Percutaneous coronary intervention and other percutaneous interventional cardiac procedures (percutaneous treatment of valvular disease and closure of cardiac defects) - technical article.
Percutaneous coronary intervention (PCI) is the term applied to a variety of percutaneous, catheter-based procedures that accomplish revascularization either by angioplasty (enlargement of a vessel lumen by modification of plaque structure), stenting (deployment of an internal armature or stent), atherectomy (removal or ablation of plaque), or thrombectomy (removal of thrombus).
The most common single indication for PCI is acute coronary syndrome. Randomized trials have shown that direct intervention for ST-elevation myocardial infarction (STEMI) is superior to initial thrombolytic therapy when performed in appropriate centres, and it can be used as a salvage procedure after failed thrombolytic therapy.
Balloon angioplasty is the traditional, basic technique of coronary intervention, but it is now uncommonly employed as a stand-alone treatment and finds its chief application in deployment of balloon-expandable stents, which have become the intervention of choice in about 90% of cases undergoing PCI. A variety of percutaneous techniques can be used to remove atheroma or thrombus from coronary arteries as a prelude to angioplasty/stenting.
There are two main types of coronary stent—’bare metal’ and ‘drug eluting’. The latter contain a drug (e.g. sirolimus, paclitaxol, etc.) that inhibits smooth muscle proliferation and thereby considerably reduces the risk of restenosis, which is the most common complication of stenting. Restenosis typically presents as exertional angina at 1 to 6 months following intervention: if it is not present at 6 months, it is unlikely to occur.
Percutaneous techniques can also be used to treat valvular stenosis and close cardiac defects in (highly) selected cases.
The birth of interventional vascular medicine is generally credited to Charles Dotter, a radiologist from Portland, Oregon, who in 1964 first dared to relieve atherosclerotic stenosis of a patient’s femoral artery by passage of a percutaneously introduced dilator. Although Dr Dotter had a few notable successes, which were widely publicized in the lay press, the scientific community scorned him. His radical concept lay dormant until a decade later when Andreas Gruentzig, a young German radiologist studying in Zurich, revived it. Dr Gruentzig was convinced that percutaneous dilatation of atherosclerotic stenosis was a sound concept and proposed that Dotter’s solid dilator be replaced by a catheter with an inflatable cylindrical balloon at its tip. Using catheters he created in his own kitchen, he proceeded carefully and logically in applying his technique first to animal models, then to human peripheral vessels, and finally in 1977 to his ultimate goal, the human coronary artery. News of Gruentzig’s percutaneous transluminal coronary angioplasty (PTCA) was quickly embraced by the medical community, and the era of percutaneous coronary intervention (PCI) was born. This chapter deals with percutaneous approaches to treating coronary, valvular, and congenital heart disease.
Percutaneous coronary intervention
Percutaneous coronary intervention (PCI) is the current general term applied to a variety of percutaneous, catheter-based procedures that accomplish revascularization either by angioplasty (enlargement of a vessel lumen by modification of plaque structure), stenting (deployment of an internal armature or stent), atherectomy (removal or ablation of plaque), or thrombectomy (removal of thrombus). Several different devices have been developed to perform these procedures. The interventional cardiologist chooses among these approaches to best suit the particular requirements of each individual patient.
The indications for percutaneous revascularization have expanded dramatically during the past 30 years. In the early days of PTCA it was indicated for subtotal, proximal occlusions of single vessels in patients with chronic, stable angina pectoris who had failed medical therapy. As experience grew and equipment improved, patients with unstable angina, total occlusions, bypass grafts, multivessel disease, and acute myocardial infarction were added to the list. Currently, the most common single indication for PCI is acute coronary syndrome.
PCI has traditionally been performed only in hospitals having cardiac surgical backup. However, as the procedure has become safer and the need for emergency bypass surgery less common (currently <1% of all cases), it has become more common, particularly in Europe, for these procedures to be performed in facilities where surgical backup is not on-site. Likewise, all patients undergoing PCI were once required to be potential candidates for bypass surgery in case of failure of the percutaneous procedure. Now some patients who are poor surgical candidates may undergo salvage intervention as their best or only avenue for revascularization. The choice of initial treatment (pharmacological, interventional, or surgical) for patients with each of the above coronary syndromes has been guided by evidence from a number of randomized clinical trials and will be treated in more detail in the later section headed ‘Outcomes’.
