Histopathology after Nd-YAG laser percutaneous transluminal angioplasty of peripheral arteries

Excimer laser ablation for valvular angioplasty in pulmonary atresia and intact ventricular septum

BACKGROUND AND OBJECTIVES

The prognosis for infants with pulmonary atresia and intact ventricular septum (PA/IVS) is poor and they present a major management challenge. Mechanical penetration of the atretic pulmonary valve is an applicable option for decompression of the right ventricle and optimization of left ventricular function. The utilization of laser energy for debulking and vaporization of the atretic valve tissue is a relevant approach due to the potential for controlled, precise mode of energy distribution.

STUDY DESIGN/PATIENTS AND METHODS

A 4-month-old female with PA/IVS whose failure to thrive was accompanied by critical hemodynamic abnormalities received successful percutaneous pulmonary valve plate ablation by a 0.9 mm pulsed-wave ultraviolet excimer laser catheter (308 nm wavelength, fluence 50 mJ/mm(2); 30 Hz). A "step-by-step" lasing technique was applied whereby the tip of the emitting laser catheter is advanced ahead of a guide wire that serves mainly as support for positioning of that catheter.

RESULTS

Adequate penetration of the atretic tissue enabled introduction of balloon dilations resulting in patency of the atretic valve, decompression of the right ventricle, improved right and left ventricular hemodynamics, and oxygenation. To further investigate the effect of excimer laser energy on atretic valvular tissue this laser was applied in a specimen of heart from an infant who died because of PA/IVS. Histopathologic examination of the irradiated tissue revealed no laser-induced injury to the pulmonary valve.

CONCLUSIONS

Thus, laser ablation and penetration of an atretic pulmonary valve is feasible and safe. The penetration of the atretic valve with the laser catheter enables subsequent introduction of various sizes balloon dilations. The application of available laser sources for treatment of congenital heart diseases is reviewed.

In vivo effect of coronary laser angioplasty on atherosclerotic plaques: histopathologic analysis

Information from histopathologic examination of coronary arterial atherosclerotic plaques treated with in vivo laser energy is sparse. Directional atherectomy provides biopsies for study of tissue changes (injury) due to coronary arterial debulking devices, including laser. Sixteen patients who presented with acute ischemic coronary syndromes underwent debulking of a total of 17 obstructive intracoronary lesions with pulsed-wave holmium:YAG laser (2.1 microm wavelength). Laser was performed with the "pulse and retreat" technique which incorporates slow catheter advancement (0.5-1 mm/s) with controlled emission of energy. Immediately postlasing, directional atherectomy was utilized to obtain irradiated plaque tissue for pathologic examination. Extent of laser-induced tissue injury to plaques was graded as 0 (no tissue damage), 1 (small foci or charring and vacuoles), 2 (large amount of charring, edge disruption and vacuoles) and 3 (extensive tissue damage). Angiographically and clinically, all 17 lesions were successfully debulked with the laser energy (mean 47+/-25 pulses), with a reduction of target lesion percent diameter stenosis from 92+/-6% to 47+/-25%. Adjunct balloon dilations further reduced the target lesions to a final of 10+/-10% stenosis. The histopathologic examination of the lased specimens demonstrated that 13 lesions (76%) had no evidence of laser-induced injury (Grade 0). Four lesions had low-level injury (Grade 1), and none had evidence of Grade 2 or 3 laser-induced trauma. Therefore, a laser debulking technique, which incorporates slow catheter advancement with controlled emission of pulses, does not cause significant injurious effects to the irradiated plaque.

Can rotational atherectomy cause thermal tissue damage? A study of the potential heating and thermal tissue effects of a rotational atherectomy device

PURPOSE

Thermal tissue damage (TTD) is customarily associated with some lasers. The thermal potential of rotational atherectomy (RA) devices is unknown. We investigated the temperature profile and potential TTD as well as the value of fluid flushing of an RA device.

METHODS

We used a high-resolution infrared imaging system that can detect changes as small as 0.1 degree C to measure the temperature changes at the tip of a fast RA device with and without fluid flushing. To assess TTD, segments of porcine aorta were subjected to the rotating tip under controlled conditions, stained by a special histochemical stain (picrisirius red) and examined under normal and polarized light microscopy.

