Extra-anatomical bypass formation and exclusion of thoracic aortic aneurysms by "paired clamp method": the development of hind leg paralysis, the thrombus formation and the pressure ratio between the excluded cavity and the aorta.

The extra-anatomical bypass formation and the exclusion of thoracic aortic aneurysms by the "paired clamp method" applied to the thoracic aorta of mongrel dogs, and the development of hind leg paralysis was studied experimentally in relation to the ratio between the mean excluded cavity pressure and the mean aortic pressure ratio (EA-ratio). The relationship between thrombus formation in the excluded cavity and the EA-ratio was also studied. Animals were divided into 4 groups: Group 1 underwent the cross-clamping of the descending thoracic aorta for 8 min; Group 2 underwent exclusion of the entire thoracic aorta under permanent bypass; Group 3 underwent ligation of 2/3 of the proximal intercostal arteries which branched from the excluded thoracic aorta; and Group 4 underwent division of the excluded thoracic aorta into 3 parts by ligation. No animals in group 1 developed paralysis. When EA-ratios were higher than 0.48, animals in groups 2 and 3 were not paralyzed, whereas all but 1 animals with EA-ratios lower than or equal to 0.48 were paralyzed. There was statistically significant difference between the EA-ratio of the non-paralyzed animals and that of the paralyzed animals in groups 2 and 3. Four out of 5 animals in group 4 were paralyzed. However, there was no statistically significant difference between the EA-ratio in these 4 paralyzed animals and that in the non-paralyzed animals in groups 2 and 3. When the EA-ratio was lower than or equal to 0.59, all but 1 excluded cavities of groups 2 and 3 animals were fully thrombosed 7 or 8 days after the operation. None of these animals showed the aggravation of the paralysis during the observation period and, conversely, the paralysis of almost all animals was ameliorated. These results suggested that the EA-ratio is useful in predicting the development of paralysis and thrombus formation in the excluded cavity after the operation of thoracic aortic aneurysms by the "paired clamp method".