Study On The Application Of The Ventricular Myocardial Band Theory In Basic Structure And Function Of Myocardium

ObjectiveTo study the universality, regularity and reality of the theory of ventricular myocardial band of the normal heart architecture, the change of the basic cardiac structure of the ventricular myocardial band after heart failure, and the relationship between this structure change and the change of cardiac functoin by establishing rabbit model of chronic congenstive heart failure (CHF), and then, investigate the feasibility of MR diffusion tensor imaging (MRDTI) technique in displaying myocardial fiber architecture.Methods1. After boiled in different time, the hearts of different species were dissected as the way described by Torrent-Guasp. After anatomy achieved, all myocardial bands were photographed at nature state for testing the length of different segment. Then, some of them were cut down to test the weight of different segment, some were decomposed to the state when they hadn't been dissected after dyed in different color according to different segment, and then were cut through different plane, and the others were decomposed to the state when they hadn't been dissected after tagged in different segment, and then were token X-ray photos.2. Twenty rabbits were devided into two groups: the study group (10) and control group (10). The CHF model was made in study group by abdominal aortic coarctation combinding with epinephrine intravenous infusion. The reduced diameter of abdominal aorta was approximately 50%~60% of their original size, and epinephrine was applicated at 2 weeks (micrograms/kg/min for 60 minutes), 4 weeks (4 micrograms/kg/min for 60 minutes) and 6 weeks (4 micrograms/kg/min for 60 minutes) after operation was completed. Systolic and diastolic functions wereassessed by echocardiography. At the 8th week after operation, the animals were sacrified, then the hearts were excised and dissected as the way described in part one. The length and weight of different segments of the myocardial ventricular band were tested.3. Five ex vivo swine heart, DTI was acquired in 25 directions 2 hour and 24 hours after excision. The myocardial fiber was reconstructed using brain white matter tractography algorithm to display its course, distribution and arrangement.Results1. With relative stabile anatomy methods, all hearts presented to be a unique integrate myocardial band, with two loops and four segments. There's no significant difference of the length percentage and weight percentage of different segment in different species hearts (P>0.05). The length percentage of the ascending segment and the weight of the descending segment were greater than other segment in all hearts. The myocardial band twists on itself extends from the origin of the pulmonary artery to the root of the aorta, which delimitates two cavities, the right and left ventricles.2. At 8 weeks after operation, the hearts of study group showed evidently dilated by echocardiography. During dissection of the ventricular myocardial band, it was confirmed that the hearts of the study group were significantly dilatated and lose its helical form to assume a spheric configuration. The oblique fiber orientation of the descending and ascending apical segments become to be a more transverse fiber orientation. Comparing with the control group, the length percentage of the descending segment of the study group's hearts was greater, while the length percentage of the ascending segment was less, but there was no significant different of the weight percentage of espective segment between groups.3. On the swine heart 2 hour after excision, MRDTI revealed the arrangement of the myocardial fiber showing laminar, helix, twist and dispersal patterns, which is partly consistent with the array of the ventricular myocardial band. After 24 hours, because of the myocardium dissolving, DTI revealed the disintegration of the myocardial fiber, showing shortening, shrinking and distortion.Conclusion1. The concept of ventricular myocardial band presented by Torrent-Guasp and his colleague is a truly basic architecture of the heart.2. The way of abdominal aortic coarctation combinding with epinephrine intravenous infusion is a valid way to establish animal model of chronic congenstive heart failure.3. The change of the basic cardiac structure of ventricular myocardial band is the foundation of the functional change of the failure hearts.4. MRDTI could reveal the myocardial fiber architecture, showing its integrity and arrangement. It has potential in the study of myocardial structure-function.