Intravascular ultrasound imaging after excimer laser angioplasty

Laser Vaporization of Intracoronary Thrombus and Identifying Plaque Morphology in ST-Segment Elevation Myocardial Infarction as Assessed by Optical Coherence Tomography

Objectives

We evaluated the thrombus-vaporizing effect of excimer laser coronary angioplasty (ELCA) in patients with ST-segment elevation myocardial infarction (STEMI) by optical coherence tomography (OCT).

Background

Larger intracoronary thrombus elevates the risk of interventional treatment and mortality in patients with STEMI.

Methods

A total of 92 patients with STEMI who presented within 24 hours from the onset and underwent ELCA following manual aspiration thrombectomy (MT) were analyzed.

Results

The mean baseline thrombolysis in myocardial infarction flow grade was 0.4 ± 0.6, which subsequently improved to 2.3 ± 0.7 after MT (p < 0.0001) and 2.7 ± 0.5 after ELCA (p=0.0001). The median residual thrombus volume after MT was 65.7 mm³, which significantly reduced to 47.5 mm³ after ELCA (p < 0.0001). Plaque rupture was identified by OCT in only 22 cases (23.9%) after MT, but was distinguishable in 36 additional cases after ELCA (total: 58 cases; 63.0%). Ruptured lesions contained a higher proportion of red thrombus than nonruptured lesions (75.9% vs. 43.3%, p=0.001). Significantly larger thrombus burden after MT (69.6 mm³ vs. 56.3 mm³, p < 0.05) and greater thrombus reduction by ELCA (21.2 mm³ vs. 11.8 mm³, p < 0.01) were observed in ruptured lesions than nonruptured lesions.

Conclusions

ELCA effectively vaporized intracoronary thrombus in patients with STEMI even after MT. Lesions with plaque rupture contained larger thrombus burden that was frequently characterized by red thrombus and more effectively reduced by ELCA.

Coronary ischemia and percutaneous intervention

The interventional treatment of ischemia is a complex issue grounded on an understanding of basic pathophysiology, but translated and implemented in practice by extensive clinical trial data representing patients with a spectrum of ischemia-causing clinical syndromes and anatomical variations of coronary artery disease (CAD). Percutaneous coronary intervention (PCI) has evolved to treat ischemia within this matrix of clinical and anatomical subsets using a wide array of techniques. Initial techniques using balloon angioplasty were promising, but demonstrated significant rates of restenosis due to negative arterial remodeling. The advent of stent technology prevented arterial recoil and provided a viable treatment for flow-limiting coronary dissections, thereby facilitating improved long-term patency of coronary vessels without the need for repeat revascularization. In-stent restenosis has been successfully addressed with drug elution, but late stent thrombosis has emerged as a complex issue involving dual antiplatelet therapy, patient compliance, and reexamination of the delicate balance between reducing restenosis and promoting endothelial proliferation. Finally, complex coronary lesions associated with heavy calcification or extensive plaque/thrombus burden that introduce unique challenges in obtaining ideal angiographic results have led to the development of new debulking devices aimed at optimizing procedural outcomes. This review will describe a variety of percutaneous coronary interventional techniques and technologies that are employed in the invasive treatment of ischemia under the guidance of clinical guidelines and evidence-based medicine.

Saline flush during excimer laser angioplasty: short and long term effects in the rabbit femoral artery

BACKGROUND AND OBJECTIVE

In this study, the effect of flushing saline on arterial wall damage (medial ruptures and necrosis), intimal hyperplasia, and arterial remodeling was determined. During excimer laser coronary angioplasty saline is flushed to reduce the size of explosive water vapor bubbles formed by intraluminal delivery of excimer laser pulses in blood.

METHODS

In the femoral artery of the rabbit, 600 excimer laser pulses (308 nm, 50 mJ/mm2 per pulse, 20 Hz) were delivered coaxially over a length of 20 mm in 10 bursts of 3 seconds each. In 24/48 procedures, saline was flushed (0.2 ml/s) via the guidewire channel. After 2 and 56 days, microscopic and angiographic results were compared.

RESULTS

At 2 days, as compared to lasing in blood, saline flush had drastically reduced the incidence of dissections (2/12 vs. 11/12, P < 0.002), but had increased the extent of medial and adventitial necrosis. The latter is attributed to direct irradiation of the arterial wall. After 56 days, in the saline group, in the middle-distal part of treated segments, medial necrosis without intimal hyperplasia was observed. However, at the edges of these lesions, intimal hyperplasia and arterial shrinkage reduced the lumen.

CONCLUSION

Flushing saline during coaxial excimer laser pulse delivery significantly reduced the incidence of vessel wall ruptures, and prevented intimal hyperplasia formation in part of the lesion. The histologic findings at 56 days are attributed to the optical window which the saline flush provides for direct ultraviolet light irradiation of the arterial wall.

