Diagnosis for the Cardiac Murmur in Horses

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Problem:
Left-sided holodiastolic, murmur with point of maximal intensity over the left base. The murmur is decrescendo shaped.

Differential diagnoses:
The most likely diagnosis for the cardiac murmur in this horse is aortic insufficiency, as a result of degenerative changes to the aortic valve. In aortic insufficiency, the murmur heard is due to regurgitation through the defective aortic valve. Aortic insufficiency presents clinically with a holodiastolic decrescendo murmur, with maximal intensity over the aortic valve7, as is heard in this case. Holodiastolic means that the murmur is occurring between the end of S2 and the beginning of S1. Decrescendo refers to a murmur that gradually declines during diastole, as the pressure gradient between aorta and left ventricle drops, as a result of run-off into the systemic circulation and the ventricle. The murmur is often musical or honking in nature7. This is a common finding in older horses4, and the most common acquired valve lesion7, usually of little clinical significance.

Another differential for the clinical signs shown is pulmonic regurgitation/pulmonic insufficiency. This is rare in horses, and these murmurs are usually very soft- often not detectable. The point of maximal intensity of pulmonic insufficiency murmurs is usually in the pulmonic valve area. Pulmonic insufficiency is usually secondary to cardiac heart failure, so carries a grave prognosis. Other causes of holodiastolic murmurs include mitral or tricuspid stenosis, and these are also rare in horses. Aortic insufficiency is a much more common diagnosis than any of these other causes of murmurs10.

Steps taken to rule in most likely diagnosis:
Upon examining this horse, a full physical examination must be performed....

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... VB, Spencer PA. Echocardiographic evaluation of equine aortic insufficiency. Am J Vet Res 1987; 48: 904-909
6) Stadler P, Hoch M, Radu I. Echocardiography in the horse with special regard to color-flow Doppler technique. Prakt Tierarzt 1995; 76: 1015
7) Sage AM. Cardiac disease in the geriatric horse. Vet Clinics Equine 2002; 18(3): 575-589
8) Brosnahan MM, Paradis MR. Assessment of clinical characteristics, management practices, and activities of geriatric horses. JAVMA 2003; 223(1): 99-103
9) Reef VB. Review Article: Heart murmurs in horses: determining their significance with echocardiography. Equine Veterinary Journal 1995; 27(S19): 71-80
10) Else RW, Holmes JR. Cardiac pathology in the horse. Equine Veterinary Journal 1972; 4(1): 1-8.
11) Patteson MW, Cripps PJ. A survey of cardiac auscultatory findings in horses. Equine Veterinary Journal 1993; 25(5): 409-415

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