Devices and techniques
Balloon angioplasty is the traditional, basic technique of coronary intervention, although it is now uncommonly employed as a stand-alone treatment. Nevertheless, it is fundamental to the deployment of coronary stents, which are currently the most widely utilized of the interventional devices. The equipment for angioplasty consists of a coaxial array of guiding catheter, balloon catheter, and steerable guide wire. The procedure is accomplished by first engaging the left or right coronary orifice with the tip of the guiding catheter to access the vessel containing the target lesion and to provide backup support during advancement of the guide wire and balloon across the lesion. Next, the guide wire is advanced through the guide catheter into the appropriate vessel and across the lesion to be treated. Typical guide wires are 0.0014 of an inch in diameter (c.0.36 mm) and have a flexible spiral coil tip that can be directed by rotating their proximal end outside the body. The balloon catheter is then advanced over the guide wire until the deflated balloon lies across the target lesion. Finally, the balloon is inflated with a solution of dilute contrast medium to a pressure sufficient to expand the cylindrical balloon to its nominal manufactured diameter. The balloon size is selected to match the estimated diameter of the nearest segment of normal vessel and the length of the target lesion. Sometimes intravascular ultrasound is used to assist in this choice. The balloon is then withdrawn and the result assessed by angiography and, occasionally, by ultrasound.
Traditional angioplasty now finds its chief application in deployment of balloon-expandable stents. However, angioplasty may serve as a stand-alone interventional technique for the treatment of lesions of small vessels (<2.5 mm in diameter) and lesions located far distally or beyond tortuous segments where more rigid devices such as stents cannot reach. In experienced hands, with appropriate case selection, the initial success rate of balloon angioplasty should exceed 95%. Abrupt closure of the vessel might be expected in about 3% of cases (usually due to dissection), but most of these can be corrected by deployment of a stent, resulting in a need for emergency bypass surgery in less than 1% of cases. The clinical consequence of vessel closure is often insufficient to justify surgery in vessels too small or distal for grafting.
The technology of guide, balloon, and guide wire systems has advanced to the point where few locations in the coronary anatomy are inaccessible. Totally occluded vessels can usually be successfully crossed with appropriate manipulation of the right guide wire, enabling successful angioplasty. The success rate for angioplasty of totally occluded vessels depends upon the age, length, and composition (thrombus vs plaque) of the occlusion; it is well over 90% in cases of acute thrombotic occlusion, and over 50% in cases of chronic occlusion (>3 months). The chief disadvantage of balloon angioplasty is the phenomenon of restenosis, which will be discussed in more detail later in this chapter, and which spurred the development of newer devices in the hope of preventing restenosis.
Bare metal stents
Stenting has become the intervention of choice in about 90% of cases undergoing PCI. A modern-day vascular stent is actually an armature, or internal skeleton, for restoring and maintaining the cylindrical structure of the diseased vessel. Most stents are made from a thin-walled stainless steel or cobalt–chromium steel tube in which slots have been carved. The slotted tube is then mounted securely on a deflated angioplasty balloon and deployed at the target lesion of the coronary artery by inflating the balloon at high pressure with dilute contrast medium. When the balloon is deflated the stent remains expanded against the vessel wall, its slots stretched into diamond-shaped apertures. Approximately 20% of the vessel wall is covered by metal, the remainder being an intrastrut aperture. This accounts for the surprisingly high patency of side branches following stent deployment, and the ability to access these side branches when necessary for further intervention.
A variation of the slotted-tube stent is a balloon-deployed coiled wire (Wallstent and others). A coiled wire made from nitinol, or another alloy with shape-retaining characteristics, is compressed into a tubular delivery sheath, which is advanced over a guide wire across the target lesion. Once in its proper position the sheath is drawn back, allowing the stent to expand to its original size and shape. As with slotted-tube stents, pre- or post-deployment dilation with a balloon may be necessary, depending upon the nature of the lesion treated and the device used. Although one of the original stent designs, the self-expanding stent is now used less commonly for coronary artery applications, but it still finds use in many peripheral vascular cases. Most current stent designs are hybrids, which incorporate desirable properties of both the slotted-tube and coiled-wire designs.
