velocity vector imaging ( vvi ) is a new echocardiographic technique based on 2-dimensional ( 2-d ) gray - scale imaging , with spatial coherence of ultrasonic ultrasound , dot tracing , and contour tracing , and is used for analysis of myocardial tissue motion and velocity . vvi acquires information on the amplitude and phase of 2-d pixels , and uses real - time speckle tracking algorithm to determine the displacement motion and vectoral direction of myocardial tissues to obtain the actual information on the direction of activity , velocity , distance , and phase of regional myocardial tissues . compared with previous imaging techniques , vvi has the advantages of being and angle - independent and highly reproducible , which makes it an exciting tool for research applications to evaluate the circumferential , radial and longitudinal velocities , and the strain and strain rates in various disease settings . vvi has quickly become the latest technology employed for analysis of myocardial mechanics and regional heart function , and can also be used to quantify parameters such as strain and strain rate and circumferential direction of long and short axis , myocardial velocity , and the precise measurement of synchronization between left ventricular ( lv ) function and lv wall motion . myocardial mechanics play an important role in cardiac mechanics and involves the mechanical characteristics of tension , length ( l ) , and speed of cardiac muscular motion . an assessment of myocardial mechanics using vvi may reflect the state of cardiac function and reveal invaluable prognostic information in cardiovascular disease conditions , for example in idiopathic dilated cardiomyopathy and coronary artery disease . accordingly , multiple studies reported that vvi is a better approach compared to other methods , such as measurement of lv ejection fraction , in determining the heart function [ 79 ] . in practice , myocardial mechanics is evaluated from 3 vvi parameters : strain , strain rate , and tissue velocity . the velocity parameter conveys information on the risk of diastolic heart failure , while the cardiac strain and strain rate , derived from the velocity data , conveys information on tissue deformity and ventricular function . strain is defined as relative myocardial deformation that measures changes in the length ( l ) of myocardium in relation to its original length ( ol ) . strain rate is defined as the deformation rate of the myocardium , which conveys the rate of shortening or lengthening of the tissue . beginning in the 1990s , tagged magnetic resonance imaging ( tmri ) has been widely used to detect various heart diseases . however , several new methods have been developed to overcome the significant disadvantages of tmri , mainly its high cost and low frame rate . in this context , vvi technique has become a popular approach for measurement and evaluation of myocardial mechanics . a feature - tracking echocardiography using vector velocity imaging ( vvi ) measures the myocardial strain , strain rate ( sr ) , and velocity of the regional myocardium through a combination of speckle tracking , mitral annulus motion , tissue - blood border detection , and the periodicity of the cardiac cycle using r - r intervals . thus , vvi is a promising tool in clinical applications for evaluation of myocardial motion and ventricular function , devoid of the inherent limitations of doppler echocardiography [ 1416 ] . previously , the clinical potential of vvi was evaluated in specific diseases or therapies such as myocardial ischemia , cardiac transplantation , myocardial infarction , or pericardial adhesion [ 15,1719 ] . the present study evaluated the feasibility of vvi to analyze the lv myocardial mechanics in normal new zealand white rabbit , an animal model widely used in cardiovascular disease research , to understand the mechanical characteristics of cardiac structures in rabbits and to lay the foundation for future studies related to human myocardial mechanics . all procedures related to animal experiments and animal care were approved by medicine ethics review committee of the second xiangya hospital of central south university . animal experiments were conducted in accordance with public health service policy on humane care and use of laboratory animals , guide for the care and use of laboratory animals ( institute of laboratory animal resources , national research council , 1996 ) . all efforts were made to minimize suffering and reduce the number of animals used for the study . all new zealand white rabbits ( 1.52.5 kg ) , including 15 males and 15 females , were obtained from the laboratory animal center of the second xiangya hospital of central south university . the current study was performed using color doppler ultrasonography ( 3d - cdu ) ( acuson sequoia 512 ) , with 7.0 mhz