Coronary artery disease ( CAD) remains the leading cause of death worldwide. Medical therapy and lifestyle modifications are the first line of therapy to minimise symptoms and retard disease progression. An Invasive therapy in the form of percutaneous coronary intervention (PCI) usually offered when medical therapy fails to improve symptoms. 1 Developments in the field of interventional cardiology have introduced advances in stents, equipment, and techniques resulting in complication rates of less than 1% for elective PCI. 2, 3 This has enabled a growing elderly population who have heavier co-morbid burden and more challenging coronary anatomy to benefit from more complex PCI which is referred to as Complex, High-risk PCI (CHiP). Whilst disparities in clinical outcomes and practices in PCI in the general population are known among different groups defined by sex, ethnicity and age, there is little data in the CHiP population. In particular, there are limited data regarding the differences in types of CHiP procedures performed, patient baseline characteristics, risk profiles, and clinical outcomes among special populations, as outlined above, in contemporary practice. Furthermore, limited data is supporting whether there are advantages in utilising certain technological advances/strategies in CHiP such as access site choice or intracoronary imaging. Consequently, this thesis was designed to determine whether there are differences in the baseline clinical and procedural characteristics, risk profile, trends, and clinical outcomes of CHiP undertaken to treat stable angina 1) among males and females 2) among different age groups and whether patients’ age has an effect in receiving invasive therapy 3) among different ethnic groups and how this has changed over time 4) according to the access approach utilised and what is the optimal access site practice to perform in a CHiP 5) and finally according the availability of on-site surgical support and whether this has a significant effect on clinical outcomes. This thesis addresses the objectives in three parts. Part 1 pertains to results in Chapters 4, 5, and 6, which systematically examine the type of CHiPs, baseline characteristics, and clinical outcomes based on sex, different age groups, and ethnic background. Chapter 4 demonstrates the existence of a sex paradox, where females have a favourable risk profile and less complex CAD yet experience worse outcomes compared to males. Chapter 5 reveals that despite Black, Asian, and other Ethnic Minorities (BAME) being younger and having a worse cardiometabolic profile, their odds for adverse events post CHiP are similar to those of their white counterparts. Finally, Chapter 6 reveals that the number of CHiP procedures performed in the older age group has gradually increased over time, but age remains an independent risk factor for worse outcomes. Part 2 pertains to results in Chapter 7, which examines the effect of certain procedural modalities/techniques on the outcomes of CHiPs and details the related differences in baseline characteristics and the changes in access site use over time. It concludes that radial access has become the most common access site used in CHiPs across all types of CHiP and that it is associated with better outcomes compared to CHiP performed via femoral access. Finally, part 3 of the thesis pertains to results in Chapter 8, which examines CHiPs undertaken according to the type of hospital facility and highlights the important differences in the type of CHiP undertaken based on the presence or absence of on-site surgical support. It concludes that, in selected cases, it is safe to perform CHiP in nonsurgical centres. Overall, this thesis provides compelling evidence of substantial variations in the types of CHiPs undertaken, as well as in the clinical and procedural characteristics, trends, and outcomes influenced by factors such as sex, ethnic backgrounds, and different age groups. Additionally, the study reveals that radial access has emerged as the prevailing approach in CHiPs, displaying superior outcomes in contrast to femoral access. Notably, performing CHiPs in non-surgical centres, in selected cases, does not exhibit any adverse impact on clinical outcomes as compared to CHiPs undertaken in surgical centres. The clinical implications of these findings, along with potential avenues for further research, are thoroughly examined and discussed
