Integrated backscatter of ultrasound reflectivity for the in-vivo detection of vitamin D3-induced cardiovascular calcification in the rat.

Purpose: calcification associated with heart valve degeneration and atheromatosis is a common finding in the elderly and conveys a bad prognosis. In this pilot study, we sought to develop a rat model of cardiovascular calcification and characterize it by using different imaging modalities.
Methods: we studied a total of 15 male Wistar rats receiving 3 subcutaneous injections of cholecalciferol (vitamin D3) 12,500 IU/kg a week (n=8), or the vehicle (control, n=7) for 12 weeks. Echocardiography was performed blindly at baseline, and after 12 weeks, followed by ex-vivo micro-CT and histopathological evaluation.
Results: At baseline, no differences between groups were found with echocardiography. After 12 weeks, there was no difference in left ventricular function between both groups (Ejection fraction 72 ± 16 % vs. 75 ± 11 %, P=0.867). The integrated backscatter (IB) of ultrasound reflectivity of the ascending aorta was significantly higher in the vitamin D3 treated animals (-22 ± -5 dB vs. -29.6 ± -2.5 dB, P=0.004) compared to controls, as for the myocardium (-28.5 ± -3 dB vs. -35.1 ± -1.8 dB, P=0.004) and mitral valve annulus (-12,5 ± -6 dB vs. -18,9 ± -3.7 dB, P=0.04). On micro-CT, the thoracic aorta (Pixel value of 30,061 ± 14,920 vs. 13,967 ± 766, P=0.005) and the myocardium (17,720 ± 2,510 vs. 13,869 ± 427, P=0.008) also showed a significantly higher maximal density in vitamin D3 rats. On histopathology, calcifications of the aortic wall, myocardium, valve annuli and cusps were only present in the vitamin D3 treated animals.
Conclusion: cardiovascular calcifications in a rat model can be detected in-vivo by echocardiographic IB, as confirmed ex-vivo by micro-CT and histopathology. This offers a unique opportunity to evaluate experimental treatment strategies.