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New Interventional Technologies in Cardiology

  • Richard S. Stack
    Correspondence
    Address reprint requests to Dr. R. S. Stack, Interventional Cardiovascular Program, Box 3111, Duke University Medical Center, Durham, NC 27710
    Affiliations
    Director, Interventional Cardiovascular Program, Duke University Medical Center, Durham, North Carolina
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      In this issue of the Proceedings (pages 747 to 752), Kaufmann and associates provide a comprehensive review of their first 50 cases of coronary atherectomy with use of the Simpson Atherocath directional atherectomy device at the Mayo Clinic. The term “atherectomy” was coined by John Simpson, the pioneer in this field, who suggested that this term be reserved for only those devices that physically and mechanically remove plaque from the diseased artery. Although this new technology is in its infancy, several techniques have now been developed either to atherectomize and remove the tissue or to ablate the target lesion. The initial success rates reported with use of these devices are remarkable, in that they greatly exceed the original results of balloon angioplasty when that technology was first developed. In addition, further technologic improvements in these devices are anticipated, and such advancements might enhance the success rates during the next several years.
      In the current article by Kaufmann and colleagues, 53 atherectomy procedures were performed in 50 patients at the Mayo Clinic between October 1988 and January 1989. These were highly selected patients who had stenoses that “seemed accessible for use of the atherectomy catheter,” inasmuch as 50 patients is a small subset of all cardiac patients treated during that time interval at the Mayo Clinic. This case selection was likely responsible for the fact that almost half of the patients treated had restenotic lesions. Because of the soft nature of these lesions, the high-profile body of the Atherocath device can be passed through the site of the lesions relatively easily. Although the relatively large protective housing may provide some degree of safety in protecting the vessel wall from the cutting blade, it is likely to be a major limitation in traversing tight native coronary stenoses in contrast with the softer restenotic lesions. The wisdom of the investigators in the careful selection of patients, however, led to an extremely high success rate and relatively modest complication rates in this overall initial series. Although investigators may tend to want to test the limits of a new technology to determine its advantages over previously available techniques, they must assume the responsibility of protecting the outcome of the patients during such initial trials. On the basis of initially accumulated knowledge, more aggressive applications of these new technologies can be attempted. It must be remembered that standard percutaneous transluminal coronary angioplasty (PTCA) has been available for more than 10 years, during which time proper patient selection has been developed.
      The procedural success in the current series described by Kaufmann and co-workers was remarkable—47 of 53 procedures (89%) were successful, and the stenoses were reduced from a mean of 87% to 15%. Three of the patients in whom atherectomy failed required a subsequent bypass operation. Complications associated with the procedure included embolization of atheromatous material in two patients, intimal dissection in two, and side-branch occlusion and transient thrombosis in one case each.
      Since the advent of the Simpson Atherocath device, several other devices designed to remove or ablate intravascular plaque by mechanical means have been developed. Another atherectomy method that operates as an axial antegrade cutter, as opposed to the Atherocath side-hole cutter, is the transluminal extraction catheter (TEC) device developed by Interventional Technologies, Inc., and Duke University. The TEC device (Fig. 1) is a percutaneously introduced flexible-torque tube that tracks over a flexible steerable guidewire under fluoroscopic control to the target lesion in the coronary artery.
      • Stack RS
      • Califf RM
      • Phillips HR
      • Pryor DB
      • Quigley PJ
      • Bauman RP
      • Tcheng JE
      • Greenfield Jr, JC
      Interventional cardiac catheterization at Duke Medical Center.
      This maneuver is similar to insertion of a PTCA balloon catheter. When the radiopaque tip is properly positioned near the origin of the lesion, a two-stage trigger is activated on the hand-held control piece. This motion causes the conical cutter to rotate at 750 rpm while, simultaneously, suction is applied through the opening of the cutting windows to extract the fragments of the plaque through the catheter and out of the patient's body. At the top of the control piece, a thumb lever is used for controlling the antegrade excursion of the cutter over the guidewire in the coronary artery. Material extracted from the artery is collected in a glass reservoir attached to the rear of the control piece. A remote battery pack provides power to the device.
      Figure thumbnail gr1
      Fig. 1Diagram showing mechanical removal of atherosclerotic plaque with use of transluminal extraction catheter. Device consists of motorized cutting head with triangular blades, controlled by steerable guidewire. Cutting head rotates at 750 rpm, and suction apparatus removes excised plaque.
      (From Stack and associates.
      • Stack RS
      • Califf RM
      • Phillips HR
      • Pryor DB
      • Quigley PJ
      • Bauman RP
      • Tcheng JE
      • Greenfield Jr, JC
      Interventional cardiac catheterization at Duke Medical Center.
