What is the optimal channel density for transmyocardial laser revascularization?

Background Transmyocardial laser revascularization (TMR) has demonstrated reproducible relief of angina in patients with end-stage coronary disease. However, the optimum dose or channel density has not been elucidated. Methods Using a porcine model of chronic myocardial ischemia, 14 animals were treated with CO₂ TMR and randomized as follows: group 1 was 1 channel per 2 cm²; group 2 was 1 channel per 1 cm²; and group 3 was 2 channels per 1 cm². Left ventricular myocardial viability and function were assessed by magnetic resonance imaging (MRI) and echocardiography pretreatment, and repeated 6 weeks later. Results The MRI assessment of group 1 (1 channel/2 cm²) and group 2 (1 channel/cm²) demonstrated similar improvement in segmental contractility posttreatment of 12.11% ± 5.15% and 12.47% ± 9.51%, respectively. In contrast, group 3 (2 channels/cm²) showed significantly worse segmental contractility posttreatment: -18.52% ± 7.16% (p = 0.01). Echocardiographic imaging revealed significant improvements in wall thickening in the ischemic zone for group 1 at 0.91 ± 0.07 cm pretreatment versus 1.30 ± 0.09 cm posttreatment, (p = 0.01); and for group 2 at 0.93 ± 0.11 cm versus 1.42 ± 0.18 cm, (p = 0.01). No significant improvement in wall thickening was seen in group 3 (0.84 ± 0.06 cm versus 0.88 ± 0.09 cm, p = n.s.). Conclusions These data corroborate the empiric finding of an effective therapeutic dose range for TMR, 1 channel per 1 to 2 cm². These results also demonstrate a detrimental effect when channel density is increased above the clinical standard of 1 channel per cm² to a density of 2 channels per 1 cm².