Pulmonary Artery Calcification in Horses

Arterial calcification, an important vascular pathology occurs in racehorses. Clinically, this translates to altered vascular mechanics, decreased arterial compliance, and degenerative changes to the medial layer of elastic arteries. In humans, vascular calcification is known to cause stiffening of the vessels wall, and is associated with increased morbidity, and mortality from cardiovascular disease.

According to findings, calcification of the tunica media, predominantly the pulmonary artery, was found in 82% of young adult racehorses. Lesions appeared as white-to-yellowish, hard, and gritty plaques of variable size. Microscopically, elastic fibers within the tunica media were thinned, fragmented and calcified, and surrounded by dense collagen matrix. Elemental analysis showed distinct peaks for calcium and phosphorus, consistent with hydroxyapatite mineral.

Fibro-calcified pulmonary artery branch of a horse.

Fragmented and calcified elastic fibers (orange arrows), throughout a disorganized lattice

network of collagen fibers (light blue). Elastin-trichrome 20X.

Biomechanical analysis showed that high wall stress levels consistently occur at the pulmonary artery bifurcation and wall ipsilateral to the bifurcation, where calcified lesions typically form. Lower stress levels were found along the trunk and the wall contralateral to the bifurcation where lesions are less frequently found.

The occurrence of vascular calcification in young racing horses indicates the need to investigate its pathogenesis and possible parallels with vascular calcification in humans. It is also important to determine the potential heamodynamic changes or adaptations associated with the lesion and whether such changes are clinically relevant.

(Click pictures for descriptions and full size images.)

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