|Year : 2020 | Volume
| Issue : 1 | Page : 3-8
Lasers for the treatment of coronary artery disease: An update
Akshyaya Pradhan, Monika Bhandari, B Snigdha
Department of Cardiology, King George's Medical University, Lucknow, Uttar Pradesh, India
|Date of Submission||06-Aug-2019|
|Date of Decision||27-Sep-2019|
|Date of Acceptance||27-Feb-2020|
|Date of Web Publication||03-Apr-2020|
Dr. Akshyaya Pradhan
Department of Cardiology, King George's Medical University, Lucknow, Uttar Pradesh
Source of Support: None, Conflict of Interest: None
In the present era, percutaneous coronary intervention is being done for various types of coronary lesions worldwide. However, calcified and fibrotic lesions have remained a major challenge in coronary interventions. Conventionally, cutting balloon and rotational atherectomy have been being used in calcified and fibrotic lesions. Excimer laser coronary atherectomy (ELCA) has emerged as a new alternative to deal with this type of complex lesion. In this update, we describe the procedure and the role of ELCA in coronary interventions.
Keywords: Coronary artery disease, excimer laser coronary atherectomy, lasers
|How to cite this article:|
Pradhan A, Bhandari M, Snigdha B. Lasers for the treatment of coronary artery disease: An update. Heart India 2020;8:3-8
| Introduction|| |
Coronary artery disease is a major cause of morbidity and mortality worldwide. Coronary revascularization is required in significantly obstructed coronary arteries. Initially, percutaneous coronary intervention (PCI) was indicated only in discrete and noncalcified coronary obstruction. In the current era, it has emerged as the primary treatment modality even in a diffuse, triple vessel and left main disease and even chronic total occlusions (CTOs). However, calcified and fibrotic lesions have remained a major challenge in coronary interventions. Conventionally, cutting balloon and rotational atherectomy (RA) have been utilized for plaque modification/debulking of such lesions. Excimer laser coronary atherectomy (ELCA) has emerged as a new alternative to deal with these types of complex lesions. The first use of lasers for treating vascular atherosclerosis was done in the 1980s. Lasers are implemented through fiber optics that can be placed directly in the coronary vessels. This makes laser implementation easy in the diagnosis and treatment of coronary artery diseases. Lasers are currently approved by the US Food and Drug Administration for few therapeutic procedures such as thrombus and plaque removal from the coronary arteries using ELCA in various types of lesions.
| Excimer Laser Coronary Atherectomy|| |
Excimer lasers are pulsed gas lasers which use an active medium to generate ultraviolet (UV) light of high energy and short wavelength [Table 1]. This active medium is a mixture of halogen and other rare gases. Short-wavelength UV light has got a lesser depth of penetration and produces less heat and this, in turn, avoids unwanted tissue damage.
| Mechanisms of Ablation|| |
Three distinct mechanisms are central to tissue ablation by Excimer laser. These are enlisted below as-
- Photochemical absorption of UV light by intravascular structures causing the breaking of carbon–carbon bonds
- Photothermal breaking of carbon bonds results in an elevation of intracellular water temperature and this produces vapor bubbles at the catheter tip
- Photomechanical fragmentation of intravascular obstruction by the expansion of vapor bubbles (see [Figure 1]).
|Figure 1: Major mechanisms of laser actions (reproduced with data from Philips Inc.)|
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| Three Important Terms in Excimer Laser|| |
The laser energy delivered for tissue ablation is described in terms of fluence, pulse repetition rate, and pulse width. These three pivotal terms are defined in [Figure 2]. Nature of the lesion decides fluence, pulse repetition rate, and pulse width of the laser. For example, fibrocalcific lesions require higher fluence and repletion rate.
| Advantages of Excimer Laser Coronary Atherectomy|| |
The advantage of ELCA is that it can be delivered on a standard 0.014” guidewire. Hence, there is no need to exchange the wire over a microcatheter as in rotablation. Furthermore, the technique is easy to master by any operator. It can also be used in ostial coronary lesions, whereas the rotablation is generally avoided.
| Limitations of Excimer Laser Coronary Atherectomy|| |
Heavy calcification is a major limitation when RA may additionally be required. This technique of using laser and RA combined is called the RASER technique. Anther limitation is that the equipment is expensive.
| The Excimer Laser Coronary Atherectomy System|| |
The current and only approved ECLA system is CVX-300 manufactured by Philips Inc., (Eindhoven, The Netherlands). The system consists of a permanent excimer laser platform coupled with disposable excimer laser catheters indicated for use in coronary lesions. It uses a wavelength of 308 nm with the catheter output fluence generated between 30 and 80 mJ/mm2. The system performs at a pulse repetition rate of 25–80 Hz and a pulse width of 125–200 ns. The console or pulse generator is 45” long, 35” high, and 24” wide. It weighs 650 pounds (295 kg approximately). The console is mounted on a trolley for easy navigation.
