Associations between depression and coronary heart disease

Abstract

Mental health, such as depression, and cardiovascular disease, such as coronary heart disease (CHD), are among two of the priority areas for health care and research in Australia and worldwide, and share many commonalities. First, depression and CHD are highly prevalent and frequently co-exist. Individually and together, they impose a significant burden of disease. Lastly, a reciprocal relationship exists, such that depressive symptoms are risk factors for the onset and progression of CHD (and vice versa), contributing to further morbidity, decreased quality of life (QoL) and mortality. The autonomic nervous system (ANS) has been implicated in the relationship between depression and CHD; and specifically, reduced heart variability (HRV; a marker of ANS activity) has been associated with both CHD and depression. Accordingly, psychological treatments with potential to enhance HRV (such as mindfulness-based cognitive therapy [MBCT]) may offer significant benefits to patients with either or both diagnoses. This thesis utilised quantitative statistical analyses to investigate the mental health of Australians, focusing on some actual and potential relationships between CHD, HRV and depression. Three independent but related studies were undertaken. The three published manuscripts, and some additional unpublished results, are presented as chapters in the thesis. Chapter One provides a context to this research, providing a comprehensive introduction to the literature on depression and its treatment MBCT, cardiac function and CHD, the relationships between depression and CHD, the ANS and HRV. Chapter Two outlines specific gaps identified in the literature leading to the thesis objectives. Chapter Three describes study measurement and types of psychometric questionnaires utilised. The three published manuscripts are then presented in Chapters Four to Six. Pre-existing datasets were used to investigate the demographic, psychological and cardiac factors associated with depression (Study 1) and subsequent mortality (Study 2) in cardiac patient samples. A clinical pilot study (Study 3) was then designed and conducted to investigate changes in physiology among mental health outpatients undergoing MBCT. A number of methods were employed to evaluate patient outcomes in the three studies. The major end points of this research focused upon patient-reported health and psychological measures (i.e., depression and QoL) and cardiac measures (i.e., HRV). Cross-sectional and longitudinal analyses were conducted using appropriate statistical analyses. Cross-sectional data were analysed using binary regression or Cox’s proportional hazards model (Studies 1 and 2) whereas longitudinal data were analysed as panel data, utilising random effects model and logistic regression (Study 3). A summary of findings, strengths and weaknesses of the three studies and their implications for future research and clinical practice form the discussion (Chapter Seven). Findings from the three studies have contributed to the epidemiological literature by providing empirical support for the relationships between depression and CHD, and between depression and mortality; and to evidence-based practice by reporting pilot data and methodological considerations concerning evaluation of the potential impact of MBCT on HRV. It is believed that results of this research will contribute to understanding the course and outcomes of depression in CHD and have implications for managing this comorbid condition.