Helical myofiber orientation after myocardial infarction and left ventricular surgical restoration in sheep.
OBJECTIVE
It has been proposed that successful left ventricular surgical restoration should restore normal helical myofiber orientation. A magnetic resonance imaging technique, magnetic resonance diffusion tensor imaging, has been developed to measure myocyte orientation. By using magnetic resonance diffusion tensor imaging, this study tested the hypothesis that (1) myocyte orientation is altered after anteroapical myocardial infarction and (2) left ventricular surgical restoration restores normal helix angles.


METHODS
Thirteen sheep underwent anteroapical myocardial infarction (25% of left ventricular mass). Ten weeks later, animals underwent either aneurysm plication (n = 8) or sham operations (n = 5). Six weeks after this operation, hearts were excised, perfusion fixed in diastole, and underwent magnetic resonance diffusion tensor imaging. Hearts from normal sheep (n = 5) were also harvested and imaged. Primary eigenvectors of the diffusion tensors from magnetic resonance diffusion tensor imaging were resolved into helix angles relative to a local wall coordinate system. Transmural samples of the helix angles were compared at the border zone of the aneurysm or repair (or a comparable distance from the base in normal sheep), 1 cm below the valves, and halfway between.


RESULTS
The helical myofiber orientation did not change after myocardial infarction. However, aneurysm plication caused myofibers in the anterior border zone to rotate counterclockwise (-35.6 +/- 10.5 degrees , P = .028) and those in the lateral border zone to rotate clockwise (34.4 +/- 8.1 degrees , P = .031).


CONCLUSIONS
Surgical restoration alters myocyte orientation adjacent to the surgical repair. However, myofiber orientation is not abnormal after myocardial infarction, and thus surgical restoration techniques intent on restoring normal helix angles might not be warranted.
Walker
Joseph C
JC
Joint Bioengineering Graduate Group, University of California Berkeley/San Francisco, USA.
Guccione
Julius M
JM
Jiang
Yi
Y
Zhang
Peng
P
Wallace
Arthur W
AW
Hsu
Edward W
EW
Ratcliffe
Mark B
MB
D000818:Animals; D006348:Cardiac Surgical Procedures; D038524:Diffusion Magnetic Resonance Imaging; D004195:Disease Models, Animal; D006322:Heart Aneurysm / Q000503:physiopathology / Q000601:surgery; D006352:Heart Ventricles / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000503:physiopathology; D021621:Imaging, Three-Dimensional; D008297:Male; D008955:Models, Cardiovascular; D009203:Myocardial Infarction / Q000503:physiopathology* / Q000601:surgery; D009206:Myocardium / Q000166:cytology* / Q000473:pathology*; D011856:Radiographic Image Enhancement; D012756:Sheep