[Laser angioplasty and recanalization]

Percutaneous transluminal coronary balloon angioplasty (PTCA) still is the most frequently applied interventional technique for treatment of coronary artery disease. Plastic deformation of the obstructive plaque with creation of splits, intimal tears and dissections is the main mechanism of PTCA for lumen widening. As a result, acute complications due to flow limiting dissections and acute vessel closure can unpredictably occur resulting in myocardial infarction, urgent bypass surgery and death. Furthermore, long-term success of PTCA is limited by restenosis. In order to overcome these limitations of PTCA, alternative interventional techniques were developed, which instead of deforming the obstructive plaque ablate this tissue. These techniques include high and low speed rotational angioplasty, directional atherectomy, the transluminal extraction catheter, ultrasound angioplasty and laser (Light Amplification by Stimulated Emission of Radiation) angioplasty. 308 nm XeCl excimer laser angioplasty today is the laser technique of choice for clinical application. This pulsed laser requires direct contact to the obstructive plaque. It creates fast (< 200 microseconds) expanding gas bubbles which induce plaque ablation. Main indications for 308 nm XeCl excimer laser angioplasty are diffuse and long coronary lesions and total coronary occlusions. Despite promising initial results this technique showed no better acute and long-term results in comparison to PTCA for the treatment of these types of lesions ("Amsterdam-Rotterdam" Study, "Excimer Rotational Balloon Angioplasty Comparison" Study). As a result, this interventional technique was rarely applied for patient treatment. More recently, the concept of plaque ablation by 308 nm XeCl excimer laser angioplasty was renewed for the treatment of in-stent restenosis. This indication is being investigated in the "Laser Angioplasty of Restenosed Stents" trial. First results document the practicability and safety of this approach. Long-term results are awaited. With ongoing miniaturization, laser guidewires were developed for the recanalization of chronic total occlusions. The randomized multicenter "Total Occlusion Trial with Angioplasty assisted by Laser guidewire "Study documented a success rate of laser wire recanalization in up to 66% in contrast to 47.5% for mechanical wires only. Long-term results are still awaited. Technical and procedural progress including saline flush during laser application, homogeneous light distribution and the concept of smooth laser ablation is pushed foreward to make excimer laser angioplasty safer, more predictable and more effective.

Early deterioration after excimer laser-assisted coronary angioplasty

Coronary lumen changes after excimer laser coronary angioplasty, after adjunct percutaneous transluminal coronary angioplasty, and at 24 hours after intervention were assessed using quantitative coronary angiography. Lesions treated with this combined technique showed significant early deterioration within 24 hours.

Excimer laser angioplasty versus balloon angioplasty in functional and total coronary occlusions

Registries of excimer laser coronary angioplasty have reported good results in the treatment of complex coronary artery disease, including total or subtotal coronary occlusions. One hundred three patients (103 lesions) with a functional or total coronary occlusion were included in a randomized trial (Amsterdam-Rotterdam [AMRO] trial, total of 308 patients), 49 patients were allocated to laser angioplasty and 54 patients to balloon angioplasty. The primary clinical end points were death, myocardial infarction, coronary bypass surgery, or repeated coronary angioplasty of the randomized segment during a 6-month follow-up period. The primary angiographic end point was the minimal lumen diameter at follow-up in relation to the baseline value (net gain), as determined by an automated contour-detection algorithm. Laser angioplasty was followed by balloon angioplasty in all procedures. The angiographic success rate was 65% in patients treated with excimer laser-assisted balloon angioplasty compared with 61% in patients treated with balloon angioplasty alone. No deaths occurred. There were no significant differences between the laser angioplasty group and the balloon angioplasty group in the incidence of myocardial infarctions (1 patient vs 3, respectively, p = 0.36), coronary bypass surgery (4 patients vs 2, respectively, p = 0.34), repeat angioplasty (10 patients vs 8, respectively, p = 0.46) or primary clinical end point (15 patients vs 12, respectively, p = 0.34). The net gain in minimal lumen diameter and restenosis rate (>50% diameter stenosis at follow-up) were 0.81 +/- 0.74 mm and 66.7%, respectively, in patients treated with laser angioplasty compared with 1.04 +/- 0.68 mm and 48.5%, respectively, in patients treated with balloon angioplasty (p = 0.59 and p = 0.15, respectively). Excimer laser-assisted balloon angioplasty demonstrated no benefit over balloon angioplasty with respect to initial and long-term clinical and angiographic outcome in the treatment of patients with functional or total coronary occlusions of >10 mm in length.

Do excimer laser angioplasty and rotational atherectomy facilitate balloon angioplasty? Implications for lesion-specific coronary intervention

OBJECTIVES

This study sought to determine whether adjunctive balloon angioplasty after rotational atherectomy and excimer laser angioplasty provides better lumen enlargement ("facilitated angioplasty") than angioplasty alone.

BACKGROUND

Adjunctive angioplasty is often used immediately after atherectomy and laser angioplasty to further enlarge lumen dimensions, but it is not known whether this practice is superior to angioplasty alone.