| Catheters in Excimer Laser Coronary Atherectomy|| |
Sizes and types of catheters
ELCA catheters are available in four diameters – 0.9, 1.4, 1.7, and 2.0 mm catheters. The 1.7-and 2.0-mm catheters (larger size) are used in >3-mm diameter vessels with the straight course. Catheters with sizes of 0.9 and 1.4 mm (smaller size) are used in smaller diameter vessels with tight stenosis and can be delivered via transradial route. Guide catheters for different ELCA catheters are mentioned in [Table 2]. The types of catheters are based on laser fiber arrangement at the tip of the catheter. They are of two types – concentric array and eccentric array [Figure 3]. Concentric array fibers are the most commonly used catheters. Eccentric array fiber catheters are used in special situations such as in-stent restenosis (ISR) where debulking of eccentric lesions is required [Figure 3]. Laser catheter type and size are selected based on
|Figure 3: The CVX-300 Excimer laser coronary atherectomy system (reproduced from Phillips Inc.). The left panel shows the two types of catheters and the right panel demonstrates the console/pulse generator. The console measures 49” × 35” × 24” and weighs up to 650 pounds|
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|Table 2: Guide catheter requirement for different excimer laser coronary atherectomy catheter sizes|
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- Consistency of the target material
- Diameter of the reference vessel
- The lesion severity.
In fibrocalcific nondilatable lesions, the 0.9 mm X-80 catheter is used due to its enhanced delivery and ability to emit laser energy at high power (80 mJ/mm2) at the highest repetition rate (80 Hz). Laser catheter types for different lesions are described in [Table 3].
|Table 3: Laser catheter characteristics preferred for specific indications|
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| Technique of Excimer Laser Coronary Atherectomy|| |
When excimer laser passes through macromolecules such as proteins, they absorb the majority of laser energy forming microbubbles, increasing the chances of dissection. Contrast media either iodinated or noniodinated and blood contain proteins due to which likelihood of dissection increases. Saline, unlike contrast, allows the passage of laser light from the tip of the catheter to the tissue without any interference, and so there is lower dissection risk.
Rarely, laser is performed in blood or contrast media for the treatment of an underexpanded stent (no risk of dissection in the stented environment) and undilatable and uncrossable lesions.
| Procedure|| |
For clearing blood from the catheter tip, 0.9% normal saline solution is connected to the manifold, and contrast syringe is exchanged with a Luer lock 20 ml syringe. Continuous saline injection is done at a rate of 1–2 ml/s throughout laser activation. It is important that the saline is delivered to the tip of the catheter. For this, the guide catheter should be coaxial and well intubated.
For routine laser catheters, laser activation takes place for 5 s with a 10-s rest period. At the end of the rest period, an alarm sound is generated which is a signal to restart the next laser cycle. For 0.9-mm X80 catheter, activation takes place for 10 s followed by 5 s rest, and so it can be used in more complex lesions.
The catheter is advanced slowly (0.5 mm/s). The laser energy is delivered as the catheter is advanced through the lesion. This allows adequate absorption and ablation. Catheter should not be advanced too rapidly as this will lead to suboptimal laser absorption by the tissue and hence suboptimal ablation [Figure 4]. In case of severe lesions with anterograde resistance, several anterograde trains are followed by the retrograde lasing.
|Figure 4: Demonstration of better ablation by slow advancement of catheter (reproduced from Philips Inc.). The left and right panels depict fast advancement (>1 mm/s) and slow advancement (<1 mm/s), respectively|
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| Contraindications - Excimer Laser Coronary Atherectomy|| |
There are no absolute contraindications. Unprotected left main disease is a relative contraindication. ELCA is not recommended when we are aware that guidewire is in subintimal tissue, like in some CTOs.
| Comparison of Various Atherectomy Devices|| |
Atherectomy devices are useful in the setting of PCI of calcified coronary arteries. While cutting and scoring balloons are useful in mild-to-moderate calcified vessels, severe calcified lesions require vessel preparation with atherectomy devices before the stent implantation.
Various atherectomy devices are as follows:
- Directional coronary atherectomy
- Transluminal extraction catheter atherectomy
- Rotational atherectomy (RA)
- Orbital atherectomy.
RA is the most commonly used device for heavily calcified lesions, and orbital atherectomy is the latest atherectomy device approved in 2013. RA requires a special Rotawire, while the ELCA can be performed on the normal 0.014” percutaneous transluminal coronary angioplasty wire. Rotablation can be done in heavily calcified lesion but is contraindicated in acute myocardial infarction (AMI) settings, while ELCA is highly useful in acute settings. [Table 4] compares the excimer laser and RA.
| Indications – Excimer Laser Coronary Atherectomy|| |
ELCA has been studied in various types of coronary lesions. The followings are the indications of ELCA [Figure 5].
|Figure 5: Indications of excimer laser coronary atherectomy (based on the trials and registries)|
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There is a high success rate when ELCA is used in uncrossable or undilatable lesions. However, the success is less when there is severe calcification in the lesion (success rate in calcified lesions is 79% vs. noncalcified lesions is 96%; P < 0.05). This is because ELCA ablates only the pliable tissue within the calcified lesion, leaving calcium as the ablative effects of ELCA on calcium are minimal.
