Mechanism of directed transluminal atherectomy

The Ongoing Saga of the Evolution of Percutaneous Coronary Intervention: From Balloon Angioplasty to Recent Innovations to Future Prospects

The advances in percutaneous coronary intervention (PCI) have been, above all, dependent on the work of pioneers in surgery, radiology, and interventional cardiology. From Grüntzig's first balloon angioplasty, PCI has expanded through technology development, improved protocols, and dissemination of best-practice techniques. We can nowadays treat more complex lesions in higher-risk patients with favourable results. Guide wires, balloon types and profiles, debulking techniques such as atherectomy or lithotripsy, stents, and scaffolds all represent evolutions that have allowed us to tackle complex lesions such as an unprotected left main coronary artery, complex bifurcations, or chronic total occlusions. Best-practice PCI, including physiology assessment, imaging, and optimal lesion preparation are now the gold standard when performing PCI for sound indications, and new technologies such as intravascular lithotripsy for lesion preparation, or artificial intelligence, are innovations in the steps of 4 decades of pioneers to improve patient care in interventional cardiology. In the present review, major innovations in PCI since the first balloon angioplasty and also uncertainties and obstacles inherent to such medical advances are described.

Intravascular ultrasound imaging of peripheral arteries as an adjunct to balloon angioplasty and atherectomy

This article reviews many of the applications of intravascular ultrasound (US) imaging for peripheral arterial diseases. In vitro studies demonstrate an excellent correlation between ultrasound measurements of lumen and plaque cross-sectional area compared with histologic sections. In vivo clinical studies reveal the enhanced diagnostic capabilities of this technology compared with angiography. Intravascular US imaging can provide valuable information on the degree, eccentricity, and histologic type of stenosis before intervention, and on the morphological changes in the arterial wall and the extent of excision after intervention. Intravascular US may also serve as a superior index for gauging the diameter of balloon, stent, laser probe, and/or atherectomy catheter appropriate for a proposed intervention. Significant new insights into the mechanisms of balloon angioplasty and atherectomy have been established by intravascular US findings. Intravascular US imaging has been shown to be a more accurate method than angiography for determining the cross-sectional area of the arterial lumen, and for assessing severity of stenosis. Quantitative assessment of the luminal cross-sectional area after the balloon dilatation should be more accurate than angiography as intimal tears or dissections produced by the dilatation may not be accurately evaluated with angiography. At the present time, intravascular US is still a controversial imaging technique. Outcome studies are currently being organized to assess the clinical value and cost effectiveness of intravascular ultrasound in the context of these interventional procedures.

Intravascular ultrasound imaging of peripheral arteries as an adjunct to atherectomy: preliminary experience

12 atherosclerotic lesions in nine patients, including four restenoses after balloon angioplasty, were treated by atherectomy under the guidance of intravascular ultrasound (US). Echogenicities of the plaques and morphological alterations in the arterial walls produced by atherectomy were evaluated. The two-layered appearance of post-angioplasty restenoses was found to be inner fibrous intimal thickening with proliferation of smooth muscle cells and outer residual collagen-rich plaque. The deep cut surfaces were shown as concave U-shaped defects. Medial tissues were present in all cases where intravascular US demonstrated the disruption of a thin hyperechoic layer of the internal elastic lamina. Intravascular US imaging may provide valuable information on the degree, eccentricity and histological type of stenosis, the presence of calcification before atherectomy, and on the extent of excision and the morphological changes in the arterial wall after atherectomy.

Animal evaluation of the prototype omnicath atherectomy catheter

A prototype directional atherectomy catheter (Omnicath) was evaluated in four Yucatan microswines. Atherectomy was performed on iliac or aortic target lesions. After control angiography, the animals were sacrificed and the target arteries were examined histologically. Atherectomy resulted in arterial ruptures in three cases, and the track of the blade was measured to be of an average depth of 0.38 mm. Maneuverability was satisfactory but aspiration was not efficient. Precise localization of the atherectomy window was difficult. We conclude that modification of the catheter seems mandatory before use in humans.

Qualitative and quantitative contrasts in the mechanisms of lumen enlargement by coronary balloon angioplasty and directional coronary atherectomy

OBJECTIVES

This study was designed to define and contrast the mechanisms of lumen enlargement from coronary balloon angioplasty and directional coronary atherectomy using intracoronary ultrasound imaging in vivo.

BACKGROUND

The mechanisms of lumen enlargement produced by percutaneous transluminal coronary balloon angioplasty and directional coronary atherectomy are not known because the coronary artery wall has not previously been studied both before and after dilation.

METHODS

We used intracoronary ultrasound to quantitate coronary lumen, vessel and plaque area both before and immediately after successful coronary angioplasty (n = 30) and directional coronary atherectomy (n = 25) at the site of most severe stenosis.

