Experimental Evaluation Of Left Ventricle Torsional Function In Volume Overload, Pressure Overload And Myocardial Contractility Individuals Using Two—Dimensional Speckle Tracking Imaging

Objective:Speckle tracking imaging (STI), which is a echocardiographic technique with higher convenience and reproducibility, has been demonstrated by numerous studies to accurately assess the LV twist and untwisting function. The effects of some factors such as volume and pressure overload on LV torsional deformation still remain controversial. The present study sought to explore left ventricular twist in beagles with different pressure loading, volume overload and myocardial contractility using speckle tracking imaging (STI).Methods:1.In 10 female beagles, methoxamine(5-10μg/kg/min)and phentolamine (5-10μg/kg/min)were injected by femoral vein, and the ascending and descending models of left pressure loading were established, respectively.2. Balloons were placed and expanded in beagles’ femoral vein to establish the descending models of preload, while normal saline (0.9%,0.2ml/kg/min) were injected by femoral vein to establish the ascending models of preload.3. Esmolol (5-10μg/kg/min) and dobutamine (5-10μg/kg/min) were injected by femoral vein to establish the models of myocardial contractility decreasing and increasing.Two dimensional echocardiography images were recorded under baseline conditions and after pressure loading, volume overload and myocardial contractility changed. Twist-related parameters were measured by STI, and left ventricular catheterization was performed simultaneously.Results:1.Effect of pressure loading:Compared with that under baseline condition, end systolic volume(ESV)of left ventricle decreased and left ventricular ejection fraction(LVEF)was increased with methoxamine; end diastolic volume(EDV)was decreased, ESV was increased and LVEF was decreased with phentolamine. The differences were statistically significant (P<0.05). Compared with that under baseline condition, peak twist angle (Ptw) was increased in left ventricular apex, base and global segments, while time to peak twist angle (tPtw) was delayed with methoxamine. Ptw was decreased in left ventricular apex, base and global segments, while tPtw was delayed with phentolamine. The difference were statistically significant (P<0.05). Compared with baseline condition, left ventricular systolic pressure(LVSP)and left ventricular end-diastolic pressure(LVEDP)was increased and ±dp/dtmax was decreased with methoxamine and phentolamine, and the difference were statistically significant(P<0.05 or P<0.01). Ptw in global segments was significantly positively correlated with +dp/dtmax under methoxamine condition(r =0.656, P=0.03)and phentolamine condition (r=0.701, P=0.02).2. Effect of volume overload:Compared with that under baseline condition, LVDd, EDV and LVEF of left ventricle decreased after the balloons were placed in femoral vein; while the three measurements mentioned above increased with saline infusion. The differences were statistically significant (P<0.05); Compared with that under baseline condition, Ptw was decreased in left ventricular apex segments and were slightly increased in base and global segments, and tPtw was delayed with balloon placement. Ptw was increased in left ventricular apex, base and global segments, and tPtw was advanced with saline infusion, and the difference were statistically significant in base and global segments (P<0.05). Compared with baseline condition, LVSP and LVEDP was decreased and the difference were statistically significant (P<0.05) with the placement of balloon, while ±dp/dtmax was decreased, but the difference was not statistically significant. After saline infusion, LVSP, LVEDP and ±dp/dtmax were all increased with statistically significant difference (P<0.05). Ptw in global segments was significantly positively correlated with +dp/dtmax after saline infusion (r=0.657,P=0.034).2. Effect of myocardial contractility:Compared with that under baseline condition, ESV of left ventricle increased and LVEF was decreased with esmolol, while ESV was decreased and LVEF was increased with dobutamine. The differences were statistically significant (P<0.05). Compared with that under baseline condition, Ptw was decreased in apex, base and global segments of left ventricular and tPtw was delayed in all segments with esmolol, and the difference were statistically significant in apex and global segments (P<0.05). With dobutamine, Ptw was increased in left ventricular apex, base and global segments, and the difference were statistically significant in apex and global segments (P<0.05), while the change of tPtw was not statistically significant. Compared with baseline condition, LVSP and LVEDP was decreased and ±dp/dtmax was decreased with esmolol, while LVSP and LVEDP was increased and ±dp/dtmax was increased with dobutamine. The difference of both the two condition were statistically significant (P<0.05). Ptw in global segments was significantly positively correlated with +dp/dtmax under esmolol and condition((r=0.623,P=0.032)and dobutamine condition ((r=0.712, P=0.023).Conclusions:Ptw in left ventricular apex, base and global segments in beagles changes along with the different pressure loading, volume overload and myocardial contractility. STI is useful in evaluating left ventricular twist in beagles with different pressure loading.