Percutaneous Coronary Interventions
Percutaneous coronary interventions (PCI) include percutaneous transluminal coronary angioplasty (PTCA) with or without stent insertion. Primary indications are treatment of
PTCA and stent placement within 90 min of onset of pain is the optimal treatment of transmural ST-segment–elevation myocardial infarction (STEMI). Elective PCI may be appropriate for post-MI patients who have recurrent or inducible angina before hospital discharge and for patients who have angina and remain symptomatic despite medical treatment.
Percutaneous transluminal angioplasty (PTA) is also used to treat peripheral arterial disease.
PTCA is done via percutaneous femoral, radial, or brachial artery puncture. The radial approach is technically demanding compared to the femoral approach but may reduce patient discomfort, improve time to ambulation, and reduce the incidence of some complications (eg, bleeding, pseudoaneurysm formation).
A guiding catheter is inserted into a large peripheral artery and threaded to the appropriate coronary ostium. A balloon-tipped catheter, guided by fluoroscopy or intravascular ultrasonography, is aligned within the stenosis, then inflated to disrupt the atherosclerotic plaque and dilate the artery. Angiography is repeated after the procedure to document any changes. The procedure is commonly done in 2 or 3 vessels as needed.
Stents are most useful for
Stents are now used frequently for acute myocardial infarction, ostial or left main disease, chronic total occlusions, and bifurcation lesions.
Bare metal stents (BMS) are made of nickel-titanium alloy. Drug eluting stents (DES) have drugs (eg, 1st-generation: sirolimus, paclitaxel; 2nd-generation: everolimus, zotarolimus) bonded to the metal that limit neointimal proliferation to reduce the risk of restenosis. Radioactive stents or pre-stent intracoronary radiation using radioactive pellets (brachytherapy) have not proven effective at limiting restenosis. Biodegradable stents are currently in clinical trials.
Various anticoagulation regimens are used during and after angioplasty to reduce the incidence of thrombosis at the site of balloon dilation. Thienopyridines (clopidogrel, prasugrel, ticagrelor) and glycoprotein IIb/IIIa inhibitors (abciximab, eptifibatide, tirofiban) are the standard of care for patients with unstable non-ST-segment elevation myocardial infarction. Thienopyridines (often in combination with aspirin) are continued for at least 9 to 12 mo after PCI to decrease the risk of in-stent thrombosis until endothelialization of the stent has occurred. Calcium channel blockers and nitrates may also reduce risk of coronary spasm.
Relative contraindications to PCI include
Lack of cardiac surgical support
Critical left main coronary stenosis without collateral flow from a native vessel or previous bypass graft to the left anterior descending artery
Diffusely diseased vessels without focal stenoses
A single diseased vessel providing all perfusion to the myocardium
Total occlusion of a coronary artery
Stenosis < 50%
Although lack of cardiac surgical support is sometimes considered an absolute contraindication to PCI, many experts advocate that when revascularization is required urgently in STEMI, experienced operators in approved catheterization laboratories should proceed with PCI even if surgical backup is not available.
Although bypass is typically preferred for patients with critical left main coronary stenosis without collateral flow from either a native vessel or previous bypass graft, PCI is increasingly being used in this scenario in selected patients.
The main complications of balloon angioplasty and stent placement are
Of all angiographic procedures, PCI has the highest risk of contrast nephropathy (due to increased contrast load and procedural time); this risk can be reduced by preprocedural hydration and possibly by use of a nonionic contrast agent or hemofiltration in patients with preexisting renal insufficiency.
Compared to coronary angiography without angioplasty or stenting, risk of death, MI, and stroke is greater.
The mortality rate following PCI varies according to patient and technical factors. Mortality scoring systems have been developed to help clinicians determine the risk of death following PCI and can be useful when counseling patients regarding available treatment options (PCI vs medical management alone).
Stent thrombosis causes complete blockage and may occur at any time:
Stent thrombosis may be due to inadequate stent expansion or apposition at the time of the procedure, discontinuation of dual antiplatelet therapy (eg, due to nonadherence, need for noncardiac surgery), or both. Rarely, the stent may break up an intracoronary clot (ie, as may be present in acute MI), which may embolize distally and cause myocardial infarction. Use of protection strategies (eg, temporarily blocking blood flow within the artery using a balloon and then aspirating the emboli, deploying a small filter distal to the site of PCI to capture emboli) may improve outcome in PCI done on a previous saphenous vein graft but is not commonly done.
With balloon angioplasty alone, risk of acute thrombosis is about 5 to 10%.
Use of stents has almost eliminated the need for emergency coronary artery bypass grafting following PCI; the rate of acute and subacute thrombosis is < 1%. However, using a drug-eluting stent increases risk of late stent thrombosis, about 0.6%/yr up to 3 yr.
Restenosis is typically due to collagen deposition and thus does not occur until several weeks after the procedure or later; it may cause partial or, less commonly, complete vessel blockage.
With balloon angioplasty alone, the risk of subacute restenosis is about 5%, and the overall restenosis rate is about 30 to 45%.
With stent use, the rate of subacute restenosis is < 1%. With bare-metal stents, risk of late restenosis is 20 to 30%. Use of a drug-eluting stent lowers late restenosis risk to about 5 to 10%.