814 
ANATOMY AND PATHOLOGY 
Figure 1. — Electron micrograph of myocardium of cat subjected to hemorrhagic hypo- 
tension for 1 hour. Note relatively normal myofibers to right and below intercalated 
disc. The zonal lesion is to the left and above intercalated disc, with fragmented Z 
bands and translocation of mitochondria which have mostly been displaced to left 
(out of field of picture) . X 14,000. 
of myofilaments, disruption of z-band material, 
and translocation of mitochondria. ^^'^^ The lat- 
ter feature accounts for the clear zone seen in 
the succinic dehydrogenase preparations. 
Zonal lesions are seen early in shock. They 
have been shown to be reversible in their initial 
stages of development,^^ but they become pro- 
gressively more severe and extensive when the 
shock period is prolonged. It is our contention 
that they represent sufficient damage to the 
anatomic integrity of the heart to account, at 
least in part, for the occurrence of eventual 
cardiac failure and "irreversibility" of the ani- 
mal to transfusion. 
Zonal lesions can be prevented by some of the 
same manipulations that prevent subendocardial 
hemorrhage and necrosis. This includes the 
avoidance of tachycardia by surgically pro- 
duced heart block,^ and blockade of beta-sym- 
pathetic activity by pronethalol treatment.*^ On 
the other hand, a clear-cut etiologic distinction 
is provided by studies in which animals were 
treated with hyperbaric oxygen. At oxygen con- 
centrations sufficient to significantly augment 
