section name header

Basics ⬇

Outline

BASICS

Definition!!navigator!!

Occurs when blood leaks from the aortic valve into the left ventricular outflow tract during diastole.

Pathophysiology!!navigator!!

  • The aortic leaflets do not form a complete seal between the aorta and left ventricle
  • During diastole, blood regurgitates into the left ventricular outflow tract, causing a left ventricular volume overload. As this volume overload worsens, stretching of the mitral annulus occurs, and MR often develops. MR compounds the severe left ventricular volume overload, and these horses often rapidly develop CHF
  • Severe regurgitation results in decreased coronary artery blood flow and decreased myocardial perfusion
  • Ventricular arrhythmias may develop secondary to decreased myocardial perfusion and increased myocardial oxygen demand during exercise

Systems Affected!!navigator!!

Cardiovascular

Genetics!!navigator!!

N/A

Incidence/Prevalence!!navigator!!

N/A

Geographic Distribution!!navigator!!

N/A

Signalment!!navigator!!

Usually horses >10 years.

Signs!!navigator!!

General Comments

Often an incidental finding during routine auscultation.

Historical Findings

  • Poor performance
  • Possibly CHF

Physical Examination Findings

  • Grade 1–6/6, decrescendo or musical holodiastolic murmur with PMI in the aortic valve area radiating to the left apex and right side
  • Bounding arterial pulses with moderate to severe regurgitation
  • Other, less common findings—AF, ventricular premature complexes, accentuated third heart sounds, and CHF

Causes!!navigator!!

  • Degenerative changes of the aortic leaflets
  • Aortic valve prolapse
  • Nonvegetative valvulitis
  • Fenestration of aortic leaflets
  • Flail aortic leaflet
  • Infective endocarditis
  • Ventricular septal defect
  • Congenital malformation
  • Disease of the aortic root

Risk Factors!!navigator!!

Old age.

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

Pulmonic regurgitation—rare; murmurs not usually detectable and should have PMI in the pulmonic valve area; differentiate echocardiographically.

CBC/Biochemistry/Urinalysis!!navigator!!

May have neutrophilic leukocytosis, elevated serum amyloid A, and hyperfibrinogenemia with bacterial endocarditis.

Other Laboratory Tests!!navigator!!

  • Elevated cardiac troponin I or cardiac troponin T with concurrent myocardial disease
  • Positive blood culture may be obtained with bacterial endocarditis

Imaging!!navigator!!

ECG

  • Ventricular premature complexes may be present with severe regurgitation
  • AF often develops with marked left ventricular volume overload and subsequent left atrial enlargement

Echocardiography

  • Most affected horses have thickened aortic valve leaflets
  • An echogenic band parallel to or a nodular thickening of the left coronary leaflet free edge are the most common findings
  • Prolapse of an aortic leaflet (usually the noncoronary leaflet) into the left ventricular outflow tract frequently is detected
  • Fenestration of the aortic leaflet, flail aortic leaflet, vegetations associated with infective endocarditis, or aortic root abnormalities are infrequently detected
  • Left ventricle—enlarged and dilated, with a rounded apex and thinner left ventricular free wall and interventricular septum with pattern of left ventricular volume overload
  • Increased septal-to-E point separation may be present
  • Normal or decreased fractional shortening with left ventricular enlargement is consistent with myocardial dysfunction
  • Dilatation of the aortic root occurs with longstanding regurgitation
  • High-frequency vibrations on the mitral valve septal leaflet or interventricular septum usually are detected, created by turbulence in the left ventricular outflow tract
  • High-frequency vibrations on the aortic leaflets usually are visualized in horses with musical holodiastolic murmurs
  • Premature mitral valve closure may indicate more severe aortic insufficiency
  • Decreasing aortic root diameter throughout diastole is another indication of increasing severity
  • Pulsed-wave or color-flow Doppler reveals a jet or jets of regurgitation in the left ventricular outflow tract. Size of the jet at its origin and its size and extent in the left ventricle represent another means of semiquantitating its severity, as is strength of the regurgitation signal
  • A steep slope and short pressure half-time of the continuous-wave Doppler spectral tracing of the regurgitation jet indicate more severe regurgitation

Thoracic Radiography

  • Left-sided cardiac enlargement presents with moderate to severe regurgitation
  • Pulmonary edema may be present with CHF

Other Diagnostic Procedures!!navigator!!

Cardiac Catheterization

  • Right-sided catheterization may reveal elevated pulmonary capillary wedge pressures and pulmonary arterial pressures with severe regurgitation and concurrent MR
  • Right ventricular and atrial pressures may be elevated with CHF
  • Oxygen saturation of blood obtained from the right atrium, right ventricle, and pulmonary artery should be normal

Noninvasive Blood Pressure Measurement

Pulse pressure >60 mmHg—progression likely.

Exercising ECG

Should be performed in all horses with moderate to severe aortic regurgitation.

Continuous 24 h Holter Monitoring

Use if ventricular premature complexes suspected.

Pathologic Findings!!navigator!!

