| IntroductionLeft ventricular torsion(LVT)is defined as the left ventricular torsional deformation of apical counterclockwise rotation and basal clockwise rotation viewed from apex,of which the value calculated by the difference between apical rotation(AR) and basal rotation(BR).With LVT,systolic left ventricular(LV)function can be sensitively evaluated.Left ventficular rotation(LVR)is defined as the angular change of LV wall rotating around LV long axis.BR is clockwise with a minimal value, whereas AR is counterclockwise with a maximal value,therefore LVT is mainly affected by AR.Role of apex in LVT has not been reported.In this study,role of apex in LVT and its mechanism were explored with echocardiography.With heating,the apex of experimental dog was damaged and became transmural necrotic one without contraction,thus the active apical rotation in the necrotic myocardium lost completely. Role of apex in LVT was evaluated by comparing LVT before and after apical heating; role of apex in LVT was also analyzed by comparing the LVT of patients with apical infarction and of healthy volunteers.Tissue Doppler imaging(TDI)could accurately reflect speed of myocardial movement,and LVT could be accurately evaluated also since LVT was calculated by rotating speed of LV wall measured with TDI,combined with the speed-integrated formula and computer programming.LV ejection fraction (LVEF)was measured with real-time three-dimensional echocardiography(RT-3DE)to reflect LV systolic function.Strain rate imaging(SRI)was used to evaluate myocardial contractility. Methods14 experimental dogs were regarded as the subjects,control group before apical heating,apical necrotic group after apical heating.After opening of chest and pericardium,apex was heated and became transmurally necrotic.The heating apparatus was an iron heated by electricity,the heating temperature was 206℃±2℃,the part of iron used to touch apical surface was circle with an area of 3.0 cm~2.The regularity of heating time and its corresponding depth of necrotic myocardium had been known by the test in living dogs beforehand.Heating time was determined by thickest wall of heating zone.Apex was symmetrically heated by making apical tip the center of heating zone.As each of the experiments had been finished,myocardial damage of heating zone and its surroundings was observed with naked eyes,light microscope and electron microscope to evaluate whether the positions of heating zone and of echocardiographic measurement were correct or not.All the echocardiographic measurements were made with Philip iE33 Sonos system.The following values were recorded.Before and after apical heating,rotating speeds of LV lateral and septal walls were recorded with TDI to calculate LV rotation and LVT combining with the speed-integrated formula and computer programming;moving speeds of anterior and posterior walls were recorded with TDI to evaluate the changing radius of LV chamber. TDI was recorded at four different LV short-axis planes:apical necrotic zone,normal region near to heating zone,equatorial region and basal region.TDI of apical necrotic zone was recorded at the thoroughly necrotic apex,i.e.,the scanned plane was slightly upper than the lowest point of LV chamber;mitral valves were regarded as the anatomic landmark of basal short-axis plane;normal region near to heating zone on which a little landmark was put(on lateral wall)was at 18mm from apical tip (myocardium beyond 5mm to heating zone was normal,the radius of circular heating zone with an area of 3.0 cm~2 was 9.9mm,i.e.,myocardium beyond 14.9mm to the center of heating zone was normal to which another 3mm was added ensuring the measured myocardium was normal,thus normal region near to heating zone was recorded at 17.9mm from apical tip,about 18mm);equatorial region was at the LV short-axis plane with equal distance from apical and basal short-axis planes on which a little landmark was put(on lateral wall).The force of LV rotation and torsion is mainly determined by transverse myocardial contraction,thus circumferential SRI of lateral and septal walls was recorded to evaluate myocardial contractility before and after apical heating,the measured LV short-axis planes included:apical region,normal region near to heating zone,equatorial region and basal region,and the locations of these four regions were identical to those of TDI measurement.Value of SRI was showed with the averaged SRI of lateral and septal walls.LVEF was measured with 3RT-DE.Systolic LV pressure was recorded with pigtail catheter inside LV chamber, and the ratio of accelerating time of systolic LV pressure(from onset of QRS to peak LV pressure)to LV systolic duration(from onset of QRS to aortic valves closure detected by pulsed Doppler wave)(RT)was measured that was showed with percentage. After the experiment was finished,myocardial tissue was taken from apical heating zone,3mm to heating zone,5mm to heating zone and beyond 5mm to heating zone for examinations of light microscope and electron microscope.Observation of LV myocardial orientations of dogs could not be performed on experimental dogs since the apex had been heated and from which myocardial tissue had been taken for pathological examination.Another eight intact hearts were taken from healthy dogs. The eight hearts that had been boiled at 100℃for fifteen minutes were peeled with naked hands as they cooled off,LV myocardial orientations of these boiled hearts were observed.27 patients with apical infarction were regarded as studying objects,and 