novel coronary interventional devices: an update

PROGRESS IN CARDIOLOGY

Novel coronary interventional devices: An

update

Kean Wah Lau, MBBS (Monash), MMed (Int Med), and Ulrich Sigwart, MD. London, England

Percutaneous transluminal coronary angioplasty (PTCA), since its inception in 1977,lp 2 has clearly established itself as an efficacious procedure in the treatment of obstructive coronary artery disease. However, despite enhanced operator experience and improvement in angioplasty technologies, PTCA is still plagued by two major problems, namely that of acute closure and restenosis.3-12 In an attempt to cir- cumvent these limitations of PTCA and to provide an approach to treat lesions that are seen as unfavorable for PTCA (e.g., chronic total occlusion, complex lesions, old vein grafts) but at the same time maintain a percutaneous transcatheter nonsurgical approach, three broad categories of new novel interventional devices have been developed and are currently being evaluated clinically. They are: (1) plaque removal (atherectomy, atheroablation, and laser); (2) welding (laser balloon angioplasty); and (3) scaffolding (intracoronary stenting). This article reviews atherectomy/atheroablation and lasers and will also provide an update of their current clinical status. Intracoro- nary stenting will not be discussed here as it has been extensively covered by our three previous articles (“Intracoronary Stents,” in the Indian Heart Jour- nal; “The current status of intracoronary stent: an overview,” in the Singapore Medical Journal; and “Restenosis: new approaches to an old problem,” in the Journal of Myocardial Ischaemia).

ATHERECTOMY

Included under this category are directional coronary atherectomy (DCA), transluminal extraction- endarterectomy catheter (TEC), and atheroablation (rotational ablation).

From the Department of Invasive Cardiology, Royal Brompton National Heart and Lung Hospital.

Received for publication July 17, 1991; accepted Sept. 6, 1991.

Reprint requests: Dr. K. W. Lau, Department of Cardiology, Singapore General Hospital, Outram Road, Singapore 0316.

4/l/34093

Directional coronary atherectomy. Of the three atherectomy devices, DCA developed by Simpson has been the one tested most extensively, with presently more than 1000 procedures performed in the United States alone. It consists of a distal, rigid, metal cylindrical housing with a 10 mm long open window encompassing about 25% of its circumfer- ence on one side and a balloon on the other. The cup-cutter, situated within the housing and driven by a disposable hand-held, battery-operated motor unit, revolves at 2000 rpm. Once the window is pressed firmly against the atheromatous plaque by the balloon, which is inflated at low pressure, the cutter is slowly advanced, excising and pushing the tissue into a distal nose cone collecting chamber. The process is repeated a number of times, repositioning the window when necessary until a satisfactory luminal result is obtained. The set-up requires a 9.5F or 11F specially designed guiding catheter (with a more gentle curve than conventional PTCA guiding catheters), an 0.014 inch guide wire, an atherectomy catheter (currently 5F, 6F, and 7F sizes are available), and a motor drive unit.

The mechanisms of coronary lumen enlargement by DCA are probably threefold. First, unlike PTCA, which does not reduce atheromatous mass, atherectomy actually debulks the latter. However, pathologic data suggest that the amount of tissue excised is quantitatively insufficient to account for the degree of angiographic improvement observed with DCA.13* l4 Sharaf et a1.,i5 using quantitative angiog- raphy, found that as much as 75 % of the luminal en- hancement seen with DCA is probably the result of the “Dottering” effect of the large atherectomy catheter. The third postulated mechanism is the result of the balloon which, when inflated to stabilize the cylindrical housing, probably dilates the wall already weakened by the deep incisions inflicted by the cutter (so-called “facilitated angioplasty”).i4

The short-term success rate is high (between 85 % and 96 % in atherectomy of a native coronary artery,

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February 1992

American Heart Journal 49% Lau and Sigwart

Table I. Clinical data of the various novel interventional devices

Clinical

Success (%) Average Diameter stenosis ($5 )

without adjunct PTCA Adjunct PTCA required

(VG) Unfavorable lesions

Complications (%) Overall Acute closure Dissection Spasm Thrombosis AM1

Q wave Non-Q wave

Em CABG Embolization Perforation Death Vascular repair

Restenosis (%) Risk factors

DCA

85-96 so 5-20

Uncommon

Calcified, dissected diffuse, old SVG, complex, inexperienced op

2.3-18 (5) l-3.7 4.5 2.5 NA 4.8 o-1.5 (1) 1.3-8 (5) 1.5-6.8 (3) l-6.9 (2) l-3 (1) O-O.6 (0.2) 1.6-3 (2) 30-50 >I cm length, <3 mm

diam, SVG, resten, subintimal resect, diffuse

TEC

90-98 95 30-40

32-85 (60) Eccentric

2-5 1-3 1.4 NA 0.5

0.5

5-7.5 (3.5) 1.4 1-2 1.5-2 NA 40-45 NA

Rotablation

85-95 so 35-45

30-40

NA

3-5 6-10 3-8 3-4 NA 6 0.9 2.5-20 (5) l-2 10-20 Rare Rare NA 30-50 SVG, OS, prox LAD

