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J Thorac Cardiovasc Surg 2005;129:382-390
© 2005 The American Association for Thoracic Surgery

Cardiopulmonary Support and Physiology

Helical myofiber orientation after myocardial infarction and left ventricular surgical restoration in sheep

^a Joint Bioengineering Graduate Group, University of California Berkeley/San Francisco, San Francisco, Calif
^b Department of Surgery, University of California, San Francisco, Calif
^f Department of Anesthesia, University of California, San Francisco, Calif
^c Department of Veterans Affairs Medical Center, San Francisco, Calif
^d Department of Biomedical Engineering, Duke University, Durham, NC
^e The Center for in Vivo Microscopy, Duke University Medical Center, Durham, NC

Received for publication November 25, 2003; revisions received March 17, 2004; accepted for publication June 1, 2004.

^* Address for reprints: Julius M. Guccione, PhD, Division of Surgical Services (112D), Department of Veterans Affairs Medical Center, 4150 Clement St, San Francisco, CA 94121 (E-mail: Julius.Guccione{at}med.va.gov).

OBJECTIVES: 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°, P = .028) and those in the lateral border zone to rotate clockwise (34.4 ± 8.1°, 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.

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