Equipment
Initially, percutaneous coronary intervention (PCI) was accomplished with balloon catheters. As a result of the technical challenges of percutaneous coronary artery balloon angioplasty, suboptimal clinical outcomes, and significant rates of restenosis after the procedure, two innovative types of devices were developed: atherectomy devices and coronary stents.
Long-term outcomes from atherectomy alone have been disappointing and, in most cases, little better than those from balloon angioplasty. Stents, particularly stents that elute medications that reduce inflammatory and cell growth responses, have resulted in greatly improved outcomes. Atherectomy is still used for specific niche indications, but the most common intracoronary device used today is a stent.
Various ancillary devices are also used for PCI.
Balloon catheters
The original description of angioplasty by Dotter and Judkins described enlargement of the vessel lumen through a mechanism of atheromatous plaque compression. This mechanism is also partially responsible for luminal enlargement with balloon angioplasty.
In addition, however, the increase in luminal diameter after balloon angioplasty also results from stretching of the vessel wall by the balloon. Balloon inflation actually results in overstretching of the vessel wall and partial disruption of not only the intimal plaque but also the media and adventitia, resulting in enlargement of the lumen and the outer diameter of the vessel.
Axial redistribution of plaque material also contributes to improvements in lumen diameter. Atherectomy devices and, subsequently, intracoronary stents were developed, in part, to decrease the early and late loss in luminal diameter observed with conventional balloon angioplasty.
Several different balloon catheter designs have existed (eg, over-the-wire, monorail, and fixed wire) and have used balloon materials with different compliance characteristics that allow varying degrees of expansion with increasing pressure. Irrespective of the balloon design, a steerable guide wire precedes the balloon into the artery and permits navigation through a considerable portion of the coronary tree.
The development of bending capability, allowing easy advancement through tortuous vascular segments (trackability), as well as increased shaft stiffness (pushability), allowing the catheter to be forced through stenotic lesions, has significantly increased the versatility of balloon catheters. Another evolving feature of catheter design has been a reduction in the diameter of the deflated balloon, allowing easier passage through very stenotic lesions.
Improvements in catheter design have been partially responsible for the improved success rates of PCI. The balloon catheter also serves as an adjunctive device for many other interventional therapies, including atherectomy and coronary stenting.
Atherectomy devices
Atherectomy devices were developed to permit drilling, grinding, or sanding of atheroma, calcium, and excess cellular material from the site of a coronary occlusion or stenosis. Both mechanical and laser-based approaches are used.
The rotational atherectomy catheter (Rotablator) is designed for the removal of plaque from coronary arteries. This device (see the image below), which has a diamond-studded burr at its tip, rotates at about 160,000 revolutions per minute (rpm) and is particularly well suited for ablation of calcific or fibrotic plaque material.
Percutaneous transluminal coronary angioplasty (PTCA). Rotational atherectomy catheter (Rotablator) is designed for removal of plaque from coronary arteries. This device has diamond-studded burr at its tip, rotates at about 160,000 rpm, and is particularly well suited for ablation of calcific or fibrotic plaque material.
Unlike other atherectomy devices that rely on tissue cutting, the rotational atherectomy device relies on plaque abrasion and pulverization. Rotational atherectomy is successful in 92-97% of these cases, with a low incidence of major complications. It causes dislodgment of particles into the microcirculation, which occasionally may lead to infarction and no-reflow (impaired distal coronary flow). Currently, the use of rotational atherectomy is largely confined to fibrotic or heavily calcified lesions that can be wired but not crossed or dilated by a balloon catheter.
The ERBAC (Excimer Laser, Rotational Atherectomy, and Balloon Angioplasty Comparison) Study showed that rotational atherectomy was associated with a higher short-term success rate than balloon angioplasty (90% vs 80%) was but that rates of major ischemic complications and repeat revascularization were higher 6 months after treatment (46% vs 37%). [58]
A meta-analysis failed to show any significant differences in mortality, major adverse cardiovascular events (MACE), or revascularization rates in patients treated with rotational atherectomy, laser, or cutting balloon angioplasty in comparison with balloon angioplasty alone. [59] In some cases, rotational atherectomy was actually associated with an increase in periprocedural myocardial infarction (MI).
However, none of these trials compared stent-related outcomes. In fact, many of these devices may be used to facilitate stent delivery in complex lesions, especially when balloon angioplasty alone has failed.
Beginning in 1987, directional coronary atherectomy (DCA) was used to debulk coronary plaques. In this procedure, a steel fenestrated cage housing a cup-shaped blade is positioned against the coronary lesion by a low-pressure positioning balloon, allowing any protruding plaque to be removed.
