Keywords

Pulmonary hypertension (PH) causes cardiac hypertrophy in the right ventricle (RV) and eventually leads to RV failure due to persistently elevated afterload. Considerable clinical and experimental animal studies have shown that abnormalities of endothelial function represent a hallmark of heart failure. However, the relationships between right coronary endothelial dysfunction and the development of heart failure remain to be fully established especially in the right heart. Synchrotron radiation (SR) microangiography has provided the temporal and spatial resolution required to visualize microvessels of various organs in vivo [1]. Therefore, in this study, we aimed to validate a new approach for the in vivo assessment of endothelial coronary function of the rat right heart using SR microangiography.

Imaging of the right coronary circulation was performed under pentobarbital anesthesia with monochromatic SR at 33.2 keV for producing maximal absorption contrast of the iodine contrast agent in the vascular lumen (Fig. 25.1a). ImageJ (ver. 1.41, NIH, Bethesda, MD) was used to identify coronary vessels and determine their caliber. Vessels were labeled and classified according to branching orders from first-order main segment (Fig. 25.1b). The visible vessel internal diameter (ID) of each vessel was determined from a single field of view for all cine sequences. The ID of each vessel was averaged over at least ten consecutive frames [2].

Fig. 25.1
figure 1

SR microangiography for assessing vascular function in a rat. Schematic of SR microangiography for the rat right coronary artery using SPring-8 facilities (a). Typical SR angiogram image of the right coronary vasculature (b). Schematic of right coronary arteries in lateral view depicting the coronary branching nomenclature used in this study (c). Range of vessel size at each of the branching generations of right coronary circulation in the normal rat (d). Asterisks indicate ~50 μm vessels not included in (d)

Full size image

The figure shows a typical imaging pattern of right coronary arteries from the aortic root to the third or fourth branching. It was possible to observe an arteriole with a diameter of about 50 μm (Fig. 25.1c). The ID of the first, second, and third branches were 312.7 ± 15.4, 159.3 ± 12.4, and 113.1 ± 7.5 μm, respectively (Fig. 25.1d). The present investigation demonstrates the ability to clearly visualize the right coronary circulation of the closed-chest anesthetized rat using SR microangiography. The use of SR microangiography provides a powerful tool for assessing coronary hemodynamics in unprecedented detail in PH models. Ultimately, future studies using SR microangiography will provide important new insights into the pathophysiology of right heart failure.