Transcript of "CORONARY ANGIOPLASTY AND INTERVENTIONAL CARDIOLOGY"
CHAPTER 24 CORONARY ANGIOPLASTY AND INTERVENTIONAL CARDIOLOGY MICHAEL W. CLEMAN, M.D. tissue, and calcium, as well as arterial muscle cells,INTRODUCTION intrude into the vessels. The plaque deposits ulti- mately cause stenosis, a narrowing of the lumen, or inner orifice of the blood vessels, which limits thePatients with severe coronary artery disease have tra- space available for blood circulation and, conse-ditionally been treated first with drug therapy and quently, the amount of blood delivered to the heartthen, if necessary, with coronary artery bypass sur- muscle.gery. In the past decade, so-called interventional car- Over time, as this process continues, the reduceddiology devices-angioplasty, atherectomy, lasers, delivery of blood means that the heart muscleand stents—have opened new vistas for successful does not get enough oxygen. This condition, calledtreatment of heart disease symptoms with techniques ischemia, may trigger chest pain, or angina pectoristhat are far less invasive than traditional surgery. —a major indicator of coronary artery disease. Ap-Rather than constructing a new route for blood flow, proximately 6 million Americans suffer from angina,as in bypass surgery, these procedures open or widen which can range in severity from mildly annoying toexisting ones. For patients in whom cardiovascular the feeling of a viselike grip in the chest that radiatesdrugs are not effective, they offer a major advantage to the left shoulder, left arm, or jaw. Angina attacksof being performed under local anesthesia, which are most often provoked by physical exertion, whengreatly hastens recovery and as a result lowers the heart needs more oxygen than it does at rest.cost. Sometimes a diseased coronary artery becomes Atherosclerotic plaque is the culprit that creates totally blocked by a blood clot, and a heart attackcandidates for these therapies, by virtue of narrowing ensues. If the ischemia has been silent—withoutthe coronary arteries. Within the walls of the arteries, pain—the heart attack may be the first indication thatplaque deposits containing cholesterol, connective there is advanced atherosclerosis. Whatever the se- 305
METHODS OF TREATMENT quence of events, severely narrowed arteries require treatment, either to lessen the pain or to prevent an Advantages and Disadvan- initial or a subsequent heart attack. (See Chapter 11.) tages of Angioplasty Advantages Disadvantages Can be performed under Generally used only for BALLOON ANGIOPLASTY local anesthesia. single- or double- vessel disease. Recovery is shorter and Is less efficient if there less painful com- are many points of Increasingly, balloon angioplasty (technically called pared to surgery. stenosis in a single percutaneous transluminal coronary angioplasty, or artery. PTCA) has replaced or has been combined with cor- Less expensive than May not be effective if surgery. plaque is calcified onary bypass surgery to open blocked coronary ar- (hardened). teries. As its name implies, the procedure actually May be feasible for Restenosis rate is 25– uses a miniature balloon which, when inflated inside patients unable to 35 percent with first a coronary artery, compresses plaques against the withstand surgery. procedure; may have artery walls and cracks them to widen the channel to be repeated. There is no noticeable Cannot be used if oc- through which blood can flow. scar. elusion is located in The angioplasty procedure was developed by the area not reachable late Dr. Andreas Gruentzig, who performed the first with catheter. human procedure at the University of Zurich, Swit- zerland, in the fall of 1977. The technique was adopted quickly in the United States, where doctors in New York and California performed the first angioplasties simultaneously in March 1988. From then on it was activities. Angioplasty may be suitable for a person adopted rapidly, growing from 2,000 procedures per- who experiences angina during mild to moderate ex- formed in 1979 to more than 227,000 in 1988. ercise. It may also be appropriate for a person with The advantage of the angioplasty procedure for silent ischemia who has had a heart attack and is physicians is that it is a faster and less invasive subsequently found to have one or two significantly method to treat atherosclerotic plaque buildup. An- narrowed vessels. Finally, angioplasty may be suit- gioplasty patients experience a quicker and less pain- able for a patient who has had reclosure of a sa- ful recovery. The procedure requires