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Basics ⬇

Outline

BASICS

Definition!!navigator!!

Occurs when the tricuspid (right atrioventricular) valve allows blood to leak backward into the right atrium and creates a systolic murmur with its point of maximal intensity in the tricuspid valve area radiating dorsally or cranially.

Pathophysiology!!navigator!!

  • Tricuspid regurgitation can occur with structurally normal valve cusps or when dysplastic, inflammatory, or degenerative disease or rupture of a chorda tendinea is present
  • During systole, blood regurgitates into the right atrium, and, if severe, increases right atrial pressure and leads to right atrial and ventricular volume overload
  • As the regurgitation becomes more severe, increases in right atrial pressure produce increased central venous pressure, hepatic congestion, and right-sided CHF

Systems Affected!!navigator!!

Cardiovascular

Genetics!!navigator!!

N/A

Incidence/Prevalence!!navigator!!

The prevalence of murmurs characteristic of tricuspid regurgitation in a middle-aged and older population of apparently healthy horses in the UK was 1.1%, and in Thoroughbreds was 22% in flat and 43% in jump racing.

Signalment!!navigator!!

Reported most frequently in athletes.

Signs!!navigator!!

General Comments

Usually an incidental finding with no effect on performance. The severity of signs is dependent on the nature and severity of valvular pathology.

Historical Findings

  • Sometimes poor performance
  • Sometimes CHF

Physical Examination Findings

  • Grade 2–6/6, band-shaped to crescendo or crescendo–decrescendo holosystolic murmur with its point of maximal intensity in the tricuspid valve area (right fourth intercostal space) radiating to the right heart base
  • Approximately 30% of horses with tricuspid infective endocarditis do not have cardiac murmurs
  • Other, less common findings—AF, jugular pulsations, generalized venous distention, and ventral edema

Causes!!navigator!!

  • Physiologic tricuspid regurgitation, a response to athletic training
  • Degenerative, inflammatory, or congenital valvular disease
  • Pulmonary hypertension
  • Ruptured chordae tendineae
  • Infective endocarditis

Risk Factors!!navigator!!

  • Infective endocarditis can be a sequela of septic jugular thrombophlebitis
  • Athletes have a high prevalence of physiologic tricuspid regurgitation

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

Ventricular septal defect—there is a loud murmur over the right hemithorax accompanied by the murmur of pulmonic stenosis over the pulmonic valve area (left third intercostal space); differentiate echocardiographically.

CBC/Biochemistry/Urinalysis!!navigator!!

Leukocytosis and hyperfibrinogenemia and elevated SAA with infective endocarditis.

Other Laboratory Tests!!navigator!!

  • Increased concentrations of cardiac troponin I with concurrent myocardial disease
  • Positive blood culture with infective endocarditis

Imaging!!navigator!!

Echocardiography

  • Most affected horses have normal tricuspid valve leaflets
  • Prolapse of a tricuspid leaflet into the right atrium frequently is detected in affected horses
  • Thickening of the valve leaflets is not seen often but diffuse thickening of the free edge of the leaflets is more common than nodular thickening of the leaflets’ free edge
  • Ruptured chordae tendineae, flail tricuspid leaflets, or vegetations associated with infective endocarditis are detected infrequently
  • Right atrium—enlarged and dilated, with a rounded appearance
  • Right ventricle—enlarged and dilated, with a rounded apex and thinning of the right ventricular free wall and interventricular septum
  • A pattern of right ventricular volume overload, including paradoxic septal motion, in severe cases
  • Dilatation of the cranial and caudal vena cava and hepatic veins in severe cases
  • Pulsed-wave or color-flow Doppler reveals a jet (or jets) of tricuspid regurgitation in the right atrium. In most horses with mild to moderate regurgitation, the jet is directed toward the aortic root. The size and extent of the jet are used to semiquantitate severity

Thoracic Radiography

Cardiac enlargement may be detected, with increased contact between the heart and the sternum.

Other Diagnostic Procedures!!navigator!!

ECG

Supraventricular premature depolarizations or AF may be present at rest and/or during exercise in horses with right atrial enlargement.

Ultrasonography

With a thrombosed jugular vein, detection of a cavitated thrombus is consistent with septic jugular vein thrombophlebitis.

Pathologic Findings!!navigator!!

  • Where the regurgitation relates to physiologic adaptation to athletic training, no pathologic findings are expected
  • Most horses have relatively normal-appearing tricuspid valve leaflets at postmortem examination
  • Focal or diffuse thickening or distortion of 1 or more tricuspid leaflets may be present
  • Ruptured chordae tendineae, flail tricuspid leaflets, vegetations due to infective endocarditis, or congenital malformations of the tricuspid valve are infrequent
  • Jet lesions may be detected in the right atrium
  • Right atrial and ventricular enlargement in cases with significant regurgitation
  • Dilatation of the cranial and caudal vena cava and hepatic veins in horses with severe regurgitation
  • Pale areas may be seen in the atrial myocardium, with areas of atrial fibrosis detected histopathologically
  • Inflammatory cell infiltrate and/or myocardial necrosis occasionally is detected in affected horses with primary myocardial disease
  • In horses with CHF, ventral and peripheral edema, pleural effusion, pericardial effusion, chronic hepatic congestion, and, occasionally, ascites may be detected

Treatment ⬆ ⬇

Outline

TREATMENT

Aims!!navigator!!