15 healthy volunteers as controls.All the echocardiographic measurements were performed with Philip iE33 Sonos system.Rotating speeds of LV lateral and septal walls were recorded with TDI to calculate LV rotation and LVT combining with the speed-integrated formula and computer programming;moving speeds of anterior and posterior walls were recorded with TDI to evaluate the changing radius of LV chamber. The measurements of SRI included circumferential SRI of lateral and septal walls and short-axis SRI of anterior and posterior walls.The locations of SRI at four LV short-axis planes were identical to those of TDI,including apical region,apex-superior region,equatorial region and basal region.Mitral valves were taken as the anatomic landmark of basal short-axis plane,papillary muscles as the anatomic landmark of equatorial short-axis plane;descending LV short-axis plane just before right ventricle disappeared as the apical-superior short-axis plane;descending LV short-axis plane just before left ventricle disappeared as the apical short-axis plane.LVEF was measured with 3RT-DE.ResultsSectional transmural light grey myocardium of heating zone was observed in all the 14 experimental dogs,showing a protein denaturation occurred in heating zone and myocardium of heating zone became transmurally coagulating necrotic.It was a symmetrical apical heating that the lowest point of LV chamber corresponded to the center of heating zone.The symmetrical apical heating was performed in all the 14 experimental dogs with the method of making apical tip the center of heating zone. Myocardium in heated zone and at 3mm to the heating zone had some changes under light microscope and electron microscope;part of myocardium at 5mm to the heating zone had some changes under electron microscope,but no change was found under light microscope,whereas myocardium beyond 5mm to heating zone had no change under electron microscope,thus myocardium 18mm to the center of heating zone was normal at which the TDI and SRI of normal myocardium near to heating zone could be reliably measured.After apical heating,LVT significantly decreased(P＜0.001)owing to the significant decrease of apical rotation(P＜0.001),but the clockwise basal rotation increased(P＜0.01);equatorial rotation and apex-superior rotation did not change significantly.After apical heating,systolic S wave of apical SRI of heating zone significantly decreased in absolute value(P＜0.001);no significant change of SRI was occurred in equatorial and apex-superior regions;systolic S wave SRI of basal region increased in absolute value to some extent(P＜0.05),which was related to basal rotation(r=0.54,P＜0.005).After apical heating,LV systolic pressure decreased(P＜0.05);RT increased(P＜0.01);LVEF decreased(P＜0.01);LV end-diastolic pressure increased(P＜0.01).LVT was closely related to LVEF(r=0.66,P＜0.001);LVT was negatively related to TR(r=—0.52,P＜0.005);TR was negatively related to LVEF(r =—0.68,P＜0.001).The angle between apical epicardial myocardial fibers and LV long axis was bigger than that of upper epicardial myocardial fibers by observing the orientation of LV myocardial fibers in eight boiled hearts.Therefore apical epicardial myocardial fibers were transverser than that of other LV parts,especially in anterior wall,but apical endocardial myocardial fibers had not the characteristic.Compared with the controls,of apical infarction the LVT significantly decreased (P＜0.001)due to the significant decrease of apical rotation(P＜0.001);apex-superior rotation significantly decreased(P＜0.002);equatorial rotation decreased to some extent without statistical significance;basal rotation did not change significantly.Of apical infarction,systolic S wave of apical circumferential SRI significantly decreased in absolute value(P＜0.001);apex-superior,equatorial and basal circumferential SRIs did not change significantly;systolic S wave of apical,apex-superior,equatorial and basal short-axis SRIs decreased in different degrees(of apex and apex-superior region, P＜0.001;of equatorial and basal regions,P＜0.05).Of apical infarction,LVEF significantly decreased(P＜0.001),which was closely related to LVEF(r=0.79,P＜0.001).Conclusions1.Apex plays a key role in LVT which is mainly determined by apical rotation.2.Role of apex in LVT is owing to apical contraction making apex rotate actively.3.The key role of apex in LVT is related to the following factors:orientation of apical epicardial myocardial fibers tends to LV transverse direction,therefore apical contraction has a largest short-axis vector of force in all of LV epicardial myocardial fibers and with a largest apical rotation in LV rotations;ratio of epicardial to endocardial volume is biggest in apex among all those of LV;the free state of apex is most significant in LV,making apex rotate freely.4.Apex plays a key role in systolic LV pressure formation and in LV ejection, which is related to the onset of LV contraction is at apex making apex contribute to LV pressure formation first;to anatomic position of apex is at the reverse direction of LV blood ejection,thus a normal apex contributes to the formation of impulse for LV ejection and resists the opposite impulse formed in LV ejection.5.Apex plays a key role in LVT,and apical rotation which dominates the value of LVT mainly stems from apical contraction;LVT is a part of LV contraction which forms a twisting force contributing to LV ejection,with LVT,LV systolic function can be sensitively evaluated...
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