Help for hearts and blood vessels

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Section: BALLOONS, LASERS AND SCRAPERS

From tiny balloons to lasers and motorized drills and scrapers, a growing array of tools for unclogging arteries--mainly in the heart and legs--helps physicians to increasingly individualize patient care. Yet unknown, however, is how much this will change the course of heart and blood vessel disease, which claims nearly a million lives each year.
Heart + Blood = Life

Beating nonstop, the heart pumps blood throughout the body, sending nutrients and oxygen to all tissue, cell waste products to the liver and kidneys, and oxygen-depleted blood to the lungs. Vessels carrying blood to the heart are veins, and those taking blood from it are arteries. The coronary arteries, encircling the heart like a crown, provide blood to the heart muscle itself.

To do its work, the heart needs a continuous, adequate blood supply. Conditions that hinder this supply cause serious, even fatal problems.

In atherosclerosis, arteries become blocked as their walls build with plaque--fibrous, usually fatty deposits. When plaque blocks the coronary arteries, bouts of chest pain may ensue. Severe blockage causes most heart attacks. Severe blockage in the kidneys can lead to organ failure. In the legs, it can lead to tissue death requiring amputation. The disease usually progresses silently to a point, but leg pain when walking can be a sign.

The fatty substance cholesterol, found in animal-derived foods, fosters plaque buildup. To protect the heart, physicians can advise a cholesterol-lowering diet, smoking cessation, and weight loss coupled with an exercise program. On occasion, they may prescribe cholesterol-lowering drugs. With long-term lifestyle changes, cholesterol-lowering medication, or both, atherosclerosis may actually regress, recent studies indicate.

When this approach doesn't work or the disease is already too severe, coronary heart bypass surgery or other procedures may help.
Heart Bypass Surgery

The first heart bypass was performed in 1967. But the procedure has changed since then, says cardiologist Eugene Passamani, M.D., director of the division of heart and vascular diseases at the National Heart, Lung, and Blood Institute.

"Initially," says Passamani, "the surgeon removed the long vein running from the thigh to the ankle, cut it into pieces, and then fashioned grafts going from the aorta [the largest artery coming from the heart] to each of the three coronary arteries--sometimes including several lesser arteries. But by 10 years later, a third of the grafts had closed up again, probably due in part to the fact veins weren't designed to be arteries.

"More recently, the consensus is that if you use the internal mammary artery from inside the chest wall, the graft tends to stay open longer."

The bypass patient undergoes general anesthesia, hours on the operating table, support from a heart-lung machine, and, barring complications, 10 to 13 days' hospital recuperation and several months' recuperation at home.

Geoffrey Hartzler, M.D., consulting cardiologist at the Mid-American Heart Institute in Kansas City, Mo., says that "a patient's first bypass procedure is associated with the lowest risk." With repeated bypass surgery, he says, deaths and complications such as heart attack and stroke "increase by two-to three-fold."
The Balloon Solution

Often, balloon angioplasty can be used in the place of bypass surgery. Hartzler reports that 10 years ago about 5 percent of heart patients were likely to have angioplasty, but that today at least half of patients do. (See chart.) Angioplasty poses less risk because the body isn't opened and the procedure requires only local anesthesia It also is less expensive. Bypass costs about two-and-a-half times more than angioplasty, and hospitalization for angioplasty generally is for less than five days, resulting in further savings.

The technical name for balloon angioplasty in the heart is percutaneous (through the skin) transluminal (along the lumen, or cavity) coronary (heart artery) angioplasty (vessel repair)--PTCA, for short. The devices used for this procedure, as well as other heart and blood vessel surgical instruments, are regulated by the Food and Drug Administration's Center for Devices and Radiological Health.