ELCA -

85-99 95 45-50

40-78

(60) Ostial, chr

occl, dissection

5 2.7-7 (5) 2-14 (10) 2-8 2-6 2-3

2-3.5 l-2 l-7.7 (1) 0.3 NA 30-60 SVG, chr occl

post ELCA >30 I:,

Numbers in parentheses are averages. NA, Not available; SW, saphenous vein grafts; op, operator; prox, proximal; diam, diameter; resten, restenosis; resect, resection; OS, ostial; chr owl, chronic occlusion; DCA, directional coronary atherectomy; TX, transluminal extraction-endarterectomy catheter; ELCA, excimer laser coronary angioplasty; AMI, acute myocardial infarction; EM, emergency; CABG, coronary artery bypass grafting; LAD, left anterior descending artery.

in vein grafts, and in a failed PTCA situation)16-27 compared with that of PTCA, frequently debulking about 17 to 18 mg of tissue per lesion17, 22 and creating a smooth lumen with only 5% to 20% residual stenosis in the process.15-171 28, 2g (Table I). The overall complication rate is about 3 % to 5 % . DCA seems to be safer and more successful in focal and soft lesions (noncalcified, restenotic lesions), type A/B1 lesions, and relatively straight and large vessels (>2.5 mm diameter, for example, the proximal LAD) and appears to be better than PTCA for lesions with thrombus.* DCA in old vein grafts is equally successful in attaining a large residual lumen; however, it seems to be associated with a particularly high incidence of distal embolization (up to 11.5%).25 Cor- onary arterial perforation, quite uncommon in PTCA, is higher with DCA, with an incidence of about 1% but probably more common when DCA is attempted in lesions with PTCA-induced flaps or major dissec-

*References 16, 1’7, 19, 20, 30, and 31.

tions.16s 18, 20-23 (Table II). This is not unexpected, as DCA has been shown to inflict deep injury to the arterial wa11.17 In fact, de Cesare et a1.32 documented an 11.6% incidence of ectasia of atherectomized segments and a subsequent high incidence of aneurys- ma1 expansion and restenosis of these lesions. Once perforation occurs, the usual course is emergency bypass surgery.

Theoretically, it would seem DCA should be able to overcome the costly and inconvenient problem of post-PTCA restenosis. First, it is capable of achieving a wider and smoother lumen than PTCA, which should translate into lesser shear force, less platelet accumulation, more space to accommodate intimal hyperplasia, and hence lower restenosis. Second, its high propensity to remove medial tissue (up to 70% of atherectomy tissue contains media) should have rendered less smooth muscle cells available to initiate the process of restenosis. Unfortunately, the converse has been shown to be true. The more aggressive tissue removal process is associated with more smooth

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Number 2 New coronary interventional devices 499

Table II. Factors affecting acute success and complication rates of directional coronary atherectomy

Factors

Lesion morphology Type A

Bl B2/C

Calcification No calcification Diffuse Focal/tubular Eccentric Concentric Restenotic De novo Old SVG Major dissection

Site LAD LCX RCA LMCA SVG

Experience First 20 cases Subsequent cases

Success (%)

93 86 69 66 96

93 86 95 60

92 75 84 77 95

84 87

Complication (75)

3.9 Major 6.4 Ischemic 11.9 Complication

10.8 1.313.5 4.5 2 1.6 5.8 11.5 (embolization) 3 (perforation)

2.8

7

9.1 4.4

Reference

31

16

20

25 18, 21

16, 20

31

LAD, Left anterior descending coronary artery: Xx, left circumflex coronary artery; RCA, right coronary artery; LMCA, left main coronary artery; SVG, saphenous vein graft.