RESULTS

Angioplasty increased lumen area by 2.80 +/- 0.25 mm2 (mean +/- SE, p < 0.0001). Eighty-one percent of this lumen gain resulted from an increase in vessel area and the remaining 19% from a reduction in plaque area. Lumen gain of individual lesions was separated into three groups: 67% had an increase in vessel area (vessel expansion), 13% had a decrease in plaque area and 20% had a combination of both. In contrast, vessel expansion contributed only 22% of the lumen gain with directional coronary atherectomy, with the majority (78%) of increase in lumen size coming from a reduction in plaque area. Directional coronary atherectomy increased lumen area from 2.36 +/- 0.05 to 7.00 +/- 0.28 mm2 (p < 0.0001). Plaque reduction was the sole mechanism in 60% of lesions, vessel expansion was the sole mechanism in 12% and a combination of both mechanisms occurred in 28%. Lumen enlargement of eccentric lesions treated with directional coronary atherectomy was more commonly associated with plaque reduction (p < 0.02), whereas eccentricity did not affect the mechanism of lumen enlargement with coronary angioplasty.

CONCLUSIONS

This is the first study to systematically examine the coronary artery wall in vivo at the site of a severe stenosis both before and after catheter-based interventions in humans. Lumen enlargement from coronary angioplasty occurs predominantly from vessel expansion or stretching, although a reduction in plaque area contributes to the lumen gain in many patients and is the sole mechanism in a few. Lumen gain from directional coronary atherectomy is predominantly from reduction in plaque area (probably owing to tissue removal), although vessel stretching (balloon effect) occurs and is the sole mechanism in a small minority of vessels. Plaque reduction is more common in directional coronary atherectomy of eccentric lesions.

Measurement by intracoronary ultrasound of in vivo arterial distensibility within atherosclerotic lesions

Arterial distensibility is diminished by atherosclerosis. This process has not been well studied in the coronary arteries. The purpose of this study was to assess changes in coronary arterial distensibility in 4 groups of patients. Group I (n = 20) consisted of patients with normal vessels, group II (n = 40) with diseased undilated vessels, group III (n = 15) after successful percutaneous transluminal coronary angioplasty (PTCA), and Group IV (n = 20) after successful directional coronary atherectomy (DCA). Intracoronary ultrasound imaging was used to assess distensibility, plaque morphology and atherosclerotic burden (expressed as the percentage of total vessel cross-sectional area occupied by plaque: percent plaque area). Distensibility was defined as percent change in lumen area in a cardiac cycle. Group I (normal vessels) had a distensibility = 14 +/- 5%, which was significantly greater than that seen in group II (distensibility = 4 +/- 2%, p < 0.001). In undilated vessels, distensibility was related to the degree of atherosclerotic burden (r = 0.75). This relation was curvilinear with a marked decrease in distensibility when percent plaque area exceeded 30%. Distensibility in group III (after PTCA) was higher than in group II (10 +/- 3 vs 4 +/- 2%, p < 0.001) despite a larger plaque burden (percent plaque area of 56 +/- 12 vs 46 +/- 11%, p < 0.005). The distensibility in group IV (after DCA) was also higher than in group II (8 +/- 4 vs 4 +/- 2%, p < 0.001) despite a similar residual percent plaque area (49 +/- 13 vs 46 +/- 11%, p = NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanisms of angiographically successful directional coronary atherectomy: evaluation by intracoronary ultrasound and comparison with transluminal coronary angioplasty

To assess the mechanisms of luminal improvement, 40 patients undergoing directional coronary atherectomy and a matched control group of 25 patients undergoing angioplasty were evaluated with intracoronary ultrasound imaging before and after intervention. Despite similar sized vessels, a similar angiographic severity of diameter stenosis (75 +/- 12% for the angioplasty group vs 69 +/- 15% for the atherectomy group, p = NS), and a similar plaque burden (percent plaque area) before intervention (84 +/- 5% in the angioplasty group vs 85 +/- 13% in the atherectomy group, p = NS), the residual plaque area after intervention was significantly smaller in the atherectomy group (54 +/- 14%) compared with the angioplasty group (65 +/- 13%, p = 0.002). Despite excellent angiographic results, significant residual plaque was noted after either successful intervention. Based on the absolute changes in lumen area, plaque area, and vessel area, improvement in the lumen area in the atherectomy group occurred as a result of plaque "compression" (48%), plaque removal (37%), and vessel expansion (15%). In the angioplasty group, plaque "compression" accounted for 94% of the improvement in lumen area, whereas vessel expansion contributed 6%. Thus "compression" of plaque remains the major mechanism of luminal improvement during atherectomy.

