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Eur J Cardiothorac Surg 2006;30:690-691
© 2006 Elsevier Science NL
Letters to the Editor |
Division of Cardiothoracic Surgery, Washington University School of Medicine, 660 S. Euclid Ave., Box 8234, St. Louis, MO 63110, United States
Received 12 June 2006; accepted 26 June 2006.
* Corresponding author. Tel.: +1 314 362 8311; fax: +1 314 361 8706. (Email: schuesslerd{at}wustl.edu).
Key Words: Ventricular myocardial band • Ventricular activation • Electromechanical function • Specialized ventricular conduction (Purkinje) system
I have no BIG dogs in this fight and no expert opinion as to the anatomic complexities of the ventricles. My role was to describe the ventricular activation sequence and its possible role, assuming the existence of a continuous convoluted ventricular muscle band. As stated in the article, such a band could not be activated sequentially along its convoluted course. Also, that a normal rapid endo- to epi- and apical to basal spread of activation might not eliminate sequential convoluted contraction along the length of the band if the action potential durations were progressively longer along its course. Although there are no comprehensive three-dimensional data to support a convoluted or helical gradient of repolarization, there are data which indicate that repolarization durations across the wall do not simply progress uniformly from endocardium to epicardium. Several studies have demonstrated longer action potential durations of midmyocardial fibers. In conjunction with a more rapid propagation along the long axis of the band, this could support some form of convoluted sequential contraction. My other point was that if the ventricular muscle band exists, it should be considered part of a complex system of the developing heart which includes the tubular looping and folding, the expansion and invagination of the endocardium carrying the Purkinje system into the wall, all of which are probably determined by intrinsic genetic conditions and the changing hemodynamic profile of the developing heart (function affecting form).
However, I also think the reviewers’ bark (opinion) is significantly greater than their bite (their data). If, as the reviewers contend [1], the unrolled ventricular muscle band is factitious, then there should be numerous results from attempts to unroll it. Instead of consistently revealing a semi-continuous strap, one might separate fiber bundles along other planes, resulting in different architectures or breaks in continuity with smaller lengths ending in sheaths, etc. In addition, no ‘piecewise’ analysis of the architecture based on transmural cross-sections can address the complex three-dimensional anatomical architecture of the ventricles. The best of such studies are those of LeGrice et al. [2]. Perhaps with more extensive cross-sectional analyses (containing many more sections) and sophisticated computer modeling, one might get closer to the actual geometry. However, even these models must make certain assumptions about how individual sections interrelate.
The ventricular muscle band dissection is intriguing and warrants further investigation in conjunction with segmental wall analysis, embryologic, molecular development studies, and computer modeling.
References
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