Heart: aortic regurgitation
Synonym(s): Aortic valve regurgitation, AR
Introduction
- Cause: degeneration of aortic valve, occasionally associated with endocarditis, congenital valvular disease or ventricular septal defect.
- Signs: often none, CHF, ventral edema, increased respiratory rate, AF, poor performance, death.
- Diagnosis: auscultation, clinical examination.
- Treatment: none required in most cases.
- Prognosis: good to guarded depending on severity of disease.
Presenting signs
- Often none.
- Congestive heart failure Heart: failure - overview.
- Ventral edema .
- Increased respiratory rate .
- Atrial fibrillation Heart: atrial fibrillation.
- Reduced athletic performance.
- Sudden death.
Acute presentation
- Most commonly presents as a cardiac murmur detected incidentally.
- Clinical signs of heart failure Heart: failure - overview.
- Collapse or death during exercise.
Geographic incidence
- Worldwide.
Age predisposition
- Any age, but increased prevalence with age (the majority of horses with this murmur are >10 years old).
Breed/Species predisposition
- Small riding breed, eg Thoroughbred and Arab or crosses thereof, are at increased risk of having AR compared to small ponies.
Cost considerations
- Can reduce horse's resale value, especially as condition can be progressive.
- Horse may require repeat echocardiographic Heart: echocardiography and exercising ECG examinations Cardiovascular: ECG (electrocardiography).
Special risks
- None when condition is fully compensated.
Pathogenesis
Etiology
- Nodular degeneration of the aortic valve, particularly the left coronary cusp, results in progressive aortic valve incompetence .
- Occasionally results from disruption of the base of the valve by the presence of a ventricular septal defect Heart: ventricular septal defect Prolapse of the non-coronary cusp of the leaflet into the defect results in aortic valve regurgitation .
- Occasionally valve prolapse results in aortic valve regurgitation without echocardiographic evidence of valve degeneration .
- Retrograde flow of blood through the incompetent aortic valve into the left ventricle causes aortic diastolic pressure to decrease and increases the diastolic dimensions and preload of the left heart.
- As a result of increased preload, left ventricular stroke volume is enhanced during systole and ultimately progressive left ventricular eccentric hypertrophy and dilation occur .
- Volume overload of the left ventricle and the resultant ventricular dilation and stretch of the mitral valve annulus results in secondary mitral valve regurgitation Heart: mitral regurgitation.
- Ultimately progressive mitral regurgitation and volume overload can → atrial fibrillation Heart: atrial fibrillation and congestive heart failure (CHF) Heart: failure - overview.
Predisposing factors
General
- Aging results in increased fibrosis and myxomatous and nodular degeneration of the valve.
Specific
- Presence of a membranous ventricular septal defect Heart: ventricular septal defect can disrupt valve support and result in valve leaflet prolapse.
- Bacterial endocarditis Heart: endocarditis (rare).
- Congenital malformation of the valve leaflets can occur sporadically, but are very rare.
Pathophysiology
- If the regurgitation is moderate to severe, the increased forward stroke volume results in a rapid rise of systolic aortic pressure and rapid run-off of arterial pressure during diastole. Marked swings in peripheral arterial pressure result in the development of hyperkinetic peripheral pulses (increased difference between systolic and diastolic arterial pressures results in a wide pulse pressure.
- Left ventricular dilation increases cardiac afterload, work and myocardial oxygen demand.
- Reduced aortic diastolic pressure simultaneously reduces coronary perfusion and myocardial oxygen delivery.
- Increased cardiac work and reduced myocardial oxygen demand increase the likelihood of myocardial ischemia developing.
- Myocardial ischemia can result in the development of ventricular arrhythmias Heart: ventricular premature complex Heart: ventricular fibrillation.
- Ischemia and associated arrhythmia are most likely to develop during conditions of increased myocardial oxygen demand, eg exercise.
- Progressive left ventricular enlargement simultaneously → mitral valve annular stretch and the development of secondary mitral regurgitation Heart: mitral regurgitation.
- Progressive left ventricular volume overload can ultimately result in left sided-heart failure Heart: failure - overview.
Timecourse
- Variable. The clinical significance and prognosis is most accurately based on history, physical examination and echocardiography.
- In many horses, mild aortic regurgitation (AR) does not significantly progress during horses active lifetime.
- In others, progression occurs more rapidly and as a result regular monitoring is required for all.
- Once decompensation occurs and there are signs of congestive heart failure Heart: failure - overview, progression to death or humane destruction is usually rapid.
- Even in moderate to severe aortic valve regurgitation, progression to decompensation can take years, but the risk of exercise-induced cardiac arrhythmias may render the horse unsuitable for ridden duties.
Epidemiology
Diagnosis
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Treatment
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Prevention
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Outcomes
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Further Reading
Publications
Refereed papers
- Recent references from PubMed and VetMedResource.
- Patteson M (2010) Prepurchase examination in horses: detection and significance of heart murmurs. In Pract 32 (9), 438-443 VetMedResource.
- Stevens K Bet al (2009) Effect of left-sided valvular regurgitation on mortality and causes of death among a population of middle-aged and older horses. Vet Rec 164 (1), 6-10 PubMed.
- Buhl R, Ersboll A K, Eriksen L & Koch J (2005) Use of color Doppler echocardiography to assess the development of valvular regurgitation in Standardbred trotters. JAVMA 227 (10), 1630-1635 PubMed.
- Cornelisse C J, Schott H C, Olivier N B et al (2000) Concentration of cardiac troponin I in a horse with a ruptured aortic regurgitation jet lesion and ventricular tachycardia. JAVMA 217, 231-235 PubMed.
- Bishop S P, Cole C R & Smetzer D L (1996) Functional and morphological pathology of equine aortic valve insufficiency. Path Vet 3, 137-158 PubMed.
- Clark E S, Reef V B, Sweeney C R & Lichtensteiger C (1987) Aortic valve insufficiency in a one-year-old colt. JAVMA 191, 841-844 PubMed.
- Reef V B & Spencer P (1987) Echocardiographic evaluation of equine aortic insufficiency. Am J Vet Res 48, 904-909 PubMed.
- Littlewort M C (1977) Cardiological problems in equine medicine. Equine Vet J 9, 173-175 PubMed.
- Sporri H & Leemann W (1972) Pathophysiology of aortic valve insufficiency in horses. Berl Munch Tierarztl. Wochenschr. 85, 441-448 PubMed.
Other sources of information
- Marr C M & Bowen I M (2010) Eds. Cardiology of the Horse. 2nd edn. Saunders Ltd, UK. ISBN: 9780702028175.
- Young L E (2003) Diseases of the Heart and Vessels. In: Equine Sports Medicine and Surgery. Eds: Hinchcliff K W, Kaneps A J & Goer R J. Elsevier Science Ltd, UK.
- Horn J (2001) Studies on Aortic Regurgitation in Horses. Royal Veterinary College - PhD Thesis.