RESULTS

There was significant heating of the rotating cam. The mean "peak" temperature rise was 52.8 +/- 16.9 degrees C. This was related to rotational speed; thus the "peak" temperature rise was 88.3 +/- 12.6 degrees C at 80,000 rpm and 17.3 +/- 3.8 degrees C at 20,000 rpm (p < 0.001, t-test). Fluid flushing at 18 ml/min reduced, but did not abolish, heating of the device (11.8 +/- 2.9 degrees C). A crater was observed in all segments exposed to the rotating tip. The following features were most notable: (i) A zone of "thermal" tissue damage extended radially from the crater reaching adventitia in some sections, especially at high speeds. This zone showed markedly reduced or absent birefringence. (ii) Fluid flushing of the catheter reduced the above changes but increased the incidence and extent of dissections in the media, especially when combined with high atherectomy speeds. (iii) These changes were observed in five of six specimens exposed to RA without flushing, but in only one of six with flushing (p < 0.05). (iv) None of the above changes was seen in control segments.

CONCLUSION

RA is capable of generating significant heat and potential TTD. Fluid flushing reduced heating and TTD. These findings warrant further studies in vivo, and may influence the design of atherectomy devices.

Development of a new technique for reducing pressure pulse generation during 308-nm excimer laser coronary angioplasty

Despite expectations that excimer laser ablation would result in a low incidence of coronary dissection, studies have documented a 15-20% incidence of dissection (including a 4-6% incidence of clinically significant dissection) during excimer interventions. This investigation sought to determine if pressure pulses produced by the exposure of fluid phase media (blood and contrast) to 308-nm excimer radiation might contribute to untoward outcomes. Pressure pulses generated in these media were quantitated to be > 100 atm. In vitro ablation of porcine aorta in the presence of blood or contrast resulted in tissue dissection, while ablation in pure crystalloid did not. Next, a "flush and bathe" technique designed to replace all blood and contrast with crystalloid was applied to a pilot population of 57 consecutive patients. There were no rhythm disturbances or laser-related clinically significant dissections in this group, and the clinical success rate was 95%. In summary, this report quantitates a potential etiology for excimer dissection and suggests that replacement of blood and contrast with crystalloid might improve procedural and clinical success rates.

Comparative long-term results of laser-assisted balloon angioplasty and atherectomy in the treatment of peripheral vascular disease

BACKGROUND

Early results of laser-assisted balloon angioplasty (LABA) and peripheral directional atherectomy (PDA) are encouraging. The true value of these procedures has remained in doubt, however, because of the absence of data on long-term objective patency rates.

PATIENTS AND METHODS

From August 1988 through October 1993, LABA and PDA were performed on 151 limbs of 124 patients. Presenting symptoms were mild-to-severe claudication in 128 limbs (63 LABA, 65 PDA) and rest pain or necrosis in 23 (7 LABA, 16 PDA). Seventy-seven percent of the atherosclerotic lesions were localized in the iliofemoral tract (77% LABA, 76% PDA). Seventy limbs were treated with LABA and 81 with PDA.

RESULTS

Initial hemodynamic and arteriographic success was achieved in 46 LABA limbs (66%) and 75 PDA limbs (93%) (P < 0.002). Mean follow-up was 16 +/- 2 months after LABA and 18 +/- 1 months after PDA. During this time, 32 failures were recorded in limbs treated with LABA, and 29 in limbs treated with PDA. The patency rate at 40 months was 23% in the LABA group and 45% in the PDA group (P < 0.005). Patency rates were not affected by the length or site of the arterial lesion or the runoff score.

CONCLUSIONS

PDA had a better long-term patency rate than LABA, but long-term results were dismal with both techniques. PDA appears to have a limited role and LABA no role in the treatment of lower extremity occlusive disease.

Excimer laser angioplasty in the atherosclerotic rabbit: comparison with balloon angioplasty

The early and late results of excimer laser angioplasty and balloon angioplasty were compared in atherosclerotic rabbit iliac arteries. Immediately after laser angioplasty (n = 13) with a bare 600 microns fiber, there was a 33% increase in angiographically measured minimum lumen diameter; after balloon angioplasty (n = 12), there was a 53% increase. Restenosis (defined as loss of at least 50% of the gain achieved by angioplasty) occurred in none of six laser-treated rabbits studied 1 month later, compared with four of six balloon-treated rabbits (p = 0.06). Planimetric measurements of cross sections of the arterial wall 1 month after angioplasty showed less intimal and medial tissue in laser-treated (1.8 +/- 0.2 mm2) than in the balloon-treated rabbits (3.0 +/- 0.4 mm2; p less than 0.05). Typical thermal effects were absent on microscopic examination of laser angioplasty sites. It is concluded that in this animal model, excimer laser irradiation results in an immediate increase in lumen diameter comparable with balloon angioplasty, but is associated with less residual atheromatous tissue than balloon angioplasty and a trend toward a lower rate of restenosis.

