Angioplasty, the remodelling of an artery, traces its roots to the pioneering work of Dotter and Judkins in the early 1960s. They utilized a series of progressively larger coaxial catheters, passed across arterial obstructions to enlarge the lumen size. In the 1970s Gruentzig advanced the technique and broadened its application with the introduction of the non-elastomeric, polyvinylchloride angioplasty balloon mounted on a flexible, double-lumen catheter. Today, percutaneous transluminal angioplasty offers a safe and effective approach to the treatment of vascular stenoses in selected applications. The evolution of percutaneous transluminal angioplasty has continued with the development of new plastic materials for the construction of low-profile-high-pressure balloon catheters, hydrophilic coated guidewires, and improvement in digital imaging technology. While contemporary techniques continue to evolve, balloon angioplasty remains the mainstay of percutaneous transluminal therapy for atherosclerotic arterial stenoses. The contributions of novel techniques such as atherectomy, intravascular stenting, and laser angioplasty are still to be defined.

Dotter and Judkins mistakenly believed that their coaxial technique resulted in remodelling and compression of atherosclerotic plaque. Instead, it is now known that plaque fracture, with or without localized dissection of the arterial media, is the major mechanism of percutaneous transluminal angioplasty (Fig. 1) 359; the result is demonstrated angiographically as clefts filled with contrast material. However, removal or distal embolization of plaque constituents is not a component of successful percutaneous transluminal angioplasty.

While overstretching to the point of adventitial rupture is obviously undesirable, lesser degrees of medial stretching represent an important part of the ‘controlled’ injury made with percutaneous transluminal angioplasty. Patients typically experience transient, localized discomfort related to balloon inflation, which is attributed to stretching of the media. Severe, unremitting pain is, instead, an unfavourable sign that should raise the suspicion of adventitial rupture or bleeding into adjacent tissues.

In the peripheral arterial system, percutaneous transluminal angioplasty can provide definitive therapy for claudication and limb-threatening ischaemia, or it may be used in combination with surgical procedures, such as iliac percutaneous transluminal angioplasty followed by femoropopliteal bypass. The ideal morphological indication for transluminal angioplasty is a single, short-segment stenosis in a medium to large vessel, such as an iliac (Fig. 2) 360,361, femoral (Fig. 3) 362,363, or popliteal artery. Other indications include multiple discrete short-segment stenoses or a short occlusion. Long-segment stenoses, long-segment occlusions, and stenoses in small (e.g. tibial) vessels may be treated by angioplasty, but with less immediate and long-term success.

The identification of appropriate targets for percutaneous transluminal angioplasty requires integration of the patient's clinical presentation, physical status, non-invasive vascular laboratory results, and, when possible, pressure gradients. Correlation of these data with the radiographic appearance of a lesion helps to determine whether intervention is warranted. Dilating stenoses without regard to the these factors, simply because a lesion is present and accessible, is inappropriate. Angioplasty is not entirely without risk, and the natural history of many lesions remains benign. In an attempt to avoid any ambiguity, many angiographers rely upon the demonstration of a significant intra-arterial pressure gradient (over 10 mmHg) before proceeding with angioplasty. For this reason, among others, appropriate haemodynamic monitors are an essential component of the angiography suite.

While the indications for peripheral angioplasty are well defined, the guidelines for visceral angioplasty are more ambiguous. For example, percutaneous transluminal renal angioplasty is most commonly performed to treat renovascular hypertension, but is also employed to preserve residual function in native or transplanted kidneys. An unsuccessful prior attempt at renal angioplasty does not affect the outcome of a subsequent surgical revascularization procedure as long as primary thrombosis of the renal artery is avoided.

Since fewer than 5 per cent of patients with high blood pressure suffer from renovascular hypertension, it is frustrating and economically imprudent to screen large populations for that condition with standard arteriography. Suggestive signs and symptoms include hypertension with a bruit, sudden-onset, accelerated, or difficult to control hypertension, or onset of renal insufficiency during treatment with an angiotensin-converting enzyme inhibitor, such as captopril. Biochemical ‘proof’ of renovascular hypertension may be provided by asymmetric elevation of selective renal vein renin levels, with the assay being at least 1.5 times higher on the affected side.