  • Focal or diffuse thickening or distortion of one or more aortic leaflets (bands, nodules, plaques, and fenestrations) may be present
  • Flail aortic leaflets, infective endocarditis, or congenital malformations of the aortic valve infrequently are detected
  • Aortic root dilatation usually is present with severe, longstanding regurgitation
  • Jet lesions usually are detected on the ventricular side of the mitral valve septal leaflet and, less frequently, on the interventricular septum
  • Left ventricular enlargement and thinning of the left ventricular free wall and interventricular septum with significant regurgitation
  • Atrial myocardial thinning with atrial dilatation has been documented in horses with AF and enlargement
  • Inflammatory cell infiltrate has been detected with myocarditis and aortic regurgitation; however, most affected horses do not have significant underlying myocardial disease

Treatment ⬆ ⬇

Outline

TREATMENT

Aims!!navigator!!

  • Management by intermittent monitoring in horses with aortic regurgitation that is mild or moderate in severity
  • Palliative care in horses with severe aortic regurgitation

Appropriate Health Care!!navigator!!

  • Most affected horses require no treatment and can be monitored on an outpatient basis
  • Horses with moderate to severe regurgitation may benefit from long-term vasodilator therapy, particularly with ACE inhibitors
  • Treat horses with severe regurgitation and CHF with positive inotropic drugs, vasodilators, and diuretics and monitor response to therapy

Nursing Care!!navigator!!

N/A

Activity!!navigator!!

  • Affected horses are safe to continue in full athletic work until the regurgitation becomes severe or ventricular arrhythmias develop
  • Monitor horses with moderate to severe regurgitation by ECG during high-intensity exercise to ensure they are safe for ridden activities. These horses can be used for lower level athletic activities until they begin to develop CHF
  • Horses with significant ventricular arrhythmias or pulmonary artery dilatation are no longer safe to ride

Client Education!!navigator!!

  • Regularly palpate for bounding arterial pulses which indicate significant left ventricular volume overload and moderate to severe regurgitation
  • Regularly monitor cardiac rhythm; any irregularities other than second-degree atrioventricular block should prompt ECG
  • Carefully monitor for exercise intolerance, respiratory distress, prolonged recovery after exercise, increased resting respiratory rate or heart rate, or cough; if detected, seek a cardiac reexamination

Surgical Considerations!!navigator!!

N/A

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

  • Severe regurgitation—consider benazepril (1 mg/kg PO every 12 h)
  • ACE inhibitors prolong the time to valve replacement in humans with moderate to severe regurgitation
  • Some horses with moderate to severe regurgitation have experienced a decrease in left ventricular chamber size with ACE inhibitors
  • Treatment of affected horses in heart failure includes digoxin, diuretics, and vasodilators

Contraindications!!navigator!!

ACE inhibitors and other vasodilators must be withdrawn before competition to comply with the medication rules of the various governing bodies of equine sports.

Precautions!!navigator!!

ACE inhibitors can cause hypotension; thus, do not give a large dose without time to accommodate to this treatment.

Alternative Drugs!!navigator!!

Other ACE inhibitors and other vasodilatory drugs should have some beneficial effect in horses with moderate to severe regurgitation, but they may be less effective than benazepril.

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

  • Frequently monitor arterial pulses and cardiac rhythm
  • Reexamine horses with mild to moderate regurgitation by echocardiography every year
  • Reexamine horses with severe regurgitation by echocardiography and with exercising ECG every 6 months to monitor progression of valvular insufficiency and determine if the horse continues to be safe to ride or drive

Possible Complications!!navigator!!

Chronic regurgitation—ventricular arrhythmias; AF; MR; CHF.

Expected Course and Prognosis!!navigator!!

  • Most affected horses have a normal performance life and life expectancy
  • Progression of regurgitation associated with degenerative valve disease usually is slow. With the typical onset of regurgitation that occurs in old horses, other problems are more likely to end a horse's performance career or shorten life expectancy
  • Affected horses with CHF usually have severe underlying valvular and/or myocardial disease and a guarded to grave prognosis for life. Most affected horses being treated for CHF respond to the supportive therapy and improve. This improvement usually is short lived, however, and most are euthanized within 2–6 months of initiating treatment

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Associated Conditions!!navigator!!

N/A

Age-Related Factors!!navigator!!

Old horses are more likely to be affected.

Pregnancy/Fertility/Breeding!!navigator!!

  • Affected mares should not experience any problems with pregnancy unless the regurgitation is severe
  • Treat pregnant affected mares with CHF for the underlying cardiac disease with positive inotropic drugs and diuretics; ACE inhibitors are contraindicated because of potential adverse effects on the fetus

Synonyms!!navigator!!

Aortic insufficiency

Abbreviations!!navigator!!

Suggested Reading ⬆ ⬇

Afonso T, Giguere S, Rapoport G, et al. Pharmacodynamic evaluation of 4 angiotensin-converting enzyme inhibitors in healthy adult horses. J Vet Intern Med 2013;27:1185–1192.

Reef VB, Spencer P. Echocardiographic evaluation of equine aortic insufficiency. Am J Vet Res 1987;48:904–909.

Reef VB, Bonagura J, Buhl R, et al. Recommendations for management of equine athletes with cardiovascular abnormalities. J Vet Intern Med 2014;28:749–761.

Ven S, Decloedt A, Van Der Veckens N, et al. Assessing aortic regurgitation severity from 2D, M-mode and Doppler echocardiographic measurements in horses. Vet J 2016;210:34–38.

Author(s) ⬆

Author: Virginia B. Reef

Consulting Editors: Celia M. Marr and Virginia B. Reef