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Basics ⬇

Outline

BASICS

Definition!!navigator!!

  • A persistently patent vascular communication between the aorta and pulmonary artery
  • The ductus arteriosus is a vessel that allows blood to shunt from the pulmonary artery to the aorta in the fetus
  • The ductus arteriosus normally constricts after birth in response to increased local oxygen tension and prostaglandin inhibition, and closure should be complete within 4 days of birth

Pathophysiology!!navigator!!

  • When the ductus arteriosus remains patent, blood shunts from the higher pressure aorta to the lower pressure pulmonary artery, creating left atrial and left ventricular volume overload
  • Size of the PDA determines severity of the volume overload—with a large PDA, stretching of the mitral annulus occurs over time, and mitral regurgitation develops; as mitral regurgitation becomes more severe, left atrial pressure increases, resulting in increased pulmonary venous pressure and clinical signs of left-sided CHF
  • PDA may also be a component of more complex congenital cardiac defects

Systems Affected!!navigator!!

Cardiovascular

Genetics!!navigator!!

  • Not yet determined in horses
  • The condition is heritable in other species but rare in horses

Incidence/Prevalence!!navigator!!

PDA is a very rare, isolated congenital defect, but it occurs more frequently in horses with complex congenital heart disease.

Signalment!!navigator!!

  • Arabian horses appear to be predisposed to complex congenital cardiac defects
  • Murmurs usually are detectable at birth
  • Diagnosed most frequently in neonates, foals, and young horses but can be found at any age

Signs!!navigator!!

General Comments

May be an incidental finding but usually is part of a more complex congenital cardiac disorder.

Historical Findings

  • Exercise intolerance—medium-sized to large PDA and those associated with complex congenital cardiac defects
  • CHF—large PDA and those associated with complex congenital cardiac defects

Physical Examination Findings

  • A grade 3–6/6 continuous machinery murmur with point of maximal intensity over the main pulmonary artery between the pulmonic and aortic valve area
  • Additional loud murmurs may be detected in complex congenital cardiac defects, with characteristics dependent on the exact nature of the defects
  • Bounding arterial pulses
  • Premature beats or an irregularly irregular heart rhythm of atrial fibrillation may be present with larger PDA or those associated with complex congenital cardiac defects

Causes!!navigator!!

Lack of constriction of the ductus arteriosus.

Risk Factors!!navigator!!

  • Premature foal
  • Hypoxia
  • Neonatal pulmonary hypertension
  • Neonatal respiratory distress syndrome
  • Mares treated with prostaglandin inhibitors during late gestation

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

  • Physiologic flow murmur—usually systolic rather than continuous murmur; differentiate echocardiographically
  • Ventricular septal defect with aortic regurgitation—pansystolic and holodiastolic murmur and point of maximal intensity of pansystolic murmur, usually in the tricuspid valve area; differentiate echocardiographically
  • Complex congenital cardiac disease—differentiate echocardiographically

CBC/Biochemistry/Urinalysis!!navigator!!

N/A

Other Laboratory Tests!!navigator!!

N/A

Imaging!!navigator!!

ECG

Atrial premature depolarizations or atrial fibrillation may be present in horses with left atrial enlargement.

Echocardiography

  • Difficult to visualize
  • The left atrium and ventricle are enlarged and dilated and have a rounded appearance
  • Pulmonary artery dilatation in horses with a large shunt
  • Color-flow Doppler may reveal the shunt from aorta to pulmonary artery through the PDA
  • Continuous, high-velocity, turbulent flow is detected with continuous-wave Doppler toward the main pulmonary artery
  • Retrograde, turbulent flow in the main pulmonary artery may be identified with color-flow and continuous-wave Doppler
  • Additional cardiac defects such as great vessel anomalies, right atrioventricular valve atresia, or hypoplastic left ventricle syndrome may be present. A segmental approach where each structure is identified and its connection to other structures documented echocardiographically is required to differentiate complex congenital cardiac defects. Color-flow and contrast echocardiography may allow documentation of the path of blood flow in affected horses

Thoracic Radiography

  • Increased pulmonary vascularity and cardiac enlargement may be detected
  • Pulmonary edema may be detected in foals or horses with CHF

Other Diagnostic Procedures!!navigator!!

Cardiac Catheterization

  • Right-sided cardiac catheterization to directly measure pulmonary arterial and capillary wedge pressures and to sample blood for oxygen content
  • Elevated pulmonary arterial and capillary wedge pressures as well as increased oxygen saturation of pulmonary arterial blood are found in horses with PDA

24 h Holter Monitoring

Continuous monitoring is useful for establishing the diagnosis in horses with suspected atrial premature depolarizations.

Pathologic Findings!!navigator!!

