Aortic rupture

Etiology

• Obscure, but Onchocerca armillata Onchocerca spp may be involved, however many carcasses inspected in the abattoir showed heavy infections but limited cardiovascular changes.
• Marfan syndrome Marfan syndrome results in reduced elasticity in various structures, it can lead to aortic aneurysm and rupture.
  • It is caused by a mutation in the fibrillin- 1 gene.
  • It is an autosomal dominant genetic disorder.
  • The majority of cases seen in adult cattle probably do not have Marfan syndrome, although some of the histological features of idiopathic aortic aneurism are similar, ie there may be an underlying connective tissue defect.
• Often idiopathic.

Pathophysiology

• An aneurysm may result from progressive degenerative changes to connective tissue. 
• Inflammation is not usually a feature.
• It is likely that this degenerative change occurs slowly, over a prolonged time period, as there is often smooth muscle hypertrophy and granulation tissue at the site of the aneurysm, in cases of spontaneous rupture.
  • Increased arterial pressure during activity is a likely precursor to arterial rupture.
• Histological changes suggest progressive weakening with attempts at repair, before final rupture and exsanguination.
• The cause of the progressive weakening is often not evident.
• Nodules/atheromatous plaques caused by Onchocerca armillata Onchocerca spp may lead to vessel wall damage, resulting in aneurysm and subsequent rupture.
•  Lack of elastin in the aortic wall (due to Marfan syndrome Marfan syndrome) may also predispose to aneurysm and subsequent rupture.

Timecourse

• Sudden death or peracute heart failure with death delayed for some hours.
• Very occasionally, animal may survive with minimal clinical signs when rupture occurs through interventricular septum and defect is restrictive.

Epidemiology

• This is usually a sporadic condition, most commonly presenting as the sudden death of a single animal. However there are (intriguing) reports that the condition may occur in clusters, with 2-4 animals dying suddenly within a few days. There is no satisfactory explanation for this phenomenon at present.