METHODS

Balloon angioplasty was performed in 1,266 native coronary lesions alone (n = 541) or after extraction atherectomy (n = 277), rotational atherectomy (Rotablator) (n = 211) or excimer laser angioplasty (n = 237). Quantitative angiographic analysis included final lumen diameter, final diameter stenosis and efficiency of balloon-mediated lumen enlargement.

RESULTS

Compared with angioplasty alone (33 +/- 12% [mean +/- SD]), final diameter stenosis was higher for adjunctive angioplasty after extraction atherectomy (37 +/- 16%, p < 0.001) and excimer laser angioplasty (37 +/- 16%, p < 0.001) and lower after rotational atherectomy (27 +/- 15%, p < 0.001). However, there was significant undersizing of balloons after all three devices. To correct for differences in balloon size, the efficiency index (final lumen diameter/balloon diameter ratio) was calculated and was higher for adjunctive angioplasty after the Rotablator (0.78 +/- 0.14, p < 0.001) than after angioplasty alone (0.69 +/- 0.12). The efficiency indexes suggested facilitated angioplasty after rotational atherectomy for ostial, eccentric, ulcerated and calcified lesions and lesions > 20 mm long. Facilitated angioplasty was also observed after extraction atherectomy and excimer laser angioplasty for ostial lesions, but not for any other lesion subsets.

CONCLUSIONS

Rotational atherectomy, extraction atherectomy and excimer laser angioplasty can facilitate the results of balloon angioplasty. However, the extent of facilitated angioplasty is dependent on the device and baseline lesion morphology, consistent with the need for lesion-specific coronary intervention.

Intravascular ultrasound findings after excimer laser coronary angioplasty

Intravascular ultrasound (IVUS) was used to study 104 lesions in 98 patients after excimer laser coronary angioplasty (ELCA). Lesion site external elastic membrane (EEM) and lumen cross-sectional areas (CSA) were measured; plaque+media (P+M = EEM - lumen) CSA and percentage of cross-sectional narrowing (CSN = P+M CSA/EEM CSA) were calculated; and the results were compared to a reference site. The lumen CSA (2.6 +/- 1.0 mm2) averaged 24% larger than the cross-sectional area of the largest laser catheter used, and 64 lesions (62%) fit the definition of arterial expansion (lesion EEM CSA > reference site EEM CSA). The residual percentage of cross-sectional narrowing averaged 83.8 +/- 8.8%. Dissections were present in 44% of lesions, and were more common in lesions with superficial calcium (59%) than in lesions with only deep calcium (31%) or no calcium (20%, P = 0.0102). Dissections of superficial calcified plaque had an unusual "shattered" or "fragmented" appearance. These findings suggest that excimer laser angioplasty causes forced vessel expansion with dissection, but limited atheroablation.

An explanation for discrepancy between angiographic and intravascular ultrasound measurements after percutaneous transluminal coronary angioplasty

OBJECTIVES

This study attempted to determine why there is a discrepancy between angiographic and intravascular ultrasound measurements after coronary balloon angioplasty.

BACKGROUND

Previous studies have shown a poor correlation between angiographic and intravascular ultrasound measurements after percutaneous coronary balloon angioplasty.

METHODS

After successful balloon angioplasty, 91 lesions in 84 patients were studied by intravascular ultrasound. Plaque morphology on intravascular ultrasound was classified as demonstrating a superficial injury if there was either no fracture or only a small tear that did not extend to the media versus a deep injury defined as the presence of a plaque fracture that reached the media. Measurements of minimal lumen diameter were compared between angiography and intravascular ultrasound.

RESULTS

On ultrasound imaging, a superficial injury pattern was observed in 44 lesions, whereas a deep injury was seen in 47 lesions. There were no statistical differences at baseline in patient or lesion characteristics. In the superficial injury group there was a significant correlation between angiography and intravascular ultrasound for minimal lumen diameter (r = 0.67) and lumen cross-sectional area (r = 0.69). In the deep injury group there was a poor correlation for minimal lumen diameter (r = 0.05) and lumen cross-sectional area (r = 0.28). After balloon angioplasty, the angiographic appearance showed a normal contour in 34%, the presence of dissection in 38% or a hazy appearance in 23%. On ultrasound imaging after angioplasty, the superficial injury group comprised 65% of lesions with a normal angiographic appearance and 67% of lesions with a hazy appearance, whereas 77% of lesions with an angiographic diagnosis of dissection were in the deep injury group by ultrasound (p = 0.0005).

CONCLUSIONS

These observations suggest that the discrepancies between angiographic and ultrasound measurements are due to differences in plaque morphology created by balloon dilation. Superficial injuries demonstrate similar results by angiography or ultrasound, whereas a deep injury to the plaque produces a difference in measurements between angiography and ultrasound. When angiography reveals a dissection, there is a high probability that intravascular ultrasound will demonstrate a plaque fracture extending to the media.