In-Stent Restenosis: Mechanisms and Treatment

Definition and Clinical Significance

In-stent restenosis (ISR) is recurrent narrowing within a previously implanted coronary stent. It represents a form of arterial hyperplastic disease arising after percutaneous coronary intervention (PCI). In contemporary practice, ISR remains the most frequent cause of PCI failure, despite its substantially lower incidence with drug-eluting stents (DES) than with bare-metal stents (BMS).

Clinical ISR is generally defined by recurrent symptoms or ischaemic events attributable to renarrowing within the stented segment or at its margins. Angiographic restenosis has traditionally been described as a follow-up diameter stenosis exceeding 50%, whereas clinical restenosis refers to recurrent angina caused by disease in the treated segment. The clinical implications range from asymptomatic angiographic disease to chronic coronary syndrome (CCS), acute coronary syndrome (ACS), myocardial infarction, and repeat target-lesion revascularization.

Restenosis after balloon angioplasty differs mechanistically from ISR. Balloon angioplasty may result in negative remodelling and reparative arterial constriction. A stent provides a rigid scaffold that limits adventitial recoil and constriction; consequently, in-stent disease is driven predominantly by tissue accumulation within the stented segment rather than by negative remodelling.

Pathophysiology

Neointimal hyperplasia

The principal mechanism of ISR is neointimal hyperplasia following vessel-wall injury. PCI and stent implantation produce local vascular injury and initiate a sustained inflammatory and reparative response. Proliferation and accumulation of tissue within the stent progressively reduce the lumen.

The stent scaffold prevents the external constriction that characterizes restenosis after balloon angioplasty. The biological response therefore occurs primarily through intimal thickening. DES release antiproliferative and anti-inflammatory agents from the stent surface and have substantially reduced this process compared with BMS.

Neoatherosclerosis

Neoatherosclerosis is a later pathological process in which lipid-laden foamy macrophages accumulate within the neointima. It may be accompanied by necrotic-core formation and calcification. Neoatherosclerosis can contribute to both ISR and stent thrombosis.

Optical coherence tomography (OCT) is currently the most suitable imaging modality for detecting neoatherosclerosis, although its resolution does not consistently permit identification of foamy macrophages. The occurrence of neoatherosclerosis helps explain why ISR and other stent-related events may arise well after the initial intervention.

Mechanical mechanisms

Mechanical abnormalities may initiate or perpetuate ISR. Important mechanisms include:

• Stent under-expansion

• Stent malapposition

• Stent fracture or collapse

• Residual edge dissection

• Incomplete lesion preparation

• Persistent stenosis within the treated segment

Mechanical factors are particularly important because correction of the underlying problem is necessary for durable treatment. Intracoronary imaging is encouraged to define the mechanism rather than relying on angiography alone.

Factors associated with restenosis

The risk of restenosis after metallic stent implantation is increased by:

• Small reference-vessel size

• A small post-procedural luminal diameter

• A high degree of residual stenosis

• Long lesion length

• Diabetes

• Untreated edge dissection

DES have reduced restenosis compared with BMS, and newer-generation DES have improved outcomes further. Nevertheless, clinically important ISR remains possible after DES implantation.

Clinical Presentation and Symptoms

The clinical spectrum of ISR is broad:

• Many patients remain asymptomatic.

• The most common symptomatic presentation is CCS, usually with recurrent angina.

• Approximately one-fifth of clinically recognized ISR presentations are ACS.

• ISR may occasionally be associated with myocardial infarction.

• The presentation can also be an ischaemic event requiring repeat target-lesion revascularization.

Compared with stent thrombosis, ISR more often presents as stable or chronic recurrent ischaemia. Stent thrombosis, in contrast, usually presents with ACS and requires urgent management.

The timing of symptoms can assist clinical interpretation. Clinical restenosis after PCI generally develops during the first 6–9 months, although ISR and neoatherosclerotic disease may present later. Other late events after PCI may result from progression or rupture of atherosclerotic plaque remote from the treated segment and should not automatically be attributed to ISR.

Evaluation and Physical Examination

Evaluation begins with clarification of the presenting syndrome and comparison with the patient’s pre-PCI symptoms. Recurrent exertional angina suggests clinically significant restenosis, whereas an ACS presentation requires urgent assessment for stent thrombosis, ISR, or another culprit lesion.