The identification of appropriate targets for percutaneous transluminal renal angioplasty takes into account both the nature of the disease producing the renal artery stenosis (for example, atherosclerosis or fibromuscular dysplasia) (Fig. 4) 364, and the location of the lesion in the renal artery. The distinction between these aetiologies is important since renal angioplasty is the treatment of choice for renovascular hypertension secondary to fibromuscular dysplasia, and since restenosis after angioplasty is more common in atheromatous renal artery stenosis than in fibromuscular dysplasia. Although fibromuscular lesions tend to be more distal in the main renal artery, or involve branch renal arteries, the atheromatous lesions are more likely to lie in the proximal renal artery. Proximal renal artery lesions may respond well to renal angioplasty (Fig. 5) 365,366, but attempts at dilating stenoses that involve the origin of the renal artery are less likely to be successful (Fig. 6) 367. Ostial stenoses are, in fact, often overhanging aortic plaques that are typically merely displaced by balloon inflation and, therefore, are impossible to fracture with a catheter in the renal artery.

Mesenteric ischaemia (‘abdominal angina’) manifests itself clinically as weight loss or postprandial abdominal pain, and is thought to be due to severe narrowing of at least two of the three arteries supplying the bowel. These abnormalities are best demonstrated using lateral or biplane aortography and, in several small series, angioplasty has enjoyed a high degree of success and almost no complications. Percutaneous transluminal angioplasty can be expected to be least effective in treating ostial lesions, which are the most commonly encountered, and the so-called median arcuate ligament syndrome.

Percutaneous transluminal angioplasty has also been employed to treat a number of disparate clinical problems, although none of the techniques is currently widely employed in clinical practice. For example, while lesions in the cervical portions of the carotid and vertebral arteries are accessible to the angiographer, fear of cerebral emboli has to date discouraged the widespread application of angioplasty at those sites. Lesions at the origin of the vertebral arteries account for approximately 40 per cent of all vertebrobasilar insufficiency, and at least 70 cases of vertebral percutaneous transluminal angioplasty have been reported, with varying results. Similarly, over 160 cases of carotid angioplasty for ischaemic cerebral symptoms have been described, but the data concerning complications and long-term follow-up are incomplete.

To define better a suspicious lesion seen on a diagnostic arteriogram, the radiologist can either obtain oblique views of the area or, as noted above, directly measure the change in intra-arterial pressure across the stenosis. After identifying a lesion to be dilated, the angioplasty may be performed at the conclusion of a diagnostic arteriogram or during a separate visit to the angiography suite. This decision is best made after considering the patient's ability to tolerate the additional time needed to dilate the stenosis and the amount of radiographic contrast that must be used to document the result.

Our approach to percutaneous transluminal angioplasty is based on a series of fundamental techniques, with minor modifications for specific anatomical sites (Fig. 7) 368. The importance of experience cannot be overemphasized, especially in atypical or difficult cases, which require extensive deviation from these basic tools. Typically, this technique would involve the following steps:

(1)adequate definition of the haemodynamically significant lesion;

(2)navigation of the lesion with an appropriate guidewire;

(3)crossing the lesion with the selected angioplasty catheter;

(4)inflation of the balloon;

(5)repeat arteriography or manometry to demonstrate the effect of treatment;

(6)removal of the catheter and compression of the puncture site to achieve haemostasis.