Coronary atherectomy versus angioplasty: the CAVA Study

Directional coronary atherectomy was developed with the hope that it would lower the risk of acute closure and restenosis by leaving a larger smoother lumen and fewer dissections than angioplasty. To evaluate this hypothesis, we compared the clinical and angiographic results of directional coronary atherectomy with those of percutaneous transluminal coronary angioplasty in well-matched groups. We studied 126 consecutive atherectomies and 127 angioplasties performed on similar lesions. Procedural results were evaluated with regard to dissections, complications, acute closure, and residual stenosis. Each patient's clinical course was followed, and each patient was contacted at 6 months for evaluation of recurrent angina, need for repeat catheterization, and angiographic rate of restenosis. Baseline clinical and angiographic characteristics of the two groups were well matched and met the criteria established as being appropriate for atherectomy. The angiographic success rate was 98% after angioplasty and 99% after atherectomy. There were fewer dissections after atherectomy (13%) compared with the number after angioplasty (22%; p = 0.03). Residual stenosis was 8.3 +/- 9% after atherectomy compared with 15 +/- 12% after angioplasty (p = 0.0001). However, there were more complications after atherectomy (p = 0.03). There was no significant difference between the two groups in the recurrence rate of angina or in the angiographic restenosis rate at 6 months. It was concluded that when lesion characteristics and vessel size are appropriate for atherectomy, the procedural success rate of either atherectomy or angioplasty is extremely high. Although atherectomy leads to a larger residual lumen and fewer dissections, the complication rate after atherectomy is higher than that after angioplasty. There is a trend toward more occlusions after atherectomy.(ABSTRACT TRUNCATED AT 250 WORDS)

Serial angiographic observations after successful directional coronary atherectomy

This study focuses on the early and late angiographic evolution observed in 82 patients with coronary artery disease who were successfully treated by directional coronary atherectomy (DCA) without adjunctive balloon angioplasty. Qualitative inspections and quantitative measurements were obtained from a selected angled-view projection in the following conditions: (1) before treatment; (2) immediately after treatment; (3) the day after atherectomy; (4) 1 month after; and (5) 6 months after. The appearance of the treated segment 24 hours after the procedure did not differ in 79 patients from that observed immediately after DCA; silent total occlusion occurred in two patients, and one had an aneurysm at the site of resection (all three patients were excluded from the analysis). At the 1-month study restenosis developed in 3 (3.6%) patients; the remaining 76 had identical appearances, with no evidence of renarrowing of the lumen. However, from 1 to 6 months after the procedure restenosis developed in 35 of the remaining 76 (46%) patients, and 41 patients were free of restenosis and symptoms. These findings, which show that early elastic recoil does not occur after successful DCA, are different from the changes observed after balloon angioplasty. At the 1-month observation restenosis is an infrequent but possible phenomenon (3.8%). From this point the healing of the arterial wall leads to no or mild renarrowing (late success); an exaggerated proliferative response produces restenosis.

Comparison of acute elastic recoil after directional coronary atherectomy versus standard balloon angioplasty

We evaluated intraprocedural "elastic recoil" in 25 patients (22 men and 3 women) undergoing directional coronary atherectomy (DCA) of left anterior descending stenoses, and compared these with 25 temporally-matched (14 men and 11 women) patients having balloon angioplasties (PTCA). Quantitative arteriography was performed using the Coronary Measurement System (Leiden, The Netherlands), with "elastic recoil" defined as the difference in maximum device or balloon size minus residual minimum diameter. In addition, we determined the effects of relative device size, specific anatomic location (proximal/mid artery), lesion length, eccentricity (symmetry index), and dystrophic calcification on acute "recoil" severity after both procedures. Although initial coronary stenoses were similar (minimum stenotic diameter, DCA = 0.59 +/- 0.20 mm versus PTCA = 0.55 +/- 0.23 mm, p = NS), less "elastic recoil" was observed after atherectomy (DCA = 0.83 +/- 0.57 mm versus PTCA = 1.26 +/- 0.56 mm, p < 0.01), and this was confirmed by absolute recoil/maximum device size ratios (DCA = 23.5 +/- 16.0% versus PTCA = 41.6 +/- 13.8%, p < 0.01). Acute "elastic recoil" was also influenced by maximum device size/"normal" coronary artery ratios [(ratio < 0.9, DCA = 0.26 +/- 0.10 mm versus PTCA = 0.84 +/- 0.13 mm, p < 0.01); (ratio 0.9 to 1.1, DCA = 0.69 +/- 0.41 mm versus PTCA 0.75 +/- 0.32 mm, p = NS); (ratio > 1.1, DCA = 1.09 +/- 0.64 mm versus PTCA = 1.59 +/- 0.48 mm, p < 0.05)].(ABSTRACT TRUNCATED AT 250 WORDS)

Acute outcome of directional coronary atherectomy vs standard balloon angioplasty in de novo left anterior descending stenoses

