Excimer laser (308 nm) based transmyocardial laser revascularization: Effects of the lasing parameters on myocardial histology

Abstract

The effect of the excimer laser (308 nm) parameters on transmyocardial revascularization (TMR) channels is not well defined. This study investigates the influence of the pulse repetition rate, the size of the delivery catheter and its advancement speed on the morphology of TMR channels in vivo. Myocardial ablation was performed in a porcine model (N = 27) using multifiber catheters of 1.0 and 1.4 mm in diameter. The catheters were advanced into the myocardium at different speeds (1.27 and 2.54 mm/sec) while ablating at various repetition rates (10-80 Hz). The radiant exposure was kept at 35 mJ/mm(2) throughout the experiments. The channel histology was quantified by digital microscopy. The channel cross-sectional area and the extent of the thermal damage decrease as the catheter advancement speed exceeds the ablation speed and vice versa. Within the parameters tested, advancement speed of about 1.3 mm/sec and pulse repetition rates of 40 Hz produce channels of size comparable to the catheter's diameter with moderate thermomechanical damage. The repetition rate, catheter size, and catheter advancement speed are closely intertwined and crucial to the histological outcome of excimer laser based TMR.