The Mechanism of Peripheral Recanalization by Laser-Assisted Thermal Angioplasty: Confirmation by Intravascular Sonography

The mechanism of recanalization during laser-assisted angioplasty in the treatment of obstructive atherosclerotic vascular disease has been controversial. Initial reports claimed that the laser-heated metal-tipped probe ablated atheroma as the hot tip “sought the lumen” and progressed down the artery as it created a new lumen in the central portion of the plaque [1 -3]. In distinction to the initial animal and clinical studies, an in vitro study of the mechanism of recanalization with laser-assisted thermal angioplasty found it to be a pre-dominantly mechanical process in which the laser probe was deflected by the hard, fibrocalcific plaque away from the true lumen and followed a dissection plane between the intimal plaque and the arterial media [4]. However, in human clinical trials, it is difficult to prove the exact pathway of the laser probe by using angiography or angioscopy. Recent work has documented the feasibility of imaging arteries in cross-section with a miniaturized catheter-mounted sonographic transducer that generates arterial images from inside the artery lumen [5, 6]. This report documents that the information obtained from the intravascular sonographic device in vivo is consistent with the hypothesis derived from our in vitro study for the mechanism of recanalization by the laser probe. A 73-year-old man with claudication had bilateral superficial femoral artery (SFA)

The mechanism of recanalization during laser-assisted angioplasty in the treatment of obstructive atherosclerotic vascular disease has been controversial. Initial reports claimed that the laser-heated metal-tipped probe ablated atheroma as the hot tip "sought the lumen" and progressed down the artery as it created a new lumen in the central portion of the plaque [1 -3]. In distinction to the initial animal and clinical studies, an in vitro study of the mechanism of recanalization with laser-assisted thermal angioplasty found it to be a predominantly mechanical process in which the laser probe was deflected by the hard, fibrocalcific plaque away from the true lumen and followed a dissection plane between the intimal plaque and the arterial media [4]. However, in human clinical trials, it is difficult to prove the exact pathway of the laser probe by using angiography or angioscopy. Recent work has documented the feasibility of imaging arteries in cross-section with a miniaturized catheter-mounted sonographic transducer that generates arterial images from inside the artery lumen [5,6]. This report documents that the information obtained from the intravascular sonographic device in vivo is consistent with the hypothesis derived from our in vitro study for the mechanism of recanalization by the laser probe.

Case Report
A 73-year-old man with claudication had bilateral superficial femoral artery (SFA) occlusions at the bifurcation with the common femoral artery. Both popliteal arteries were reconstituted, and distal runoff was good. The patient refused surgical intervention but was willing to undergo percutaneous angioplasty.
The length of the occlusion of the right SFA was 20 cm, and the left SFA was occluded 23 cm.
The right femoral artery was recanalized in a retrograde fashion from a puncture in the popliteal fossa. A 1 .5-mm-diameter laser probe (Model PLA-plus, Trimedyne Inc., Santa Ana, CA) was inserted and advanced under fluoroscopic control through an introducing sheath and an 8-French angioplasty guiding catheter. The laser probe was used as a cold mechanical device without turning on the argon laser. The laser probe was advanced by using intermittent forward pressure to puncture the occlusive atheroma.
The course of the laser probe was followed under fluoroscopic control until it advanced to the proximal end of the SFA and reentered the lumen of the common femoral artery. The laser probe was then removed, and a guidewire was inserted through a 7-French diagnostic catheter, which was used   At a more proximal level, in the area of the SFA that was recanalized, the sonogram showed the pathway that was taken by the laser probe (Fig. 1B). Moving from the peripheral portion of the artery on the right side of the image across to the left, the following structures are visualized: The adventitia is intensely echo-reflective followed by an echolucent circumferential line of media, followed by the echogenic thin line from the reflections from the internal elastic membrane. More central is a dissection plane in which the sonographic imaging catheter is situated.
To the left and medial to the catheter are dense echoreflections from calcium and atheroma that had previously occluded this portion of the SFA, but were mechanically pushed aside by the laser probe and guiding catheter as they created the dissection plane between the atheroma and the internal elastic membrane.
After this initial observation with the sonographic catheter, balloon angioplasty was performed from the level of the adductor canal to the common femoral artery. The angiogram ( Fig. 1 C) showed adequate patency of the SFA. The sonographic catheter was reinserted, and multiple images were obtained along the length of the SFA. Examples of the effect of balloon dilatation as visualized by the sonographic catheter in vivo are shown in Figures 1 B and 1 C. At the midportion of the SFA (Fig. 1 B), the lumen is reconstituted and measures 6.1 x 5.2 mm in diameter or 23.8 mm2 in cross-sectional area. In addition, a dissection is present around the eccentric atheroma plaque, which separates the atheroma from the media. The atheroma plaque is 1 6.4 mm2 in area and has a deformation consist- At a more proximal portion ofthe SFA (Fig. 1 C), the balloon inflation created almost a complete circumferential dissection with separation of the atheroma from the wall of the artery for 3000. In real time on the video monitor, the atheroma appeared to move independently of the media and external wall of the artery. In addition, because of the relatively slow flow in the lumen, intermittent pulsations of echo-catheter sheath and also in a portion of the dissection plane (at 12 o'clock), indicating that blood was flowing within this newly created dissection.
This type of dissection plane suggests that the atheroma plaque was torn away from the media wall by a force of torsion, which might explain why the dissection was completely circumferential. This type of torsion dissection was observed in our in vitro study [41; however, it was believed that this was an artifact of the in vitro preparation. The observation from the intravascular sonographic study shows that this type of dissection also exists in vivo and is not due to manual manipulation or histologic preparation.