transducer frequency and 50 frames / s frame rate of dynamic gray scale imaging . the 2-d echocardiography images were acquired , which included the parasternal left long - axis views and short axis views at the level of lv mitral valve , papillary muscles and apex . myocardial velocity , strain and strain rate curve for each segment in long - axis and short - axis view of the lv and rotational angles and rotational velocities curve in short - axis view of the lv were obtained based on a 16-segment model of the american society of echocardiography . segmental myocardial peak systolic velocities ( vs ) and peak diastolic velocities ( vd ) were measured from lv velocity curves . segmental myocardial peak systolic strain ( ss ) was also obtained from the strain curve . myocardial peak systolic strain rate ( srs ) and peak diastolic strain rate ( srd ) for each segment was measured from the strain rate curve . from the rotation and velocity curves , peak apical rotation , peak apical rotation velocity , peak apical untwist velocity and peak basal rotation , peak basal rotation velocity , and peak basal untwist velocity were measured . statistical significance of multiple measurement data was analyzed using variance with the significance level at 0.05 . a p - value of less than 0.05 was used to define a significant difference . all procedures related to animal experiments and animal care were approved by medicine ethics review committee of the second xiangya hospital of central south university . animal experiments were conducted in accordance with public health service policy on humane care and use of laboratory animals , guide for the care and use of laboratory animals ( institute of laboratory animal resources , national research council , 1996 ) . all efforts were made to minimize suffering and reduce the number of animals used for the study . all new zealand white rabbits ( 1.52.5 kg ) , including 15 males and 15 females , were obtained from the laboratory animal center of the second xiangya hospital of central south university . the current study was performed using color doppler ultrasonography ( 3d - cdu ) ( acuson sequoia 512 ) , with 7.0 mhz transducer frequency and 50 frames / s frame rate of dynamic gray scale imaging . the 2-d echocardiography images were acquired , which included the parasternal left long - axis views and short axis views at the level of lv mitral valve , papillary muscles and apex . myocardial velocity , strain and strain rate curve for each segment in long - axis and short - axis view of the lv and rotational angles and rotational velocities curve in short - axis view of the lv were obtained based on a 16-segment model of the american society of echocardiography . segmental myocardial peak systolic velocities ( vs ) and peak diastolic velocities ( vd ) were measured from lv velocity curves . segmental myocardial peak systolic strain ( ss ) was also obtained from the strain curve . myocardial peak systolic strain rate ( srs ) and peak diastolic strain rate ( srd ) for each segment was measured from the strain rate curve . from the rotation and velocity curves , peak apical rotation , peak apical rotation velocity , peak apical untwist velocity and peak basal rotation , peak basal rotation velocity , and peak basal untwist velocity were measured . statistical significance of multiple measurement data was analyzed using variance with the significance level at 0.05 . a p - value of less than 0.05 was used to define a significant difference . in the longitudinal direction , the myocardial motion in lv pointed to the apical segment of the heart in systole , while in diastole the myocardial motion pointed to the basal segment of the heart , and the motion vectors decreased from basal to apical segment . in the brachy - diagonal direction , simultaneously , there was a clockwise rotation in the basal segment of heart with opposite rotation in the apical segment . moreover , the direction of myocardial motion was also in opposite directions during systole and diastole . as illustrated in figures 1 and 2 , the velocity curves in the long and short axes were both composed of positive and negative waveform . the positive waveform represented movement toward the reference in systole . by contrast , the negative waveform represented the myocardium moving away from the reference in diastole . the myocardium shortened in systole and lengthened in diastole and returned to its ol at the end of diastole ( myocardial l in end diastole which marked as zero in the curve ) . the strain rate curve showed a negative waveform in the systolic period and a positive waveform in diastolic period , which represented myocardial shortening in systole and lengthening in diastole , respectively . the vvi parameter of the lv in long and short axes is shown in tables 1 