Stents have gained remarkable popularity, mainly for three reasons. First, immediate complications are reduced because abrupt closure of the vessel due to dissection is less likely, emphasized by the fact that a stent is the best treatment for a balloon-induced dissection. Second, the immediate result is better in terms of the diameter and smoothness of the lumen, which turns out to be of more than cosmetic value because the early gain in lumen size relates directly to the late outcome. Thirdly, stents have been demonstrated in randomized clinical trials to be effective in reducing the likelihood of late restenosis. However, stents do have some disadvantages, which include the fact that they cannot be deployed under some circumstances, their propensity to subacute thrombosis, and the persistence of some degree of restenosis (depending upon the size of the vessel and length of the lesion). Subacute thrombosis, a complication unique to stents, usually occurs within a few weeks after stent deployment. By contrast to restenosis, which is a gradual phenomenon, stent thrombosis is usually sudden, presenting as acute myocardial infarction and requiring emergency revascularization, usually by balloon angioplasty. The likelihood of subacute thrombosis has been reduced to less than 1% by antiplatelet therapy with a combination of aspirin along with clopidogrel, ticlopidine or prasugrel.
The development of stents that gradually elute a drug into the surrounding vessel wall has reduced the need for repeat intervention due to restenosis from approximately 15% for bare metal stents to less than 5%. This technology is largely responsible for the rapid and sustained growth in popularity of stent procedures such that most patients requiring coronary revascularization are now treated by percutaneous rather than surgical techniques. The design of the drug-eluting stent incorporates a polymer matrix coating that contains a drug which inhibits the proliferation of smooth muscle cells in the surrounding vessel wall. The active drug slowly elutes from this coating into the underlying tissue while the vascular response to injury caused by vessel dilation is most active. Drug elution is usually complete by two months following stent deployment, but by modulating the proliferation of smooth muscle cells the growth of neo-intima covering the stent struts is limited, reducing the likelihood of restenosis of the treated vessel. The first two types of drug-eluting stents to be commercially available use sirolimus and paclitaxol as the active drug. These drugs inhibit cell proliferation through different mechanisms, but have proven to be equally effective. Other drugs currently available include everolimus and zotarolimus. Although excessive neo-intimal growth is undesirable, some is needed in order to cover the stent struts and prevent thrombosis. Dual antiplatelet drug therapy is necessary to minimize this risk as long as the struts are exposed. Bare metal stents are usually fully covered by 2 months, but drug-eluting stents may remain uncovered for 6 months or longer. For this reason, most cardiologists recommend that clopidigrel ticlopidine, or prasugrel be continued along with aspirin for at least 1 year following deployment of drug-eluting stents.
The cutting balloon has several tiny longitudinally mounted blades that become erect when the balloon is inflated and create linear cuts along the vessel wall. This was conceived as a method to dilate a vessel less traumatically and thereby reduce the likelihood of restenosis. This goal was never realized for de novo lesions, but the device has been advantageous for treatment of recurrent stenosis within previously deployed stents (in-stent restenosis) and for dilating lesions located at the ostium of a vessel, which are otherwise often subject to elastic recoil when dilated.
Rotational ablation (Rotablator) is a method of pulverizing plaque into particles smaller than the size of a capillary, which wash away with the circulating blood. This process is accomplished by means of a diamond-studded burr, which rotates at approximately 150 000 rev/min and is advanced along a guide wire into the plaque. The diamond studs on the forward face of the olive-shaped burr selectively cut into hard substances such as plaque and calcium, sparing the soft surface of normal tissue. During rotational atherectomy a vasodilating solution is infused into the artery proximal to the burr to prevent spasm and to maintain maximal coronary flow, which carries away particulate debris. Burrs are manufactured in sizes ranging from 1.5 mm to 2.5 mm in diameter. Atherectomy often requires the use of two or three burrs of progressively larger size until an adequate lumen size is achieved. Although occasionally used as a stand-alone procedure, rotational ablation is usually employed to ‘debulk’ lesions prior to final dilatation with a balloon or stent.