To begin the procedure, the cardiologist places a very thin wire through a tiny puncture into a thigh artery (commonly, the large femoral artery) and threads this guide wire to the heart, watching its progress on an x-ray monitor. Next, a guide catheter (a thin flexible tube about the diameter of a pencil) is passed over the wire, and a second catheter (about the width of a spaghetti noodle), tipped with a deflated balloon, is threaded through the guide catheter. As the balloon catheter tip reaches the blockage, the balloon is inflated to compress the plaque against the inner artery walls; this may be repeated if necessary. The balloon is deflated, and the catheter withdrawn. As with other surgical procedures, the more experience a cardiologist has in performing angioplasty, the higher the patient success rate usually is.

"A major disadvantage," says Lynne Reamer, who heads CDRH review of these devices, "is that the procedure is hard on the blood vessel, stretching the walls, and possibly injuring the inner lining with cracking."

There can be blood loss, blood pressure drop, and heart attack, which may require emergency bypass surgery or even lead to death. Thus, a bypass team always stands by--though Hartzler says that improved technology and increased experience have reduced the need for emergency bypass at his institute from 9.8 percent in 1980 to 0.8 percent in 1988 and 1989.

"The question,"'says Passamani, "is whether angioplasty is better or worse than bypass. With bypass, you can fix all the arteries, but it's open-heart surgery. But while the body isn't opened in angioplasty, no one is quite sure about its long-term outcome. A third of those successfully done get narrow again within six months. About half a dozen trials are studying whether one ought to have angioplasty or bypass."

Also, PTCA can't always be used. The smallest coronary guide wire is only about 1/10,000th of an inch in diameter, but often the plaque is too hard to penetrate. Some other limiting conditions are damage from past heart attacks; hard plaque, which resists compression; disease in several vessels; and blockage in the left main artery, the heart's major supplier of blood, where a complication could have grave consequences, including heart attack or death.

Balloon angioplasty also is used to open arteries in the kidneys, arms and legs.
What Is That Scraper in the Window?

For some patients with clogged heart arteries, there is another alternative: the Simpson Coronary AtheroCath (Devices for Vascular Intervention, Redwood City, Calif.), a catheter instrument. Through a window in the instrument, a scraper shaves off the plaque blockage, which is then removed from the body. In October 1990, the AtheroCath became the newest FDA-approved device for clearing heart arteries. Its proponents believe that removing the plaque eliminates the "seeds" that can cause it to build up again, says Reamer, adding that this is yet unproven.

Like PTCA devices, the AtheroCath is threaded to the heart from a thigh artery, its progress followed on a monitor. Unlike balloon angioplasty, this procedure allows the cardiologist to focus treatment on the diseased side of the artery, sparing stress on the normal part of the vessel wall.

At one end of the AtheroCath is a tubular housing that encloses a cylindrical cutter and has a window on one side, a balloon on the other. Aiming the window at the plaque, the cardiologist inflates the balloon to hold the device in place and turns on the motor. The cutter at the window then shaves off the plaque, which is stored in the nose cone for removal. The balloon is deflated and the device is withdrawn or repositioned to remove more plaque. An added benefit is the research opportunity to study the extracted slices of plaque.

The AtheroCath was invented by John Simpson, M.D., Ph.D., a cardiologist at Sequoia Hospital in Redwood City. As Simpson, Tomoaki Hinahara, M.D., and others wrote in the March 1990 Circulation, the device is unsuitable for highly curving vessels because of the rigid metal housing and for long plaque masses because their removal would take a long time.
For Leg Arteries Only

Additional motorized devices, approved solely for unblocking clogged leg arteries, are the Simpson Peripheral AtheroCath, the Kensey Catheter, the Transluminal Endarterectomy Catheter (TEC), and the Rotablator.

With any of these devices, the physician makes a tiny incision and threads the cutter end into the vessel through an "introducer" catheter. With most of the devices, a contrast dye is used to improve x-ray imaging. Complications of the procedures are like those for PTCA and include vessel spasm or sudden closure and blood clots. Whenever a contrast dye is used, there is the possibility of an allergic reaction.