Angioplasty catheters are described in terms of several variables: catheter shaft size (in the French scale; mm diameter/&pgr;), balloon outer diameter (in mm), and balloon length (in cm). For a particular case, the selected balloon has a diameter approximately equal to that of the ‘normal’ portions of the affected vessel and a length exceeding that of the lesion to be dilated. Employing the uncorrected dimensions (that is, not compensating for radiographic magnification) results in the use of balloons which are approximately 20 per cent larger than the native vessel, allowing for some over-distension, which is important in the mechanism of angioplasty. Typically employed balloon sizes range from 8 to 10 mm in the iliac arteries and about 6 mm in the superficial femoral artery. The size of the catheter shaft determines the size of the percutaneous arteriotomy and may affect the ability to traverse a particular lesion. Smaller catheters are often able to cross tighter stenoses, while larger catheters are stronger and may tolerate higher pressures. The development of so-called low-profile balloons, in essence larger balloons with a smaller cross-sectional diameter (due to tighter wrapping of the balloon and smaller catheter shaft size), has increased the number of lesions that can be successfully crossed and dilated.

The targeted lesion should be carefully crossed with an appropriate guidewire. To avoid the risk of intimal injury or extraluminal catheter passage after initial attempts at angioplasty, the wire should not be withdrawn across the stenosis until the conclusion of the procedure. Since balloon dilation requires transient arterial occlusion, intravenous heparin is administered prior to crossing the stenosis with a catheter, to minimize the risk of thrombosis. While not a risk in the iliac or superficial femoral arteries, spasm is a common complication of infrapopliteal or visceral angioplasty; intra-arterial nitroglycerine (50–200 mcg) is generally also administered at this time.

After advancing the catheter across the lesion, the balloon is inflated by hand under direct fluoroscopic visualization, using a 50 per cent mixture of low-strength contrast and saline in a 10 ml syringe and held in this position for 30 s. This method allows the angiographer to monitor the procedure for safety and often demonstrates the elimination of a ‘waist’ of stenotic plaque compressing the balloon as the lesion is dilated. While the routine use of a manometer is often unnecessary, it is helpful in avoiding balloon rupture. It is good practice to leave a set length of guide-wire extending beyond the catheter tip, in order to avoid traumatizing the wall of the vessel with that structure as the catheter contorts during balloon inflation. This precision becomes especially important when working near bifurcation points or smaller vessels. Follow-up radiographs or intra-arterial pressure measures can then be obtained in the same manner as for the original diagnostic study.

In experienced hands, most above-knee stenoses are accessible by contralateral retrograde arterial puncture, obviating the need for a second arteriotomy after the diagnostic study. Arterial access for distal femoral and popliteal angioplasty may require antegrade puncture of the diseased vessel, which is technically more challenging than is the retrograde approach. Just as with retrograde access, the antegrade arteriotomy must be made below the level of the inguinal ligament, in order to permit adequate haemostasis with compression alone at the conclusion of the procedure. Retrograde popliteal artery puncture has been described as an alternative approach but is not widely applied. Technical success of percutaneous transluminal angioplasty is defined using the same criteria employed to measure the haemodynamic significance of the original lesion. In the procedure room, obliteration of a previously defined pressure gradient is the desired outcome. If the lesion cannot be recrossed (because, for example, the guidewire has been withdrawn or because adequate haemodynamic measurements cannot be obtained), the angiographer can rely upon improved postprocedure lower-extremity pulse-volume recordings. Repeat arteriography in the same plane as was used to demonstrate the original lesion can illustrate enlargement of the arterial lumen and contrast-filled clefts indicative of focal plaque fracture and medial dissection. If the angiographer is dissatisfied with the result, the dilation can be repeated using a balloon of larger diameter. The angiogram taken after percutaneous transluminal angioplasty is presently the best means of demonstrating the degree of medial dissection and the irregularity of the intima, and is, therefore, an important part of the postprocedure evaluation. Patients with extensive dissection and marked disruption of the intima are predisposed to arterial thrombosis and should be given the anticoagulant intravenous heparin, for 24 to 48 h after haemostasis is achieved.