The source material does not provide a detailed physical-examination protocol for ISR. Physical findings should therefore be interpreted in the context of the clinical syndrome, with particular attention to evidence of acute ischaemia or haemodynamic compromise when ACS is suspected.

Diagnostic Evaluation

Coronary angiography

Coronary angiography establishes the presence, location, and apparent severity of recurrent narrowing. It can demonstrate:

• Focal ISR within the stent

• Diffuse in-stent narrowing

• Disease at the stent margins

• Associated complex lesions

• Other potential culprit lesions

• Stent thrombosis or an alternative explanation for ACS

Angiography alone may not identify the underlying mechanism. Radiological stent enhancement is encouraged where available, particularly when stent integrity or fracture is suspected.

Intracoronary imaging

Intracoronary imaging is central to mechanism-directed management. Intravascular ultrasound (IVUS) and OCT can assess stent expansion, apposition, integrity, edge complications, and the tissue characteristics of restenosis.

Guideline recommendations support the use of IVUS to detect stent-related mechanical problems leading to restenosis and regard IVUS as a reasonable method for determining the mechanism of stent restenosis. IVUS may also be considered when evaluating the mechanism of stent thrombosis. IVUS or OCT should be considered in selected patients to optimize stent implantation.

OCT is particularly useful for identifying neoatherosclerosis, although the resolution is insufficient to detect foamy macrophages consistently.

Distinguishing ISR from stent thrombosis

Patients with stent thrombosis usually present with ACS. Urgent invasive coronary angiography is indicated to confirm the diagnosis and provide treatment. Once coronary flow has been restored, intracoronary imaging should be performed to identify mechanical failure.

The distinction is clinically important because stent thrombosis requires urgent restoration of coronary flow and treatment according to ACS guidance, whereas ISR treatment is directed at the stenotic segment and its mechanism.

Biomarkers and Laboratory Findings

The source material does not describe a specific biomarker profile for uncomplicated ISR.

When ISR is associated with myocardial infarction, the event may meet criteria for PCI-related type 4c myocardial infarction. This is defined by focal or diffuse restenosis, or a complex lesion in the infarct territory, with no other angiographic explanation such as another culprit lesion or thrombus, together with a rise and/or fall in cardiac troponin above the 99th-percentile upper reference limit using the criteria applied to type 1 myocardial infarction.

Treatment and Management

General principles

The indication to treat ISR is the same as for native coronary artery disease. Treatment should be based on the clinical presentation, the significance of the lesion, and the underlying mechanism.

Management should be focused on the stenotic segment. Durable treatment requires both lesion preparation and correction of mechanical abnormalities where present. Repeated treatment without identifying the cause of ISR may result in recurrent disease.

Lesion preparation

The available lesion-preparation strategies described in the source material include:

• Ultra-high-pressure balloon dilation

• Intravascular lithotripsy

• Rotational atherectomy

The appropriate technique depends on the mechanism and morphology of the restenotic segment. Lesion preparation is particularly relevant where under-expansion, calcification, or resistant tissue limits adequate expansion.

Drug-coated balloon angioplasty

Drug-coated balloon (DCB) angioplasty delivers antiproliferative therapy without adding another permanent metallic layer. This is clinically relevant because repeat DES implantation may create two or more layers of metal within the artery and has raised concerns regarding subsequent stent thrombosis.

DCB angioplasty and repeat DES implantation were similarly effective and safe for BMS ISR in the cited evidence. For DES ISR, DCB angioplasty was less effective than repeat paclitaxel DES implantation in the initial comparisons described. At 10-year follow-up, however, no difference in clinical endpoints was observed between DCB angioplasty and DES implantation, and both were more effective than balloon angioplasty alone in preventing target-lesion revascularization. Everolimus DES was associated with better long-term outcomes than drug-coated balloons.

A further comparison of paclitaxel-coated balloon treatment with balloon angioplasty alone in ISR involving either BMS or DES showed lower target-vessel failure at 1 year with the drug-coated balloon. The same analysis reported fewer target-vessel myocardial infarctions and no stent thrombosis in the drug-coated-balloon group, whereas stent thrombosis occurred in the balloon-angioplasty group. These findings support DCB therapy as an important option, although treatment selection remains dependent on lesion mechanism, prior stent type, anatomy, and the feasibility of achieving adequate lesion preparation.

Repeat DES implantation

Repeat DES implantation is indicated when mechanical failure involves:

• Stent fracture

• Stent collapse

• Residual edge dissection

DES implantation may also be selected after appropriate lesion preparation for recurrent ISR. Everolimus DES has demonstrated better long-term outcomes than drug-coated balloons in the cited data.

