Tissue doppler imaging for the assessment of left ventricular function in an older population
Creators: name: Jacobson, Benjamin Matthew
Publisher: name: The Australian National University
Year: 2018

description: Tissue Doppler Imaging (TDI) is an established tool in the echocardiographic assessment of cardiac function. Longitudinal cardiac fibres are particularly sensitive to fibrosis, hypertrophy and ischaemia, and impaired long-axis function can therefore provide a sensitive index for the assessment of myocardial function. This thesis is based on clinical and echocardiographic data from a population-based prospective cohort study of older adults in the Australian Capital Territory (ACT), the Canberra Heart Study. I review the epidemiology of heart failure (HF) and highlight the importance of early diagnosis (Chapter 1). TDI may assist in the early detection of HF and help reduce its increasing burden on the healthcare system. Chapter 2 details study methodologies, including echocardiographic evaluation of cardiac function and the assessment of cardiac biomarkers. Mitral annular systolic velocities (s') provides a measure longitudinal LV systolic function. Their clinical determinants are evaluated in a population-based study for the first time (Chapter 3). S' velocities declined with age, and were lower in females. Negative correlations were observed with clinical parameters associated with adverse LV loading conditions. The division of systolic and diastolic heart failure into distinct disease entities has been debated for some time, and this approach has led to significant controversy and misunderstanding about the pathophysiology and progression of HF. The relationship between LV systolic function using s' and LV diastolic dysfunction (DD) was independent of the effects of other echo-clinical factors (Chapter 4), supporting the concept that diastolic and systolic dysfunction represent a continuum of the same disease. We hypothesized that s' may provide a more sensitive index than LVEF for assessing LV systolic function, and examined the relationship between LV long axis systolic function using s', LVEF and LV filling pressure (Chapter 5) and observed a continuum between longitudinal and radial systolic function. The findings in Chapter 5 are supported in Chapter 6 by our assessment of the association between s', LVEF, LV filling pressure and cardiac biomarkers, amino-N-terminal pro-B-type natriuretic peptide (NT-proBNP) and high sensitivity troponin I (hs-cTn), . Cardiac biomarkers increased with advancing LV dysfunction, providing insight into mechanisms involved in the progression of HF. LV dyssynchrony has been linked to increased morbidity, mortality and arrhythmia susceptibility in patients with HF. Quantification of systolic dyssynchrony by the standard deviation of time-to-peak systolic myocardial velocity (Ts-SD) using TDI has previously been validated in small clinic-based populations. Understanding the determinants of Ts-SD should facilitate a better understanding of the pathophysiology and natural history of LV dysfunction, and provide insights to why this measure is a suboptimal marker for the selection of HF patients who may benefit from cardiac resynchronization therapy (Chapter 7). LV systolic dyssynchrony (assessed by Ts-SD), was highly prevalent and determined by the opposing influences of aortic pulsatile load and ventricular preload, total systolic time, and intrinsic properties of LV structure and diastolic function. Finally, I provide a brief outline of future directions for research that may be guided by the results emanating from this thesis.