      By permission of Reed Publishing USA.)
      In a recent abstract,
      • Stack RS
      • Perez JA
      • Newman GE
      • McCann RL
      • Wholey MH
      • Cummins FE
      • Galichia JT
      • Hoffman PU
      • Tcheng JE
      • Sketch Jr, MH
      • Lee MM
      • Phillips HR
      Treatment of peripheral vascular disease with the transluminal extraction catheter: results of a multicenter study (abstract).
      the preliminary results of a multicenter pilot study of the use of the TEC device in the treatment of peripheral vascular disease were reported. This study included 36 patients at four medical centers. A total of 57 lesions were treated, 49 by the TEC device alone and 8 by a combination of debulking with the TEC device followed by further dilation with angioplasty. The primary angiographic success rate was 98% (56 of 57 lesions). Success was defined as 50% or less residual diameter stenosis. In order to be considered a successful debulking plus PTCA procedure, the TEC had to traverse the target lesion entirely and retrieve tissue before the use of PTCA. Debulking plus PTCA was used for those vessels with a diameter that exceeded the largest cutting diameter of the TEC device (9 F for peripheral vessels and 7 F for coronary vessels). The mean luminal diameter stenosis in the peripheral arteries was reduced from 72 ± 17% to 29 ± 16%. No vessel perforation or distal embolization occurred. Two patients required vascular repair at the sheath insertion site. In two additional patients, thromboses developed at remote sites that had been treated by PTCA alone and were successfully treated with thrombolytic agents. An article describing our initial results with the use of the TEC device in coronary arteries will soon be published. The overall success rate was 90%, comparable to the results obtained by Kaufmann and associates with use of the Atherocath device.
      Another device intended to ablate but not necessarily remove the plaque material is the Auth Rotoblator catheter. The device consists of a high-speed rotary metal burr, available in sizes ranging from 1.25 to 4.5 mm in diameter (for use in peripheral vessels) (Fig. 2). The burr, the distal half of which is embedded with fine diamond abrasive particles (approximately 40 μm), rotates at a very high speed (100,000 to 120,000 rpm). A flexible drive shaft permits the passage of a 0.009-inch (0.02-cm) stainless steel wire with a flexible steerable tip. The wire can be advanced and steered independently from the burr. Compressed oxygen or nitrogen powers a turbine motor, which delivers rotational energy to the burr through the drive shaft. The percutaneous intravascular delivery technique used with this atherectomy device is similar to that of balloon angioplasty. The wires are used to traverse the lesion under fluoroscopic guidance, and the burr is advanced to the origin of the lesion. Then the rotating burr is advanced through the lesion several times. Because most particles are smaller than 5 to 10 μm, they are allowed to travel downstream through the capillary system and eventually are trapped in the reticuloendothelial activating system.
      • Hansen DD
      • Auth DC
      • Hall M
      • Ritchie JL
      Rotational endarterectomy in normal canine coronary arteries: preliminary report.
      • Ahn SS
      • Auth D
      • Marcus DR
      • Moore WS
      Removal of focal atheromatous lesions by angioscopically guided high-speed rotary atherectomy: preliminary experimental observations.
      Although recent unpublished reports have described a curious no-reflow phenomenon after the use of this device in a few patients, determining the actual safety and efficacy of this device and its specific application in particular subsets of patients will necessitate further investigation.
      Figure thumbnail gr2
      Fig. 2Photograph of Rotoblator rotational device, designed to pulverize plaque material without retrieval. Rotary metal burr is available in a spectrum of sizes, the smallest (top) and largest (bottom) of which are depicted. See text for further discussion.
      (From Ahn and associates.
      • Ahn SS
      • Auth D
      • Marcus DR
      • Moore WS
      Removal of focal atheromatous lesions by angioscopically guided high-speed rotary atherectomy: preliminary experimental observations.
      By permission of the Society for Vascular Surgery and North American Chapter, International Society for Cardiovascular Surgery.)
      Another device that was originally used for treatment of lesions in peripheral vessels is called the Kensey rotational device. Although this catheter was designed to “pulverize” plaque material into extremely small pieces, reports of large embolic material slowed the application of this approach to ablation of coronary atheroma. At the time of this writing, no attempts to use this device in the coronary arteries have been reported.
      Because each of these devices is in the early phases of clinical testing in coronary and peripheral arteries, the exact advantages and limitations of the various techniques are currently unknown. If these devices are found to be safe and effective, they may likely play a complementary role in different types of atherosclerotic lesions in various parts of the coronary anatomy. An example of such a synergistic relationship might be the use of the Simpson catheter for large vessels or grafts with eccentric lesions, the use of the TEC device for lesions in the coronary vessels of 3 mm or less (particularly tight lesions or long diffuse lesions), and the use of the Rotoblator for smaller vessels, especially those with short discrete lesions in more distal sites. It is too early, however, to determine which, if any, of these devices will be the preferred therapy for most coronary atherosclerotic lesions.

