Non-Invasive Measures of Heart Failure
Abstract: Heart failure is a clinical syndrome characterized by an inability of the heart to meet the metabolic demands of the body. Approximately 1-2% of the population in the western society has the diagnosis, and the 5-year mortality rate is comparable with the common cancer diagnoses. The lack of reliable objective measures of heart failure motivates research in this direction. Blood flow is an essential parameter in hemodynamics and it can be expected that the blood flow is altered in patients with heart failure. A possible scenario is that backward failure could lead to increased pulmonary blood volume (PBV), which in turn could reduce the variation in PBV variation (PBVV). Using magnetic resonance imaging (MRI) it is possible to measure blood flow non-invasively with excellent accuracy, and both PBV and PBVV can be quantified using 2D-flow MRI. Furthermore, the intracardiac flow patterns have previously been found altered in heart failure. This can be assessed in detail by means of time-resolved three-directional (4D-flow) MRI. The results of the present work confirm the potential of MRI in this context. In study I, we found that the PBVV decreased by approximately 60% after experimentally induced myocardial infarction in pigs. This was interpreted as a consequence of stiffened vessels in the pulmonary circulation due to backward failure. However, contrary to our expectations, no difference was found in PBV. In study II we explored if patients with systemic sclerosis (SSc), who have an increased risk for developing pulmonary arterial hypertension and heart failure, had altered PBV and PBVV compared to healthy controls. We found no difference in PBVV, but a lower PBV indexed to lung volume in patients with SSc. This was interpreted as signs of early vascular changes in patients with SSc, however with preserved vascular distensibility. In study III we investigated the possibility to acquire 4D-flow data without respiratory navigator. The respiratory navigator is used to reduce motion artifacts. This is achieved, however, at the cost of prolonged scan time, which can be problematic for orthopneic patients. We found that the data quality of intracardiac measures are similar when acquired without as with the respiratory navigator. In study IV we explored whether the kinetic energy (KE) and the KE patterns measured using 4D-flow technique differ between patients with heart failure and controls. The results show that the KE indexed to stroke volume (SV) and cardiac index (CI) is higher in patients, indicating wasteful flow conditions accompanying heart failure. Moreover, we found that patients with heart failure present three distinct KE patterns, unrelated to current staging methods. This means that KE pattern analysis may be a conceptually new approach to staging and quantifying heart failure.
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