Does laser type impact myocardial function following transmyocardial laser revascularization?

Background Transmyocardial laser revascularization (TMR) is currently clinically performed with either a CO₂ or Ho:YAG laser for the treatment of severe angina. While both lasers provide symptomatic relief, there are significant differences in the laser-tissue interactions specific to each device that may impact their ability to enhance the perfusion of myocardium and thereby improve contractile function of the ischemic heart. Methods A porcine model of chronic myocardial ischemia was employed. After collecting baseline functional data with cine magnetic resonance imaging (MRI) and dobutamine stress echo (DSE), 14 animals underwent TMR with either a CO₂ or Ho:YAG laser. Transmural channels were created with each laser in a distribution of 1/cm² in the ischemic zone. Six weeks post-treatment repeat MRI as well as DSE were obtained after which the animals were sacrificed. Histology was preformed to characterize the laser-tissue interaction. Results CO₂ TMR led to improvement in wall thickening in the ischemic area as seen with cine MRI (40.3% vs. baseline, P < 0.05) and DSE (20.2% increase vs. baseline, P < 0.05). Ho:YAG treated animals had no improvement in wall thickening by MRI (-11.6% vs. baseline, P = .67) and DSE (-16.7% vs. baseline, P = 0.08). Correlative semi-quantitative histology revealed a significantly higher fibrosis index in Ho:YAG treated myocardium versus CO₂ (1.81 vs. 0.083, P < 0.05). Conclusions In a side-by-side comparison CO₂ TMR resulted in improved function of ischemic myocardium as assessed by MRI and echocardiography. Ho:YAG TMR led to no improvement in regional function likely due to concomitant increase in fibrosis in the lasered area.