Is there an acceptable level of incomplete revascularization after PCI in elderly ACS?

Background As global life expectancy rises, elderly patients constitute an expanding proportion of acute coronary syndrome (ACS) presentations. Although the evidence-based treatment goal is complete revascularization, it is often not feasible in this population due to frailty, diffuse calcific and complex disease, and elevated procedural risk. Elderly patients therefore require tailored revascularization strategies, yet evidence to guide optimal decision making remains limited. Objective To evaluate whether residual coronary disease after percutaneous coronary intervention (PCI), quantified by the residual SYNTAX score (rSS) and the SYNTAX Revascularization Index (SRI), can define clinically meaningful targets of incomplete revascularization in elderly ACS. We hypothesized that a range of incomplete revascularization would yield clinical outcomes comparable to those achieved with complete revascularization in this population. Methods This retrospective study included 500 patients aged ≥65 years who underwent PCI for ACS at a tertiary cardiac center and were followed for a median of 46 months. Three interventional cardiologists independently calculated the baseline SYNTAX score (bSS), rSS, and SRI ([1 − rSS/bSS] × 100). Patients were categorized into three predefined SRI groups: <50%, 50%–<100%, and 100% to reflect increasing degrees of revascularization completeness, consistent with prior literature. Primary outcomes were all-cause and cardiovascular mortality. The secondary outcome was major adverse cardiovascular events (MACE). Survival was assessed using Kaplan–Meier analysis and the log-rank test. Following predefined SRI categorization, ROC analyses were performed separately for mortality and MACE to refine outcome specific prognostic thresholds, followed by Cox proportional hazards modeling. Patients were subsequently reclassified according to ROC-derived cut-offs for further analyses. Results Lower SRI values were associated with greater anatomical complexity and higher event rates. All-cause mortality increased from 17.8% in patients with SRI 100% to 37.5% in those with SRI <50% (p<0.001), with similar gradients observed for cardiovascular death and MACE (both p<0.001). ROC analysis identified an optimal SRI threshold of approximately 40% for predicting all-cause mortality (AUC:0.605; p < 0.001), with SRI <40% independently associated with increased risk of death (HR 2.48; p<0.001). For MACE, an optimal threshold near 70% was identified (AUC:0.611; p < 0.001) and SRI <70% independently predicted events (HR 1.39; p=0.006). Above these thresholds, clinical outcomes were comparable to those observed after complete revascularization. Conclusion This study moves beyond the binary concept of complete versus incomplete revascularization by identifying distinct mortality and MACE related thresholds, defining a clinically acceptable range of incomplete revascularization to guide personalized treatment in elderly ACS patients.