In vivo assessment of vascular pathology resulting from laser irradiation. Analysis of 23 patients studied by directional atherectomy immediately after laser angioplasty

BACKGROUND

The pathological consequences of cardiovascular laser irradiation have been studied extensively in vitro. Previous in vivo studies of laser-induced injury have included analyses of acute and/or chronic findings in experimental animals. Little information, however, is available regarding the acute effects of laser irradiation of human vascular tissues in vivo.

METHODS AND RESULTS

To determine the acute pathology resulting from laser irradiation of human vascular tissue in vivo, specimens retrieved from 23 patients by directional atherectomy immediately after laser angioplasty (19 peripheral and four coronary) were examined by light microscopy. Of the 23 patients, three (13.0%) were treated with a metal-capped ("hot-tip") fiber coupled to a continuous-wave neodymium:yttrium-aluminum-garnet (Nd:YAG) laser using up to 18 W power and 18-305 seconds of cumulative exposure time; in all three patients (100%), thermal injury, including frank charring several cell layers thick, was seen along the luminal borders of the atherectomy specimen. In eight of the 23 patients (34.5%), laser angioplasty was performed using a 250-microseconds holmium:YAG laser at fluences up to 2,300 mJ/mm2, a repetition rate of 5 Hz, and 25-200 seconds of cumulative exposure; in seven of eight patients (85.5%), the atherectomy specimen showed signs of vacuolar injury consisting of central and satellite Alcian-blue-negative vacuoles. In two patients (25.0%), there was a "smudged" or "shredded" edge, whereas in one patient, frank signs of thermal injury were observed. Finally, in 12 of the 23 patients (52.2%), laser angioplasty was performed using a 120-nsec excimer laser at fluences up to 60 mJ/mm2, a repetition rate of 25 Hz, and a cumulative exposure time of 21-315 seconds. Pathological findings among these 12 patients were limited to nine patients (75%) in whom a weakly basophilic, smudged, and/or shredded appearance approximately one cell layer thick was observed along the luminal border of the atherectomy specimen and two patients (16.7%) with small foci of vacuolar injury. None of the atherectomy specimens retrieved after excimer laser angioplasty disclosed signs of thermal injury.

CONCLUSIONS

These findings document that acute pathological alterations resulting from in vivo laser angioplasty are variable, depending on the laser source used, and are similar to that predicted by experimental studies performed previously in vitro. The prognostic implications of these varying pathological features remain to be clarified.

New technologies for the treatment of obstructive arterial disease

The well-known limitations of balloon angioplasty include unpredictable abrupt closure, chronic total occlusion, diffuse disease, and restenosis, among other factors. These limitations have prompted the development of new technologic approaches to angioplasty including laser applications for plaque ablation, mechanical device applications for plaque removal/debridement, and stent devices for structural maintenance of vascular lumen patency. Devices which directly apply laser energy for ablation of plaque material include a balloon-centered laser angioplasty system, excimer laser ablation catheter systems, and a fluorescence-guided spectral feedback laser system. Experience with these devices indicates that plaque can be successfully ablated by using laser energy. Vessel perforation and dissection are complications reported with these devices and the effects of laser angioplasty on restenosis remain unclear. Indirect application of laser energy has been tested by using a "hot tip" catheter and a laser balloon angioplasty system. Although the hot tip device has received FDA approval for use in peripheral arteries, it appears to have very limited applications in the coronary arteries. Laser balloon angioplasty appears to be beneficial in the setting of threatened acute closure; the device continues to be evaluated for potential beneficial impact on restenosis. Mechanical atherectomy catheters are designed to remove atherosclerotic plaque from the arterial system and include the AtheroCath, the Transluminal Extraction Catheter (TEC), and the Pullback Atherectomy Catheter (PAC). The Rotablator is an atheroablation device which debrides the obstructing plaque material with distal embolization of the particulate debris. Successful removal/debridement of atherosclerotic plaque has been demonstrated with the AtheroCath, Rotablator, and the TEC device. Pre-clinical studies demonstrate successful removal of plaque material with the PAC device. Despite the theoretic advantage of removing plaque material when performing angioplasty with these devices, there has been little or no reduction in restenosis rates based on a significant experience with the AtheroCath and the Rotablator. Intravascular stent devices including one self-expanding device design and two balloon-expandable device designs have been employed successfully in the elective setting to treat recurrent restenosis lesions. Two of the devices have been successfully tested in the setting of threatened acute closure. Early follow-up studies suggest some improvement in restenosis rates in certain clinical settings following intravascular stenting. Acute and subacute thrombosis remain substantial problems for stent devices and very aggressive anticoagulation regimens are necessary to minimize the adverse events. In summary, a number of a new technologic approaches for treatment of atherosclerotic lesions have been developed and are undergoing significant clinical evaluation.(ABSTRACT TRUNCATED AT 400 WORDS)