muscle cell proliferation and hence with a high restenosis rate, as has been noted by a substantial number of investigators.* The restenosis rate after about 6 months post DCA is around 30 % to 50 % . There are certain angiographic risk factors that predispose to a higher restenosis rate (Table III). These include certain lesion morphologic characteristics: lesions that are situated in vessels of diameter <3 mm33; lesions at the ostium36 or mid-distal segments37, lesions in vein grafts, especially if they are restenotic lesions26 or have sustained subintimal injury during atherectomy (up to 100 % restenosis in such cases)2g; lesions that are calcified33; and lesions longer than 1 cm or tubular/diffuse in nature.33, 38

Although directional atherectomy has been shown to be feasible and safe, often achieving an excellent immediate angiographic luminal geometry (large, smooth lumen usually free of intraluminal haziness/ flap/dissection), up to this stage it has not convinc- ingly demonstrated a clear-cut superiority over conventional PTCA. Acute closure persists at 1% to 4 % of sites,i6v 20* 3g and DCA-induced coronary perforation hovers around 1% , both of these conditions often requiring emergency coronary artery bypass

*References 17, 25, 26, 29, and 33 to 36.

grafting. Furthermore, restenosis continues unabated. Hopefully, however, steps have been taken to solve these problems. A less aggressive approach that produces less deep tissue injury, has a lower infla- tional pressure, takes advantage of developing im- proved catheter modifications, avoids old vein grafts, tortuous vessels, and lesions with major dissection/ flap or heavy calcification, and atherectomizing noncalcified, focal de novo lesions in large vessels, especially if they contain thrombus (e.g., in the proximal left anterior descending coronary artery [LAD] where restenosis following conventional balloon angioplasty is high), seems the best program to adopt at this stage. When these cautionary measures are observed, the success rate is high, the acute complication rate is low, and restenosis is infrequent (as favorable as 96 % , 1.3 % , and 14 % , respectively).ls 20, 38

Tranluminal extraction-endarterectomy catheter. Compared to DCA, there are a paucity of data available on TEC, a device developed by Spears et al. at the Duke University Medical Center, Durham, N.C. It is introduced through a 10F guiding catheter as an over-the-wire system (as with all the clinical atherectomy devices) and consists of a distal conical cutter that revolves at 750 rpm, powered by a hand-held motor unit. The debris excised is aspirated through the central lumen of the catheter. Unlike the piece-

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Table Ill. Factors affecting restenosis following directional coronary atherectomy

Factors Restenosis (%) Reference

Lesion morphology Length >l cm

<l cm Vessel size <3 mm

>3 mm Calcification No calcification Tubular/diffuse Focal

Site Mid-distal segment native CA Proximal segment SVG: Without subintimal damage

With subintimal damage Overall

Native coronary: Without subintimal damage With subintimal damage Overall

Restenotic SVG lesion Native coronary de novo lesion Restenotic SVG lesion Native de novo lesion

50 30 44 29 39 19 44 14

61 18-26 43 100 73 42 50-63 45-50 71 37 81 36

33

33

33

38

37

29

29

35

26

SVG, Saphenous vein graft; CA, coronary artery.

meal nature of the tissue specimens retrieved by DCA, the tissues extracted by TEC are too frag- mented for histologic analysis. The current catheters come in five sizes; 5.5F, 6F, 6.5F, 7F, and 7.5F.

The immediate success rate is encouraging, being usually in excess of 90% (in conjunction with PTCA) for both native coronary arteries and vein grafts, electively or in acute ischemic syndromes.40-44 As in the case of DCA, TEC removes thrombus effectively.42, 44 The overall acute complication rate is comparable with that of PTCA (about 3% to 5%). The incidence of distal embolization is about the same as with DCA (1.4%), and perforation occurs in about 2% of patients41 (Table I). Leon et a1.43 reported a somewhat higher complication rate when TEC was attempted in eccentric lesions (7%). In the TEC Multicenter Registry, 41 there was no procedure- related mortality, but the in-hospital death rate was 0.5% for patients without infarcts and 12% for patients with infarcts. In contrast to DCA where the final residual stenosis is excellent, most of the time obviating the need for adjunct PTCA, TEC often leaves behind a significant stenosis that requires further dilatation by conventional PTCA in about 65 % of lesions attempted.41

ty.43 Recommendations on the use of TEC will have to await further trials and data, although there is a suggestion its potential clinical application might be in treating lesions that are unfavorable for the PTCA approach, such as vein grafts in native coronary arteries with diffuse disease or thrombus.43v 44

