Restenosis is the principal cause of lack of long-term clinical success after a short-term clinical success has been achieved. Restenosis is not a complication; it is the expected biological response to vascular injury. The frequency of clinically important reste- nosis may be judged by the frequency with which subsequent revascularization procedures are performed on target arteries after the index procedure. 3.2. Predictors of Clinical Outcome After PCI Factors associated with increased PCI complication rates include advanced age, diabetes, CKD, ACS, congestive heart failure, and multivessel CAD.8,230 232 Several models have been developed and refined over the past 2 decades to predict mortality with PCI.230,233 236 At present, perhaps the best accepted system is from the ACC National Cardiovascular Data Registry (NCDR) CathPCI Risk Score system, which uses clinical variables and PCI setting to predict inpatient mortality (Appendix 4A).236 In general, these models perform very well (C statistic: approximately 0.90), although predic- tive capability decreases in high-risk patients. Models have also been developed to predict procedural success. Presently, the modified ACC/AHA score230 and the SCAI score (Appendix 4B)237 are both in use, with the latter slightly outperforming the former. Discrimination as mea- sured by the C statistic is generally good to very good (0.70 to 0.82), depending on the outcome variable and patient population. The angiographic SYNTAX score238 has been developed to predict long-term risk of MACE after multivessel interven- tion. The SYNTAX score and its potential utility in helping guide revascularization strategies are discussed in Section 2. Composite models including angiographic and clinical vari- ables have been developed but generally require validation in larger cohorts of patients. 3.3. 