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Basics ⬇

Outline

BASICS

Definition!!navigator!!

A defect in the wall of the aorta at the aortic root, usually in the right sinus of Valsalva or the aortic arch.

Pathophysiology!!navigator!!

  • Aortic rupture can result in dissecting aneurysm, exsanguination into the thoracic cavity, cardiac tamponade from hemopericardium; a shunt between the aorta and heart if the defect is located in the aortic root; or a shunt between the aorta and pulmonary artery if the defect is located in the aortic arch
  • With an aortic rupture confined to the right sinus of Valsalva, an aorticocardiac fistula is created. Blood from the aorta shunts into the right side of the heart, at either the atrial or ventricular level, depending on the site of the rupture
  • Subendocardial dissection of blood into the interventricular septum is common, with subsequent rupture into the right or left ventricle (more commonly, the rupture is into the right ventricle)
  • Often associated with a unifocal ventricular tachycardia that may be associated with dissection of blood into the interventricular septum
  • Aortic arch rupture leads to periaortic hematoma, aortopulmonary fistulation, and pseudoaneurysm

Systems Affected!!navigator!!

Cardiovascular

Incidence/Prevalence!!navigator!!

Rare

Signalment!!navigator!!

  • Aortic root rupture more frequently occurs in old horses, particularly males and often during or after breeding or other exercise
  • The Friesian breed is predisposed to aortic arch rupture and signs occur in young adults

Signs!!navigator!!

General Comments

Often interpreted by owners as colic, because the horse appears distressed, may be looking at its flanks, and acts uncomfortable.

Historical Findings

  • Acute onset of colic or distress, particularly with aortic root rupture
  • Subacute or chronic low-grade colic, particularly with aortic arch rupture
  • Less commonly, exercise intolerance; syncope, CHF

Physical Examination Findings

  • Tachycardia
  • Tachypnea
  • Continuous machinery murmur—usually loudest on the right side
  • Bounding arterial pulses
  • Other, less common findings—jugular pulses and distention, ventricular tachycardia (unifocal), and CHF

Causes!!navigator!!

  • A congenital aneurysm in the wall of the aortic root, usually in the right sinus of Valsalva, predisposes to aortic root rupture
  • Necrosis and degeneration of the aortic media have been associated, especially in old breeding stallions
  • Aberrant parasite migration in the ascending aorta is unlikely
  • Hereditary connective tissue disorders suspected to be an underlying cause in Friesians

Risk Factors!!navigator!!

  • Aortic aneurysm
  • Aortitis
  • Friesian breed

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

Ventricular Septal Defect with Aortic Regurgitation

  • Murmurs are systolic (band shaped and pansystolic) and diastolic (holodiastolic and decrescendo), not continuous
  • Arterial pulses usually are not bounding, unless the associated aortic regurgitation is severe
  • No history of acute colic or distress
  • Differentiate echocardiographically

Patent Ductus Arteriosus

  • No history of acute colic or distress
  • No unifocal ventricular tachycardia
  • Differentiate echocardiographically

CBC/Biochemistry/Urinalysis!!navigator!!

Increased serum creatinine and blood urea nitrogen may occur because of impaired renal perfusion, which is associated with sustained ventricular tachycardia and blood loss.

Other Laboratory Tests!!navigator!!

Serum cardiac troponin I can be elevated with significant myocardial cell injury.

Imaging!!navigator!!

ECG

Uniform ventricular tachycardia with a heart rate of >100 bpm may be present with aortic root rupture.

