Classification Systems for In-Stent Restenosis
The Mehran classification is the other primary classification system used for in-stent restenosis (ISR), which categorizes lesions into four patterns (I-IV) based on lesion length and geographic distribution relative to the stent, with direct prognostic implications for target lesion revascularization rates. 1, 2, 3
Mehran Classification System
The Mehran classification divides ISR into four distinct angiographic patterns based on the length and location of neointimal hyperplasia 1, 3:
Pattern I (Focal): Lesions ≤10 mm in length within the stent, associated with the best prognosis and 19% target lesion revascularization (TLR) rate 1, 2, 3
Pattern II (Intrastent Diffuse): ISR >10 mm confined within the stent boundaries, with 35% TLR rate 1, 2, 3
Pattern III (Proliferative): ISR >10 mm extending beyond the stent edges (either proximal or distal), with 50% TLR rate 1, 2, 3
Pattern IV (Total Occlusion): Complete occlusion of the previously stented segment, carrying the worst prognosis with 83% TLR rate 1, 2, 3
Clinical Significance and Prognostic Value
The Mehran classification provides critical prognostic information that directly guides treatment decisions 2, 3:
Progressive worsening: TLR rates increase systematically from Pattern I through Pattern IV (19% → 35% → 50% → 83%), demonstrating the classification's strong predictive validity 1, 2, 3
Independent predictor: ISR pattern class is an independent predictor of TLR (odds ratio 1.7), along with diabetes (odds ratio 2.8) and previously recurrent ISR (odds ratio 2.7) 3
Treatment stratification: Patterns I and II are typically managed with balloon angioplasty and repeat stenting, while Patterns III and IV often require atheroablation devices or consideration of coronary artery bypass grafting 1, 2, 3
Validation and Accuracy
The Mehran classification has been validated through multiple imaging modalities 3:
Intravascular ultrasound (IVUS) confirms the angiographic accuracy of pattern assignment 3
The classification demonstrates high inter-rater reliability and reproducibility in clinical practice 3
Pattern distribution in clinical series shows Pattern I in 42% of cases, Pattern II in 21%, Pattern III in 30%, and Pattern IV in 7% 3
Application Beyond Coronary Arteries
A similar classification system has been adapted for carotid artery stenting, with five patterns (I-V) that include an additional category for end-stent lesions, demonstrating the classification's broader applicability 4:
Type IV lesions (diffuse proliferative extending outside the stent) in carotid ISR show 58.8% TLR rates, comparable to coronary Pattern III-IV lesions 4
The carotid adaptation maintains the same prognostic principles, with diffuse proliferative patterns predicting worse outcomes (odds ratio 5.1 for TLR) 4
Critical Clinical Pitfalls
The most common error is treating all ISR patterns identically without considering the Mehran classification, which leads to suboptimal treatment selection and higher recurrence rates. 2, 3 Pattern IV ISR warrants consideration of surgical revascularization rather than repeat PCI given the 83% TLR rate, while Pattern I lesions can be successfully managed with drug-eluting stents alone 2, 3.