 2 , respectively . 05 ) , whereas the peak strain and strain rate did not change significantly ( p>0.05 ) . in the posterior left ventricle , the peak systolic velocity in middle segment and peak diastolic velocity in basal and middle segments were significant higher than the other segments of interventricular septum ( p<0.05 ) . for short axis , there were significant differences of velocity , strain and strain rate between the segments . specifically , the velocity in anterior septal and anteroseptal was significantly higher than the lateral , posterior and inferior walls ( p<0.05 ) . strain and strain rate in anterior wall and lateral wall were also significantly higher than in the other segments ( p<0.05 ) . rotation of the base ( clockwise ) and apex of left ventricle ( counter - clockwise ) in opposite directions during systole and diastole were observed from the apex . the rotation angle , rotation velocity and unwinding velocity in the apex were higher than the basal segment ( p<0.05 ) and the twist angle of the left ventricle was 10.762.24 ( table 3 , figure 3 ) . in the longitudinal direction , the myocardial motion in lv pointed to the apical segment of the heart in systole , while in diastole the myocardial motion pointed to the basal segment of the heart , and the motion vectors decreased from basal to apical segment . in the brachy - diagonal direction , simultaneously , there was a clockwise rotation in the basal segment of heart with opposite rotation in the apical segment . moreover , the direction of myocardial motion was also in opposite directions during systole and diastole . as illustrated in figures 1 and 2 , the velocity curves in the long and short axes were both composed of positive and negative waveform . the positive waveform represented movement toward the reference in systole . by contrast , the negative waveform represented the myocardium moving away from the reference in diastole . the myocardium shortened in systole and lengthened in diastole and returned to its ol at the end of diastole ( myocardial l in end diastole which marked as zero in the curve ) . the strain rate curve showed a negative waveform in the systolic period and a positive waveform in diastolic period , which represented myocardial shortening in systole and lengthening in diastole , respectively . the vvi parameter of the lv in long and short axes is shown in tables 1 
 2 , respectively . 05 ) , whereas the peak strain and strain rate did not change significantly ( p>0.05 ) . in the posterior left ventricle , the peak systolic velocity in middle segment and peak diastolic velocity in basal and middle segments were significant higher than the other segments of interventricular septum ( p<0.05 ) . for short axis , there were significant differences of velocity , strain and strain rate between the segments . specifically , the velocity in anterior septal and anteroseptal was significantly higher than the lateral , posterior and inferior walls ( p<0.05 ) . strain and strain rate in anterior wall and lateral wall were also significantly higher than in the other segments ( p<0.05 ) . rotation of the base ( clockwise ) and apex of left ventricle ( counter - clockwise ) in opposite directions during systole and diastole were observed from the apex . the rotation angle , rotation velocity and unwinding velocity in the apex were higher than the basal segment ( p<0.05 ) and the twist angle of the left ventricle was 10.762.24 ( table 3 , figure 3 ) . vvi , a new b - mode echo technique , is angle - independent and can evaluate radial , circumferential , and longitudinal velocities , and strain . our study examined the characteristics of myocardial mechanics in new zealand white rabbits by using vvi . our results clearly detected 3-d motions in the lv , including the contraction movement along the long axis and short axis of the heart , and the twist motion along the long axis of the heart from the heart apex to the heart bottom . the significance of these results is that the unique 3-d structure of myocardial fiber is a key factor of ventricular mechanical characteristics and vasomotion , and plays an important role in lv ejection and filling . our findings also revealed that at basal state , the direction of long axis in myocardium of rabbits shows velocity differences , with basal segment exhibiting the peak velocity , followed by the middle and apical segments . this result suggested that contraction of descending myocardial fiber causes the heart bottom to move up to the heart apex , while the heart apex is relatively fixed . however , the peak values of regional strain and strain rate showed no significant difference between the basal , middle , and apical segments , indicating uniform deformation of lv wall in the long - axis direction of the myocardium . the explanation for this result might be that