Rotational ablation. Atheroablation, first performed by Fourrier et a1.45 in human coronary arteries in 1988, involves the use of an abrasive burr (sizes range from 1 to 2.5 mm in diameter, the tip of which is en- crusted with fine diamond chips 30 to 40 km in size) attached to a long flexible drive shaft tracking along a central 0.009 inch flexible guide wire. A compressed air turbine drives the shaft and burr (but not the guide wire) at 160,000 to 190,000 rpm. It selectively pulverizes atheromatous plaques into small micro- particles of generally less than 5 pm (unless large burrs are used), which pass through the coronary mi- crocirculation and are subsequently picked up by the reticuloendothelial system.14 Experimental studies have shown that about 5 % to 10 % of microfragments are large enough to occlude distal small vessels, causing microinfarcts. 46 The degree of this problem will depend on the burr size and the atheromatous tissue burden.

Preliminary long-term results, although limited, The procedural success rate is about 90 % to 95 % , have identified a restenosis rate of about 44 % ?l The but the procedure requires adjunctive PTCA in restenosis rate seems not to be affected by recent about one third of cases because of unsatisfactory re- myocardial infarction, lesion length, or eccentrici- sidual luminal narrowing (averages 35 % to 45 % di-

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ameter stenosis).47-51 This is because the size of the burr is unfortunately limited by the internal diameter of the guiding catheter. The acute complication rate is generally about 5% (Table I), although the Western Collaborative Group52 (where most of the patients had severe diffuse disease) and some other investigators have noted a high incidence of non-& wave infarction, thrombotic occlusion, and transient ischemia/AV block/coronary vasospasm.14* 45p 4g, 53, 54 These complications, together with the “no reflow” phenomenon observed by others, have been attrib- uted to distal embolization after atheroablation (or activation of platelets by the microemboli). Perfora- tion, however, is uncommon as rotational ablation typically creates a smooth lumen without deep cuts into the vessel wa11.28, 46, 55 The incidence of angiographic dissection/flap is only 8% with rotablator compared with about 30% to 40% with the use of PTCA.56 This form of atherectomy seems particularly well suited for complex lesions, as demonstrated by the Rotational Atherectomy Multicenter Regis- try,51 where despite 90% of the patients enrolled having complex lesions, the success rate was exceed- ing high and the complication rate was appreciably low. The acute infarction rate was 6% (mostly non-& wave infarction) and there was no death. On intracoronary ultrasonic examination, this device proved effective in treating heavily calcified and more echogenic (hard) lesions.28

Only preliminary restenosis results are available at this time.48~4g~51.57,58 The overall incidence is between 30 % and 50 % and is not influenced by the use of adjunct PTCA. In contrast to DCA, the restenosis rate following rotational ablation seems to be higher for proximal lesions (45 % versus 20% for mid-distal ablation) and de novo lesions (54% versus 29% for ablation of restenotic lesions).58 Both rotational ablation and DCA, however, afforded the same high restenosis rate for ostial and vein graft instrumenta- tion.58 Until further clinical experience and follow-up data are gathered, the precise role of rotational ablation in the treatment of coronary artery disease cannot be firmly defined, although it seems to be promising for treating lesions unsuitable for PTCA such as complex lesions, especially heavily calcified ones, lesions in tortuous vessels, and small caliber vessels where the success and complication rates are favorable and the restenosis rate is low with atheroablation.

LASER ANGIOPLASTY

The term laser is a descriptive acronym for Light Amplification by Stimulated Emission of Radiation. Its application in the treatment of obstructive arte-

rial disease can be broadly divided into various categories based on the radiation emission characteristics (continuous or pulsed wave) and its mode of energy transmission to tissues (direct-e.g., excimer laser, balloon-centered argon laser, fluorescence- guided “smart” laser, or indirect-e.g., laser balloon angioplasty, hot-tip laser). Laser angioplasty achieves tissue ablation via a number of mechanisms.5g (1) Photothermal effects. This seems to be the predom- inant mechanism by which continuous wave lasers (e.g., argon, CO2, neodymium aluminum garnet) accomplish tissue ablation. The tissue absorbs the laser energy and generates intense heat, often resulting in a central crater with a rim of carbonization. (2) Pho- toacoustic trauma. This adverse effect evidenced by an area of vacuolization subjacent to the rim of carbonization is closely related to the use of continuous wave lasing. It is the result of the shock waves produced by sudden disruption of cell membranes by rapidly formed intracellular water vapour. (3) Pho- tochemical effects. These effects, the means by which the pulsed wave laser achieves its tissue destruction, are the result of the disruption of chemical bonds. The extent of laser-induced tissue ablation is in turn dependent on a number of factors-the wavelength and total amount of energy delivered, the light absorption characteristics of the tissue, the size of the laser fiber and its distance from the target, the emission characteristics, and the medium in which lasing is performed.50 There are currently a wide variety of coronary laser systems being evaluated clinically. Excimer laser and laser balloon angioplasty (LBA) will be discussed in more detail in this section, as they are the types most extensively tested. Some of the rest will be briefly mentioned toward the end.

