|MadSci Network: Medicine|
Hi Donald! Thanks for your question!
You asked: "Why don't they scrape out clogged veins? If cholesterol clogs veins and arteries, why don't doctors try to scrape the buildup out of them instead of going around them? Like bypass or shunts?"
Yes, doctors do remove the buildup of plaque or thrombus inside arteries and veins, either manually or with the use of catheters that scrape away or obliterate the plaques. Let's take a look:
Often, the vessels that are blocked with plaque are easily accessible by a tiny incision, such as the carotid arteries in the neck. When these get blocked, surgeons can perform a carotid endarterectomy. They simply make a tiny skin incision down to the location of the artery where the block is, and then place a temporary shunt (a mini-bypass) so blood can pass around the block (very important in the case of carotid arteries, since they supply blood to the brain!). They then make a little incision into the artery and manually remove the plaque.
Doctors can also remove plaque using a catheter --- this procedure is called an atherectomy, and it is performed by cardiologists in the cath lab. The cath lab is a room where there are machines that can take movies of the blood flow through vessels in your body (sort of like an X-ray movie). The doctors pass a catheter to the particular vessel in your body that they think may be blocked and then inject a special dye to flow along with the blood in that vessel. This dye is radiopaque, which means it shows up under those X-ray beams, so the doctors can see directly if vessels are blocked. Check out these fluoroscopy images to see what I'm describing.
In atherectomy procedures, the doctors pass a catheter which has a tiny device on the tip for removing or obliterating the plaque. One particular type of procedure, directional coronary atherectomy, uses a catheter which has a horizontal blade that rotates inside the vessel to literally shave off the plaque lining the vessel walls. It works kind of like a pencil sharpener (except that the blade is on the outside), collecting the plaque shavings inside a little compartment. Once the procedure is finished, the doctors simply remove the catheter, which now contains all the little plaque bits. Pretty clever!
Another catheter, the rotablator, is basically a drill with a diamond-coated burr which, once placed at the site of the plaque, can spin up to 200,000rpm! At this speed, the friction generated literally obliterates the plaque by pulverizing it into microscopic fragments tinier than the size of red blood cells. These miniscule bits can then safely circulate through the bloodstream until the body breaks them down. Other catheters obliterate plaques using laser energy to vaporize them with photon bursts. The nice advantage of lasers is that the energy applied does not create heat or friction energy --- much better for the vessel walls.
Another type of atherectomy procedure, called transluminal extraction uses catheters that have either that rotating blade design or use pulsed bursts of saline to break apart the plaque. Instead of collecting the plaque bits inside a tiny container, however, the catheter is connected to or generates its own suction so the little bits get vacuumed up through a tiny tube and removed from the body.
There is always a danger with passing catheters into vessels that contain plaques. If a piece of plaque was accidentally knocked free, it might flush downstream (distal) as far as it could fit into the tiniest arterioles, where it would eventually lodge (if it were larger than a red blood cell). This could be very dangerous, because it would block tissue from getting its usual amount of blood flow. This could lead to ischemia and all sorts of complications associated with reduced blood flow to a particular area of the body, including pulmonary embolus (to the lung), stroke (to the brain), and myocardial infarction (in the heart). Knowing this potential danger, companies have made devices which can be placed distal to those atherectomy devices to catch plaques that may have escaped from the atherectomy tool. Check out some of these here.
The advantage of all these catheters is that they can be snaked along though the body to get to that particular vessel that needs to be cleaned out without requiring major surgery and general anesthesia. This is especially nice when the vessels of the heart are involved. Coronary artery bypass surgery, although quickly becoming more minimally-invasive, still requires a chest incision and general anesthesia, and often requires that the patient go on bypass (the heart is arrested for a short period of time so that the surgeon can sew the bypass vessel/graft onto a non-moving target --- much easier than when the heart is beating!). By snaking catheters to these vessels (these procedures are called "minimally-invasive"), only the tiniest of incisions or punctures are made, so the site is much less painful, and the patients have a shorter hospital stay and a faster recovery.
Hope this helped to answer your question!
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