Rotational ablation was originally conceived as a potential solution to the problem of postintervention restenosis. Unfortunately, it has failed to outperform balloon angioplasty in this regard and has assumed the role of a ‘niche’ device for special situations. It is most commonly used in the treatment of heavily calcified lesions that do not respond well to balloons and stents. It is also useful in treating diffuse, osteal, and bifurcating lesions. The frequency with which rotational ablation is employed varies by operator, but averages less than 5% of most centres’ cases. It has the disadvantages of being an expensive addition to other interventional modalities, is unable to adequately increase the lumen of large vessels, and is contraindicated in lesions containing thrombus. Due to its tendency to transiently decrease contractility during the ablation process, it is also relatively contraindicated in patients whose left ventricular function is severely impaired.
Directional coronary atherectomy
Directional coronary atherectomy (DCA) is achieved with a device that utilizes a rotating cylindrical blade which is advanced across an open aperture near the tip of a cone-shaped catheter directed by a guide wire. Opposite the aperture is an eccentric balloon, which when inflated compresses plaque of the opposite vessel wall into the aperture, where it is cut away by the rotating blade and pushed into the nose cone. The direction of the aperture can be rotated so that slices of plaque are removed in a radial fashion by multiple cuts taken at different locations around the circumference of the vessel. The catheter can then be withdrawn and the excised plaque removed from the nose cone. The catheter may be reintroduced, if necessary, for more atherectomy.
Although DCA was originally devised with the hope of reducing the incidence of restenosis, it has failed to outperform balloon angioplasty in most circumstances. It has therefore assumed the role of a ‘niche’ technology, which is useful in particular situations such as very eccentric proximal lesions, and lesions involving the ostia of major side branches. Removal of plaque at branch points seems to reduce the likelihood of plaque shifting from one branch to another as the respective lesions are dilated with balloons or stents. However, DCA has the disadvantage of requiring a rather large, stiff device, limiting its application to proximal lesions of large vessels. Furthermore, the removal of plaque seems to have surprisingly little effect on restenosis. DCA is currently employed in less than 5% of interventional cases.
The transcutaneous excision catheter (TEC) device was developed at about the same time as directional coronary atherectomy. It employs a rotating conical blade that cuts away plaque and clot as it is advanced over a guidewire. The resulting debris is sucked back through the catheter into a reservoir outside the body. Although originally developed as an atherectomy device, it has found its chief application in treating clot-laden lesions, but it has not gained wide usage.
Excimer laser coronary atherectomy (ELCA) employs a fibreoptic catheter directed by a guide wire to deliver bursts of excimer laser energy to the plaque. Disintegrated plaque washes away in the circulation. However, ELCA has also failed to solve the restenosis problem, is used uncommonly in most centres, but remains the sole surviving member of a number of laser applications that have been tried and failed over the past 30 years. It finds its most frequent application in treatment of osteal lesions, stent restenosis, and diffuse calcified disease. Because of the limitations of fibre size it is usually followed by balloon or stent treatment.
Thrombectomy is an adjunct to angioplasty and stent procedures in patients with acute myocardial infarction and thrombus-laden lesions. Its purpose is to prevent distal embolization by removing the thrombus prior to balloon dilation and stent deployment. The devices for achieving this have become simpler over time. The simplest and least expensive is called a Pronto, which is a catheter delivered over a guide wire that has a relatively large inner lumen that is attached to a suction syringe. As blood is withdrawn through the catheter, its tip is moved back and forth through the thrombus, picking it up and removing it. A more complex device called AngioJet uses the Venturi effect from a high-velocity jet of water, which draws thrombus into a window near the tip of a catheter directed by a guide wire and propels it into a reservoir. Another device called the Excisor employs a helical screw at the end of a catheter, which breaks up the clot so that it can be withdrawn through the catheter. Both these devices currently find their chief application in the treatment of degenerated and clot-laden vein-graft lesions.
Distal protection devices are methods of capturing and collecting thrombus and other debris that may embolize distally from the target lesion during the use of many of the interventional tools mentioned above. They may be particularly beneficial during the treatment of old, degenerated vein grafts in which distal embolization is especially common. Two general approaches are employed. The simplest is a guide wire with a filter on its end (Filterwire). The filter looks like a windsock and catches debris released proximal to it. The other approach (PercuSurge) is to use a guide wire with a balloon near its tip which is progressively inflated until it occludes the distal portion of the vessel being treated. Intervention is then performed over the guide wire proximal to the occlusion balloon. Once the intervention is complete an export catheter is advanced over the guide wire and any debris removed by suction. Finally, the distal balloon is deflated, restoring flow and the guide wire removed.