Intimal injury with exposure of the media to the bloodstream is a necessary part of this technique, but is highly thrombogenic. Therefore, aspirin is prescribed to inhibit platelet aggregation and clot formation at the treatment site. The effects of aspirin vary according to dose, and the dose that would be ‘best’ for most people has never been identified. Most physicians who perform percutaneous transluminal angioplasty prescribe either one baby aspirin (1.25 grain = 81.25 mg) or one adult aspirin per day. Some prescribe aspirin only around the time of the procedure while others prescribe it indefinitely.

In general, the likelihood of technical success and long-term patency are directly related to the diameter of the vessel being dilated. In the iliac arteries (Table 1) 201 initial success can be expected in over 90 per cent of cases, and most series report 5-year patency rates between 70 and 80 per cent. Few complete life-table analyses have been performed to assess the long-term patency of infrainguinal angioplasty procedures. Those available, while incomplete, suggest that approximately 80 per cent of femoropopliteal percutaneous transluminal angioplasty procedures are technically successful and that about two-thirds remain patent after 2 years of clinical follow-up (Table 2) 202.

The results of renal artery angioplasty remain more controversial. The indications for percutaneous transluminal renal angioplasty and reported rates of technical success vary widely amongst institutions, as do the definitions of technical success. A recent review of the largest percutaneous transluminal renal angioplasty series showed that renovascular hypertension may be cured in about one-quarter of patients, but that up to one-third of patients may derive no benefit. In both the short and long term, renal artery stenoses due to fibromuscular dysplasia respond more favourably to this technique than do those secondary to atherosclerosis (Table 3) 203. For stenoses due to fibromuscular dysplasia, patency rates in excess of 90 per cent may be expected at 2 years, while fewer than 65 per cent of atherosclerotic lesions will remain patent after that interval.

As with diagnostic arteriography, the complications of percutaneous transluminal angioplasty may be divided into two groups: those due to direct arterial injury and those related to the administration of radiographic contrast (including acute renal failure and drug allergy). As a rule, the rate of complications is inversely related to vessel size and the experience of the operator. Approximately 2.5 per cent of patients who undergo angioplasty suffer a complication that requires surgery or other treatment. Entry-site trauma, including haematoma and pseudoaneurysm, occurs in 2 to 3 per cent of cases, while complications due to thromboemboli are identified after 4 to 5 per cent of angioplasty procedures. Arteriovenous fistula has been reported as a complication in less than 0.1 per cent of procedures; limb or organ loss and even death are described, but these are very uncommon complications of angioplasty.

Although the ablation of atherosclerotic plaque by a laser was first described in 1962, the use of a laser for arterial recanalization is still experimental. Theoretical benefits offered by laser therapy include the ability to treat long-segment occlusion by debulking (instead of displacing atheromatous material as in balloon angioplasty), and the potential of treating the luminal surface to minimize myointimal proliferation. The introduction of laser systems initially generated intense scientific and proprietary enthusiasm on the part of investigators and manufacturers, but clinical experience with these devices has not met the exaggerated expectations. In the peripheral vascular system, laser recanalization is most frequently followed by balloon angioplasty, because the luminal diameter created is that of the probe (1–2 mm) which is insufficient to maintain flow. Lasers are, therefore, an adjunct to balloon angioplasty (Fig. 8) 369. It is important to understand some fundamentals of laser energy delivery before summarizing clinical experiences.

The word LASER is an acronym for light amplification by stimulated emission of radiation. Although several different laser systems have been used, major differences between them preclude their being compared to each other. Three fundamental characteristics make each laser system unique; these are wavelength, pulse duration, and energy output.

The laser hardware consists of a resonator cavity that contains a translucent medium between a partial and totally reflecting mirror. The lasing medium, which gives the laser its name, is activated by an energy source, such as an electric current or a flashlamp. The specific molecules in the lasing medium are excited to their characteristic higher energy levels and, reaching a threshold, they produce a series of laser light emissions at specific wavelengths. The energy output at each wavelength is determined by the number of molecules at the corresponding energy level. The wavelength emitted is theoretically possible throughout the entire electromagnetic spectrum, ranging from X-rays through to microwaves.