  • The PDA is present between the aorta and main pulmonary artery
  • Left atrial and ventricular enlargement and thinning of the left atrial and ventricular free wall in horses with a significant shunt
  • Dilatation of the main pulmonary artery and right and left pulmonary arteries in those horses with a large shunt and in those with pulmonary hypertension
  • Thickened media of the pulmonary arterioles in horses with chronic pulmonary hypertension
  • Pulmonary edema in horses with CHF
  • PDA is often identified in conjunction with additional defects in a variety of complex congenital cardiac defects including hypoplastic left ventricle syndrome, transposition of the great arteries, critical pulmonic stenosis, and atresia of the right atrioventricular orifice

Treatment ⬆ ⬇

Outline

TREATMENT

Aims!!navigator!!

  • Management by intermittent monitoring in horses with small isolated PDA
  • Palliative care in horses with large PDA and those in which there are multiple cardiac defects

Appropriate Health Care!!navigator!!

  • Most newborn foals with PDA should have the underlying pulmonary disease or pulmonary hypertension treated if present
  • Monitor affected horses on an annual basis
  • Horse with PDA and CHF could be treated for the CHF with positive inotropic drugs, vasodilators, and diuretics. Consider euthanasia, however, because only short-term, symptomatic improvement can be expected

Nursing Care!!navigator!!

N/A

Activity!!navigator!!

  • Horses with a small PDA may be able to perform successfully at lower levels of athletic activities, but they are unlikely to be able to perform satisfactorily at upper levels
  • Monitor affected horses echocardiographically on an annual basis to ensure they are safe to ride. Dilatation of the pulmonary artery should prompt discontinuation of ridden activities as it can be a precursor to pulmonary artery rupture
  • Affected horses that develop atrial fibrillation need a complete cardiovascular examination to determine if lower levels of athletic performance are safe

Diet!!navigator!!

N/A

Client Education!!navigator!!

  • Regularly monitor the horse's rhythm; any irregularities other than second-degree atrioventricular block should prompt ECG examination
  • Carefully monitor the horse for exercise intolerance, respiratory distress, prolonged recovery after exercise, increased resting respiratory or heart rate, or cough; if detected, obtain a cardiac reexamination

Surgical Considerations!!navigator!!

  • Closure of the PDA is possible with a transvenous umbrella catheter or coil having a diameter large enough to close the defect
  • Surgical closure is not financially feasible or practical for obtaining an equine athlete at this time

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

N/A

Contraindications!!navigator!!

N/A

Alternative Drugs!!navigator!!

N/A

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

Frequently monitor the horse's cardiac rate, rhythm, respiratory rate, and effort.

Prevention/Avoidance!!navigator!!

N/A

Possible Complications!!navigator!!

Large PDA and those forming part of complex congenital cardiac defects—atrial fibrillation, CHF, and pulmonary artery rupture.

Expected Course and Prognosis!!navigator!!

  • Horses with a small PDA may have a normal performance life for lower levels of athletic competition and a normal life expectancy
  • Horses with a moderate to large PDA may develop atrial fibrillation and have a guarded prognosis; these horses should have a shortened performance life at lower levels of athletic competition and a shortened life expectancy
  • Horses with pulmonary artery dilatation have a grave prognosis for life and are not safe to ride
  • Horses with associated CHF usually have a guarded to grave prognosis for life. Most horses with a PDA being treated for CHF should respond to the supportive therapy and transiently improve, but once CHF develops euthanasia is recommended

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Associated Conditions!!navigator!!

  • Complex congenital cardiac disease is the rule, rather than the exception, in affected horses
  • Mitral regurgitation can develop in horses with PDA associated with stretching of the mitral annulus secondary to significant left atrial and ventricular volume overload
  • Pulmonary artery rupture can occur secondary to the pulmonary artery dilatation and elevated pulmonary arterial pressures

Age-Related Factors!!navigator!!

Young horses are more likely to be diagnosed with this defect.

Zoonotic Potential!!navigator!!

N/A

Pregnancy/Fertility/Breeding!!navigator!!

Breeding affected horses should be discouraged even though the condition is rare and the heritable nature of this defect is not known.

Synonyms!!navigator!!

N/A

Abbreviations!!navigator!!

  • CHF = congestive heart failure
  • PDA = patent ductus arteriosus

Suggested Reading ⬆ ⬇

Buergelt CD, Carmichael JA, Tashjian RJ, Das KM. Spontaneous rupture of the left pulmonary artery in a horse with patent ductus arteriosus. J Am Vet Med Assoc 1970;157:313–320.

Marr CM. Cardiac murmurs: congenital heart disease. In: Marr CM, Bowen M, eds. Cardiology of the Horse, 2e. Edinburgh, UK: Saunders Elsevier, 2010:187–197.

Reef VB. Cardiovascular ultrasonography. In: Reef VB, ed. Equine Diagnostic Ultrasound. Philadelphia, PA: WB Saunders, 1998:215–272.

Schwarzwald CC. Sequential segmental analysis—a systemic approach to the diagnosis of congenital cardiac defects. Equine Vet Educ 2008;20:305–309.

Scott EA, Kneller SK, Witherspoon DM. Closure of ductus arteriosus determined by cardiac catheterization and angiography in newborn foals. Am J Vet Res 1975;36:1021–1023.

Author(s) ⬆

Author: Virginia B. Reef

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