Time-dependent regional myocardial denervation as a nonspecific response to transmyocardial laser revascularization

It is known that denervation occurs in the regions of myocardium treated by laser transmyocardial revascularization (TMR). The purpose of this study was to determine when regional denervation occurs in the early postoperative period and whether or not it is specific to laser TMR when compared with TMR using ultrasonically activated energy.

Dogs with normal myocardium underwent either holmium:yttrium-aluminum-garnet laser TMR, TMR using an ultrasonic activated surgical blade, or a thoracotomy as sham operation. The responses of mean arterial pressure to topical application of bradykinin were examined at 3 time points: before, 1 hour after, and 2 weeks after surgery. The hearts were excised for Western blot and immunohistochemical analysis.

The response of mean arterial pressure to bradykinin was similarly attenuated in both TMR groups 1 hour after treatment and decreased to almost none after 2 weeks compared with pretreatment values. By comparison, the sham group showed persistent responses at both time points. Tissue tyrosine hydroxylase content of the treated area decreased significantly compared with the non-treated area in both TMR groups. Immunohistochemistry using anti-Protein Gene Product 9.5 and anti-synaptophysin antibodies showed a significant decrease in the number of positive nerve fibers in both TMR treatment groups compared with the sham group.

Transmyocardial revascularization caused partial alteration in myocardial innervation immediately after TMR. Tissue responses may continue to occur for the first 2 weeks after treatment. Tissue responses may also contribute to the development of denervation regardless of the energy source in non-ischemic canine myocardium.