Another laser parameter is the pulse duration or the amount of time that the laser emits light energy—from picoseconds (10&supminus;¹² s) to continuous wave. The third important laser characteristic is energy, and the high concentration of coherent light energy produced provides lasers with many of their capabilities.

The laser radiation can interact in several different ways with the tissue by conversion of the light energy into other forms, which may or may not be desirable. There are essentially four different mechanisms of light energy conversion; they include luminescence, photothermal reaction, plasma formation, and photochemical reaction. The first three mechanisms have had applications in the therapy of atherosclerotic occlusive vascular disease.

Luminescence can be described as the emission of light energy from a molecule at specific longer wavelength(s), than the wavelength absorbed. The luminescence wavelength profile is usually a characteristic of the particular substance irradiated. It can be used for the identification of a particular tissue, as in the fluorescent discrimination between atherosclerotic plaque and normal arterial wall.

A photothermal reaction is the conversion of the light energy into heat energy. The effect on tissue depends on the method by which the energy is delivered, the amount delivered, the duration of the exposure, and the wavelength used. It is the mechanism employed for the ablation and recanalization of non-calcified atherosclerotic plaque, and the welding of blood vessels.

A plasma is a high-energy state resulting from a high-intensity, short-pulse duration (<10&supminus;&sup6; s) of laser light. Cavitation occurs, resulting in shock waves that disrupt tissue through a mechanical mechanism. It is through this mechanism that specific high-intensity laser systems can ablate calcified atheroma.

Specific tissues can absorb different wavelengths of light because of their different biochemical composition. With the choice of a specific wavelength that is preferentially absorbed by the target tissue, selective tissue ablation can be performed. The energy of exposure and the duration of exposure are also important to avoid overriding this process or to permit diffusion of heat from the selected target to the adjoining non-targeted tissues. Two cardiovascular applications for this selective use of laser irradiation include the selective ablation of plaque and thrombus, the ablation of plaque having undergone clinical investigation. By choosing the appropriate wavelengths, one can target the yellow carotenoid chromophores in plaque, or the red haemoglobin chromophores in clot. In this fashion, one can irradiate the selected tissues at energies that ablate them, but which are below the thresholds of ablation of the surrounding normal or non-targeted tissues. This process can be expanded by the administration of exogenous chromophores that preferentially localize in the target tissue. Examples of this include the haematoporphyrin derivative, tetracycline, and carotenoids.

The initial clinical use and trials of laser therapy for the treatment of obliterative atherosclerotic disease utilized available commercial lasers, including the CO&sub2;, neodymium:yttrium aluminium garnet (Nd:YAG), and Argon (Ar⫀) lasers. Quartz fibres, commercially developed for the communications industry, improved the applicability of laser systems with wavelengths between 280 nm and 2.5 &mgr;m, because of their ability to transmit high-intensity radiation along their length without significant loss of energy. In these initial laser systems the energy was delivered in a continuous wave through the end of a cleaved fibre; it was difficult to control the irradiated energy during the ablation process. The elevated thermal effects, including tissue charring, unwanted coagulation, spasm, perforation, thrombosis, and subsequent development of aneurysms, limited the application of these systems. The development of the ‘hot tip’ was the first attempt at controlling the energy delivery of continuous-wave radiation by encasing the tip of the fibres with a metal jacket that was heated by the latter (Fig. 8) 369. Although it improved the safety of laser recanalization of arteries, it has suffered several drawbacks. It is very user-dependent because it requires constant, rapid, to-and-fro motion, using a primarily mechanical means of recanalization; it causes vessel spasm and a large adjacent area of thermal injury; it is ineffectual against calcified plaque; and the devices advance along the mechanical path of least resistance—a problem with very eccentric plaques. Indeed, the primary mode of action of this device is probably mechanical and not related to any property of the laser energy. Clinical results have not been very promising in patients with clinically important atherosclerotic obstructive disease. Although the initial series claimed around a 90 per cent technical success rate and a 70 per cent 1-year patency, most of these lesions were short (<5 cm), superficial femoral obstructions in claudicators, and would probably respond in a similar fashion to conventional balloon angioplasty. When patients with critical ischaemia were treated, the results were significantly worse, with a less than 10 per cent 6-month clinical success rate.