the motion along the short axis involves concentric exercise of left ventricle , i.e. , muscle contraction leading to muscle shortening , and the circumferential motion has a tangential relationship with lv . concentric exercise is measured by the velocity of myocardial motion and is the result of coordinated contraction of 3 layers of myocardial fibers , while circumferential motion is measured by myocardial strain and strain rate and is generally determined by the contraction of annular myocardial fibers in the middle of the ventricle . our results also demonstrated that peak velocity , strain , and strain rate in the short axis of individual segments at the same level showed significant differences between each other . the peak velocities of both anteroseptal and anterior lv walls were higher than the lateral , posterior , and inferior . the peak strains and strain rates of both anterior and lateral lv walls were higher than the rest of the segments , which can be explained by the fact that the anterior and lateral lv walls are mostly composed of middle circular myocardial fibers . it is accepted that the configuration of myocardial fibres determines the displacement of ventricular walls . in systole , the base rotates clockwise and the apex rotates counter - clockwise , resulting in twisting of the heart . in diastole , the base rotates counterclockwise and the apex rotates clockwise , leading to untwisting . during these 2 processes , significant differences between the apical and basal rotation were observed , particularly our results showing that the rotation angle , rotation rate , and reverse rotation rate of the apex were all significantly higher than the corresponding values observed for the base . based on the collective results obtained from this study , it is reasonable to speculate that vvi is a helpful tool for evaluating the mechanical characteristics of left ventricle myocardium . reported the use of vvi in cardiac magnetic resonance ( cmr ) imaging and suggested that vvi was reproducible for analysis of strain of lv myocardial mechanics in hypertrophic cardiomyopathy ( hcm ) . further , dae - hee et al . compared vvi with speckle tracking echocardiography ( ste ) and showed that vvi was significantly better at determining the major apical and basal rotation , as well as parameters related to twist , and proposed the use of vvi in other contexts such as heart function , left atrial function , and regional myocardial function . thus , vvi parameters allow qualitative and quantitative assessment of myocardial motion and both our results and observations from previous studies demonstrate the feasibility of vvi for assessment of ventricular myocardial mechanics . our vvi results reveal that contraction of left ventricle myocardium along the long axis and short axis of the heart , as well as the twist motion , happens with regularity . further , our results strongly support the use of vvi to evaluate the mechanical characteristics of left ventricle myocardium , and demonstrate the feasibility of using vvi in diagnostic imaging in humans and in pre - clinical models of cardiovascular diseases in new zealand white rabbits .
backgroundour study aimed to investigate the feasibility of velocity vector imaging ( vvi ) to analyze left ventricular ( lv ) myocardial mechanics in rabbits at basal state.material/methodthe animals used in this study were 30 new zealand white rabbits . 
 all rabbits underwent routine echocardiography under vvi - mode at basal state . the 2-dimensional ( 2-d ) echocardiography images 
 acquired included parasternal left long - axis views and short - axis views at the level of lv mitral valve , papillary muscles , and apex . 
 images were analyzed by vvi software.resultsat basal state , longitudinal lv velocity decreased from the basal to the apical segment ( p<0.05 ) . in the short axis direction , 
 the highest peak myocardial velocity was found between the anterior septum and anterior wall for each segment at the same level ; the peak strains and strain rates ( sr ) were the highest in the anterior and lateral wall compared to other segments ( all p<0.05 ) . during systole , 
 lv base rotated in a clockwise direction and lv apex rotated in a counter - clockwise direction , while during diastole , both lv base and apex rotated in the direction opposite to systole . the rotation angle , rotation velocity and unwinding velocity in the apical segment were greater than the basal segment ( p<0.05).conclusionsvvi is a reliable tool for evaluating lv myocardial mechanics in rabbits at basal state , and the lv long - axis short - axis and torsional motions reflect the normal regular patterns . 
 our study lays the foundation for future experimental approaches in rabbit models and for other applications related to the study of human myocardial mechanics .