NONTRANSMURAL LASER TREATMENT INCOMPLETELY DENERVATES CANINE MYOCARDIUM

Background-Clinical experience with transmyocardial laser revasculariz ation (TMLR) has reproducibly demonstrated an improvement in angina cl ass. Denervation has been implicated as a mechanism whereby this clini cal effect may be achieved, Because endovascular techniques for TMLR a re currently under development, we investigated the impact of nontrans mural endoventricular laser treatment on cardiac nerves in a canine mo del. Methods and Results-Five mongrel dogs underwent creation of nontr ansmural endoventricular channels in the anterior left ventricle with a Holmium:YAG laser. Cardiac afferent nerve function was assessed in c ontrol and treatment regions by the epicardial application of bradykin in, a potent algesic, at initial thoracotomy before laser treatment, a nd at repeat thoracotomy 2 weeks later. The resulting central nervous system-mediated decrease in systemic mean arterial pressure seen in al l animals at baseline was reduced by 90% at 2 weeks in the laser-treat ed territory but was preserved in controls. Immunoblot analysis of tis sue samples taken from laser-treated regions demonstrated a 66% reduct ion in tyrosine hydroxylase, a sympathetic nerve-specific enzyme, as a ssessed by densitometry. Enzyme content was unchanged in control regio ns. Conclusions-These data suggest that nontransmural endoventricular laser treatment only partially denervates the heart. This may have imp lications for the clinical efficacy of the endovascular approach in th e relief of angina pectoris.