Echocardiography

  • 2-dimensional echocardiography is diagnostic for a defect in the aortic root at the sinus of Valsalva or for a sinus of Valsalva aneurysm
  • The rupture may be a small, irregular defect in the aortic wall (usually associated with the right aortic leaflet) or be visualized flailing in the right atrium or ventricle
  • Anechoic to echoic fluid may be detected dissecting subendocardially into the interventricular septum, most frequently along the right ventricular side; however, dissection of blood subendocardially along the left side also occurs
  • Use color-flow Doppler, pulsed-wave Doppler, or contrast echocardiography to localize the shunt associated with the aortic cardiac fistula
  • Transthoracic echocardiography may demonstrate pulmonary artery dilation, displacement of the pulmonary artery, and aortopulmonary fistulation (best visualized from the left cranial window) with aortic arch rupture
  • Transesophageal echocardiography is potentially useful with aortic arch rupture

Thoracic Radiography

  • An enlarged cardiac silhouette should be present in horses with a large aorticocardiac shunt
  • Pulmonary overcirculation and edema may be detected

Other Diagnostic Procedures!!navigator!!

Cardiac Catheterization

  • Elevated right ventricular pressure, pulmonary arterial pressure, pulmonary capillary wedge pressure, and oxygen saturation of the blood are detected in horses with aorticocardiac fistula into the right ventricle
  • With a shunt into the right atrium, right atrial pressures and oxygen saturation also are elevated

Arterial Blood Pressure

Demonstrates the wide difference between peak systolic pressure and end-diastolic pressure associated with continuous shunting of blood from the aorta into the heart.

Pathologic Findings!!navigator!!

  • Postmortem examination confirms the site and extent of the rupture and the presence of aorticocardiac or aortopulmonary fistula
  • Path of the dissection can be traced
  • Dissecting tracts into the interventricular septum usually are lined with immature and mature fibrous tissue, and disruption of the conduction system has been detected
  • Degeneration and necrosis of the aortic media have been reported in some horses with aortic rupture but not in other affected horses
  • An absence of media in the right sinus of Valsalva was reported in one horse with a sinus of Valsalva (i.e. aortic root) aneurysm
  • Fibrosis and scarring of the rupture site have been reported in old breeding stallions that died of unrelated causes

Treatment ⬆ ⬇

Outline

TREATMENT

Aims!!navigator!!

Palliative care.

Appropriate Health Care!!navigator!!

  • Closely monitor affected horses with ventricular tachycardia if the tachycardia is uniform, the heart rate is <100 bpm, no R-on-T complexes are detected, and no clinical signs of cardiovascular collapse are observed
  • If ventricular tachycardia is multiform, R-on-T complexes are detected, heart rate is >100 bpm, or with clinical signs of cardiovascular collapse, institute antiarrhythmic treatment on an inpatient basis
  • If CHF also is present, institute treatment for CHF as well. Consider humane euthanasia, however, because the horse is no longer safe to use for athletic work

Nursing Care!!navigator!!

  • Perform continuous ECG monitoring during the attempted conversion from ventricular tachycardia to sinus rhythm
  • Keep horses quiet and unmoving during antiarrhythmic treatment

Activity!!navigator!!

  • Stall confinement until conversion to sinus rhythm has been successfully achieved
  • Restrict athletic activity as much as possible once ventricular tachycardia has been converted

Client Education!!navigator!!

  • Affected horses are not safe to ride or use for any type of athletic work because of the risk of sudden death associated with further aortic rupture or development of fatal ventricular arrhythmia
  • If the horse is a breeding stallion and such continued use is desired, warn the stallion and mare handlers (and all other personnel involved) about the risk of sudden death
  • Develop an emergency plan in the event the stallion becomes unsteady or unsafe to handle

Surgical Considerations!!navigator!!

N/A

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

Antiarrhythmics

  • Indicated with multiform ventricular tachycardia, R-on-T complexes, heart rate >120 bpm, or clinical signs of cardiovascular collapse
  • Drug selection depends on severity of ventricular tachycardia and associated clinical signs
  • Lidocaine (0.25 mg/kg IV slowly, can repeat in 5–10 min) is rapid acting and has a very short duration of action. However, it also has central nervous system effects in horses and, thus, must be used carefully
  • Procainamide (1 mg/kg/min IV to total dose of 20 mg/kg) and quinidine gluconate (0.5–2.2 mg/kg IV every 10 min to total dose 10 mg/kg) have been effective in converting sustained, uniform ventricular tachycardia but have a slower onset of action
  • Magnesium sulfate (2.2–4.4 mg/kg IV slowly, can repeat in 5 min to total dose of 55 mg/kg) has been successful in converting sustained ventricular tachycardia and is not arrhythmogenic

Contraindications!!navigator!!

