Plaque Biology, Realizing the Clinical Potential

Drs. Ghosh and Baguneid agree with our conclusion that ‘‘It may well be that success rates will improve with increasing power .’’, although multivariate analysis showed no relation between power and outcome. However, the references quoted provide little assistance. Mordon et al. studied a mechanical model and reported that ‘‘for a 3 mm vein diameter. for 10 W and 2 mm/s pullback speed. a minimum of 100 J/cm.,’’ and that ‘‘for a 5 mm vein diameter. for 15 W and 2 mm/s pullback speed. a minimum of 150 J/cm.’’ is required to damage the vessel wall. Theivacumar et al. reported median energy density of 48 J cm 1 in limbs with complete occlusion and 37 J cm 1 in those with partial occlusion; it is unlikely that these would differ significantly from the median 44 J cm 1 reported in our study. The techniques in both references differed from ours and, therefore, comparisons cannot be made. Prince et al. reported no difference for early re-canalisation rates for energy ranging from 100 J cm , whereas Vuylsteke et al. reported a significantly higher mean fluence for veins that remained occluded than for those that failed early. Proebsle et al. reported that low fluence increased risk for early failure, and that patients treated with 30 W had better medium-term results than for those treated with 15 W. These studies also used techniques other than those used in our report. The effect of laser energy is dependent on wavelength, power, probe-withdrawal rate and whether energy is continuous or pulsed. Commercial systems use wavelengths from 810 nm to 1500 nm. Planck’s formula indicates that energy is proportional to frequency so that higher wavelengths require more exposure time. Published reports use either continuous orpulsedpowerat various levels to15 W.WeagreewithGhosh and Baguneid that determining best protocols to provide highest long-term occlusion rates with least patient discomfort requires randomisation for these variables with long-term surveillance, and we thank them for stimulating discussions.