only a two- to phenous vein or left internal mammary artery graft three-day hospital stay and recuperation time is min- used for previous coronary bypass surgery. imal. Coronary artery bypass surgery, which involves The ideal—though by no means the only—can- opening the chest cavity, requires several hours un- didate for angioplasty has a single, well-defined der general anesthesia and necessitates a week or two obstruction in the left anterior descending, left cir- in the hospital, followed by several weeks more of cumflex, or right coronary artery; good heart func- recuperation for a patient to mend completely at tion (pumping quality) as shown on diagnostic tests; home. (See box, “Advantages and Disadvantages of angina that cannot be controlled by drugs and that Angioplasty.”) affects quality of life; and good general health that would not be expected to pose complications for the procedure. Sometimes two dilations may be done in a single vessel if it is narrowed in two places in close IDENTIFYING ANGIOPLASTY CANDIDATES proximity. Although balloon angioplasty sounds like the ideal The presence of coronary heart disease does not therapy for patients with angina that does not re- automatically qualify a candidate for angioplasty. To spond to medication, it is not right for everyone. For begin with, not all plaques respond to the angioplasty example, a patient with triple vessel disease—that is, technique. Lesions vary in their size, location, and blockages in three or more coronary arteries-is gen- composition; some are too long or much too calcified erally a better candidate for bypass surgery. Angio- —hardened by age—for angioplasty. Some lesions plasty is more appropriate for a person who has are out of reach of a balloon-tipped catheter. significant blockage of only one or two arteries that In other instances, the guide wire used to thread causes recurrent angina and restricts his or her daily the balloon catheter into the vessel may be unable to
penetrate hardened plaque that has completely is introduced. To start the balloon procedure, the op-clogged (occluded) the artery. Or the patient may have erator makes a small incision and inserts a hollow,so many stenoses that bypass surgery would restore Teflon-coated guide catheter through the femoral ar-much more blood flow than would an angioplasty. tery and, using a fluoroscope to visualize the path, threads it up toward the heart into the particular cor- onary artery that contains the blockage. The car-THE PROCEDURE diologist will first confirm the size and location of theAngioplasty is performed in a cardiac catheterization obstructions by using the dye to outline the arteries,laboratory. (See Figure 24.1 A-E.) Before the proce- a procedure known as coronary angiography. (Seedure begins the patient is usually given a sedative Chapter 9.)and will receive local anesthesia at the site of the Another catheter, tipped with an inflatable bal-femoral artery in the groin where the balloon catheter loon, is then inserted into the guiding catheter and 307
METHODS OF TREATMENT moved to the point where blood flow is thwarted by small percentage of patients experience abrupt clo- a plaque. The plastic balloon itself is tiny and sausage- sure of the artery during the procedure. This may shaped. Once inflated it will span the width of a nor- happen because the artery goes into spasm, is split mal artery-anywhere from 1/10 to 2/10 inch. A flexible by the catheter, or is occluded by a blood clot. The wire (a “bumper” guide wire) extends beyond the physician will reinflate the balloon to open the artery deflated balloon tip and is used to navigate the twists when this happens. But if this fails, or the artery clo- and turns of the arterial tunnels of the human body. ses after the angioplasty has been completed, emer- Once the catheter reaches the site of the blockage, gency bypass surgery may be needed. the surgeon looks for an opening in the obstruction About 3 percent of all angioplasty patients expe- through which to pass the balloon. If the plaque has rience a heart attack during the procedure—which calcified, this may require probing. The deflated bal- may then require emergency bypass surgery. Usually loon is then moved forward over the guide wire, into this happens when the artery involved in the proce- position next to the lesion in the artery. Dye maybe dure closes. However, a heart attack maybe triggered injected through the balloon so that the operator can by a smaller arterial branch snapping shut because gauge the exact location of the lesion, its nature, and