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J Thorac Cardiovasc Surg 2005;129:243-245
© 2005 The American Association for Thoracic Surgery

Editorials

Imaging, models, and reality: A basis for anatomic-physiologic planning

Gerald D. Buckberg, MD*

Department of Cardiothoracic Surgery, UCLA Medical Center, Los Angeles, Calif

Received for publication June 23, 2004; revisions received September 23, 2004; accepted for publication September 28, 2004.

* Address for reprints: Gerald D. Buckberg, MD, Department of Cardiothoracic Surgery, Room 62-258 CHS, Box 951741, UCLA Medical Center, Los Angeles, CA 90095-1741 (E-mail: gbuckberg@mednet.ucla.edu).

The first 300 words of the full text of this article appear below.

The report in this volume by Walker and associates1 is an important attempt to apply diffusion tensor magnetic resonance imaging (MRI) analysis to determine whether the helical fiber orientation of the normal heart geometry is changed when the heart becomes dilated in heart failure and then is restored toward normal as cardiac structure is rebuilt by restoration.

The problem with this study is that the method misses the global disease while focusing on analysis of isolated regions. The flaw in these diffusion tensor MRI studies is failure to use the correct model of the failing heart for the analysis. The basic concept of heart failure is that the dilated heart becomes spherical through a change in the radius of curvature of the ventricular wall. This geometric change characterizes the loaded heart that is stretched rather than the unloaded, decompressed, nonfunctioning heart that is analyzed in this article.

A simple geometric analysis can show that an oblique fiber angle on a surface with a certain radius of curvature will attain a shallower angle as the surface projects itself to one with a larger radius of curvature and with a shorter long axis, as in the case for dilated heart. This change in the angle of fibers is inherent to any such surface deformation. To clarify this important point, we have modeled the ventricle as an ellipsoid of revolution that is fixed to a certain size base (Figure 1). As the heart dilates to a larger ellipsoid (ie, more spherical), one can calculate the decrease in the angle of any helically oriented line on the surface of the ellipsoid. For example, for a 65° fiber angle, if the short axis of such an ellipsoid changes from 5 to 8 cm, a 10° change in the fiber angle can be expected. . . . [Full Text of this Article]






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