Diagnosis of conditions referable to the cardiovascular system was made in 191 horses necropsied at the Livestock Disease Diagnostic Center between January 1, 1993 and December 31, 1995. During this period 4,757 equine necropsies were performed with cardiovascular disease representing 4% of the equine cases. All ages of horses were represented with 79% of the cardiovascular cases being Thoroughbreds, while 73% of the total equine necropsy cases were Thoroughbreds.
Two conditions were by far the most common, representing 63% of all cardiovascular cases. These were rupture of the uterine or ovarian artery (101 cases) and cranial mesenteric arteritis (20 cases). Ninety cases of rupture of the uterine or ovarian artery were Thoroughbreds, 5 Standardbreds and the remainder single cases representing several breeds. Rupture of an artery resulted in fatal hemorrhage and, as in other similar reports, was a condition of older mares, with an average age of 18 years (range 7-26 years). Most cases occurred around the time of parturition; the mare typically exhibited acute death or signs of colic or shock. Necropsy examination usually revealed free blood in the abdominal cavity and a large hematoma within the broad ligament and uterine wall.
Cranial mesenteric arteritis, also called verminous arteritis, is a condition resulting from damage to the cranial mesenteric artery caused by Strongylus vulgaris larvae. Larvae penetrate the intestine and migrate to the cranial mesenteric artery where they cause damage and inflammation which can result in occlusive thrombotic lesions. Of the 20 cases, most were in adult animals average 8 years (range 4 months – 26 years); however, only 4 cases were in Thoroughbreds. This probably represents area management practices rather than breed resistance.
Other diseases affecting the heart included inflammatory conditions in which the cause was usually unknown. In this group were 11 cases of endocarditis, 10 myocarditis, 2 epicarditis, and 5 pericarditis. These diagnoses were based on microscopic demonstration of inflammatory cells in an area of the heart. The cause of these conditions is usually believed to be an infectious agent.
Other cardiac conditions included 13 cases of congestive heart failure, 6 of endocardiosis, 2 of cardiomyopathy, and congenital malformations. Congenital malformations of the heart were rare with 5 Thoroughbred foals diagnosed with this condition over the 3 year period. Within this group were 4 cases of ventricular septal defect and 1 with both patent ductus arteriosus and patent foramen ovale. There were 5 cases of non-specific vasculitis, 5 rupture of the vena cava and 3 of an umbilical blood vessel. Three cases of rupture of the vena cava were foals occurring at the time of parturition, with the tear in the vena cava just caudal to the liver or at the diaphragm. Interestingly, all 3 were reported to be “red bag” (premature placental separation) deliveries. The cases of umbilical vessel rupture also occurred at the time of foaling and were the result of trauma, the foal dying from intra-abdominal hemorrhage.
Cardiovascular neoplasia was rare with 3 cases diagnosed. All were hemangiosarcomas and in adult horses. Sites included liver, spleen, lung and nasal sinus.