Repeat stenting should not substitute for correction of an underlying mechanical abnormality. In particular, inadequate expansion or malapposition should first be addressed with appropriate balloon therapy or other lesion-preparation methods.

High-pressure balloon dilation

High-pressure non-compliant balloon dilation is indicated for:

• Stent under-expansion

• Stent malapposition

This approach directly addresses inadequate stent expansion or contact with the vessel wall. Intracoronary imaging should be used to identify and document the mechanical problem and to guide optimization.

Management of stent thrombosis

Because most patients with stent thrombosis present with ACS, they should be managed according to contemporary ACS guidance. Urgent invasive coronary angiography is required for diagnosis and treatment. After flow has been restored, intracoronary imaging should identify the mechanism, including possible stent fracture, collapse, under-expansion, malapposition, or edge dissection.

The source material identifies inadequate adherence or hyporesponsiveness to antiplatelet treatment as frequent contributors, together with anatomical and mechanical factors. Early discontinuation of dual-antiplatelet therapy after DES implantation is associated with increased risk of late stent thrombosis. Newer-generation DES have reduced stent thrombosis and restenosis compared with earlier-generation devices and BMS, and shorter durations of dual-antiplatelet therapy may be possible in selected circumstances; the exact duration is not specified in the source material for coronary ISR management.

Drugs and Antiplatelet Therapy

The source material does not provide specific drug doses for the treatment of ISR.

Antiplatelet treatment is central to prevention of stent thrombosis. Aspirin combined with a P2Y12 inhibitor constitutes dual-antiplatelet therapy. Lack of adherence or reduced responsiveness to antiplatelet treatment may contribute to stent thrombosis. Early discontinuation after DES implantation increases risk, although newer-generation DES have reduced this hazard and may permit shorter treatment durations in selected patients.

Drug-eluting stents incorporate antiproliferative agents, and drug-coated balloons provide local antiproliferative therapy without implantation of an additional stent layer. The source material does not specify individual antiplatelet doses, duration for a particular ISR intervention, or laboratory testing strategies for platelet responsiveness.

Guideline Recommendations

The principal recommendations relevant to ISR and related PCI failure are summarized below.

The indication for treatment of ISR follows the same principles used for native coronary artery disease. Treatment decisions should therefore incorporate symptoms, ischaemia, clinical presentation, lesion morphology, and procedural feasibility.

Prevention of ISR and PCI Failure

Prevention depends on appropriate stent selection, adequate lesion preparation, complete deployment, and correction of edge complications. DES have markedly lowered restenosis compared with BMS, and newer-generation DES have further improved outcomes.

Mechanical optimization is particularly important. Under-expansion, malapposition, fracture, collapse, and untreated edge dissection can contribute to recurrent stenosis or thrombosis. Intracoronary imaging can identify these problems and assist in optimizing implantation.

Adherence to antiplatelet therapy is important in preventing stent thrombosis. The risk of late thrombosis is increased when dual-antiplatelet therapy is discontinued prematurely. Contemporary DES have reduced the need for uniformly prolonged therapy, but the appropriate duration remains dependent on the clinical and procedural context.

Prognosis and Follow-Up

Clinical recurrence from restenosis is less frequent after DES than after earlier PCI strategies. The cited late-outcome data describe clinical recurrence rates of approximately 3–5% after DES placement, compared with 10–20% after stent implantation overall and 20–30% after balloon angioplasty in the first year. Another source reports that clinical in-DES restenosis may occur in up to 10% within the first 10 years after implantation, reflecting differences in definitions, populations, and follow-up approaches.

ISR generally emerges during the first 6–9 months after PCI, but neoatherosclerosis and late stent-related disease can occur subsequently. Long-term events may also arise from progression of atherosclerosis or plaque rupture at sites remote from the treated lesion. Consequently, recurrent symptoms require fresh diagnostic evaluation rather than an assumption that the original stent is responsible.

The source material does not define a specific routine surveillance schedule for coronary ISR. Follow-up should be clinically directed, with reassessment of recurrent symptoms or ischaemic events and use of coronary angiography and intracoronary imaging when restenosis, stent thrombosis, or a mechanical complication is suspected. After treatment, imaging-guided confirmation of adequate expansion and correction of the causal abnormality is important for optimizing durability.