Excimer Laser Coronary Angioplasty. Excimer laser coronary angioplasty (ELCA) emits pulsed energy in the ultraviolet portion of the spectrum and ablates only when the catheter tip is in direct contact with the plaque (contact ablation).14 Its theoretical advantages over the continuous wave laser system include minimal thermal effect and hence minimal tissue damage (as reflected by its lack of tissue char- ring and more rapid tissue healing), less thrombo- and vasospasmogenicity, precise ablation with clean tissue cuts, and the ability to ablate calcified plaques.14,50 Most clinical experience with ELCA is derived from the 308 nm XeCl system, which utilizes a fairly flexible over-the-wire coaxial multifiber catheter (sizes range from 1.3 to 2.4 mm in diameter) introduced through any conventional 8F or 9F guiding catheter.

Since its first clinical usage by Litvack et a1.60 in August 1988, much experience has been gained. A

502 Lau and Sigwart February 1992


high success rate of about 90% to 95% (Table I) is observed in both native coronary arteries and in vein grafts, although PTCA assistance is required in about 60% of cases because the residual post-ELCA stenosis remains substantial (averages 45 % ).62-70 The luminal size achieved following ELCA approximates the catheter diameter. However, following PTCA, the stenosis is further reduced to about 25 o/;, . The success rate seems more modest in total chronic occlusions (about 70%).62, 6g The overall incidence of major complication (5 % to 6% ), acute occlusion (5 % ), emergency coronary artery bypass grafting (CABG) (3.5 % ), and mortality (0.3 % ) with ELCA is comparable with that of PTCA. Karsch et a1.61 however, noted a high acute closure rate (20 % ) following ELCA, most of which were able to be recanalized with conventional balloon angioplasty. Like DCA and TEC, the perforation rate is about 1% .62-65, 68-71 For- tunately, some of the latter problems may resolve with prolonged balloon inflation without sequelae. The risk of perforation seems to be accentuated in ostial lesions.66 In the experience of Litvack et a1.,63 ELCA in lesions with major preexisting post-PTCA dissection predisposes to acute closure and the need for emergency bypass surgery. Hence it is probably wise to avoid ELCA in such a situation. Karsch et a1.61 found a higher acute complication rate in patients with unstable angina. In contrast to the high risk of complication in patients with ostial or dissected lesions, excimer laser has proved feasible, effective, and safe in treating calcified lesions, where a success rate of 96% with no perforation or death and only a low incidence of myocardial infarction (2 %) and emergency bypass surgery (2 ‘% ) was demonstrated by Levine et a1.68

Recent preliminary data62, 641 65y 71-73 identifying a 30 % to 40 % overall post-ELCA restenosis rate have not been encouraging; this rate is no better than that of standard balloon angioplasty. Restenosis is generally not influenced by the use of adjunct PTCA or by a history of previous PTCA.72, 73 There are, however, certain risk predictors of recurrence following ELCA. These include laser disobliteration of chronic total occlusion (restenosis of 48 % compared with 34 % for reopened stenotic but nonoccluded lesions)62 and in lesions with a residual stenosis of more than 30% following ELCA (restenosis of 63 % versus 25 s’o if the lesion was less than 30% ).64 The catheter tip energy dose was also found to have an influence on restenosis by Margolis et al. 73 Higher energies were associated with lower restenosis.

The clinical implementation of ELCA in coronary artery disease cannot be made with certainty at the moment until further data are gathered. However, it

does seem to have an advantale over PTCA in lesions that are either heavily calcified or diffusely diseased, where the success rate with the excimer laser is high and the complication rate is low, or in the uncommon situation where a guide wire has crossed the lesion but not the balloon.

