Effects of a stiffened arterial tree on ventricular-arterial coupling in healthy and diseased hearts

In this thesis we study ventricular-arterial coupling in rodents under the influence of arterial stiffening and myocardial infarction (MI), combination of the two considered as a novel cardiovascular research model for diseased hearts pumping against an aged, stiffened arterial tree. The stiffened arterial tree yields isolated systolic hypertension and is obtained by administration of vitamin D and nicotine (VDN). The investigation cardiac performance and ventricular-arterial coupling using such a combined model (VDN/MI) is of particular relevance to cardiac research, as cardiac disease in elderly often takes place in presence of a atherosclerotic or stiff arterial tree.. The thesis consists of an Introduction, 4 scientific papers and a brief Conclusion. The Introduction is an overview of the epidemiology of heart failure, structure and functional changes that occur during MI and VDN, material and methods used in evaluating cardiac function invasively and non-invasively (using trans-thoracic echocardiography, TTE), methods for evaluating arterial function, and finally an overview of the interaction between the heart and vessels. Paper 1: This paper addresses the issue of the universality of the normalized time-varying elastance curve. It is demonstrated that the waveform of the normalized time-varying elastance curve (En(tn)) is qualitatively comparable between the control and MI hearts, however, when En(tn) is compared quantitatively between the two groups, statistical significance is found at the ejection phase and during diastole. These differences need to be taken into account when assessing cardiac contractility based on a generalized En(tn) in different animal models or in the human in different physiological or pathological states. Paper 2: Using trans-thoracic echo (TTE), we were able to follow serial changes of cardiac function post MI using two novel parameters, the myocardioal performance index (MPI) and its ratio to left ventricular fractional shortening (LVFS/MPI), both indices being monitor successfully and as efficiently as other classical TTE parameters. More so, LVFS/MPI visually expressed better the serial modifications in cardiac function. Both MPI and LVFS/MPI were correlated to the load-independent contractile parameter, PRSW, and to the preload parameter, LVEDP, being thus pertinent in following preload changes post MI. Finally, chamber remodeling post MI can successfully be followed due to the fact that ESV and EDV both correlate to MPI and LVFS/MPI. Paper 3: We studied hemodynamics, arterial function, cardiac function and ventricular-arterial coupling in a rat model of reduced arterial compliance. The results show that arterial stiffening after VDN treatment provokes important changes in vascular impedance and wave reflections, leading to isolated systolic hypertension and LV hypertrophy, Ventricular-arterial coupling was also altered. The effects are quantitatively similar to those of arterial stiffening with age. Paper 4: We studied changes in cardiac geometry, structure and function in response to MI in control and VDN-treated (stiffened aorta) rats. The combined VDN/MI model showed the largest compromise in cardiac structure and function and exhibited the strongest biochemical signs of heart failure as compared to all other groups. The addition of MI on top of a raised afterload, seems to have accelerated the progression of heart failure. Vascular alterations also reflected well a model of ageing and calcification. This combined pathology model of failing hearts in presence of a stiff arterial tree might be fruitful in better understanding the evolution of disease and may help improving or developing novel treatment therapies. The Conclusion chapter summarizes the findings of the thesis and brings into perspective their importance and future relevance into cardiovascular research models.

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