PCI complications: restenosis

# Overview
Restenosis can occur in the implanted stent after performing PCI. One of the classification systems categorized restenosis based on being multifocal or its location in the stent (such as at the edge of the stent, or at the articulation or gap. The main mechanism causing restenosis after stent implication is neointimal hyperplasia. Restenosis after drug eluting stent implantation is generally more focal than following bare metal stent placement. Risk of ISR is lowered after presentation of new generations stents such as DES compared to BMS and first-generation DES. Balloon angioplasty, drug eluting stents, drug-coated balloons, scoring or cutting balloons, and vascular brachytherapy are some of the common approaches that have been explored as the restenosis treatment. Among all the treatment options, drug eluting stents appear to provide the most benefit.

# Classification
The following are one of the classifications for restenosis:
- Pattern I:   Focal ( 10 mm in length) lesions
Ia : Restenosis within the stent
Ib : Restenosis at the edge of the stent
Ic : Restenosis at the articulation or gap
Id : Restenosis multifocal
- Ia : Restenosis within the stent
- Ib : Restenosis at the edge of the stent
- Ic : Restenosis at the articulation or gap
- Id : Restenosis multifocal
- Pattern II:  ISR >10 mm within the stent
- Pattern III: Includes ISR > 10 mm extending outside the stent
- Pattern IV:  ISR totally occluded
The need for recurrent target lesion revascularization (TLR) increased with increasing ISR class, increasing from 19%, 35%, 50%, to 83% in classes I to IV, respectively (P <0.001).

# Pathophysiology
- Restenosis can occur in the implanted stent after performing PCI.
- The main mechanism causing restenosis after stent implication is neointimal hyperplasia.
- The pathophysiology of restenosis can be anticipated based on the time period that restenosis occurs.
Early stent thrombosis is usually due to residual target-lesion thrombus, stent failure, or nonadherence to dual antiplatelet therapy.
Late stent thrombosis is usually associated with inadequate neointimal coverage or incomplete healing.
- Early stent thrombosis is usually due to residual target-lesion thrombus, stent failure, or nonadherence to dual antiplatelet therapy.
- Late stent thrombosis is usually associated with inadequate neointimal coverage or incomplete healing.
- Restenosis after drug eluting stent implantation is generally more focal than following bare metal stent placement., and, with the sirolimus eluting stent, more is commonly at the margin of the stent due to balloon injury that is not covered with stent

# Epidemiology and Demographics
ISR is found in 5% to 10% of patients undergoing PCI.

# Causes
- Risk of ISR is lowered after presentation of new generations stents such as DES compared to BMS and first-generation DES.
- Factors such as stent type, procedural characteristics, lesion location and patient-related factors are critical in the pathophysiology of stent thrombosis or restenosis.

# Diagnosis
- It is necessary to evaluate the underlying cause of stent thrombosis with intracoronary imaging (IVUS and OCT) in order to plan the proper treatment.
- In the setting of in-stent restenosis (ISR) after bare metal stent (BMS) implantation, the risk of recurrence can be predicted by the pattern of restenosis.

## Treatment
- The following approaches have been explored for restenosis treatments:
Balloon angioplasty
Drug eluting stents
Among all the treatment options, drug eluting stents appear to provide the most benefit.
Everolimus-eluting stents showed the best efficacy among other forms of drug eluting stents.
Drug-coated balloons
Scoring or cutting balloons
Vascular brachytherapy
Vascular brachytherapy can be used as an additional tool to aid revascularization among patients with multiple stent layers or in those who have recurrent in stents restenosis with an artery that is not suitable to receive another DES, or undergoing a bypass surgery.
- Balloon angioplasty
- Drug eluting stents
Among all the treatment options, drug eluting stents appear to provide the most benefit.
Everolimus-eluting stents showed the best efficacy among other forms of drug eluting stents.
- Among all the treatment options, drug eluting stents appear to provide the most benefit.
- Everolimus-eluting stents showed the best efficacy among other forms of drug eluting stents.
- Drug-coated balloons
- Scoring or cutting balloons
- Vascular brachytherapy
Vascular brachytherapy can be used as an additional tool to aid revascularization among patients with multiple stent layers or in those who have recurrent in stents restenosis with an artery that is not suitable to receive another DES, or undergoing a bypass surgery.
- Vascular brachytherapy can be used as an additional tool to aid revascularization among patients with multiple stent layers or in those who have recurrent in stents restenosis with an artery that is not suitable to receive another DES, or undergoing a bypass surgery.
- Overall, if chosen properly, vascular brachytherapy can bypass the need to implant another stent in patients who do have challenging circumstances.
Atheroablative therapies
CABG
CABG is recommended as an effective treatment among the following patients with in stents restenosis:
When a patient experiences recurrent restenosis despite repeat PCI with DES
When a patient experiences recurrent restenosis with diffuse in stents restenosis in large vessels
When a patient experiences recurrent restenosis with a complex presentation such as CTO with multivessel disease
CABG could be the preferred treatment in those with suitable anatomy
- Atheroablative therapies
- CABG
CABG is recommended as an effective treatment among the following patients with in stents restenosis:
When a patient experiences recurrent restenosis despite repeat PCI with DES
When a patient experiences recurrent restenosis with diffuse in stents restenosis in large vessels
When a patient experiences recurrent restenosis with a complex presentation such as CTO with multivessel disease
CABG could be the preferred treatment in those with suitable anatomy
- CABG is recommended as an effective treatment among the following patients with in stents restenosis:
When a patient experiences recurrent restenosis despite repeat PCI with DES
When a patient experiences recurrent restenosis with diffuse in stents restenosis in large vessels
When a patient experiences recurrent restenosis with a complex presentation such as CTO with multivessel disease
CABG could be the preferred treatment in those with suitable anatomy
- When a patient experiences recurrent restenosis despite repeat PCI with DES
- When a patient experiences recurrent restenosis with diffuse in stents restenosis in large vessels
- When a patient experiences recurrent restenosis with a complex presentation such as CTO with multivessel disease
- CABG could be the preferred treatment in those with suitable anatomy
- The type of in stent restenosis is essential in deciding one treatment over the others and the ultimate decision should be made individualized.

# 2021 ACA Guidline Recommendations