Holmium YAG laser coronary angioplasty with multifiber catheters

Excimer lasers are being extensively used for coronary angioplasty along with multifiber over-the-wire catheters. To determine whether another wavelength could be an alternative, the laser-tissue interaction and the clinical usefulness of an infrared laser were studied. The laser consisted of a Holmium YAG pulsed laser coupled into a multifiber catheter. Experimental data from our laboratory showed that this solid state laser had the ability to cut calcified tissue, to be preferentially absorbed by atheroma, and to ablate tissue even when the catheter tip was positioned at a distance from the target. These results were obtained with only minimal thermal effects. After assessment of the efficacy and safety of this technique, laser angioplasty was performed in 53 consecutive patients with totally occluded (40%) or stenosed (mean percent 94) coronary arteries with a mean length of 6 mm. The primary laser and the procedure success rate were 64% and 94%, respectively. Failures were due to inability to advance the catheter against the lesion or to cross the obstruction. Stand-alone laser therapy could be achieved in only 18% of patients. In previous dilatation failures, laser irradiation allowed for subsequent balloon angioplasty to be successfully performed at a lower inflation pressure than that used in the failed dilatation. Complications included abrupt (during the procedure) and early (within 24 hours) vessel closure in 19% of cases, dissection without hemodynamic consequence in 28% and spasm. Reoccluded arteries could all be recanalized with dilatation.(ABSTRACT TRUNCATED AT 250 WORDS)

Initial results and subsequent outcome of laser thermal-assisted balloon angioplasty of 56 consecutive femoropopliteal lesions

Laser thermal-assisted balloon angioplasty (LABA) was prospectively applied in the treatment of 56 atherosclerotic femoropopliteal occlusive lesions in 51 consecutive patients. All procedures were performed in the operating room using a neodynium:yttrium-aluminum-garnet (Nd:YAG) laser source, and patients were evaluated for immediate and long-term hemodynamic and clinical improvement. Technically successful recanalization was achieved in 82% of cases, with 57% of all patients (32 of 56) obtaining early hemodynamic and clinical improvement. Long-term clinical success (by life-table analysis) was obtained by only 22.5% at 6 months, and only 13.5% at 12 months. Patients presenting with intermittent claudication did significantly better than those presenting for limb salvage (p = 0.01), and trends toward improved outcome were noted for short versus long lesions as well as for patients with "good" versus "poor" distal runoff (NS). Procedure-related morbidity occurred in 14%, and there was one peri-procedural mortality (1.8%). We conclude that the use of LABA is associated with long-term clinical success in only a small proportion of patients, and that widespread clinical application of this technique is not indicated at the present time.

Early and late arterial healing response to catheter-induced laser, thermal, and mechanical wall damage in the rabbit

Pulsed lasers are being promoted for laser angioplasty because of their capacity to ablate obstructions without producing adjacent thermal tissue injury. The implicit assumption that thermal injury to the artery is to be avoided was tested. Thermal lesions were produced in the iliac arteries and aorta of normal rabbits by a) electrical spark erosion, b) the metal laser probe, and c) continuous wave neodymium-yttrium aluminum garnet (Nd-YAG) laser energy through the sapphire contact probe. High-energy doses were used to induce substantial damage without perforating the vessel wall. Thermal lesions (n = 77) were compared with mechanical lesions (n = 22) induced by oversized balloon dilation. Medial necrosis was induced by all four injury methods. Provided no extravascular contrast was observed after the injury, all damaged segments were patent after 1 to 56 days. The progression of healing with myointimal proliferation was remarkably similar for all injuries. At 56 days, the neointima measured up to 370 microns. In conclusion, provided no perforation with contrast extravasation occurred, the normal rabbit artery recovered well from transmural thermal injury. The wall healing response is largely nonspecific.

