Hemodynamic results of acute thoracic aortomyoplasty in a canine model: comparison of stimulation regimens.

Our previous investigations in a sheep model demonstrated that when electrical stimulation (ES) was applied to a newly mobilized latissimus dorsi muscle (LDM) in a work-rest regimen and at a rate of 15 contractions per minute, it did not damage this muscle. This regimen was used twice during a 60 minute period, once a day for 16 days, with no LDM damage. The goal of our current investigation was to apply this regimen in studies of acute thoracic aortomyoplasty. In two experimental groups, we mobilized the LDM but left it in situ. Two hours later, contractile force (CF) testing (20 g/kg preload, six impulses per burst) was performed until CF dropped to 50% of baseline. Recovery time needed to completely restore CF was calculated. In one group (six sheep), we applied continuous ES; in another (six sheep), we applied ES in a work-rest regimen (1 min work, 1 min rest). In two other groups of six dogs each, aortomyoplasty was performed; the LDM flap was subjected to ES immediately postoperatively (six impulses per burst; ventricular-LDM delay, 290 ms). Again, one group received continuous ES, and the other received work-rest ES. In the mobilized LDM under continuous ES, CF decreased to 50% of baseline values after 52 +/- 8 minutes, and returned to baseline after 84 +/- 16 minutes of rest. Under the work-rest regimen, this decrease took 105 +/- 8 minutes, and the return to baseline took 25 +/- 6 minutes (p < 0.05). In LDM subjected to work-rest ES, light microscopy revealed no additional damage to LDM tissue than was seen immediately after mobilization. However, LDM subjected to continuous ES had evidence of increased basophilic degeneration and wavy fibers. After acute thoracic aortomyoplasty, assisted hemodynamic values under the continuous ES exceeded unassisted values for only 40 minutes, compared with 100 minutes for work-rest ES (p < 0.05). When counterpulsation was completed, for continuous ES, recovery time to baseline was 96 +/- 9 minutes; for work-rest ES, it was only 43 +/- 6 minutes. In conclusion, a work-rest regimen of ES can be started safely immediately postprocedure.