      Comparison of Atherectomy and Other New Technologies.

      Currently, in addition to atherectomy, two other new interventional technologies of considerable interest are the laser catheter and the coronary stent prosthesis. Various types of laser catheters are beginning to be used in human coronary clinical studies. In one such device, laser energy is used to heat the metal tips of probing catheters. This so-called hot-tip laser catheter, manufactured by Trimedyne, Inc., is currently being used in early clinical trials in human coronary arteries.
      • Linnemeier TJ
      • Cumberland DC
      • Rothbaum DA
      • Landin RJ
      • Ball MW
      Human percutaneous laser-assisted coronary angioplasty: efforts to reduce spasm and thrombosis (abstract).
      A second type of device, the “laser balloon,” was developed by Dr. Richard Spears and USCI, Inc.
      • Spears JR
      • Reyes V
      • Sinclair IN
      • Hopkins B
      • Schwartz L
      • Aldridge H
      • Plokker HWT
      Percutaneous coronary laser balloon angioplasty: preliminary results of a multicenter trial (abstract).
      This device uses a combination of balloon angioplasty and relatively high levels of heat developed from laser energy. A third approach is the use of a bare optic fiber that could potentially traverse chronic occlusions, which could then be followed by insertion of a standard balloon angioplasty catheter.
      • Foschi AE
      • Zapala CA
      Direct argon laser irradiation of high-grade stenoses and total occlusions in native human coronary arteries and bypass grafts: initial clinical experience (abstract).
      At the time of this writing, clinical trials with each of these devices have just begun, and their relative merits and limitations cannot be assessed. In the past, the potential problems associated with the use of these laser devices in peripheral arteries have been a relatively high rate of perforation and a high frequency of reocclusion. Nevertheless, continued advancements may improve the safety and efficacy of these devices. One important potential application would be the ability to create a central passageway through chronic total obstructions to allow insertion of a standard flexible steerable guidewire that could then be followed by any type of definitive device such as a balloon catheter, a wire-based atherectomy device, or a larger laser catheter.
      The other recently evolving major coronary technology is the use of coronary stent prostheses. The first of these devices was the Medinvent, Inc., stent developed by Dr. Ulrich Sigwart. This self-expanding stent is introduced over a guidewire in a region of a vessel that has previously been dilated with PTCA. The stainless steel stent is then deposited in place, and the delivery system is removed. Other stents for which clinical trials have begun in the United States are the Palmaz-Schatz stent (Johnson & Johnson, Inc.) and the Gianturco-Roubin stent (Cook, Inc.).
      Thus far, stents have produced favorable results in terms of successful placement to prevent abrupt reclosure of vessels in patients who have undergone balloon angioplasty. The results in terms of avoiding restenosis remain to be determined in long-term follow-up studies. Perhaps stents will eventually be compatible with other technologies such as the TEC atherectomy procedure or other mechanical or laser approaches to remove vascular plaques. Thus, a plaque could initially be ablated and subsequently a stent prosthesis could be inserted in an effort to avoid long-term restenosis at the atherectomy site. If atherectomy ultimately is associated with a substantially reduced rate of restenosis in comparison with PTCA, stent placement in such sites will likely be unnecessary.

      Limitations in the Development of New Technologies.

