Imaging of right ventricular volumes

Volume assessment by imaging is hampered by the complex crescent-shaped cross-section of the right ventricle, dense free-wall trabeculation disrupting edge detection, overlap of other cardiac chambers, and effects of imaging angle (which can introduce errors of up to 30 per cent). Contrast ventriculography, magnetic resonance imaging, and CT scanning are standard techniques, but are not readily applicable in the ICU ( Oldershaw 1992).


Multiple slices can be used to compute right ventricular volume. Transthoracic imaging is impeded by mechanical ventilation and its position beneath the sternum, and volume assessment is hampered by wall trabeculation, changes in wall reflection in disease, and the complex right ventricular shape. Transesophageal echocardiography and automated border detection may help. Even so, defining the right ventricular boundary by the innermost trabeculae often leads to underestimation. Technological advances may extend the value of echocardiography to the ICU assessment of the right ventricle.

Radionuclide studies

First-pass studies using red corpuscles labeled with technetium-99m and a right anterior oblique projection of 20° to 30° allow temporal separation of the right from the left ventricle, and can assess right ventricular end-systolic and end-diastolic volumes and ejection rates. After tracer equilibration with the intravascular pool (equilibration studies), images gated to different parts of the cardiac cycle can be acquired. Radioactivity in overlapping structures (e.g. the left ventricle, the right ventricular outflow tract, and underlying right atrium) diminishes accuracy. Even with a left anterior oblique projection of 20° and a caudal angulation of 20°, the right atrium may contribute 30 per cent of the signal. Ventricular separation by a 40° left anterior oblique projection is incomplete if the right ventricle is dilated.

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