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Heart: aortic regurgitation

pequis

Synonym(s): Aortic valve regurgitation, AR

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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.
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Pathogenesis

Etiology

  • Nodular degeneration of the aortic valve, particularly the left coronary cusp, results in progressive aortic valve incompetence Heart: aortic regurgitation 02 - echocardiograph.
  • Occasionally results from disruption of the base of the valve by the presence of a ventricular septal defect Heart: ventricular septal defect Heart: aortic regurgitation 03 - echocardiograph  Prolapse of the non-coronary cusp of the leaflet into the defect results in aortic valve regurgitation Heart: aortic regurgitation 04 - echocardiograph.
  • Occasionally valve prolapse results in aortic valve regurgitation without echocardiographic evidence of valve degeneration Heart: aortic regurgitation 05 - valve prolapse - echocardiographHeart: aortic regurgitation 06 - color echocardiograph.
  • 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 Heart: aortic regurgitation 07 - volume overload - echocardiograph.
  • 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

  • Limited prevalence of audible murmurs.
  • Ranging from <1% in young horses to >10% in horses over 16 years.
  • The prevalence of aortic regurgitation viewed by color flow Doppler techniques exceeds 30% in performance horses Heart: aortic regurgitation 08 - color echocardiograph.

Diagnosis

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Treatment

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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.

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