Overview of Excimer Laser Coronary Angioplasty
Laser treatments for heart artery blockages, known as laser coronary angioplasty, first came about in the early 1980s. This treatment was mainly developed to manage hardened arteries that could not be improved with balloon treatments. However, due to the high cost of the laser systems, disappointing outcomes, and complications tied to the type of lasers available at that time, this technique didn’t become popular.
In particular, the continuous waveform of certain types of lasers (argon and Nd: YAG lasers) was associated with a number of complications. But later in the 1980s, a new type of laser, called an excimer laser, was developed. Excimer is short for the term ‘excited dimer’, and it produces a unique type of laser energy that is ultraviolet, pulse-like, and has a short wavelength.
Unique characteristics of the excimer laser, such as its precise way of removing plaque tissue with minimal heat damage to the artery, and its short wavelength which means less penetration and therefore less collateral damage, made it a much-improved tool for this procedure. Alongside these technological advancements, adjustments in the design of the treatment tube (catheter), better patient selection, and evolving safety protocols all contributed to the reintroduction of laser technology into routine medical practice.
As a milestone event in 1988, the first successful human treatment with an excimer laser coronary angioplasty was performed at the Cedar Sinai Medical Center in Los Angeles.
Anatomy and Physiology of Excimer Laser Coronary Angioplasty
A laser is a device that generates a concentrated beam of light by making specific gas molecules release energy. Specifically, for an excimer laser, the required gas mixture involves xenon gas and a watered-down hydrogen chloride solution. Once electricity is passed through this mixture, it results in the generation of special molecules like xenon chloride. These molecules release energy packets that form ultraviolet light.
Reflection equipment is then used to enhance this process and deliver the energized laser light to the target tissues in the body. When this beam hits the tissue, it modifies it through three main processes:
1. Photochemical: This process breaks the connections between molecules.
2. Photothermal: In this, the heat from the laser causes the water inside cells to evaporate, forming bubbles. The bubbles cause the cells to break down.
3. Photokinetic/Photomechanical: The heat-generated bubbles join together to form larger ones, which further breaks down unwanted tissue.
The end product of these processes are tiny fragments, small enough to be safely removed by the body’s natural waste disposal system. This ensures that they don’t get inadvertently carried to other parts of the body.
Why do People Need Excimer Laser Coronary Angioplasty
The US Food and Drug Administration (FDA) has approved excimer laser coronary angioplasty (ELCA) for certain heart conditions. ELCA is a procedure that uses a laser to open up blocked arteries and restore blood flow to the heart. Here’s what it’s officially okayed for:
1. Lesions (damage or disease-triggered changes) that a balloon cannot go across or dilate (widen).
2. Clumps of thrombotic (which cause blood clots) lesions in saphenous vein grafts (veins taken from the leg to replace blocked coronary arteries).
3. Chronic total occlusion (CTO), a complete blockage of a coronary artery.
4. Moderately calcified lesions, which are hardened spots due to calcium buildup.
5. Ostial lesions, which are blockages located where coronary arteries branch off from the larger aorta.
6. Eccentric lesions, abnormal spots that are not evenly rounded.
7. Long lesions, which are more than 20mm.(almost an inch) long.
8. In-stent restenosis, which happens when an artery narrows again after a stent (a tiny wire-mesh tube) has been placed to keep it open.
In addition to these official uses, some doctors have successfully used ELCA for:
1. Helping with common procedures to open blocked arteries (percutaneous coronary intervention, or PCI) when stents (small tubes to hold the artery open) aren’t expanding or deploying the way they should, or when there is a large amount of blood clot.
2. Modifying the proximal cap (the starting point) of heavily calcified (hardened with calcium) lesions when initial attempts to cross with a special wire (used in a procedure known as rotablation) are not successful.
When a Person Should Avoid Excimer Laser Coronary Angioplasty
There aren’t any complete no-go conditions for a heart procedure called excimer laser coronary angioplasty (ELCA). However, there are a few conditions where it might not be the best option:
If the heart vessel bends sharply, more than 45 degrees.
When there’s a tear in the wall of a heart artery, known as coronary dissection.
When the main heart artery on the left side of the heart is unprotected.
On top of these, ELCA is currently not advised for heart lesions that are hard to see or heavily hardened due to calcium build-up. Also, if the lesions are smaller than the smallest available size of the tube used in the procedure (0.9 mm), ELCA might not be the best choice.
Equipment used for Excimer Laser Coronary Angioplasty
The equipment used for Excimer laser coronary angioplasty (ELCA), a procedure to open up blocked or narrowed coronary (heart) arteries using laser energy, includes a laser generator and special tubes called catheters of various sizes that deliver the laser energy. Currently, there’s only one such laser system approved for use in the United States by the FDA.
This specific system creates a pulsed laser energy beam in the UV-B range. This laser beam is designed to penetrate tissues between 0 to 30 micrometers or millionths of a meter in depth and has an output range of 30 to 80 millijoules per millimeter squares, a unit of energy measurement. It can generate 25 to 80 pulses per second and each pulse lasts between 125 to 200 nanoseconds.