Laser balloon angioplasty. The present technique of LBA involves the application of a continuous wave neodymium: yttrium-aluminum-garnet (Nd: YAG) laser irradiation transmitted through a fiberoptic system into a helical diffusing tip that heats up the balloon positioned at the culprit lesion. The new modified catheter has a heating element that has been extended to cover the entire balloon length with two gold leaflets placed at the ends of the balloon to prevent the laser energy from diffusing out of the tips. These modifications allow a wider area of vessel wall to be heated up and yet minimize the risk of thrombus formation.14 This catheter is used after PTCA over a conventional exchange guide wire.

The immediate technical success rate has been excellent (95 % ) in both elective and acute bailout situations using either low or high energy doses.74T75 This method has uniformly and substantially further reduced the post-PTCA stenosis severity74, 76 and has proven itself extremely useful as an emergency procedure following post-PTCA acute closures, often reestablishing antegrade flow, salvaging myocardium, and circumventing the need for emergency bypass grafting.75, 77 The short-term complication rate is notably 10w.~~

In sharp contrast to LBA’s efficacy in short-term closure, its long-term results have been disappoint- ing. Theoretically, LBA has the potential to overcome restenosis. It reduces elastic recoil, seals dis- sections/flaps, produces a larger and smoother lumen, desiccates any residual thrombus, and can decimate smooth muscle cells photothermally.78And, as these factors have been shown to play an active role in the process of restenosis, LBA should have pre- vented or at least reduced restenosis. Unfortunately, this has not been the case. LBA, like most current interventional devices, shares the common denomi- nator of inducing extensive tissue damage, which has been shown to bear a direct relationship to the amount of smooth muscle cell proliferation and hence restenosis.7g Preliminary data74 indicate a restenosis rate of 50% over 6 months. This high restenosis rate was further enhanced if high laser energy was used (67 ‘?A), especially in restenotic lesions (80 % ). In contrast, restenosis was 29 % when low energy was applied to de novo lesions. Mast et a1.80 confirmed this high propensity for restenosis with a high energy format. Restenosis has also been prob-

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lematic following the use of LBA in short-term closure.75 It appears that LBA, with its current design and protocol, is inadequate in preventing restenosis. However, despite this shortcoming, it has established itself as a useful interventional tool in the treatment of post-PTCA acute closure.

Other laser devices Balloon-centered argon laser. The balloon-cen-

tered argon laser incorporates a single fiberoptic through the central lumen of a conventional angioplasty catheter with a sapphire lens at its distal tip to create a 40-degree divergence of the laser beam. By doing so, there is rapid dissipation of the amount of energy delivered to the vessel. The balloon when inflated aligns the laser coaxially. This system, designed to facilitate standard balloon angioplasty by creating a central lumen when conventional guide wires/balloon catheters are unable to cross the lesion, requires a relatively straight arterial segment to avoid perforating the vascular wall. It also has the inherent inability to approach ostial or very proximal lesions. Recent preliminary reports81-83 on its use in severely stenosed and occluded native coronary arteries and vein grafts have been favorable, with a high success rate and an acceptable complication rate reported. The device’s long-term results are pending.

Fluorescence-guided “smart” laser. Also called spectroscopy-directed laser angioplasty, the fluorescence-guided “smart” laser’s operational principle is based on the fact that atheromatous plaques contain substances that fluoresce on exposure to laser irradiation. This dual laser system directs a low energy he- lium-cadmium “diagnostic” laser toward the target lesion and induces a fluorescent pattern that allows a computer-based spectroscopic set-up to differenti- ate atheromatous tissue and thrombus from normal tissue using a very complex algorithm.@ A second high energy “treatment” laser is then fired at the plaque and ablates it, sparing normal vessel wall. Al- though conceptually it may appear simple, its clinical application requires very sophisticated technology, a complex spectroscopic feedback system, and a computerized algorithm and it is not infallible.85~86 Like the argon balloon-centered laser assembly, the purpose is to “burn out” a small channel to allow the use of adjunct PTCA. Coronary experience with this laser is very preliminary.77

Hot-tip laser (laser probe). The hot-tip laser (laser probe) is an argon laser device that has a 1.5 to 2.0 mm metallic cap at the distal tip of its catheter in an attempt to negate the problems of perforation faced by the bare single optic system. Although some pub- lications involving small numbers of patients have reported a good success rate, the majority of these

patients still required adjunct PTCA.87$ aa Further- more, there was a notably high incidence of coronary thromboembolism and vasospasm and this probe was not appropriate for use in tortuous or small coronary arteries because of the increased risk of complications.8g-g2 It proved to be ineffective for ablating calcified lesions, a characteristic typical of thermal lasers.g1 Its long-term results remain unknown.

