<title>Myocardial tissue ablation by single high-energy laser pulses for ELR and TMR</title>

Abstract

The objective of this study is to compare the ablation sites induced by two different laser and application systems for myocardial laser revascularization. One system used was an 800W CO2 laser, which is clinically established for transmyocardial laser revascularization (TMR). The second system was a self-designed Holmium laser emitting single high energy pulses for the minimal invasive approach of endocardial laser revascularization (ELR), whereby the laser light is transmitted via optical fibre into the left ventricle to ablate the myocardial channels from the inside.The laser energy was applied to Polyacrylamide (PAA) as transparent tissue phantom and in water as blood phantom. The ablation dynamics were investigated by high speed flash photography recording a picture series of a single event. Reperfused ex-vivo porcine hearts were treated to quantify differences in the thermal-mechanical damage ranges by polarisation light microscopy. Ablation dynamics in water revealed oscillatory changes of the axial length of the steam bubbles between 3mm and 12mm during the CO2 laser pulse. For the Holmium laser pulse a maximal axial and lateral length of 5mm was observed. The lateral dimensions ofthe bubbles were maximal 1mm with the C02-and 3.5 mm with the Holmium laser system. In PAA bubbles also collapse during the laser pulse which affects the size of the ablated channels. Using 12J Holmium laser pulses for ablation ofPAA, channel depths around 7mm were found.Single Holmium laser pulses demonstrate ablations comparable in size and thermal-mechanical collateral damage to those achieved with the standard CO2 laser. The results are very encouraging for single pulse ELR and demonstrate the potential of a catheter based minimal invasive procedure for laser heart reperfusion.