The local, catheter-based delivery of β or γ radiation has been demonstrated to reduce the incidence of recurrent stent restenosis. Radiation is delivered with the assistance of a radiation therapist after initial treatment of stent restenosis with a cutting balloon, Rotablator, or conventional balloon. The benefit of brachytherapy appears to be limited to treatment of stent restenosis and it is not recommended following initial deployment of a stent. Brachytherapy also prolongs the period of risk for subacute thrombosis, making it necessary to treat patients with both aspirin and clopidogrel for at least 6 months following treatment. However, the need for brachytherapy has been virtually eliminated by drug-eluting stents. Not only is restenosis less likely after initial deployment of a drug eluting stent, but restenosis—when it does occur—is most effectively treated by concentric deployment of a second drug-eluting stent.
PCI exposes the patient to all the potential complications of cardiac catheterization presented in this article: Cardiac catheterization and angiography. In addition, it carries the risk of other complications unique to interventional procedures. Most of these stem from four general processes that cause adverse outcomes in coronary artery intervention: abrupt closure, distal embolization, stent thrombosis, and restenosis. Patient characteristics such as age, acute coronary syndrome, previous bypass surgery, and renal insufficiency are major determinants of risk. When considering PCI for a patient, it is important to weigh the likelihood of these adverse outcomes against the expected chance of adverse events without intervention. The approximate frequencies of various specific complications from percutaneous coronary intervention are listed in Table 1. As in diagnostic catheterization, the likelihood of these complications also depends upon operator skill.
|Table 1 Complications of percutaneous coronary intervention|
|Acute myocardial infarction||2–5|
|Emergency bypass surgery||0.5–3|
|Subacute stent thrombosis||<1|
|Peripheral arterial complications||5|
a These rates are approximate and vary widely with the clinical setting and patient characteristics. These are in addition to the usual complications of cardiac catheterization presented in the article on Cardiac catherization and angiography.
Abrupt closure and distal embolization
Abrupt closure and distal embolization account for most of the immediate complications of PCI, especially acute myocardial infarction and emergency coronary artery bypass surgery. Dissection, spasm, and thrombosis are the leading causes of abrupt closure. The availability of stents has reduced the need for emergency bypass surgery to less than 1% because these are an effective treatment for acute dissection in most cases. Nevertheless, dissection sometimes extends with the addition of each stent, and occasionally the stent itself can be the cause of dissection at one of its edges. Acute thrombosis may occur in spite of routine prophylactic treatment with heparin and aspirin: glycoprotein IIb/IIIa inhibitors may stop this process and are often given prophylactically, especially in high-risk cases. Incomplete stent deployment seems to be a leading cause of thrombotic occlusion. Distal embolization is surprisingly uncommon, except when patients have acute coronary syndromes or visible thrombus. It is especially troublesome for patients with degenerated or thrombus-laden vein grafts. Embolization may result in discrete occlusion of branch vessels or the phenomenon called ‘no reflow’, which is manifest by reduced flow without identifiable occlusion and thought to be due to capillary plugging from showers of microemboli. Distal protection devices may help prevent these problems. Both abrupt closure and no reflow usually cause some degree of myocardial infarction, the likelihood of infarction being a matter of how it is defined: non-ST elevation infarction indicated only by a rise of troponin or creatine kinase enzymes is more common than ST elevation (Q wave) infarction.
