| Objectives1. To uncover the relationships between the myocardial band and the sequential contractile process of the left ventricular (LV) by instantaneous velocity vector tracking the movements of the LV wall in whole cardiac cycle and analysis the ventricular movements in different periods (isovolumic contraction, torsion, post-ejection isovolumic phase and rapid filling) based on the spiral structure theory of the myocardial band.2. To discover the pattern of the opposite rotation direction of the apical segment and basal segment with the help of newly applied cardiovascular magnetic resonance feature tracking (CMR-FT) and to analyze their rotation degree, rotation velocity and timing hiatus both in normal group and in patients with coronary artery disease (CAD), and compare the rotation differences between these different groups.3. By self-matching comparison of the rotation movement changes between pre and post coronary artery bypass grafting (CABG), the study attempted to evaluate the clinical value of the ventricular torsion as a sensitive indicator of cardiac function.Methods and materials1. The hearts of different species (pig hearts and goat hearts) were dissected as previously described methods by Torrent-Guasp. After the heats were dissected, they were unfolded to stretching state and different segments were dyed in different colors. Then the hearts were recovered to the original state and were cut through corresponding planes in MRI short-axis view sections.2. After 20 patients received MRI screening, their 4-chamber view images were analyzed by the software (TOMTEC Imaging Systems,2D Cardiac Performance Analysis MR, Version 1.2, Munich, Germany) which divided the endocardium of the LV into 48 segments after manual contours of the endocardium were performed on an end-diastolic image, and the software automatically tracked the segments for each frame of the cardiac cycle. The direction and magnitude of the segments’instantaneous velocity vector revealed the sequential change of the LV wall during different periods (isovolumic contraction, torsion, post-ejection isovolumic phase and rapid filling).3. A total of 54 normal people’s hearts (different ages and genders) were screened by MRI and their short axis views of the whole heart were acquired. The apical and basal planes’endocardium were tracked and their peak rotation, rotation velocity and time-to-peak value were calculated. Viewed from the LV apex, counterclockwise rotation was identified as a positive value, while the clockwise rotation was denoted as a negative value. Torsion and recoil are the net difference between the apex and base.4. There were 33 CAD patients with previous myocardial infarction (MI) and LV ejection fraction (EF) between 30%-50% were prospectively included in this study and received cardiovascular magnetic resonance imaging (MRI), including 16 patients with anterior MI and 17 patients with posterior MI. The apical and basal peak rotation, rotation velocity and time-to-peak value were compared with normal group respectively.5. Of the 33 CAD patients included in previous study,12 patients underwent both a preoperative MRI study (18.3±19.9 days before CABG, median 13 days) and a postoperative MRI examination at least 89 days (237.6±99.1 days after CABG, median 225 days), and self-matching comparison was perform to observe the improvement of torsion movement, which was compared with the improvement of ejection fraction to identify the sensitivity of torsion as the indicator of cardiac function, and their correlation analysis was also performed.Results1. Using the previously described methods, all the hearts can be dissected into an integrated myocardial band included apical loop and basal loop. The apical loop is constituted by the descending and ascending segments which conform to the right-and left-handed helical arrangement. The septum is composed of the left-handed and right-handed helix, and their distribution was asymmetry both in the upper and lower septum. The basal loop is circumferential which wraps around the upper two thirds of LV free wall, composed of three layers of fibers, and the right ventricle but does not involve the septum.2. Tracking of the ventricular myocardium showed that during the isovolumic contraction period, LV narrows and rotate counterclockwise prompted by the shortening of circumferential and descending segments, whereas the lower one third of LV free wall composed of ascending segment is static. In torsion period, the apex rotates in a counterclockwise direction while the base moves clockwise, and the heart twists like wringing out a wet towel. The septum also twists and the vector angulation is directed towards the apex, results in LV shortening and narrowing. When the heart starts to relax, the basal loop and descending segment stop shortening while the ascending segment is still contracting, and this time hiatus is about-80 ms. The whole heart rotates clockwise by the recoil force of circumferential fibers and its elongation caused by ascending segment erection create a deceleration of LV pressure and increasing vacuum that causes suction after the LV pressure is lower than atrial pressure. After untwisting and elongation movement, the heart begins to widen by rapid filling and atrial contraction. The whole cardiac cycle can be divided into four periods of narrow, torsion, lengthen and widen and the result was the interactions among the simultaneously contraction of circumferential fibers and spiral fibers.3. In normal heart, the apex rotated counterclockwise in systolic period with the peak rotation was 10.2 ± 4.8°, and time-to-peak value was 234.1 ± 42.3ms. The peak twisting and untwisting velocities of apex were 51.1 ± 30.5°s and-38.6 ± 28.1°s. Meanwhile, the base rotated clockwise as the peak rotation was 7.0 ± 3.3° with the peak time of 312.1 ± 56.20ms, and the peak twisting and untwisting velocities of base were-43.1 ± 22.8°/s and 29.4 ± 26.9°/s. The rotation degree of apex was significantly greater than that of the base, and the time hiatus of untwisting between apex and base was 78.0±14.0ms, during which period the heart recoils and its suction set the stage for the following rapid filling period.4. Compared with normal group, the apical and basal peak rotations were significantly decreased in anterior MI patients, while the decrease of rotation velocity was not significant. The untwisting of apex was significantly delayed and the time hiatus disappeared in anterior MI patients. In the posterior MI group, the basal rotation and rotation velocity were significantly decreased, whereas the apical rotation and rotation velocity were similar to normal group. The time hiatus in posterior MI group still existed but significantly shortened compared with the one in normal group.5. By self-matching comparison, it was found that after CABG, the postoperative apical and basal rotation and rotation velocity were improved compared with preoperative ones. The improvement of torsion was significant (P<0.05) by self-comparison but EF, the traditional indicator of cardiac function, didn’t show significant improvement, while the two indicators correlate well with each other (r= 0.83).Conclusion1. These results support the hypothese that myocardial band is universal across mammalian species and by using MRI, the non-invasive golden standard to measure myocardial deformity, we first uncovered the potential relationship of the myocardial band and cardiac sequential movement, and proved that ventricular torsion may be a uniform measure of ventricular ejection in mammalian species with different heart sizes.2. With the help of newly applied cardiovascular magnetic resonance feature tracking (CMR-FT) software, we proved the pattern of torsion movement in normal hearts, which is the apex rotates in a counterclockwise direction while the base moves clockwise, and the heart twists like wringing out a wet towel. The time hiatus measured as 70-80ms in our study was similar to the results of previous study by 2D echocardiogram, and is essential to cardiac relaxation and suction process.3. It is the first time that we use CMR-FT to compare the difference of torsion movement between normal people and MI patients. We found that apical and basal rotations were significantly declined and time hiatus decreased or even disappeared when the heart suffered MI, meaning both systolic and diastolic function were impaired.4. This study was the first to evaluate the effects of CABG on torsion movement and we found CABG could improve patients’apical and basal rotation and the torsion was more sensitive to the cardiac function improvement compared with traditional EF. |
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