressure difference and shear stress on the MVL might directly initiate SAM in HOCM.Successful septal myectomy enlarged the coaptation-to-septal distance sufficiently to keep the MVL away from the ejection flow,thereby eliminating SAM.Part Ⅱ Echocardiographic study on systolic anterior motion of themitral valve in hypertrophic obstructive cardiomyopathyObjective:To identify echocardiographic indicators which are related to the initiation of systolic anterior motion(SAM)in hypertrophic obstructive cardiomyopathy(HOCM).Methods:A total of 480 cases of septal myectomy were performed by a single surgeon in our institution.Those patients whose post-operative echocardiography was conducted by a designated doctor were recruited,and patients with unclear images were excluded.Eventually,106 patients were included in this study.Except for 6 patients with isolated mid-ventricular obstruction,the remaining 100 patients were divided into three groups based on their echocardiographic results,which were patients without residual SAM(n=61),patients with residual SAM but no residual obstruction(defined as pressure gradient more than 30 mmHg,n=30),and patients with residual SAM and obstruction(n=9).In the left ventricular short-axis sections at the coaptation level,cross-sectional area of the outflow tract and the left ventricle were measured,and the ratio(R)= area of the outflow tract/area of the left ventricle.The measuring point was the frame when the mitral valve just closed.Results:In the early systole,before SAM actually began,the pre-operative ratio was quite small in the three groups(no residual SAM:0.252±0.047,n=42;residual SAM without obstruction:0.236±0.076,n=12;residual SAM and obstruction:0.236±0.077,n=5).After surgery,the post-operative ratio in patients without residual SAM increased significantly,which was much higher than the other two groups with residual SAM(no residual SAM:0.388±0.062,n=61,residual SAM without obstruction:0.31 ±0.069,n=30,residual SAM and obstruction:0.279±0.061,n=9,p<0.001).SAM was not observed in patients with isolated mid-ventricular obstruction,and the pre-operative ratio was quite large in these patients.Conclusion:Through comparing the area ratio of the left ventricular outflow tract in different subgroups,we confirmed that,the space between the septum and the coaptation in the early systole was a key factor influencing the initiation of SAM and its severity.