Complications (eg, distal embolization of plaque, transient side-branch occlusion, coronary vasospasm, the no-reflow phenomenon, non–Q-wave MI) are more frequent with DCA than with balloon angioplasty. Because of the increased complication rates and the greater technical demands of DCA as compared with balloon angioplasty or stenting, the use of DCAs has greatly decreased in recent years.
A 2006 meta-analysis demonstrated that DCA was superior to stenting alone with regard to acute angiographic results and target-lesion revascularization, with a similar prevalence of late MACE. There was, however, a higher prevalence of early MACE with DCA before stenting, which was probably related to distal embolization. [60]
Although the development of laser atherectomy generated considerable initial excitement, the procedure is not widely used at present, because of the technical demands imposed by the device and the lack of any clear improvements in outcome versus other devices.
Orbital atherectomy has only come into clinical use relatively recently. Orbital atherectomy utilizes an eccentrically mounted “crown” that is diamond-coated and rotates at speeds ranging from 60,000 to 200,000 rpm. Unlike the rotational atherectomy device, the orbital atherectomy crown is eccentric in shape and therefore has an elliptical orbit rather than spinning concentrically on the wire.
The ORBIT (Evaluate the Safety and Efficacy of OAS in Treating Severely Calcified Coronary Lesions) II trial was a prospective single-arm multicenter study designed to evaluate orbital atherectomy for vessel preparation before stent implantation in severely calcified lesions. [61] A total of 443 patients were enrolled, and the median follow-up was 25.1 months. The 2-year outcomes were reported as follows:
-
MACE, 19.4%
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Death, 7.5%
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Cardiac death, 4.3%
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Target vessel revascularization, 8.1%
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Target lesion revascularization (TLR), 6.2%
These rates were lower than those previously reported with alternative strategies. However, they once again highlighted detrimental effects of severe calcium in coronary revascularization. As expected, the TLR rate was threefold higher with bare-metal stents (BMSs) than with drug eluting stents (DESs), making the use of a DES more attractive in these circumstances. [61]
Intracoronary stents
Intracoronary stents have been used widely since the early 1990s. Various stents are available, differing with respect to composition (eg, cobalt chromium or platinum chromium), architectural design, and delivery system (see the images below).
Bare-metal coronary artery stents are used in PCI for a variety of indications, including stable and unstable angina, acute myocardial infarction (AMI), and multivessel coronary artery disease (CAD). Drug-eluting coronary artery stents have a stent framework with a polymer coating that elutes an antiproliferative drug into the coronary wall for weeks after stent implantation. They were developed to reduce restenosis (ie, recurrent narrowing) rates in stented coronary lesions.
The development of DESs revolutionized coronary intervention to the same degree that balloon angioplasty and bare-metal stents did in the 1980s and 1990s. The first-generation DESs were sirolimus-eluting (Cypher) and paclitaxel-eluting (Taxus) stents. The major clinical endpoint difference between BMSs and first-generation DESs was significantly lower rates of restenosis and target lesion revascularization with DESs.
The goals of further reducing the rate of restenosis and decreasing the frequency of stent thrombosis led to the evolution of second-generation DESs. Those currently used in the United States are either everolimus-eluting (Xience, Promus) or zotarolimus-eluting (Resolute).
DESs have been extensively tested in a wide spectrum of coronary lesions, all of which have demonstrated significant reductions in restenosis and target-lesion revascularization rates in comparison with BMSs or first-generation DESs. The zotarolimus-eluting stent and the everolimus-eluting stent have improved deliverability, thinner struts, and a thinner polymer layer, and they may have clinical advantages over sirolimus-eluting and paclitaxel-eluting stents. [62, 63]
A meta-analysis of 28 randomized, controlled clinical trials involving more than 34,000 patient-years of follow-up indicated that in comparison with BMSs, newer-generation DESs, particularly the everolimus-eluting stent, significantly reduced the risk of target vessel revascularization in patients with ST-segment elevation MI (STEMI) without increasing the risk of adverse safety outcomes, including rates of stent thrombosis. [64]
Currently, DESs have more favorable outcomes than BMSs do, primarily because of significantly lower target vessel revascularization. Therefore, DESs are preferred to BMSs in most PCI settings, including chronic total occlusion (CTO) recanalization, saphenous vein graft (SVG) PCI, bifurcation PCI, aorto-ostial lesions, calcified lesions, PCI in diabetic patients, and PCI in patients with cardiac allograft vasculopathy.
BMSs are recommended for use in patients who have a high bleeding risk, are unable to comply with 1 year of dual antiplatelet therapy, have very large arteries, or are likely to undergo invasive or surgical procedures in the next year.