Although all clinical laser systems use thermal mechanisms of ablation, short-pulse laser ablation is much more efficient than is pure thermal vaporization because the former uses a microexplosive mechanism for the removal of tissue with the concomitant formation of microdebris (Fig. 9) 370. Pulsed laser radiation is different from continuous-wave radiation because it delivers discrete quanta of irradiation at set time intervals of the order of picoseconds (10&supminus;¹² s) to seconds. Although a chopped beam of continuous irradiation is technically considered a pulse, ablative pulsed laser irradiation has come to signify high-intensity light delivery; that is, a laser pulse that carries a significant amount of energy to ablate the irradiated tissue while being delivered in a short enough amount of time to cause minimal thermal effects to adjacent tissues. For most tissue this is adiabatic time-frame microseconds (10&supminus;&sup6; s) to milliseconds (10&supminus;³ s). The type of tissue irradiated is therefore quite important, since mechanically weaker tissue will be more easily ablated at the same energy fluence than mechanically strong tissue. When pulses are of much shorter duration, one of the major problems that arises is that the intensity is too high to be able safely to couple the laser energy into a quartz fibre.

These considerations suggest that, depending on the application, the laser used, and the delivery system employed, there is an optimal laser pulse duration. However, it may be difficult to engineer the requisite power supply or to maintain activation of the lasing media for production of adequate laser output for specific pulse durations.

One other important factor in pulsed irradiation is the frequency of the pulses. If the laser pulse output is at a very high frequency, there may be accumulative thermal effect on the adjacent tissue that could make the system almost indistinguishable from continuous-wave laser irradiation. There are many variables that determine the optimal frequency. Despite the desire to obtain high efficiency by high pulse frequencies, power supply limitations usually keep the laser from a high delivery rate.

Pulsed lasers have not yet been used to a great extent in the treatment of atherosclerotic obstructive disease. There are three main systems: the 308 nm XeCl excimer, the pulse-dye, and the holmium:YAG (Ho:YAG), 2.1 &mgr;m laser. The infrared Ho:YAG laser is at a very early stage in its clinical application and there are only very scant data regarding its efficacy.

The pulse-dye laser used in Great Britain and in France is similar to the system used by the authors. Data concerning treatment of ‘critical ischaemia’ or severe disabling claudication demonstrate a 73 per cent acute clinical success rate and only a 10 per cent occlusion rate in the first 7-month follow-up. Data from use of the excimer laser are more extensive when used in peripheral arteries, but not all of the data are published. In one published series of 23 cases treated below the inguinal ligament, there was a 52 per cent success rate in recanalizing occluded arteries and an 80 per cent success rate in improving the luminal diameter in stenotic lesions. Of these cases, 47 per cent remained patent, with a mean follow-up to 10 months. These patients all had critical lower-extremity ischaemia (mean ankle/brachial index, 0.49), and all were treated with balloon angioplasty at the conclusion of the case. While these results are promising, it is still early to come to any conclusions about the effectiveness of these techniques.

The long-term patency of laser-treated atherosclerotic obstructive lesions is unknown. There are many theoretical and experimental advantages of pulsed systems over continuous-wave lasers, and most emerging new clinical laser systems for the treatment of obstructive atherosclerosis are of this type. However, there are several shortcomings (Fig. 10) 371. At present most of these systems are limited to providing access for balloon angioplasty in total occlusions, and cannot provide the definitive therapy if used alone. Because they are relatively inefficient for tissue ablation, the inexperienced operator used them, mostly for mechanical advancement of the devices and not for ablation and removal of tissue. For this reason one may predict that the results of their use would be similar to those of balloon angioplasty.

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