To assess the immediate outcome of directional coronary atherectomy (DCA) versus standard balloon angioplasty (PTCA) in de novo left anterior descending coronary stenoses, 25 consecutive atherectomies (22 men, 3 women) performed at The Toronto Hospital, between July 1990 and March 1991 were compared with 25 (14 men, 11 women) temporally matched successful angioplasties. Coronary stenoses were analyzed by quantitative arteriography, using the Coronary Measurement System (Leiden, The Netherlands), with estimation of transstenotic hemodynamics by fluid dynamic equations. Before and after procedure qualitative blood flow (TIMI criteria) was also evaluated, as was intimal haziness and coronary dissection. In comparison to PTCA, coronary atherectomy produced less residual minimum stenotic diameter (DCA, 2.75 +/- 0.55 vs PTCA, 1.70 +/- 0.44 mm, p < 0.001), and relative percent diameter stenosis (DCA, 17.9 +/- 10.7 vs PTCA, 34.4 +/- 10.7 percent, p < 0.001), with less transstenotic obstructive gradient (DCA, 0.2 +/- 0.2 vs PTCA, 1.0 +/- 1.5 mm Hg, p < 0.05), and greater estimated stenotic flow reserve (DCA, 4.86 +/- 0.15 vs PTCA, 4.50 +/- 0.48 x baseline, p < 0.05). Coronary atherectomy "normalized" TIMI flow patterns in virtually all patients (DCA, 2.96 +/- 0.20 vs PTCA, 2.72 +/- 0.45, p < 0.05), while creating less intimal haziness (DCA, 10/25 [40 percent] vs PTCA, 23/25 [92 percent], p < 0.01), and coronary dissection (DCA, 6/25 [24 percent] vs PTCA, 16/25 [64 percent], p < 0.05). Therefore, when compared with standard balloon angioplasty, DCA produces less residual stenosis, better transstenotic hemodynamics, while decreasing the frequency of coronary artery damage, in de novo left anterior descending stenoses.

Mechanisms of balloon angioplasty and directional coronary atherectomy as assessed by intracoronary ultrasound

OBJECTIVE

This study was designed to use intracoronary ultrasound imaging to elucidate the physical effects of balloon angioplasty and directional coronary atherectomy in vivo in humans.

BACKGROUND

The proposed mechanisms of coronary artery interventions such as balloon angioplasty and directional atherectomy are based on animal studies or pathologic findings and these data may not be applicable to living patients. Intracoronary ultrasound findings correlate highly with pathologic results and may allow in vivo assessment of the mechanisms of such interventions in humans.

METHODS

Intracoronary ultrasound imaging was performed in 45 patients after a successful coronary intervention (balloon angioplasty in 30, directional coronary atherectomy in 15). Ultrasound images obtained at the treatment site and at an adjacent angiographically normal references site were analyzed quantitatively for minimal lumen diameter, cross-sectional lumen area, are enclosed by the internal elastic lamina, plaque area (internal elastic lamina area--lumen area) and percent area stenosis (plaque area/internal elastic lamina area). Qualitative analysis included assessment of presence of dissection, plaque composition and plaque topography.

RESULTS

The results of the two procedures were similar with respect to minimal lumen diameter (angioplasty 2.6 +/- 0.5 vs. atherectomy 2.6 +/- 0.3 mm, p = NS), lumen area (0.07 +/- 0.03 vs. 0.07 +/- 0.02 cm2, p = NS) and percent area stenosis (59 +/- 14% vs. 51 +/- 21%, p = NS). However, after angioplasty, the internal elastic lamina area was significantly larger at the treated site than at the reference site (delta = +0.03 +/- 0.04 cm2, p = 0.01). There was no significant difference between the two sites after atherectomy (delta = -0.01 +/- 0.05 cm2, p = NS). In addition, dissection was seen significantly more often after balloon angioplasty than after atherectomy (50% vs. 7%, p less than 0.01). The results were similar when stratified for plaque composition and morphology. These data were confirmed in six additional patients who underwent ultrasound imaging before and after the intervention.

CONCLUSIONS

Thus, the improvement in lumen dimensions after coronary balloon angioplasty is a result of both vessel stretch, demonstrated by a larger internal elastic lamina area at the treated site, and dissection. Both vessel stretch and dissection are uncommon after atherectomy, a finding consistent with plaque removal as the major mechanism for improved lumen area after this procedure.

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.

Directional peripheral atherectomy: histopathologic aspects of a new interventional technique

Among the new transluminal vascular interventions currently being explored, directional atherectomy is unique in that it improves vessel patency by resecting intact portions of atherosclerotic plaque. Experimental atherectomy studies show that strips of plaque are cut away, leaving behind confluent defects within the stenotic lesions. Histologic examination of tissues excised during clinical peripheral atherectomy documents the heterogeneous morphology of peripheral atherosclerosis and shows that intimal hyperplasia is the most common cause of restenosis after therapeutic vascular interventions.