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Prevalence and clinical importance of heart murmurs in racehorses

Nikolaus G. KrizDepartment of Veterinary Clinical Sciences, University of Sydney, New South Wales 2006, Australia.
Present address is Department of Veterinary Clinical Studies, Faculty of Veterinary Medicine, University of Glasgow, Bearsden Road, G61 1QH, Glasgow, UK.

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 Dr Med Vet, MVetClinStud
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David R. HodgsonDepartment of Veterinary Clinical Sciences, University of Sydney, New South Wales 2006, Australia.

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Reuben J. RoseDepartment of Veterinary Clinical Sciences, University of Sydney, New South Wales 2006, Australia.

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 DVSc, PhD

Abstract

Objective—To determine the prevalence of various types of heart murmurs in Thoroughbred racehorses and assess their association with performance by echocardiography and review of the horses' race records for the preceding 2 years.

Design—Clinical and retrospective study.

Animals—846 Thoroughbred racehorses.

Procedure—Cardiac auscultations were performed by 3 individuals; for 30 horses, Doppler echocardiographic examinations were also performed. Statistical analyses of race records for 753 horses were performed to assess association of heart murmurs with performance.

Results—Heart murmurs were detected by cardiac auscultation in 686 of 846 (81.1%) horses. Systolic murmurs over the heart base were most common; 365 (43.1%) horses had systolic murmurs that were loudest over the pulmonary valve area, and 232 (27.4%) horses had systolic murmurs that were loudest over the aortic valve area. Systolic murmurs over the tricuspid valve area were detected in 241 (28.5%) horses, whereas systolic murmurs over the mitral valve area were detected in only 32 (3.8%) horses. Diastolic murmurs were much less common than systolic murmurs. Review of race records did not reveal a significant association between murmurs and performance.

Conclusion and Clinical Relevance—Results suggest that heart murmurs are a common finding in racehorses; most of these heart murmurs do not appear to be clinically important. (J Am Vet Assoc 2000;216:1441–1445)

Abstract

Objective—To determine the prevalence of various types of heart murmurs in Thoroughbred racehorses and assess their association with performance by echocardiography and review of the horses' race records for the preceding 2 years.

Design—Clinical and retrospective study.

Animals—846 Thoroughbred racehorses.

Procedure—Cardiac auscultations were performed by 3 individuals; for 30 horses, Doppler echocardiographic examinations were also performed. Statistical analyses of race records for 753 horses were performed to assess association of heart murmurs with performance.

Results—Heart murmurs were detected by cardiac auscultation in 686 of 846 (81.1%) horses. Systolic murmurs over the heart base were most common; 365 (43.1%) horses had systolic murmurs that were loudest over the pulmonary valve area, and 232 (27.4%) horses had systolic murmurs that were loudest over the aortic valve area. Systolic murmurs over the tricuspid valve area were detected in 241 (28.5%) horses, whereas systolic murmurs over the mitral valve area were detected in only 32 (3.8%) horses. Diastolic murmurs were much less common than systolic murmurs. Review of race records did not reveal a significant association between murmurs and performance.

Conclusion and Clinical Relevance—Results suggest that heart murmurs are a common finding in racehorses; most of these heart murmurs do not appear to be clinically important. (J Am Vet Assoc 2000;216:1441–1445)