Although stents are conventionally placed after balloon predilation, a meta-analysis by Piscione et al suggests that in selected coronary lesions, direct stenting may lead to better outcomes. [65] MI rates were lower with direct stenting than with conventional stenting (3.16% vs 4.04%), whereas rates of target vessel revascularization were comparable.
Metallic stents (including both BMSs and DESs) have a low but definite rate of very late adverse events, such as stent thrombosis (0.2-0.6% annually) and restenosis. These late events are partly attributable to the persistence of the polymer and the metallic frame in the vessel. Therefore, the current investigational focus is on developing metallic DESs with bioabsorbable polymers, polymer-free metallic DESs, and bioresorbable scaffolds. Two such stents have been approved by the US Food and Drug Administration and are available for commercial use.
The SYNERGY (Boston Scientific, Marlborough, MA) is an everolimus-eluting platinum chromium stent with an abluminal coating of bioabsorbable polymer. This polymer, poly DL-lactide-co-glycolide (PLGA), is mixed with everolimus (the same drug used in the Promus Element DES made by Boston Scientific). In-vivo studies showed that the polymer degradation is essentially complete by 4 months, leaving just the metal stent behind (in contrast to conventional DESs, in which both metal and polymer are permanent). This polymer is believed to play at least a partial role in late stent thrombosis.
The EVOLVE II was a prospective multicenter randomized, controlled, single-blind non-inferiority study (N = 1684) that compared the SYNERGY stent with the Promus Element stent. The primary end point, target lesion failure (TLF), was defined as ischemia-driven revascularization of the target lesion, MI related to the target vessel, or cardiac death at 12 months. The SYNERGY stent was noninferior to the Promus Element stent for TLF (6.7% vs 6.5%; P = 0.0005) in the intention-to-treat population. There were no significant differences in the secondary end points of stent thrombosis (0.4% vs 0.6%; P = 0.50), death (1.1% vs 1.1%; P = 0.95), MI (5.4% vs 5.0%; P = 0.68) or TLR (2.6% vs 1.7%; P = 0.50). [66]
The 2-year results presented at the American College of Cardiology’s scientific session in 2016 showed numerically lower definite/probable stent thrombosis with the SYNERGY stent as compared with the Promus Element stent. Long-term data will help determine whether complete degradation of the polymer truly reduces the incidence of very late stent thrombosis.
The Absorb GT1 Bioresorbable Vascular Scaffold (BVS) System (Abbott Vascular, Abbott Park, IL) releases everolimus to limit the growth of scar tissue, but unlike the contemporary metallic stents, it gradually (in ~3 years) dissolves. That is, the scaffold and the polymer are both bioresorbable, leaving behind only the platinum markers at the scaffold edge for fluoroscopic landmarking. The Absorb GT1 is the first BVS stent to receive FDA approval, and it offers a new treatment option for patients who are candidates for PCI but prefer an absorbable device to a permanent metallic stent.
ABSORB III was a multicenter randomized trial of 2008 patients who were randomized to receive either the Absorb or an everolimus-eluting cobalt chromium stent (Xience; Abbott Vascular). [67] At 1 year, the Absorb stent was noninferior for TLF (cardiac death, target vessel MI or ischemia driven target-lesion revascularization). Device thrombosis was more common with the Absorb stent (1.5% vs 0.7%; P = 0.13) and in this study was attributed to a higher rate of in-device postprocedural residual stenosis as a consequence of greater strut thickness or recoil. This is an area of great interest, and future generations will have thinner struts.
Thrombectomy
In addition to balloons, stents, and atherectomy devices, other devices, such as thrombus extraction catheters and distal embolic protection devices, play a role in PCI.
In the TAPAS (Thrombus Aspiration during Percutaneous Coronary Intervention in Acute Myocardial Infarction) trial, thrombus aspiration with an Export catheter before stenting yielded reductions in all-cause mortality (4.7% vs 7.6%) and cardiac death (3.6% vs 6.7%) at 1 year as compared with conventional PCI. [68]
In a pooled analysis of data from three prospective randomized trials, De Vita et al found that although increasing time to treatment was associated with a decreased rate of optimal reperfusion in patients receiving standard PCI, this trend was not seen in patients treated with thrombus aspiration. [69] The investigators concluded that the use of thrombus aspiration limits the adverse effects that prolonged time to treatment has on myocardial reperfusion.