The catheters used in ELCA come in four sizes (0.9 mm, 1.4 mm, 1.7 mm, and 2.0 mm) and two types depending on how the fiberoptic fibers are arranged inside the catheter: they can be arranged concentrically, which means oriented evenly around a central point, or eccentrically, which means oriented more towards one side. The 0.9 mm catheter is used most often. Also, catheters can be of the traditional type that are maneuvered over a wire guide or the newer, rapid-exchange type that are quicker to place and offer better control. Currently, the rapid-exchange type catheters are more frequently used due to their advantages.
Preparing for Excimer Laser Coronary Angioplasty
Before starting the procedure, it’s important that everyone in the room, including the patient, wears special tinted goggles. These goggles protect the eyes from damage that could be caused by the UV laser being used. The procedure should take place in a room with tinted windows and a locked door to make sure no one accidentally enters and gets hurt.
Turning on the laser generator used in the procedure takes about 5 minutes. Once it’s ready, a special tool called a catheter is prepared. This catheter must be appropriately sized – it shouldn’t be bigger than two-thirds of the vessel it will be used in. It also needs to deliver just the right amount of energy to treat the targeted area. The kind of catheter used can differ, but the most commonly used kind is known as concentric catheters. However, if the procedure focuses on different areas, eccentric catheters are preferred because they can be turned towards the target area easily.
Once the catheter is properly chosen and prepared, it is hooked up to the laser unit and carefully checked, or calibrated, to make sure it works correctly. This calibration is done by placing the catheter’s tip near an energy detector on the laser unit, and then turning on the laser. After this, the laser unit is then placed in a standby mode, ready for the procedure.
How is Excimer Laser Coronary Angioplasty performed
When performing an excimer laser coronary angioplasty (ELCA), a routine medical wire is usually advanced until it crosses the problem area in your heart vessel. Then, a special medical tube is moved over it until its tip directly reaches the problem area. This is a benefit over other techniques which often need special wires. The energy level, the rate of bursts, and how long each burst lasts is then set. The system starts at a standard level, but if the doctor faces resistance, they can slowly increase these settings. It’s important to go slow, because using too much energy or too many bursts can increase the chance for complications such as tearing or creating holes in the vessel.
Before the procedure begins, they use a saline flush protocol. The idea behind this is that both blood and the medical contrast liquid consist of large molecules including proteins, which can absorb most of the laser energy and form un-dissolvable gas bubbles. This also raises the risk of complications such as tearing off the inner layer of the vessel or creating holes. On the other hand, saline (essentially salt water) provides a clearer path for the laser energy to reach directly to the problem area. To do the flush, a bag filled with saline is attached to one side of the manifold ports through a stopcock. Then, they replace the syringe filled with contrast liquid with a clean one. They use that to flush all the contrast and blood out from the system. After this, the doctor injects a small amount of saline through the guiding tube and starts the lasing (laser procedure) right away, along with a continuous flow of saline throughout the duration of laser activation.
For the procedure, the machine is programmed to run the laser for about 5 to 10 seconds, followed by a resting period of the same duration. When the rest period ends, an alert will sound, and the next lasing sequence can start. This helps possibly prevent problems from using the laser on the vessel for too long.
It’s also advised to move the tube very slowly (less than 1 mm/s) inside the vessel. This allows the plaque (a build-up of fat, cholesterol, and various other substances) enough time to properly absorb the light energy, resulting in ideal vaporizing and reduction of the plaque.
Possible Complications of Excimer Laser Coronary Angioplasty
With advancements in laser catheters and the development of safety procedures such as the saline infusion process, previously common serious complications like vessel tearing and puncturing have decreased significantly. Other actions that can help prevent these negative outcomes include not applying too much pressure and not using high laser settings for a long time. Vessel punctures can happen more often if the wrong size or type of catheter is used. For instance, using a catheter designed for a straight path on an unevenly placed blockage could cause problems. Similarly, applying laser energy to a previously injured area could also result in complications. If any of these happen, the use of the laser should be stopped immediately, and the issue should be handled according to standard procedures.
What Else Should I Know About Excimer Laser Coronary Angioplasty?
Excimer laser coronary angioplasty (ELCA) is a safe and proven method that enhances the results of routine artery-clearing procedures. It is mainly used for stubborn blockages that cannot be cleared out with traditional balloons. In certain complex cases, the laser energy in ELCA helps in reshaping the obstacle to allow for the usual procedure to continue.
The ELCA method can also reduce blockages in previously bypassed veins, which are prone to causing undesired backflows. Experts advise using special safety tools to avoid such complications, but these tools are often hard to use due to their size. Therefore, ELCA is discovered to be a safer alternative for most cases, as it has a lesser chance of causing backflows.
In-stent restenosis (ISR), which means the narrowing of the artery after placing a stent, an occurrence that’s been considerably reduced with the arrival of drug-eluting stents. Even in cases where ISR occurs, ELCA is a safe technique that doesn’t tamper with the stent, while simultaneously getting a larger clearing, greater luminal gain and getting a better control on unwanted tissue growth as compared to the balloon angioplasty method.
Furthermore, ELCA has shown to also remove plaque from both inside and outside. It is therefore particularly useful in situations where an ill-placed stent causes ISR. The method can ensure that the stent is better placed against the artery wall, potentially reducing the chances for future artery-clearing procedures.