Thrombosis is a serious complication of particular concern for stents. It rarely occurs after the first 24 h following isolated balloon angioplasty or atherectomy. However, when a stent is deployed it may occur at a later time and is manifest by acute myocardial infarction. It is a medical emergency that must be managed in a fashion similar to spontaneous acute infarction. Emergency reperfusion by balloon angioplasty is usually preferred, unless a catheterization laboratory is unavailable, in which case thrombolytic therapy is recommended. In the early days of stenting this complication occurred in over 3% of cases in spite of vigorous anticoagulation including intravenous heparin and warfarin, a treatment that required several days of hospital stay for the initiation of warfarin therapy and delayed the widespread acceptance of stenting. However, once the current treatment of oral antiplatelet agents was proven to be superior, the length of hospital stay and local bleeding complications were reduced, and the use of stents grew rapidly. Stent thrombosis now occurs in less than 1% of cases. Thrombosis is defined as subacute when it occurs between 1 day and 1 month following stent deployment. Subacute thrombosis is equally likely for bare metal and drug-eluting stents. Thrombosis occurring more than 1 month after stent deployment is called late stent thrombosis and is particularly associated with drug-eluting stents. To minimize the risk of late stent thrombosis, dual antiplatelet therapy with aspirin and clopidigrel should be continued without interruption for at least 1 year following implantation of drug-eluting stents.
Restenosis was once the Achilles heel of coronary intervention. In patients undergoing isolated balloon angioplasty the likelihood of restenosis at 6 months following intervention lies between 30 and 50% if defined by angiographic criteria, and approximately 25% if defined by the clinical recurrence of symptoms. The use of bare metal stents reduced the angiographic rate of restenosis to about 25% and the clinical rate to as little as 10%. Drug-eluting stents have further reduced the rate to 5% or less, depending upon clinical and anatomic circumstances. The risk of restenosis varies according to individual factors such as vessel diameter and lesion length. Restenosis typically presents clinically as exertional angina at 1 to 6 months following intervention: if it is not present at 6 months, it is unlikely to occur. As described above, it is caused by the proliferation and migration of smooth muscle cells into the lumen of the treated vessel, a process that can be significantly modulated by use of drug-eluting stents.
Chronic stable angina
Randomized clinical trials have shown that patients with single- and double-vessel disease experience a more rapid and complete resolution of symptoms, and a greater improvement in treadmill exercise performance, when treated by balloon angioplasty rather than by pharmacological therapy for chronic stable angina pectoris. However, this comes at the price of a greater likelihood of repeat intervention or bypass surgery at 6 months, largely due to the need to treat restenosis. Nevertheless, the rate of bypass surgery becomes equal in both groups by 3 years. When compared to coronary bypass surgery, angioplasty provides similar relief of symptoms and similar rates of mortality and myocardial infarction at 5-year follow-up, with the exception of diabetic patients who have somewhat better 5-year survival rates when treated surgically. Otherwise, the main difference between patient groups randomly assigned to surgery or angioplasty is that repeat catheterization or revascularization is less frequent for those having surgery. Again, this difference is largely due to the effect of restenosis in the angioplasty group. Few of the interventionally treated patients in these trials received stents, so the likelihood of repeat procedures might be expected to be less using current devices. See: Stable angina management and treatment for further discussion.
The choice between initial aggressive treatment (catheterization and revascularization) and initial conservative treatment (medical therapy with catheterization and revascularization only for those who have continued evidence of ischaemia) for patients with unstable angina has been controversial. However, recent studies favour an aggressive approach to these patients. See: Management of acute coronary syndrome for further discussion.
Percutaneous intervention has been shown to be an effective treatment for acute myocardial infarction with ST segment elevation (STEMI), both as a salvage procedure after failed thrombolytic therapy and as a direct initial approach to reperfusion. Randomized trials have shown that direct intervention for STEMI is superior to initial thrombolytic therapy when performed in centres with expert interventionists and catheterization facilities that are available around the clock. Direct PCI is also an option for patients presenting outside these centres provided that they can be transferred and effectively treated in less than 90 min. In any case, direct PCI is the treatment of choice for patients in whom thrombolytic therapy is contraindicated and for patients who are haemodynamically unstable. See: Management of acute coronary syndrome for further discussion.
The cost of equipment and supplies for percutaneous coronary procedures may become a limiting factor, particularly in developing countries and in health care systems with stringent budgets. Most catheters, guide wires, and other supplies are intended for one-time use. Expendable supplies alone cost approximately £750 ($US 1200) for a simple balloon angioplasty procedure. That cost may be multiplied several-fold when drug-eluting stents are used—these are two to three times more costly than bare metal stents, although the added cost is offset somewhat by the reduced likelihood of repeat procedures necessitated by restenosis. The coverage of this additional cost varies considerably throughout the world depending upon insurance and government policies. Nevertheless, the cost of a single percutaneous revascularization procedure usually remains less than that of a comparable coronary bypass operation. However, when the added cost of repeat percutaneous revascularizations necessitated by restenosis is considered, the price difference between the two therapeutic approaches narrows.
