Transmyocardial laser revascularization dose response: Enhanced perfusion in a porcine ischemia model as a function of channel density

Background. Transmyocardial. laser revascularization (TMR) appears to provi de symptomatic relief to patients with ischemic heart disease, but evidence that TMR enhances perfusion to ischemic myocardium remains limited. Furthe rmore, it is uncertain whether there exists a TMR dose-response relationshi p that is a function of channel number. We therefore compared restoration o f blood flow as analyzed by rest and stress Tc-99m-sestamibi scans and hist ologic grading of neovascularization after 50-channel, 25-channel, or 10-ch annel TMR using the excimer laser in an established model of porcine myocar dial ischemia. Methods. Yorkshire swine underwent a thoracotomy and placement of an ameroi d constrictor around the proximal circumflex coronary artery. Three weeks l ater, the animals underwent resting and adenosine stress Tc-99m-sestamibi s cans for evaluation of ischemia immediately before repeat thoracotomy and T MR with either 50 channels (n = 4), 25 channels (n = 4), or 10 channels (n = 4) in the circumflex territory. The animals underwent repeat perfusion an alyses 4 weeks later, after which the animals were sacrificed and the heart s were perfusion fixed for histologic evaluation of neovascularization. Res ults. All animals survived to sacrifice. Semiquantitative analyses of the s estamibi perfusion scans 4 weeks after lasing demonstrated significant impr ovement (p < 0.04) in stress-induced ischemia in the 50-channel TMR animals , but not in the 25- or 10-channel TMR groups, as compared with scans obtai ned immediately before lasing. A computerized image analysis of perfusion s cans similarly demonstrated an improvement in the area of ischemia of 42% /- 22% in the scans obtained 4 weeks after lasing compared with scans obtai ned immediately before lasing in the 50-channel group (p < 0.004), but only a 12% +/- 9% improvement in the 25-channel group and an 8% +/- 4% improvem ent in the 10-channel group (p > 0.05). Histologic assessment of neovascula rization demonstrated significantly greater number of microvessels per low- power field in the 50- versus the 25- and 10-channel groups (p < 0.001). Conclusions. In an animal model of myocardial ischemia, TMR appears to enha nce myocardial perfusion. A dose-response relationship related to channel n umber may be of significance when evaluating the efficacy of various treatm ent strategies. (C) 2001 by The Society of Thoracic Surgeons.