Purpose:Evidence continues to accumulate associating mitral leaflet elongation with systolic anterior motion(SAM) of mitral valve(MV) by increasing leaflet mobility and providing a geometry that promotes this condition in patients with obstructive hypertrophic cardiomyopathy(HCM).However,whether similar findings happen to thenon-obstructive HCM or latent-obstructive HCM patients has not been fully clarified.Thus,the present study was designed tocompared the mitral leaflet length between the non-obstructive HCM patients and the latent-obstructive patients.Methods:We considered 34 HCM patient studied with exercise stress echocardiography on a semi-recumbent and tilting bicycle Ergometer(Lode BV,Groningen,the Netherlands)using a standard clinical protocol.Conventional measurement were performed.Left ventricular outflow tract pressure gradients(LVOT-PG) were measured at rest and during exercise,and the HCM patients were classified into non-obstructive(< 30 mmHg at rest and with exercise) and latent-obstructive(< 30 mmHg at rest and ≥ 30 mmHg with exercise) thereby.SAM of MV was defined as absent and present(incomplete and complete).The tenting area(TA) of MV comprised the area between the MV leaflets and the annulus plane,and the tenting height(TH) was measured at coaptation from the most protruding mitral leaflet tip to the annulus plane.Moreover,the anterior leaflet length(AL) and posterior leaflet length(PL) were measured in diastole on the apical3-chamber view.Then,the residual length(RL) was the uncoapted portion of the MV that protrudes distally beyond the coaptaton point.Results:Patients in both groups were well matched with respect to the age,gender,body surface area(BSA),the episodes of angina pectoris and syncope.There were no significant differences in maximal left ventricular wall thickness(MLVWT)and left ventricular mass index(LVMI) between both groups.Left ventricular ejection fraction(LVEF),LVOT-PG at rest and during exercise were significantly higher in the latent-obstructive HCM patients(all p < 0.05),while the first two were all in normal range.With respect to the MV parameter,the latent-obstructive HCM patients had more prominent SAM of MV.Furthermore,the RL of MV showed a clear trend of high values in the latent-obstructive HCM patients than the non-obstructive patients,whereas other parameters such as TA,TH,AL,and PL did not show any significances between the two groups.Conclusions:In the present study,we found that mitral leaflet elongation,by increasing RL,was also evident in the latent-obstructive HCM patients,as compared to the non-obstructive HCM,which was diagnosed with exercise stress echocardiography.Such mitral leaflet elongation or redundancy may play an important role in promoting SAM in response to LVOT forces,leading to the symptoms of patients.