Percutaneous treatment of valvular disease
Allain Cribier of France developed the treatment of valvular stenosis by means of balloon catheters in the 1980s. The clinical utility of the procedure depends upon the valve treated and the age of the patient. Percutaneous aortic valve replacement and treatment for mitral regurgitation are emerging technologies.
Balloon valvuloplasty of the mitral valve has become the treatment of choice for selected patients with rheumatic mitral stenosis. The concept is similar to the aortic valvuloplasty. The most common approach to the mitral valve is via trans-septal puncture of the left atrium from percutaneous access of the right femoral vein. After passing a stiff guide wire with a curved soft tip across the mitral valve, an appropriately sized balloon is centred on the valve and inflated with dilute contrast medium, tearing open the fused commissures and allowing the valve to open more normally. A dumbbell-shaped balloon, named after Dr Inoue, is often utilized, preventing the balloon from slipping off the valve during inflation. Clinical improvement, complications, and durability of the outcome from balloon mitral valvuloplasty have been shown to be comparable to surgical commissurotomy in appropriately selected patients. To be a candidate for balloon mitral valvuloplasty a patient must have no evidence of thrombus in the left atrium. Other features which auger poorly include immobility of the valve leaflets, severe calcification, thickening of the chordae tendineae, and more than mild regurgitation.
Percutaneous treatment of mitral regurgitation is being approached by two different strategies. The first involves applying a clip to the mitral valve commissures, effectively creating a dual orifice valve. The second approach is to pass a ring into the coronary sinus which constricts the mitral valve annulus, enabling better coaptation of the valve leaflets. Experience is greatest with the clip device (EValve). The EVEREST II trial indicates that the severity of mitral regurgitation can be safely reduced in two thirds of cases. An attractive aspect of this procedure is that its performance does not preclude surgical repair if subsequently needed.
Experience with balloon valvuloplasty for patients with aortic stenosis has been disappointing, largely due to an almost universal tendency for the stenosis to recur within 1 year. Consequently, the procedure is now performed only under unusual circumstances. It is occasionally used as a bridge to later surgery for patients who are initially too ill to safely undergo valve replacement. It is also sometimes performed for the temporary palliation of patients who are not candidates for valve replacement. It also has a role for children with congenital aortic stenosis, where temporary treatment by valvuloplasty may allow the child to complete growth before requiring surgical valve replacement. Percutaneous implantation of a bioprosthetic valve has been studied in a randomized trial comparing the Edwards SAPIEN percutaneous valve with medical therapy in patients who are at high or prohibitively high risk for surgical valve replacement. This study (PARTNER) showed improved outcome at one year for patients receiving the percutaneous valve, and such valves are now approved in Europe for these indications.
Balloon valvuloplasty is the treatment of choice for patients with pulmonary stenosis. Most are children whose valves respond well to this treatment, the advantage of avoiding surgery outweighing the moderate tendency for restenosis of these valves.
Percutaneous closure of cardiac defects
Atrial septal defects and patent ductus arteriosus can be closed percutaneously with catheter-delivered devices. One such device, called a clamshell (brand names include Amplatzer, Helex and STARFlex), has been used for this purpose for a number of years. It is now available throughout the world and is useful for closing smaller defects, although larger defects still require surgical closure. A concurrent, non-randomized trial comparing outcome for percutaneous versus surgical closure of atrial septal defect suggests shorter hospital stay and fewer complications for the percutaneous approach, which is now often preferred for patients with smaller ostium secundum type defects.
Closure of patent foramen ovale can be accomplished by devices similar to the clamshell used for atrial septal defect. However, no study has yet proven that percutaneous closure reduces the likelihood of recurrent stroke due to paradoxical embolism. Patent foramen ovale closure has also been advocated for migraine sufferers, but the MIST trial did not show significant reduction of the primary study endpoint, although the overall burden of migraine was reduced. Consequently, the closure of these defects remains controversial.