In the majority of patients with noncrossable or nondilatable lesions, the 0.9-mm X80 catheter is selected and this catheter can be used via a 6F guiding system.
| Raser Technique (Rotational Atherectomy + Laser)|| |
The default technique remains RA in heavily calcified lesions. The utility of ELCA comes when Rotawire (less deliverable wire) could not be delivered directly into the distal coronary vessel. In this situation, ELCA can be used to modify the lesion to create a channel through which a RotaWire can subsequently be delivered distally (usually via a microcatheter) to permit RA.
This combined use of RA and ELCA is particularly effective for heavily calcified noncrossable, nondilatable lesions.
Chronic total occlusions
ELCA in CTOs is for lesions where the wire could cross the lesions, but the rest of the equipment could not cross. ELCA may reduce the risk of thrombotic complications due to its antithrombotic and platelet-suppressive effects. Anterograde injections with saline are usually avoided to prevent extension of dissection.
Stents sometimes remain underexpanded even after maximum balloon dilation. This has to be dealt with, because underexpansion of the stent remains a major risk factor for stent thrombosis. The only technique that can modify lesions underlying stent is ELCA. This is done by delivering laser to the abluminal stent surface.
High-power laser energy (80 mJ/mm2/80 Hz) is delivered, using the 0.9-mm X80 catheter with contrast injection. Delivering laser with contrast appears safe in the stented environment, and this increases the ablative effects of the laser.
ELCA in underexpanded stents was studied in ELEMENT registry.
| Ellement Registry|| |
In ELLEMENT registry, a total of 28 patients with underexpanded stents were studied. Procedural success was seen in 96.4% (27/28) of cases. Procedural success is defined as increase of either as luminal gain of 10% by quantitative coronary angiography or 1 cm2 by intravascular ultrasound (IVUS)-derived minimum stent area (minimal stent diameter).
Sometimes, dealing with ISR is very complex and ELCA is effective in making the procedure successful. The excimer laser was tested in stent environment and was found that the laser does not alter the endurance of stainless-steel stent, and it does not liberate any material from the stent.
ELCA in ISR lesions was studied in the LARS registry. In this study, 98 patients with ISR lesions demonstrated that lesions treated with ELCA had a greater luminal gain and IVUS cross-sectional area compared with balloon angioplasty alone.
Saphenous vein grafts
Saphenous vein graft (SVG) occlusion consists of degenerative plaques containing thrombus and therefore is highly prone to distal embolization. Distal protection devices are bulky in nature; thus, ELCA was advocated in such situations. ELCA allows a fair amount of debulking during SVG-PCI and thereby halts distal embolization. In view of this low rate of distal embolization, it was thought that distal embolic protection devices will not be required during ELCA. However, later on, it was found on intracoronary imaging that there remain friable fragments that could embolize and cause no-reflow following ELCA (CORAL trial). However, in such situations, most operators choose to open a native vessel. Nevertheless, it is advisable to use distal protection devices with ELCA for SVG-PCI.
In bifurcation lesions, ELCA helps in debulking the side branch lesion, allowing the main vessel-only stenting approach. This, the main vessel only stenting strategy increases the success rate of bifurcation lesions. However, it was later found that because of side branch angulation, chances of dissection in side branch were high, necessitating side branch stenting. ELCA is successful in cases of side branch re-stenosis (mainly due to stent underexpansion).
Acute coronary syndromes and myocardial infarction
ELCA is highly effective in thrombus removal; in addition, it promotes fibrinolysis, platelet stunning, and concomitant plaque debulking. This makes ELCA very useful in AMI setting. ELCA in the AMI setting has been studied in the past in CARMEL and LASER AMI studies [Table 5]. In 2017, a study conducted in Japan, the ULTRAMAN registry concluded that ELCA is safe and effective in thrombus-containing lesions.
|Table 5: Role of excimer laser coronary atherectomy in acute myocardial infarction setting was studied in two large studies - CARMEL and Laser acute myocardial infarction study|
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| Safety Precautions|| |
The operator and laboratory staff need to wear laser protection glasses during the technique. The catheterization laboratory doors also need to be closed while the ELCA procedure is on.
Complex PCI in calcified and fibrotic lesion remains an unmet need in intervention cardiology. Various atherectomy devices are in vogue though only few have stood the test of time. ELCA is the latest addition to the list. Although expensive, it has the potential to play a major role in complex PCI situations in both acute settings such as AMI and chronic settings such as calcified, fibrotic, undilatable, uncrossable lesions.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]