Applications and limitations of laser-assisted angioplasty

Laser-assisted angioplasty is rapidly evolving into a promising adjunct to or replacement for standard vascular procedures. A protocol was devised to evaluate the technique in a non-selected, consecutive patient population to define the applications and limitations of the technique. In a 12-month period, 358 lower-limb atherosclerotic lesions were treated with laser/balloon angioplasty [percutaneously (52%) or open (48%)] in 206 consecutive patients. Overall, the laser/balloon technique recanalised 234 lesions (65% laser success), judged clinically effective by a greater than 0.15 improvement in the ankle/brachial index and elimination of symptoms. Operative complications included: perforation (15, 4.2%); thrombosis (16, 4.5%); spasm (5, 1.4%); and false aneurysm at the puncture site (7, 2.0%). Of the 124 failures (35%) categorised for analysis, the most common cause was inability to cross the lesion in 20 cases. This experience has identified three significant clinical limitations to successful laser recanalisation: calcification, inadequate distal circulation, and inability to control restenosis/reocclusion (collapsible lesions and accelerated plaque deposition). Further research is needed to determine if thermal injury seriously compromises the safety and long-term outcome of laser-assisted angioplasty.

Utilization of laser arterial angioplasty

Arterial angioplasty with continuous wave laser radiation is now available in clinical practice and, coupled with balloon catheter angioplasty, has been successful in the treatment of lower limb arterial disease. It appears premature to apply laser angioplasty to coronary artery lesions because of the high incidence of severe complications observed in clinical trials. Experimental studies suggest that some of these complications are related to thermal injury induced by continuous wave laser energy and that they could be minimized by the utilization of pulsed laser sources. Because of recent technologic advances, pulsed laser sources coupled with flexible fiberoptic devices will soon be available for peripheral arterial angioplasty in clinical practice.

Role of laser and thermal ablation devices in the treatment of vascular diseases

Since the first coronary angioplasty in 1977, both the number and complexity of interventional procedures have grown dramatically. Continuous-wave and pulsed lasers may further extend the capabilities of balloon angioplasty. Fiberoptic catheters may be used to transmit continuous-wave laser energy to ablate plaque via thermal mechanisms. Pulsed laser systems (such as the excimer) are technologically more complex than the continuous-wave systems, but may prove superior in small vessels given their ability to ablate plaque with minimal associated effects. On the other hand, modifications of the fiber-optic tip, such as the placement of a metal cap, have yielded even better results than current bare fiber systems. Such laser thermal techniques have proved a useful adjunct to balloon dilatation in peripheral vessels, but further research is necessary to determine their effect on coronary arteries. New, nonlaser technologies, however, may provide simpler power sources for thermal angioplasty. Although balloon angioplasty remains the cornerstone of interventional vascular therapy, new technologies should help to further expand the indications for nonsurgical interventions.

Histopathology of human laser thermal angioplasty recanalization

Laserprobe thermal-assisted balloon, angioplasty (LTBA) has demonstrated promising initial clinical results in recanalizing stenotic or occluded superficial femoral and popliteal arteries. Over the past year we have obtained six specimens of laserprobe thermal (LT) and LTBA treated total occlusions (avg. length 12 cm) for histopathologic examination from patients who were treated for limb salvage. Three tissue specimens were obtained acutely, and one was obtained at 6, 8, and 13 days, respectively, after laser angioplasty at the time of revision for complications or failed procedures. Serial histologic sections of the treated LT segments demonstrated recanalization of atherosclerotic lesions to approximately 60-70% of the probe diameter. The LT channels were lined by a thin layer of carbonized or coagulated tissue and several layers of cell necrosis. The histology of the thermal injury was similar regardless of whether it was produced by the heated metal cap or by free argon laser energy. Stellate balloon angioplasty fractures were frequently filled with thrombus. Analysis of these human LT and LTBA specimens revealed that the thermal device produces a confined injury through the path of least resistance. Balloon dilatation produces fragmented cracks in the vessel wall, which appear to be more thrombogenic than the carbonized LT surface. With improved guidance methods, LTBA shows potential for continuing development.