Residual difference in LDL cholesterol as an indicator of adherence to lifestyle changes during cardiac rehabilitation

Abstract Background Cardiac Rehabilitation can help achieve target LDL by optimization of pharmacological lipid-lowering therapy and lifestyle changes after ST-segment elevation myocardial infarction (STEMI). Purpose To study the characteristics of patients with suboptimal LDL reduction after STEMI in a Phase 2 ambulatory Cardiac Rehabilitation Program (aCRP) and describe the relative contribution of adherence to lifestyle changes to this instance. Methods We studied 41 STEMI patients who completed an exercise-based Phase 2 aCRP. Conventional or cardiopulmonary exercise testing (C/CPET) was performed before and after Phase 2 and peak oxygen consumption (peak VO2) was assessed. Several questionnaires were used to analyse quality of life (SF-36), adherence to Mediterranean diet (PREDIMED), weekly physical activity (IPAQ) and therapeutic adherence (Morisky-Green). Lipid-lowering therapy and LDL were registered before STEMI, at the start of Phase 2, and at the end of Phase 2. At the end of Phase 2, we analysed the difference between measured and theoretical LDL (LDL before STEMI minus expected LDL reduction by prescribed lipid-lowering therapy), which was defined as "residual difference in LDL" (RD-LDL). Comparisons were performed between patients with positive RD-LDL (lower than theoretically expected) and patients with negative RD-LDL (higher than theoretically expected). A p<0.05 was considered statistically significant. Results Mean age of the cohort was 60.1±10.2 years and most patients were male (82.9%). Most patients (n=33, 80.5%) underwent lipid-lowering therapy up-titration during Phase 2 aCRP, and an LDL<55mg/dL target was achieved in 31 (75.6%) patients. During Phase 2 aCRP, 25 (61%) patients depicted higher than expected LDL reduction (negative RD-LDL) and 16 (39%) patients showed lower than expected LDL reduction (positive RD-LDL). Patients with positive RD-LDL reported less weekly physical activity before Phase 2 aCRP (957±1130.34 vs. 2202.3±2749.7 METS/week, p=0.04) and were less likely to achieve LDL<55mg/dL (50% vs. 92%, p=0.002). No differences were found in adherence to Mediterranean diet or pharmacological treatment at the end of Phase 2. However, a significant higher improvement in quality of life (+18.4±29.2 vs. +2.1±17.2 points in SF-36, p=0.03) and in weekly physical activity (4436.4±4116.3 vs. 1557.7±2267.4 METS/week, p=0.02) was noted compared to patients with negative RD-LDL. Peak VO2 increased similarly in both groups at the end of Phase 2 (mean increase of 4.64±5.67 vs. 3.81±3.95 ml/kg/min, p=0.83). Conclusions Up-titration of lipid-lowering therapy is required in most patients throughout our Phase 2 aCRP to achieve target LDL. More than a third of patients showed lower than expected LDL reduction (positive residual difference in LDL), which cannot be attributed to worse adherence to Mediterranean diet, pharmacological treatment, or physical exercise recommendations.Residual difference in LDL cholesterol.