the angioplasty has dislodged a blood clot. If the ves- its severity on X-ray, and then follow the progress sel is small, it is unlikely that emergency surgery will through the procedure. be needed. At the site of each lesion, the physician uses a hy- The mortality rate for angioplasty in a single vessel draulic device to suck any air out of the balloon. Then, is very low, about 0.1 percent (compared to 1 to 2 using a mixture of contrast dye and saline (sterile salt percent for bypass surgery). water), it is inflated several times for 30 to 120 or more The major problem of angioplasty is the rela- seconds each time. Each inflation blocks the blood tively high rate of restenosis, or renewed blockage. flow and squeezes the lesion back against the arterial Roughly a third of all patients will experience a recur- wall to restore or enlarge an open channel. The bal- rence of arterial narrowing within the first six months loon effectively stretches out the blood vessel like an following the procedure. Many kinds of restenosis injection mold. may occur. Hyperplasia is an overgrowth of cells that While the plaque isn’t removed, the balloon pres- is thought to be mediated in part by the body’s re- sure compresses and imbeds it into the wall rather sponse to injury-in this case, the cracking of the than leaving the lesion loosely attached to the wall. artery walls during the angioplasty procedure itself. Upon completion of the procedure, the entire cath- Or the atherosclerotic lesion may grow up again and eter system is pulled out and another angiogram is incorporate a blood clot. But once a patient passes performed to confirm the results. The small incision the six-month mark successfully, the likelihood of is generally closed by direct compression without plaque building up in that particular spot in that ar- stitches and the patient is usually sent to the coronary tery is much smaller. care unit or other special holding area for special The prescription for restenosis generally is an- observation. After one or two days of observation, other angioplasty. It could take as many as three or the patient will be able to leave the hospital and return four procedures to maintain the patency of the ar- to a full range of activities. terial channel. A physician will usually follow the patient with periodic exercise stress testing. In selected cases, par- ticularly if there are residual or recurrent symptoms, a repeat angiogram may be recommended in the fol- LASER ABLATION lowing months to see how well the procedure holds up. More than 90 percent of angioplasty patients have a good immediate result, defined as an arterial chan- Angioplasty using a laser instead of a balloon has nel that is at least 50 percent open. For the patient, been developed over the past decade and may prove the most obvious indication of this result is the free- to be a useful supplement to the treatment of coro- dom from chest pain. nary artery disease. Indeed, lasers are increasingly used in conjunction with the balloon technique. It should be noted, however, that laser angioplasty re- COMPLICATIONS mains an experimental procedure and is available at Like all surgical and interventional procedures, an- only a few research centers. gioplasty poses the possibility of complications. A The procedure is similar to that of balloon angio-
CORONARY ANGIOPLASTY AND INTERVENTIONAL CARDIOLOGYplasty, except that the laser catheter is tipped with a ency (opening) of an artery when a patient who hasmetal probe or a fiber optic probe heated by a light undergone angioplasty turns out to need an emer-beam, which melts through fatty lesions—both sten- gency coronary artery bypass graft. Thus, the stentoses (narrowing) and occlusions (blockages). The may assist in preventing a heart attack and allow thelaser procedure in some cases surpasses the balloon bypass surgery to be done as an elective rather thanin its ability to melt away calcified lesions as well. an emergency procedure. Generally physicians use a guide wire with a bal- The problem of restenosis following angioplastyloon to attack hard plaque first before using a laser. or laser ablation has galvanized interest in intravas-Contrary to popular belief, the laser does not vaporize cular stents. They can be useful in controlling dis-plaque in a puff of smoke. Rather, the laser ablates, section of the vessel walls after balloon angioplastyor removes, the lesion layer by layer. The laser homes or another coronary intervention. Stents provide thein and eradicates tiny areas of plaque. The plaque is means