The Simpson leg AtheroCath works the same way as the heart device and, similarly, is not for long plaque masses.

From inside the flexible Kensey catheter (Cordis, Miami), a torsion-driven wire twirls a tiny projection at its tip about 100,000 revolutions per minute (rpm) to crush the plaque. Through an adjacent channel, jets of fluid cool and lubricate the spinning tip. The jets' whirling, in turn, stretches the artery, centers the device, and forms a vortex to suck up and emulsify the pieces. The device, however, tends to slide off plaque capped with fibrous tissue without destroying it.

In the TEC (InterVentional Technologies Inc., San Diego) and Rotablator (Heart Technology, Bellevue, Wash.), a guide wire inserted ahead of the cutter assists steering.

The TEC system consists of a catheter tipped with a stainless steel cutter. The catheter shaft rotates at 750 rpm, the steel tip cutting the plaque into pieces small enough to be sucked into the hollow catheter and into an exterior vacuum bottle.

"The challenge," says Kevin Daly of the manufacturing firm, "was to fashion a catheter that was-flexible, yet able to transfer the force from the motor outside the body to the cutting tip in the artery. We designed the cutter catheter using 'composite' technology--that is, using plastic, epoxy, and metal wire wound in a spiral its entire length. The same technology is used in jet fighter aircraft, where flexibility and strength are required."

The Rotablator's turbine motor drives more than 1,000 microscopic diamonds on the tip of a flexible shaft to a speed of about 190,000 rpm. This pulverizes the plaque into fragments smaller than red blood cells to be removed by the bloodstream. The manufacturer states that the tiny diamonds remove only hard or mushy plaque, which is inelastic, whereas healthy tissue, which is elastic, deflects away from the cutter to avoid injury and then springs back.
Laser Angioplasty: Still Evolving

Of limited usefulness in opening arteries, lasers continue to evolve and are under study. Three laser devices are approved for use in clogged leg arteries that are difficult or impossible to treat with balloon angioplasty alone, as when there is complete obstruction. Lasers pose the potential risk of burning a hole in the artery.

The physician can directly vaporize plaque with the LASTAC System laser (GV Medical, Inc., Minneapolis), whose energy emanates from an argon laserlight fiber centered in the vessel by a balloon attached to the laser catheter. A computer controls operating specifications, such as seconds of laser exposure, and provides immediate feedback.

The physician inserts the balloon-fiber portion, moves it to the blockage, and inflates the balloon to stem the blood flow while the system's automatic irrigation clears the area to be lased. The laser is fired, and its energy burns off a bit of plaque; the effectiveness of each firing can be observed on the computer screen. Then the balloon is deflated and the steps repeated until a channel forms so that regular balloon angioplasty can be used to finish opening the artery.

Another type of laser applied directly is the so-called "Holmium" laser (Trimedyne, Inc., Tustin, Calif.), so named because it's powered by a holmium YAG crystal. (Holmium is a rare metal.) A laser-light fiber inside a catheter is snaked over a guide wire to the obstruction. The laser energy is emitted in extremely rapid pulses from the fiber to burn away the plaque.

The Laserprobe (also Trimedyne) combines a metal-tipped fiberoptic probe with an argon or YAG laser. The physician threads the probe through the artery to the blockage and fires the laser to heat the tip to about 750 degrees Fahrenheit (400 degrees Celsius). Thermal energy from the hot tip, rather than laser energy, vaporizes the plaque, creating a channel for an angioplasty balloon to enter and finish the job.

Initially, it was thought that laser devices, particularly the Laserprobe, would be useful for long plaque deposits. Results have been disappointing, says Frank Criado, M.D., a surgeon with the Maryland Vascular Institute in Baltimore.

"For long blockages," he says, "the success rate with any procedure other than bypass is really dismal. Only 20 to 25 percent of the vessels will still be open a year later. Our results with leg bypass are at least three times better. For low-risk patients with severe symptoms from extensive blockage, Criado uses bypass because he finds it predictable and knows the outlook is quite good "in the long term, not just the short term."

