The Role of Cardiopulmonary Exercise Testing for Identifying Possible Silent Myocardial Ischaemia in People with Coronary Heart Disease

This thesis investigates the utility of cardiopulmonary exercise testing (CPET) in assessing and managing patients with coronary artery disease (CAD), particularly focusing on the significance of oxygen pulse (O2Pulse) inflections as a marker for myocardial ischemia. The research encompasses a comprehensive analysis of O2Pulse morphology, inflection point identification, and the impact of exercise-based cardiac rehabilitation (exCR) programs, specifically high-intensity interval training (HIIT) and moderate-intensity steady-state (MISS) training, on patients with CHD.
Chapter 3 examines the reliability of CPET in detecting suspected myocardial ischemia through O2Pulse and ΔV̇O2/ΔWR inflections in chronic total occlusion (CTO) patients. This study was considerable hampered by poor recruitment and the outbreak of COVID-19. Subsequently only four patients were enrolled, three of whom exhibited no inflections in O2Pulse. In the one patient who did have O2Pulse inflections they occurred at similar work rates (10W) and heart rates (5bpm). Chapter 5 extends the inquiry into the short-term reliability and agreement of O2Pulse curve parameters in a healthy cohort demonstrating that the mean percent minimal detectable change for filtered O2Pulse was 13.5 ± 3.2. Building on these findings, Chapter 6 evaluates the inter- and intra-rater reliability in identifying O2Pulse inflections, comparing subjective assessments with an objective algorithmic method. Almost perfect agreement between the algorithm and human raters was demonstrated, with a Fleiss’ Kappa statistic of 0.89. Chapter 7, a subset analysis from the HIIT or MISS UK trial, delves into the rate of O2Pulse inflections in outpatient cardiac rehabilitation (16%) and how different exercise interventions affect O2Pulse inflections in CAD patients.
The results highlight a considerable potential for CPET, particularly O2Pulse inflections, in the diagnosis, treatment, and management of CAD. The research underscores the potential reliability of O2Pulse as a diagnostic tool, the effectiveness of exCR in improving cardiopulmonary fitness, and the relevance of O2Pulse inflections as a surrogate marker for myocardial ischemia. The findings suggest that both HIIT and MISS can positively influence O2Pulse inflections, offering a non-invasive means to monitor and potentially improve the health outcomes of CAD patients.
This thesis contributes to the understanding of CPET in clinical settings, advocating for its broader application in cardiac rehabilitation. It identifies areas for further research, including the exploration of different exercise modalities, to optimize exCR programs and enhance patient care.