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Background: Acute aortic regurgitation (AR) is an urgent medical condition with acute change of volume and pressure load. Because of the mixed hemodynamic nature of AR, evaluation of left ventricular (LV) contractility is troublesome in clinical situation. Recently, left ventricular twist mechanics has been suggested as a load-independent parameter for LV function, and it can be reliable measurable by echocardiography using 2D speckle tracking method. We investigated the LV twist mechanics in acute AR in canine experimental model and evaluated the role of LV twist in assessment of LV function.Method: Acute AR model was made in seven mongrel dogs. Endomyocardial biopsy catheter was used to make injury to aortic valve through a cutdown into a left carotid artery with monitoring of transthoracic echocardiography. Serial transepicardial echocardiography was performed at baseline before generation of AR (no AR) and at mild, moderate, or severe AR. Concomitant hemodynamic evaluation for LV function (maximal slope of systolic pressure increment (dP/dt)) was also recorded using conductance catheter. Using the speckle tracking technique, LV apical and basal twist was calculated.Result: Overall, 31 different condition of no AR to severe AR was made and analyzed. dP/dt was moderately correlated with LV EF (r=0.59, P<0.001) and end systolic pressure (r=0.67, p<0.001). Peak apical rotation velocity at systole was highly correlated with dP/dt (r=0.82, P<0.001) and apical rotation, LV twist, peak LV twist velocity showed moderate correlation with dP/dt (r=0.71, r=0.66, r=0.69, and p<0.001 in all cases). Basal rotation and rotation velocity did not show any significant correlation with dP/dt. Multivariate analysis showed that peak apical rotation velocity is the independent factor from pressure and volume loading for explanation of dP/dt.Conclusion : Apical rotation velocity and apical rotation was well correlated with invasive measured LV contractility parameter, dP/dt, independently from pressure or volume overload in acute AR model and possibly reliable non-invasive parameter to evaluate the LV contractility in acute AR patients.