Holmium laser. The holmium laser employs a “cold” pulsed holmium-YAG solid-state laser. The catheter presently in use is an over-the-wire system with multiple fibers centered around the central lumen, a design similar to some of the other laser catheters. Its attractiveness lies in the fact that experi- mentally it has been shown to be able to selectively ablate atheromatous plaque with minimal thermal damage to the surrounding normal tissue and does so without direct contact of the fiber.g3, g4 In two small recent clinical studies involving patients with stenos- edloccluded coronary arteries and vein grafts, it proved promising. g5, g6 The success rate with the assistance of PTCA (in more than two thirds of patients) was high. However, vasospasm was com- monly encountered, confirming the experimental work by Pickering et al. g7 Generally, this laser system looks exciting but its clinical applicability will have to await further trials and data.

Conclusions. Conventional balloon angioplasty has planted itself assuredly in the armamentarium of interventional therapeutic cardiology. Its major limitations, namely those of acute closure, recanalization of chronic total occlusion, and restenosis have main- tained their presence despite improvement in catheter technologies and operator expertise. For new in- vestigational devices to establish their roles, they must be able to effectively demonstrate some clear- cut superior advantages over balloon angioplasty where the latter tends to do poorly (e.g., complex lesions) or prove their clinical utility in overcoming some of the residual problems of conventional angioplasty (acute closure and restenosis). To date, results so far on atherectomy and lasers have generally not been able to sustain the initial euphoria they gener- ated among interventional cardiologists. Although immediate success rates have been ubiquitously high with the new tools and complications acceptably low, these devices have not eliminated the problems of acute closure and restenosis. In fact, some of them have introduced more adverse effects and problems, such as a higher perforation rate or a higher restenosis rate than balloon angioplasty. However, there have been some possible scenarios where some of these devices might prove useful-e.g., in treating noncalcified, focal de novo lesions in large vessels

504 Lau and Sigwart

with directional atherectomy, in vein grafts with diffuse disease or thrombus with a transluminal extraction device, in heavily calcified lesions or diffusely diseased arteries with rotational ablation or an excimer laser, and in acute post-PTCA closure with laser balloon angioplasty. Needless to say, all these preliminary recommendations will need confirmation by well-conducted randomized clinical trials comparing the various devices in various lesional morphologic situations. Further improvement and refinement in instrumental technologies and the targeted use of new novel devices will eventually indicate the right direction to pursue. For numerous reasons, not the least of which is the cost of these new devices, conventional balloon angioplasty will not soon be- come obsolete.

SUMMARY

Interventional cardiologists today are over- whelmed by a hugh array of new high technology in- vestigatory devices at their disposal for the treatment of coronary arterial obstructive disease. These include the various atherectomy and laser devices, developed and introduced into clinical practice with the promise and intent of solving the limitations of conventional balloon angioplasty, namely those of acute closure and restenosis. But as more experience and data are obtained from the application of these devices, it is becoming clear that the latter have generally not been able to accomplish what they were intended to do. Although the immediate success rates have been uniformly high, acute closure has persisted and restenosis remains unabated. Nevertheless, some of these new devices have shown some fairly encouraging results in specific clinical circumstances. The targeted use of these instruments may prove to be a step in the right direction. This article reviews the current state of the art and the potential utility of certain of these devices.

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10. Holmes DR, Vlietstra R, Smith H, et al. Restenosis after PTCA: a report from the PTCA registry of the NHLBI. Am J Cardiol 1984;53:77C81C.

11. Serruys PW, Luijten HE, Beatt KJ, et al. Incidence of restenosis after successful coronary angioplasty: a time-related phenomenon. Circulation 1988;77:361-71.

12. Nobuyoshi M, Kimura T, Nosaka H, et al. Restenosis after successful PTCA: serial angiographic follow-up of 229 patients. J Am Co11 Cardiol 1988;12:616-23.

13. Erny RE, Gelbfish JS, Safian RD, et al. Does tissue removal explain all atherectomy improvement? [Abstract]. Circulation 1989;8O(suppl II):II-582.

14. Fischell TA, Stradius ML. New technologies for the treatment of obstructive arterial disease. Cathet Cardiovasc Diagn 1991;22:205-33.

15. Sharaf BL, Williams DO. “Dotter effect” contributes to angiographic improvement following directional coronary atherectomy [Abstract]. Circulation 1990;82(suppl III):III- 310.

16. Simpson J, Rowe M, Robertson G, et al. Directional coronary atherectomy: success and complication rates and outcome predictors [Abstract]. J Am Co11 Cardiol 1990;15:196A.