      In the past, third-party payers were willing to accept variations in standard PTCA therapy as alternatives to balloon PTCA and were usually willing to provide the financial support necessary to perform clinical trials in patients. More recently, with certain notable exceptions, third-party payers have refused to participate in the development of new technologic devices. In fact, some have taken the position that if a new technologic device is used in the investigational phases for the treatment of patients, financial coverage for the entire hospitalization will be denied. Several key investigative centers for new atherectomy and laser devices have suffered substantial economic losses as a result of these decisions. Although some companies are able to underwrite the overall costs of the enormous hospital bills for these coronary patients, many of the small firms, which are essential for developing new ideas and creating competition in the marketplace, cannot afford such expenses. One of the major challenges during the next several years will be to identify means of making progress in the field of investigational devices under these unfavorable economic conditions. In the final analysis, the burden for the cost of the development of these new technologies will likely be shared among the hospitals (who will benefit from having access to the latest high-technologic devices), the companies (who will benefit from the eventual sale of these products if they are found to be successful), and the patients (who will benefit from the application of these devices).

      Summary.

      If atherectomy procedures are found to be safe and effective for removal of plaque in human coronary arteries, they can be expected to provide an important alternative to balloon angioplasty for the treatment of many types of coronary lesions. In addition, many patients who are candidates for coronary artery bypass procedures could likely benefit from these less invasive procedures. Although atherectomy has a theoretic potential for reducing the rate of restenosis by removing the plaque rather than pushing it to the side, it is unlikely to eliminate the restenosis problem completely. A more important advantage of atherectomy may be the potential for successful treatment of lesions that are anatomically unsuitable for PTCA. Even though balloon catheter technology has evolved to the point that almost all lesions in the coronary anatomy can be successfully negotiated, approximately half the coronary patients who require invasive therapy in the United States are still undergoing open-heart bypass procedures. Thus, if atherectomy can expand the indications for interventional therapy to the types of lesions that are currently considered unsuitable for PTCA, the large number of patients who are currently unable to benefit from interventional catheterization techniques could be treated.
      With all the new devices under investigation, carefully controlled prospective randomized trials must be conducted once the developmental phases have been completed. Each new technology must be compared with the current state-of-the-art techniques of balloon angioplasty and coronary artery bypass operation. Finally, all the new procedures and devices must be directly compared with each other to determine the best use of each new technology. The overall clinical value can be assessed only after late angiographic follow-up studies have been performed to determine the long-term benefit in various subgroups of patients who have been treated with these new technologies.

      REFERENCES

        • Stack RS
        • Califf RM
        • Phillips HR
        • Pryor DB
        • Quigley PJ
        • Bauman RP
        • Tcheng JE
        • Greenfield Jr, JC
        Interventional cardiac catheterization at Duke Medical Center.
        Am J Cardiol. 1988; 62: 3F-24F
        • Stack RS
        • Perez JA
        • Newman GE
        • McCann RL
        • Wholey MH
        • Cummins FE
        • Galichia JT
        • Hoffman PU
        • Tcheng JE
        • Sketch Jr, MH
        • Lee MM
        • Phillips HR
        Treatment of peripheral vascular disease with the transluminal extraction catheter: results of a multicenter study (abstract).
        J Am Coll Cardiol. 1988; 13: 227A
        • Hansen DD
        • Auth DC
        • Hall M
        • Ritchie JL
        Rotational endarterectomy in normal canine coronary arteries: preliminary report.
        J Am Coll Cardiol. 1988; 11: 1073-1077
        • Ahn SS
        • Auth D
        • Marcus DR
        • Moore WS
        Removal of focal atheromatous lesions by angioscopically guided high-speed rotary atherectomy: preliminary experimental observations.
        J Vasc Surg. 1988; 7: 292-299
        • Linnemeier TJ
        • Cumberland DC
        • Rothbaum DA
        • Landin RJ
        • Ball MW
        Human percutaneous laser-assisted coronary angioplasty: efforts to reduce spasm and thrombosis (abstract).
        J Am Coll Cardiol. 1988; 13: 61A
        • Spears JR
        • Reyes V
        • Sinclair IN
        • Hopkins B
        • Schwartz L
        • Aldridge H
        • Plokker HWT
        Percutaneous coronary laser balloon angioplasty: preliminary results of a multicenter trial (abstract).
        J Am Coll Cardiol. 1988; 13: 61A
        • Foschi AE
        • Zapala CA
        Direct argon laser irradiation of high-grade stenoses and total occlusions in native human coronary arteries and bypass grafts: initial clinical experience (abstract).
        J Am Coll Cardiol. 1988; 13: 60A