Micro Computed Tomography in Experimental Pulmonary Arterial Hypertension

ight ventricular (RV) function is now recognized as one of the most important predictors of prognosis in many cardiovascular disease states, including pulmonary hypertension and left heart failure with reduced and persevered ejection fraction. 1,2This is particularly important for patients with pulmonary arterial hypertension (PAH) where RV failure not only drives symptomology but is also the leading cause of death. 3,4In prospective cohorts, the response of the RV to PAHtherapy is a critical prognostic marker with decreasing function portending a worsening prognosis, irrespective of any changes in pulmonary vascular resistance. 5he importance of assessing RV function is thus evident, yet detailed assessment of RV function remains difficult-even with contemporary imaging modalitiesgiven the complex 3-dimensional geometric shape, bellows-like motion, and load dependence of RV function.Small animals are frequently used in the evaluation of experimental PAH and right heart failure; their similarities to humans in cardiovascular physiology, relatively fast reproductive rate, and ease of animal handling make them ideal models for research.However, their small size and fast heart rates can limit in-vivo imaging and phenotyping of the RV.Echocardiography, magnetic resonance imaging (MRI), and microPET are established tools for the evaluation of RV function and physiology in small animal research.Although each imaging modality can be readily adapted from bench to bedside in translational research, the challenges of RV imaging in humans remain evident in small animal models.In clinical practice, powerful noninvasive imaging tools have emerged with capabilities extending beyond global RV assessment to now include regional and even molecular information.MRI is considered the 'gold-standard' for the noninvasive assessment of RV function, volumes, and mass, but imaging costs and accessibility continue to limit widespread clinical application. 6At most institutions, 2-dimensional echocardiography constitutes first-line imaging for patients with suspected right heart failure and pulmonary hypertension; limitations in qualitative assessment of function may be overcome with recent advancements in 3-dimensional echocardiography and speckle tracking/train imaging, yielding more reliable estimates of right ventricular ejection fraction with less operator dependence. 7Computed tomography (CT) has superior spatial resolution but inferior contrast resolution as compared to MRI.Indeed, this is particularly relevant for assessing ventricular volumes in rodents whose heart rates range from 300 to 600 bpm.The use of a contrast agent and fast gantry rotation times may help improve contrast and temporal resolution, respectively, to allow for a detailed assessment of ventricular volumes. 8It is important to note that all of these noninvasive assessments of RV function are dependent on RV preload and afterload and, therefore, do not fully characterize the intricacies of