to “tack up” intimal debris (the cells and de-converted into gaseous products and microscopic posits that accumulate on the intima, the inner sur-particles, face of the blood vessel walls) and to seal off a tear The laser procedure is a delicate one, requiring the in the blood vessel wall that may result from angio-surgeon to focus the laser energy on lesions without plasty.creating a hole in the wall of artery or making a me- After balloon angioplasty, a stent can be deliveredchanical puncture. To make laser ablation more ef- inside a catheter to the site of earlier blockage andfective and safer, researchers still have to perfect the expanded within the arterial lumen. The size of aguide wires and the mechanism’s overall flexibility spring in a ballpoint pen, the stent has metal wiresfor taking the tight corners of the coronary arteries. that imbed themselves within the intima, the inner-The equipment will also have to be made more com- most of the three layers of a blood vessel.patible with vascular tissue, so as not to induce spasm A variety of stent designs have been developed.or encourage deposition of fibrin (a blood-clotting They have received varying degrees of acceptance bysubstance). the medical community. The Palmaz-Shatz stent is A number of different types of lasers are under one of the more popular ones. It is a flexible stainless-investigation, but the cool excimer laser appears steel tube that appears meshlike. The device is 1/2 inchpromising. It delivers energy at an average temper- long, is as narrow as a piece of spaghetti, and weighsature of 40 degrees Celsius. to avoid cooking or burning the sur- as little as a straight pin.rounding tissue with short pulses of energy. Others The potential for developing thrombi (blood clots)under review include continuous wave laser radia- is ever present when there has been an injury to thetion, such as that emitted by Nd:YAG or C02 lasers. arterial lining. However, successful application of aThese ablate plaque without thermal (heat) damage stent requires a certain amount of clotting, becauseto the nearby wall. endothelium cannot grow on bare metal. The cells require a thin layer of fibrin and thrombus (clotting material), and the Shatz stent configuration best al- lows for the development of fibrin and thrombus to-STENTS gether. The stent is completely covered by native blood vessel cells in two to three weeks. The wires themselves become embedded within these cells,Another way to attack the narrowing of coronary which proliferate at the site of implantation.blood vessels is to use a mechanical apparatus called The use of stents is still in the experimental stagea stent. These tiny metal “scaffolds” are inserted and in the United States, and further study is required toerected in a collapsing artery to keep it open in a determine risks to patients. Very little is known aboutmanner similar to the way construction workers the long-term effects of putting metal devices in cor-might use supports to prop up a collapsing tunnel. onary arteries. Patients may need anticoagulation Stents can be used in a variety of medical situa- drug therapy for a short time after stent delivery.tions. During angioplasty, they are employed as sec- Researchers must determine whether blood clot for-ondary supports to hold a vessel open while the mation at the stent site will be a problem and whetherphysician presses back lesions, thus preventing stents actually reduce the incidence of restenosis afterabrupt closure. Stents are also a stopgap measure for angioplasty.patients who aren’t immediately medically fit for sur- Research conducted recently in Europe showedgery. That is, the stent may provide temporary pat- poor results (commonly complete reocclusion or sig-
METHODS OF TREATMENT nificant restenosis) with one particular type of stent, Grinding plaque in this way has its limits. One the Wall stent. Newer models, however, especially concern is that not all the debris (atheroma) will be those impregnated with chemicals that are intended captured from the far side of the blockage by suc- to retard clot formation, may prove more effective. tioning the blood around that area, and that this de- Clearly, more study is needed. bris may flow through the bloodstream to collect in a smaller artery and cause blockage. Researchers us- ing the Auth Rotabiator report that the debris is usu- ally too small to clog capillaries. Other atherectomy ATHERECTOMY devices are designed to capture and hold the ather- oma protruding into the vessel in a capsule until it is removed. Another