Three-dimensional assessment of cardiac function; When right is wrong
Abstract: Assessment of the right side of the heart is important in patients with heart disease; especially in patient with elevated pressure in the lung circulation. Decreased right ventricular function and elevated pressure in the right atrium are of poor prognostic value. Two-dimensional echocardiography (ultrasound of the heart) is the most commonly used method to assess the hearts function, but the right ventricle is hard to assess with this method. This is partly due to a 2-dimensional method has intrinsic problems to assess a 3-dimensional complex structure such as the right side of the heart. Magnetic resonance imaging of the heart and 3-dimensional (3D) echocardiography can be used for imaging in three dimensions. The aim of this thesis is to assess how 3D echocardiography and magnetic resonance imaging of the heart can be used to determine the right heart function; and due to this determine how the heart pump physiology is altered by elevated right atrial and pulmonary pressure. In this thesis, echocardiography and magnetic resonance imaging is used with 2D and 3D technique. Study I showed how to acquire 3D echocardiography for volume assessment of both atria and ventricles in adult cardiac patients. Acquisition from the apex of the heart, with at times an 'off-axis' approach, should be used for volumetric assessment with 3D echocardiography. While the atria and the left ventricle were well visualized, the right ventricle was a challenge. Study II aimed to validated right ventricular volumes and function, in a population of adult cardiac patients, with 3D echocardiography using magnetic resonance imaging as a reference. The study showed the difficulty to asses right ventricular volumes and function, even when using 3D echocardiography in a clinically unselected population. Furthermore, the study showed the importance of manual corrections to achieve reasonably valid measurements, when compared to magnetic resonance imaging. Study III assessed elevated right atrial pressure by quantifying right atrial volumes with 3D echocardiography in patients with elevated pressure in the lung circulation. The volumes were compared to invasively measured pressure values and magnetic resonance imaging. The study showed that 3D as well as 2D echocardiographic volume assessment of the right atrium were better than the conventional echocardiographic methods to determine elevated right atrial pressure. This was despite a substantial underestimation of the 3D echocardiographic volumes compared to magnetic resonance imaging. Study IV examined the different contributions to right and left ventricular stroke volume in patients with elevated pressure in the lung circulation; and compared to those of healthy adults. Magnetic resonance imaging was used given the results of study II and pressure was quantified by right sided catheterization. The study showed that longitudinal and lateral contribution to left ventricular stroke volume was altered in patients with elevated pressure in the lung circulation compared to the control group. Right ventricular longitudinal and lateral contribution to stroke volume did not differ between patients and controls. The septum moved to the left in both groups, however less in patients than in healthy adults. In patients with elevated pressure in the lung circulation and hence pressure loaded right ventricles, the different components of pump function are altered in a different compared to volume loaded right ventricles. This is new information that helps understand the hearts physiology.
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