The TASTE (Thrombus Aspiration in ST-Elevation Myocardial Infarction in Scandinavia) trial randomly assigned 7244 STEMI patients to undergo manual thrombus aspiration followed by PCI or to undergo PCI alone. [70] At 30 days, there was no significant difference in all-cause mortality between the thrombus aspiration group (2.8%) and the PCI-only group (3%). At 30 days, the rates of hospitalization for recurrent MI were 0.5% and 0.9% in the two groups, respectively, and the rates of stent thrombosis were 0.2% and 0.5%, respectively.
When followed out to 1 year, the TASTE trial showed that routine thrombus aspiration before PCI in STEMI patients did not significantly reduce the rate of death from any cause or the composite of death from any cause, rehospitalization for MI, or stent thrombosis at 1 year. [71]
In TOTAL (Trial of Routine Aspiration Thrombectomy with PCI versus PCI Alone in Patients with STEMI), the largest trial on routine thrombus aspiration, 10,732 patients with STEMI were randomly assigned to upfront manual aspiration thrombectomy or PCI alone. [72] There were no differences between the two groups with respect to cardiovascular death, recurrent MI, cardiogenic shock, or New York Heart Association (NYHA) class IV heart failure within 180 days. The rates of stent thrombosis or target-vessel revascularization were also similar.
As suggested in a previous meta-analysis, the thrombectomy group had a higher incidence of stroke within 30 days: 0.7% in the thrombectomy group versus 0.3% in the PCI-alone group (hazard ratio, 2.06; 95% CI, 1.13-3.75; P = 0.02). [72] Interestingly, there was a continued increase in strokes even at 30 days and 180 days in the thrombectomy group, which could not be easily explained and could also be a matter of chance. The subgroup analysis showed no benefit in heavy thrombus burden, TIMI 0-1 flow, or anterior infarcts.
A meta-analysis of these three thrombectomy trials showed no benefit of routine aspiration thrombectomy with respect to death, reinfarction, or stent thrombosis. There was small but nonsignificant increase in stroke with thrombectomy. [73]
In the 2016 update of STEMI guidelines from ACC/AHA/SCAI, routine aspiration thrombectomy was no longer recommended before primary PCI. The level of recommendation was changed from class IIa to class III. Because of insufficient data, “bailout” thrombectomy was a class IIb recommendation. [74]
Distal embolic protection devices
PCI in a saphenous vein graft (SVG) is considered a high-risk procedure, given the increased incidence of distal embolization and no-reflow phenomenon. The SAFER (Saphenous Vein Graft Angioplasty Free of Emboli Randomized) trial initially proved the benefit of embolic protection devices (EPDs) in reducing the 30-day incidence of MACE (9.6% vs 16.5%), MI (8.6% vs 14.7%), and no-reflow (3% vs 9%). [59]
Although the ACC/AHA guidelines gave EPDs in SVGs a class I recommendation, EPD use remains low, for a variety of reasons (eg, anatomic challenges, cumbersome devices, increased complications, and emergence of alternate techniques such as direct stenting, mesh stents, undersizing stents with higher stent-to-lesion length ratio) and laser atherectomy.
Observational data from the NCDR Cath Registry on 49,325 patients who underwent SVG intervention reported low EPD use (~21%) and no reduction in adverse events after 3 years of follow-up. In fact, in the EPD group, there were higher procedural complications of no-reflow, dissection, perforation, and periprocedural MI.
One of the conclusions that can be inferred from the available data is that not all SVG interventions are the same. The decision to use EPDs should be based on thrombus/plaque burden, risk of embolization, anatomic complexity, and operator familiarity with the devices. [75]
There is no indication for EPD use in native coronary arteries. A 15-month follow-up of the DEDICATION (Drug Elution and Distal Protection in ST Elevation Myocardial Infarction) trial found that in primary PCI for STEMI, routine use of distal protection increased the incidence of stent thrombosis and clinically driven target lesion/vessel revascularization. [76]
Vascular closure devices
For transfemoral catheterizations, hemostasis can be achieved either by manual compression or by use of vascular closure devices. The results of four meta-analyses suggested that vascular closure devices do not decrease vascular complications, bleeding complications, or the need for blood transfusions, whereas they do decrease time to hemostasis and time to ambulation. [77, 78, 79, 80]
For transradial catheterizations, hemostasis is generally achieved with manual compression using transradial bands and patent hemostasis technique.
Patient Preparation
PCI is performed on an elective as well as an urgent or emergency basis. Elective patients present to the hospital on the morning of the procedure at a scheduled time. A history is obtained and a physical examination performed. Basic blood tests (including a complete blood count [CBC], basic metabolic profile [BMP], and coagulation profile) and electrocardiography (ECG) are performed. Informed consent is obtained.
