Aortic rupture and aorto-pulmonary fistulation in the Friesian horse: characterisation of the clinical and gross post mortem findings in 24 cases.

REASONS FOR PERFORMING STUDY In horses, aortic sinus of Valsalva aneurysms or tears in the aortic root are well-recognised conditions in breeding stallions, often leading to sudden death. A more uncommon form of aortic rupture, located proximal to the ligamentum arteriosum has been reported in 3 Friesian horses. OBJECTIVES The purpose of this study was to phenotypically characterise aortic rupture and aorto-pulmonary fistulation in Friesian horses in terms of clinical and post mortem data based on 24 cases. METHODS Friesian horses that were diagnosed with aortic rupture and aorto-pulmonary fistulation over a period of 13 years (1997-2010) at the Department of Equine Sciences of Utrecht University (n = 15) and Wolvega Equine Hospital (n = 9), were included in this study. Case history, results of clinical examination and gross post mortem findings were screened and analysed. RESULTS Some cases were found dead without prior symptoms, but in several cases signs such as recurrent colic, peripheral oedema and sustained tachycardia were present for several weeks prior to cardiac failure. Clinical examination during hospitalisation revealed increased rectal temperature, peripheral oedema and increased jugular pulse with a bounding arterial pulse. In the majority of horses an aortic rupture of the aortic arch near the ligamentum arteriosum, concurrent with a circumferential cuff of perivascular haemorrhage and aorto-pulmonary fistulation, was found at post mortem examination. CONCLUSIONS Aorto-pulmonary fistulation in conjunction with aortic rupture is more common in Friesians than previously estimated. In some cases findings demonstrate a progressive pathology rather than acute cardiac failure and sudden death. An appropriate approach is necessary during post mortem examination of the heart in order not to overlook the diagnosis. POTENTIAL RELEVANCE Equine practitioners should realise that in Friesian horses presented with a history of recurrent false colic, coughing, sustained tachycardia and/or peripheral oedema, aortic rupture and aorto-pulmonary fistulation should be included in the differential diagnosis.