17. Safian RD, Gelbfish JS, Erny RE, et al. Coronary atherectomy. Clinical, angiographic and histological findings and observations regarding potential mechanisms. Circulation 1990;82:69- 79.

18. Robertson GC, Rowe MH, Selmon MR, et al. Directional coronary atherectomy for lesions with complex morphology [Ab- stract]. Circulation 1990;82(suppl III):III-312.

19. Popma JJ, de Cesare NB, Ghazzal ZMB, et al. Predictors of improvement in quantitative coronary dimensions following coronary atherectomy [Abstract]. Circulation 1990;82(suppl III):III-311.

20. U.S. Directional Atherectomy Investigator Group. Complica- tions of directional coronary atherectomy in a multicenter experience [Abstract]. Circulation 1990;82(suppl III):III-311.

21. Whitlow PL, Robertson GC, Rowe MH, et al. Directional coronary atherectomy for failed PTCA [Abstract]. Circulation 1990;82(suppl 111):111-l.

22. Robertson GC, Simpson JB, Selmon MR, et al. Experience of directional coronary atherectomy over 4 years [Abstract]. J Am Co11 Cardiol 1991;17:384A.

23. Vetter JW, Simpson JB, Robertson GC, et al. Rescue directional coronary atherectomy for failed balloon angioplasty [Abstract]. J Am Co11 Cardiol 1991;17:384A.

24. Garratt KN, Edwards WD, Kaufmann UP, et al. Differential histopathology of primary atherosclerotic and restenotic lesions in coronary arteries and saphenous vein bypass grafts: analysis of tissue obtained from 73 patients by directional atherectomy. J Am Co11 Cardiol 1991;17:442-8.

25. Selmon MR, Hinohara T, Robertson GC, et al. Directional coronary atherectomy for saphenous vein graft stenoses [Ab- stract]. J Am Co11 Cardiol 1991;17:23A.

26. Ghazzal ZMB, Douglas JS, Holmes DR, et al. Directional coronary atherectomy of saphenous vein grafts: recent multicenter experience IAbstract]. J Am Co11 Cardiol1991;17:219A.

27. Kaufman UP, Garratt KN, Vlietstra RE, et al. Coronary atherectomy: first 50 patients at the Mayo Clinic. Mayo Clinic Proc 1989;64:747-52.

28. Keren G. Pichard AD. Satler LF, et al. Intravascular ultra- sound of coronary atherectomy [Abstract]. J Am Co11 Cardiol 1991;17:157A.

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50. Holmes DR, Bresnahan JF. Interventional cardiology. In: Crawford MH, Abrams J, eds. Cardiology clinics. Philadel- phia: WB Saunders, 1991;9:115-34.

51. Buchbinder M, Warth D, O’Neill WW, et al. Multicenter registry of percutaneous coronary rotational ablation using the rotablator [Abstract]. J Am Co11 Cardiol 1991;17:31A.

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53. Bertrand ME, Fourrier JL, Dietz U, de Jaegere P. European experience with percutaneous transluminal coronary rotational ablation: immediate results [Abstract]. Circulation 1990;82(suppl 111):310.

54. Rodriguez AR, Zacca N, Heibig J, et al. Coronary rotary ablation-using a single large burr and without balloon assistance [Abstract]. Circulation 1990;82(suppl 111):310.

55. Fourrier JL, Stankowiak C, Lablanche JM, et al. Histopathol- ogy after rotational angioplasty of peripheral arteries in human beings IAbstractl. J Am Co11 Cardiol 1988:11:109A.

56. Bertrand MyFourrier J, ‘Buchbinder M, et al. Abrupt closure following rotational ablation with rotablator-short term clinical follow-up [Abstract]. J Am Co11 Cardiol 1991;17:22A.

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60. Litvack F, Grundfest W, Goldenberg T, et al. Percutaneous laser coronary angioplasty of aortocoronary saphenous vein grafts. J Am Co11 Cardiol 1989;14:803-8.

61. Karsch KR, Haase KK, Voelker W, et al. Percutaneous coronary excimer laser angioplasty in patients with stable and unstable angina pectoris. Circulation 1990;81:1849-59.

62. Buchwald A, Werner GS, Unterberg C, Wiegand V. Resteno- sis after excimer laser angioplasty of coronary stenoses and chronic total occlusions [Abstract]. Circulation 1990;82(suppl 111):313.

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novel coronary interventional devices: an update

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