A full dose of aspirin (325 mg) is given on the day of procedure. If patients have had prior allergic reactions to contrast, prednisone is generally given for at least three doses beforehand. Some laboratories also use Benadryl, a histamine H1 blocker, or both. Patients with food allergies and asthma are also occasionally premedicated with steroids. Coronary angiography is performed with full sterile technique. Preprocedural antibiotic prophylaxis is not recommended.
Anesthesia and positioning
The patient is placed in the supine position, prepared and draped in a standard sterile fashion. The procedure is performed with the patient under conscious sedation (in most instances, using midazolam and fentanyl).
Safe access is extremely important for the success of PCI, and therefore, special attention is paid to the technique. Lidocaine 2% is used as the local anesthetic agent.
Hydration
In patients undergoing coronary angiography or PCI, the use of sliding-scale hydration guided by left ventricular end-diastolic pressure (LVEDP) reduces not only the risk of contrast nephropathy but also the risk of clinical events at 6 months. [81]
In the POSEIDON (Prevention of Contrast Renal Injury with Different Hydration Strategies) trial, patients treated with the LVEDP-guided hydration and conventional-hydration strategies were given 3 mL/kg of 0.9% saline over the course of an hour before the procedure. [81] During the procedure, patients in the standard arm received 1.5 mL/kg/hr, whereas patients in the LVEDP-guided arm received 5 mL/kg/hr if the LVEDP was below 13 mm Hg, 3 mL/kg/hr if the LVEDP was 13-18 mm Hg, and 1.5 mL/kg/hr if the LVEDP was above 18 mm Hg.
The use of sliding-scale hydration reduced the primary endpoint (defined as a 25% or 0.5-mg/dL increase in serum creatinine levels) by 59%. [81] At 6-months’ follow-up, LVEDP-guided treatment significantly reduced the composite endpoint of death, MI, and dialysis by 68%.
On the basis of several studies, the most widely recommended hydration regimen is isotonic crystalloid (1.0-1.5 mL/kg/hr) for 3-12 hours before the procedure and 6-24 hours after the procedure.
Earlier studies on N-acetyl-L-cysteine produced conflicting results; however, ACT (Acetylcysteine for Contrast-Induced Nephropathy Trial) study data on 2308 randomly assigned patients demonstrated no benefit with respect to reducing the incidence of contrast-induced acute kidney injury or other clinically relevant outcomes in at-risk patients. [82]
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Percutaneous transluminal coronary angioplasty (PTCA). Rotational atherectomy catheter (Rotablator) is designed for removal of plaque from coronary arteries. This device has diamond-studded burr at its tip, rotates at about 160,000 rpm, and is particularly well suited for ablation of calcific or fibrotic plaque material.
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Percutaneous transluminal coronary angioplasty (PTCA). TRISTAR stent.
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Percutaneous transluminal coronary angioplasty (PTCA). NIR stent.
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Percutaneous transluminal coronary angioplasty (PTCA). Wallstent.
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Example of intravascular ultrasonography (IVUS) image in percutaneous transluminal coronary angioplasty (PTCA).
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Mechanism of restenosis following percutaneous transluminal coronary angioplasty (PTCA).
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Fractional flow ratio (FFR). Pressure wire is advanced across left anterior descending (LAD) artery stenosis, and intracoronary adenosine is given. FFR ratio is recorded at baseline and then after adenosine push is given. Here, LAD lesion and FFR post adenosine are shown.
Tables
Endpoint |
Pocock et al* |
Pocock et al† |
BARI Study‡ |
|||
CABG (N=358) |
PTCA (N=374) |
CABG (N=1303) |
PTCA (N=1336) |
CABG (N=914) |
PTCA (N=915) |
|
Death (%) |
0.3 |
1.9 |
2.8 |
3.1 |
10.7 |
13.7 |
Death or MI |
4.5 |
7.2 |
8.5 |
8.1 |
11.7 |
10.9 |
Repeat CABG |
1.4 |
16.0§ |
0.8 |
18.3§ |
0.7 |
20.5§ |
Repeat CABG or PTCA |
3.6 |
30.5§ |
3.2 |
34.5§ |
8.0 |
54.0§ |
More than mild angina |
6.5 |
14.6§ |
12.1 |
17.8§ |
... |
... |
*Meta-analysis of results of 3 trials at 1 year. Patients with single-vessel disease were studied. [23] †Meta-analysis of results of 3 trials at 1 year. Patients with multivessel disease were studied. [23] ‡Reported results are for 5-year follow-up. Patients with multivessel disease were studied. [22] § P < .05. BARI = Bypass Angioplasty Revascularization Investigation; CABG = coronary artery bypass grafting; MI = myocardial infarction; PTCA = percutaneous transluminal coronary angioplasty. |
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