Significance of the biopsy site of the latissimus dorsi muscle for fiber typing.

The use of the latissimus dorsi muscle for cardiomyoplasty requires accurate assessment of the outcome of methods used to convert fast fibers to slow fibers. A knowledge of the normal distribution pattern of slow fibers within the latissimus dorsi is necessary for this endeavor. Fresh latissimus dorsi and teres major muscle tissues from seven pigs, one rabbit, two sheep, one monkey, and four dogs were studied with myosin adenosine triphosphatase staining. Fiber counts were made visually. With the exception of the rabbit, the distribution patterns were similar for all species: (1) intersegmentally--the number of slow fibers decreased steadily from the teres major to the anterior edge of the lateral segment; (2) intrasegmentally--slow fibers were more frequent in the deep layer than the superficial layer; and (3) intrasegmentally--the slow fibers tended to cluster in rosette formations around the neurovascular bundles. These patterns of distribution indicate the need for careful location of biopsies to ensure valid comparison of the amount of slow fibers in tissue before and after treatment.