Selective laser ablation of venous thrombus: implications for a new approach in the treatment of pulmonary embolus.

Laser radiation was employed to ablate venous thrombus or emboli with parameters that would not injure endovascular tissues. Output from a 482-nm, 1-microsec pulsed dye laser was delivered through a 320-microns-diameter fiber to in vitro samples of fresh thrombus (T), venous or pulmonary emboli (VE), inferior vena cava (IVC), pulmonary artery (PA), pulmonary valve, and endocardium (atrial and ventricular). The mean threshold fluences for ablation of T and VE were 1.1 and 5.1 J/cm2, respectively. In contrast, the mean threshold fluences for IVC and PA were significantly higher (P less than 0.0001), at 120 and 124 J/cm2, respectively. Ablation efficiency of thrombus was in excess of 100 mg/J, under conditions that caused no histologic injury to the pulmonary artery. To correlate ablation studies with optical absorption by the tissues, optical properties of fresh T, VE, IVC, and PA were studied. Hemoglobin species accounted for the more than 10 times higher 482-nm absorption by T and VE compared to IVC and PA. This explains the differences in ablation thresholds and, thus, the selectivity encountered. These observations demonstrate, more than any other study in the vascular system, that with pulsed optical radiation, efficient laser ablation of venous thrombus is feasible with a wide margin of safety, and without damage to the surrounding vascular tissue.