Other problems can occur. For instance, the tip of the argon-heated probe can slip off hard plaque instead of vaporizing it, to possibly burn through the vessel wall, reported Jonathan Tobis, M.D., and colleagues in the June 1989 Journal of the American College of Cardiology.

Criado has used the Laserprobe successfully on short total blockages, 7 centimeters or less. He stopped using it last year, however, in favor of a technique that combines medication with increased balloon angioplasty capability, with which he says he can penetrate 75 percent of all short leg blockages.

"Usually," he explains, "it's a blood clot that makes a partial blockage into a total blockage. So first, I try to dissolve the clot with drugs, usually urokinase. Then I use a new type of guide wire--not really wire, but plastic--coated to attract water. When it's wet, as in the blood, it becomes extremely slippery, which helps it slide through the tiny space left by the dissolved clot, making way for the balloon catheter."

Criado sees a future for laser technology in this area, "once some refinements are made and we have a better understanding of the interaction between laser energy and plaque and blood vessel tissue. But that's going to be in the next several years, not around the corner."
More Future Possibilities

In Criado's near future is a research project in which he'll use ultrasound energy to clear blockages from leg arteries.

"Interestingly," he says, "ultrasound can both disintegrate plaque and dissolve blood clots, so we may be able to deal with both aspects of blockage at the same time."

Investigators also are experimenting with plaque-removing devices in heart arteries and the carotid arteries that feed the brain. Others are studying implanted stents--mesh metal devices that keep the artery open after balloon angioplasty--as well as a bioabsorbable stent that dissolves into the vessel after several months.

An FDA advisory panel of experts in conditions of the heart and blood vessels recently recommended approval to market a stent for use in leg arteries and an excimer laser for unclogging heart arteries.

Numerous issues remain unresolved. Other complications aside, not one technique has yet solved the problem of plaque reforming in arteries and grafts. Plaque itself isn't fully understood. And while the current therapy wonderland offers high hopes for improved care, it's often unclear which technique is best for which patient.

As Gordon Johnson, M.D., director of health affairs in the Center for Devices and Radiological Health, puts it:

"There are many considerations to an individual patient's condition. The plaque may be hard or soft, within easy reach or inaccessible, on a straight or curved surface, in a graft or primary vessel, in a wide or narrow vessel, or in an artery or a vein. On the other hand, one or another technique, instrument or procedure may be more convenient or easier to use, or it may have better longterm or short-term results. The ultimate goal is to match the technology to each patient's situation, but it's too early to do this with certainty or to know which therapies will stand the test of time."

In the summer of 1990, Passamani convened a meeting at the National Heart, Lung, and Blood Institute in Bethesda, Md., to gather information and opinion about these different treatments. As a result, the institute has extended its angioplasty registry to collect long-term safety and effectiveness data on the new procedures and subsequently to develop guidelines for use.

PHOTO (COLOR): Bypass Surgery: Routes blood around blockage through mammary artery or a vein graft.

PHOTO (COLOR): Balloon Angioplasty: Through a catheter in a leg artery, a deflated balloon is threaded to the blockage. When inflated, it opens the vessel by pressing plaque to the artery walls.

PHOTO (COLOR): Motorized Scraper: Reaching the heart from a leg vessel, the device is aimed at plaque without stressing normal vessel wall portions. An inflated balloon holds it in place, and a motor-driven cutter shaves off the plaque.

PHOTO (COLOR): Experimental Mesh Metal Stent: Collapsed over the deflated angioplasty balloon at insertion, it expands with inflation, staying to brace the leg artery after the balloon is removed.

PHOTO (COLOR): Drill-Type Scrapers: Plaque from leg artery is scraped off and cut into pieces small enough to be removed by bloodstream or mechanical suction

GRAPH: GAP NARROWS BETWEEN BYPASS AND ANGIOPLASTY

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by Dixie Farley

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