Left ventricular diastolic dysfunction in a community of African ancestry
Peterson, Vernice Roxanne
Almost half of all cases of heart failure have a preserved ejection fraction. However, therapy targeting the mechanisms of this disorder has not improved outcomes. Left ventricular (LV) diastolic dysfunction is a characteristic feature of heart failure with a preserved ejection fraction. A more sound understanding of the mechanisms responsible for LV diastolic dysfunction produced by risk factors may lead to better approaches to preventing this syndrome. Although obesity is thought to be a major risk factor for LV diastolic dysfunction, this does not occur in all obese individuals. In the present thesis I have demonstrated in 737 randomly recruited participants from a community sample of African ancestry, that the relationship between insulin resistance (homeostasis model) and LV diastolic function, as assessed from trans-mitral velocity (E/A) and tissue Doppler imaging of the lateral and septal walls of the LV (e’ and E/e’), is markedly altered by the presence of a more concentrically remodelled LV (as indexed by LV relative wall thickness [RWT]). Importantly, insulin resistance was only associated with LV diastolic function or dysfunction in those with an RWT above a threshold value. In contrast no interactive effects on LV diastolic function between either blood pressure or age and RWT were noted. These data therefore suggest that obesity will only translate into LV diastolic dysfunction if it is associated with insulin resistance and a concentrically remodeled LV. Although hypertension is thought to play an important role in contributing to LV diastolic dysfunction, the pulsatile hemodynamic change primarily responsible for this effect is uncertain. In 524 randomly selected individuals from a community sample I have demonstrated that independent of confounders including left ventricular mass and RWT, aortic backward wave pressure effects (as determined using wave separation analysis), antedate the impact of aortic stiffness (indexed by aortic pulse wave velocity) or the factors determined by aortic stiffness (the time of backward wave return or forward wave pressures) on LV filling pressures (E/e’). These data therefore suggest that to adequately prevent LV diastolic dysfunction, targeting aortic backward wave pressures may be required. As conventional risk factors account for only a portion of the inter-individual variations in LV diastolic function, it is thought that the genetic factors may play a iv significant role. In 694 randomly recruited participants of African ancestry belonging to nuclear families, I demonstrated that independent of conventional risk factors, heritability accounts for approximately 50% of the variation in LV RWT, an important LV structural determinant of LV diastolic function. Moreover, in 442 randomly recruited individuals of African ancestry belonging to nuclear families, I also demonstrated that heritability accounts for approximately 50% of the variation in the index of LV filling pressures, E/e’, independent of LV mass or RWT remodeling and aortic function. These data provide strong evidence that genetic factors responsible for LV diastolic dysfunction and the structural determinants thereof should be sought. In conclusion, the results provided in the present thesis have advanced our knowledge of possible pathophysiological mechanisms that play a role in the development of LV diastolic dysfunction and hence possibly heart failure with a preserved ejection fraction.
A thesis submitted to the Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Doctor of Philosophy. Johannesburg, South Africa 2017.
Peterson, Vernice Roxanne (2017) Left ventricular diastolic dysfunction in a community of African ancestry, University of the Witwatersrand, Johannesburg, <http://hdl.handle.net/10539/23157>