  • Management by intermittent monitoring in horses with tricuspid regurgitation that is mild or moderate in severity
  • Palliative care in horses with severe tricuspid regurgitation and signs of right-sided or CHF

Appropriate Health Care!!navigator!!

  • Most affected horses require no treatment and can be monitored on an outpatient basis
  • Treat horses with severe regurgitation and CHF with positive inotropic drugs, vasodilators, and diuretics on an inpatient basis, if possible, and monitor response to therapy

Nursing Care!!navigator!!

N/A

Activity!!navigator!!

  • Most horses with tricuspid regurgitation are safe to continue in full athletic work unless the regurgitation is severe or the horse develops exercise intolerance or CHF
  • Horses with significant right ventricular dysfunction and exercise intolerance are no longer safe to ride

Diet!!navigator!!

N/A

Client Education!!navigator!!

  • Monitor the cardiac rhythm regularly; any irregularities should prompt ECG
  • Carefully monitor for exercise intolerance, jugular or generalized venous distention, jugular pulses, ventral edema, prolonged recovery after exercise, increased resting heart rate or increase in the intensity of the murmur of tricuspid regurgitation; if detected, perform a cardiac reexamination

Surgical Considerations!!navigator!!

N/A

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

Treat affected horses in CHF with furosemide, torsemide, vasodilators such as benazepril or quinapril, or the inodilator pimobendan. Antimicrobials are indicated with infective endocarditis.

Contraindications!!navigator!!

  • ACE inhibitors are contraindicated in pregnancy
  • Diuretics, 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!!

N/A

Possible Interactions!!navigator!!

N/A

Alternative Drugs!!navigator!!

N/A

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

  • Frequently monitor cardiac rhythm and respiratory system
  • Annual echocardiographic reexaminations are recommended in moderate to severe cases

Prevention/Avoidance!!navigator!!

N/A

Possible Complications!!navigator!!

Chronic cases—AF; CHF.

Expected Course and Prognosis!!navigator!!

  • Many affected horses have normal performance and life expectancy
  • Prognosis for horses with tricuspid valve prolapse and mild regurgitation is excellent, and, in many, the amount of regurgitation remains unchanged for years
  • Progression of regurgitation associated with degenerative valve disease usually is slow. If regurgitation is mild, these horses have a good to excellent prognosis
  • Horses with ruptured chordae tendineae, flail tricuspid valve leaflets, or infective endocarditis have a more guarded prognosis, because the regurgitation usually becomes more severe and may result in a shortened performance and life expectancy
  • Affected horses with CHF usually have severe underlying valvular heart and myocardial disease and a guarded to grave prognosis for life
  • Most affected horses being treated for CHF respond to supportive therapy and improve. Such improvement usually is short lived, however. Most of these horses are euthanized within 2–6 months of initiation of treatment

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Associated Conditions!!navigator!!

Mitral regurgitation.

Age-Related Factors!!navigator!!

Physiologic regurgitation due to cardiac adaptation to athletic training is the most common form and is usually diagnosed in horses of racing age.

Zoonotic Potential!!navigator!!

N/A

Pregnancy/Fertility/Breeding!!navigator!!

  • Affected mares should not experience any problems with the pregnancy unless regurgitation is severe
  • The volume expansion of late pregnancy places an additional load on the already volume-loaded heart, which may precipitate CHF in mares with severe regurgitation
  • Pregnant mares with CHF should be treated 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!!

Tricuspid insufficiency.

Abbreviations!!navigator!!

Suggested Reading ⬆ ⬇

Leroux AA, Detilleux J, Sandersen CF, et al. Prevalence and risk factors for cardiac diseases in a hospital-based population of 3,434 horses (1994-2011). J Vet Intern Med 2013;27:1563–1570.

Reef VB. Heart murmurs in horses: determining their significance with echocardiography. Equine Vet J Suppl 1995;19:71–80.

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.

Stevens KB, Marr CM, Horn JN, et al. Effect of left-sided valvular regurgitation on mortality and causes of death among a population of middle-aged and older horses. Vet Rec 2009;164:6–10.

Young LE, Rogers K, Wood JL. Heart murmurs and valvular regurgitation in thoroughbred racehorses: epidemiology and associations with athletic performance. J Vet Intern Med 2008;22:418–426.

Author(s) ⬆

Author: Celia M. Marr

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

Acknowledgment: The author acknowledges the prior contribution of Virginia B. Reef.