experimental approach to reopening nar- The main difference between atherectomy and bal- row coronary vessels is atherectomy. This procedure loon angioplasty lies in the methods by which they uses a rotary device-a high-speed cutting drill dispatch the plaque in artery walls. Angioplasty splits mounted on a catheter-that literally shaves off the plaque and stretches the vessel wall. Atherectomy plaque from an artery wall. The main reason for using removes sections of diseased intima and leaves a pol- an atherectomy device is to traverse small and tor- ished surface devoid of plaques. Compared to laser tuous coronary arteries that are difficult to navigate angioplasty, atherectomy carries a lesser risk of per- with thin angioplasty guide wires alone. foration, because the device affords greater control. A variety of device designs are under review by Also, an atherectomy device can remove calcified le- the medical community. One type, the Auth Rotabla- sions while a laser angioplasty usually cannot. tor, uses a high-speed oblong burr that may range in diameter from 1.25 to 4.5 millimeters. Imbedded in the bit are fine diamond abrasive particles that whir at up to 120,000 revolutions per minute to finely ablade the tissue. A flexible driveshaft allows for the VALVULOPLASTY passage of a stainless-steel guide wire with a flexible spring tip. The wire moves ahead and can be steered Just as atherosclerotic buildup in coronary arteries independently from the shaft and the burr, which do can be relieved with angioplasty, a heart valve that not start rotating until the guide wire reaches the becomes clogged or narrowed by calcium can be plaque in a selected artery. opened by a procedure called valvuloplasty. The val- Once the Rotablator is in place, its operation is vuloplasty procedure, developed over the last decade, similar to that of a dentist’s drill. Compressed air or involves opening the valve with a larger balloon- nitrogen powers a turbine to deliver rotational en- tipped catheter, which is then inflated to press back ergy to the burr through the driveshaft. The air pres- the calcium in the valve or to correct the anatomical sure controls the speed of the burr’s rotation. During deformity that has caused the narrowing. rotation, sterile saline runs through the catheter All four heart valves are subject to this treatment. sheath to cool the entire system. Mitral stenosis is a condition in which the mitral The atherectomy device is delivered to the site of valve, which controls blood flow from the left atrium the blockage via a catheter, in the same way as the (upper chamber) to the left ventricle (lower chamber) balloon device in conventional angioplasty. Once the of the heart becomes narrowed, so that blood flow is device is in place and the drill is turned on, it is al- diminished. In adults, it is most commonly the result lowed to reach a certain rate of rotation before the of a previous bout of rheumatic fever. Mitral valvu- abrasive tip is advanced over the guide wire. When loplasty appears to be relatively successful, produc- the physician feels the plaque resist the drill, the tip ing a restenosis rate of less than 10 percent within is successively pulled back and then thrust out again the first year. to maintain high-speed rotation. The drill is with- The aortic valve controls blood flow from the left drawn once it punctures the lesion. ventricle to the aorta, the blood vessel that carries Before the rotational device and guide wire are blood from the heart to various parts of the body. completely withdrawn, dye is injected to verify the When the aortic valve is affected by stenosis, or quality and success of the procedure. If the stenosis narrowing, surgical valve replacement remains pre- is still sizable, balloon angioplasty may be performed ferable, because the disease is a degenerative one, to improve the result. diagnosed increasingly in older patients. Putting in
CORONARY ANGIOPLASTY AND lNTERVENTIONAL CARDIOLOGYan artificial valve provides a more favorable outcome a new valve. Tricuspid and pulmonic stenosis arethan trying to widen the passage. Indeed, restenosis quite common but can be treated safely and effec-rates for aortic valvuloplasty hover at 50 percent. In tively with balloon valvuloplasty. The short-term andsome cases, however, the procedure is used to in- long-term success rates are similar to that seen withcrease blood flow temporarily in aortic valve patients mitral valvuloplasty. (For additional information, seeuntil they are strong enough to undergo surgery for Chapter 25.) 311