Other vasodilators or antihypertensive drugs have the potential to adversely affect the stallion's libido, breeding performance, or fertility.

Precautions!!navigator!!

Affected horses could experience sudden death at any time; thus, everyone working around these horses must be aware of the safety issues involved.

Possible Interactions!!navigator!!

Any antiarrhythmic drug has the potential to cause development of a more adverse arrhythmia as well as to convert to sinus rhythm.

Alternative Drugs!!navigator!!

Propranolol

  • The IV form is less likely to be effective but should be considered in affected horses with refractory ventricular tachycardia
  • Lowers systolic blood pressure

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

  • Routine monitoring of heart rate and of respiratory rate and rhythm after conversion to sinus rhythm
  • Persistent tachypnea, tachycardia, or new arrhythmias indicate deterioration in clinical status
  • Return of venous distention and jugular pulsations or development of ventral edema or coughing indicate the onset of CHF and worsening of ventricular volume overload

Prevention/Avoidance!!navigator!!

  • With intact aneurysms of the sinus of Valsalva, control of systemic blood pressure may prolong the time until rupture occurs
  • With degenerative changes in the aortic media, antihypertensive drugs theoretically should have some benefit. However, identification of horses at risk has not yet been accomplished

Possible Complications!!navigator!!

  • Deterioration of uniform ventricular tachycardia into fatal ventricular arrhythmia
  • Severe, acute CHF from massive right atrial or ventricular, left atrial, and left ventricular volume overload
  • Tricuspid valve rupture, leading to massive tricuspid regurgitation and CHF
  • Rupture of a chorda tendinea of the tricuspid or mitral valve, leading to massive tricuspid or mitral regurgitation, respectively, and acute right- or left-sided CHF
  • Sudden death

Expected Course and Prognosis!!navigator!!

  • Prognosis for life of affected horses is grave and sudden death is possible
  • Although the condition is invariably fatal, some horses can live relatively comfortably for several months after diagnosis

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Associated Conditions!!navigator!!

Aortic root aneurysm.

Age-Related Factors!!navigator!!

Old horses are more likely to be affected with aortic root rupture, but horses as young as 4 years have been diagnosed. Aortic arch rupture typically presents in horses <4 years old.

Pregnancy/Fertility/Breeding!!navigator!!

  • Rupture of a sinus of Valsalva aneurysm has been seen in one late-gestation pregnant mare. The volume expansion of late pregnancy may predispose pregnant mares to aortic rupture at this time
  • Aortic root rupture has been seen in one mare during early pregnancy. This mare experienced acute onset of ventricular tachycardia and subendocardial dissection of blood into the interventricular septum but survived to have the foal

Synonyms!!navigator!!

  • Aortic cardiac fistula
  • Aorticocardiac fistula

Abbreviations!!navigator!!

CHF = congestive heart failure

Suggested Reading ⬆ ⬇

Lester GD, Lombard CW, Ackerman N. Echocardiographic detection of a dissecting aortic root aneurysm in a Thoroughbred stallion. Vet Radiol Ultrasound 1992;33:202–205.

Marr CM, Reef VB, Brazil T, et al. Clinical and echocardiographic findings in horses with aortic root rupture. Vet Radiol Ultrasound 1998;39:22–31.

Ploeg M, Saey V, van Loon G, Delesalle C. Thoracic aortic rupture in horses. Equine Vet J 2017;49(3):269–274.

Reef VB, Klump S, Maxson AD, et al. Echocardiographic detection of an intact aneurysm in a horse. J Am Vet Med Assoc 1990;197:752–755.

Roby KA, Reef VB, Shaw DP, Sweeney CR. Rupture of an aortic sinus aneurysm in a 15-year-old broodmare. J Am Vet Med Assoc 1986;189:305–308.

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.