Ebstein's anomaly

From Dog
Radiograph of a Jindo with Ebstein's anomaly, showing a globoid cardiac silhouette, distended caudal vena cava, dorsal displacement of the trachea, and an enlarged hepatic shadow[1]

Ebstein’s anomaly is a congenital heart disease of dogs characterized by downward displacement of the tricuspid valve leaflets (parietal and septal leaflets) into the right ventricle. It is considered a variant of tricuspid valvular dysplasia[2].

Consequently, the right ventricle is divided into an atrialized portion above the valve leaflets and a muscular portion below the valve leaflets. Due to high pressure in the right atrium, postnatal closure of the atrial septum is often incomplete, resulting in an atrial septal defect or patent foramen ovale[3].

As the dog matures, severe displacement of tricuspid valvular leaflets and valvular regurgitation occurs, leading to pulmonary hypertension, right-sided cor pulmonale and congestive heart failure, with consequential pulmonary edema, ascites and hepatomegaly.

In humans, maternal exposure to lithium and benzodiazepine has been implicated but such scenarios have not been reported in dogs[4].

This condition has also been reported in dogs with concurrent Cor triatriatum[5].

A predisposition has been reported in both genders of the Jindo, Labrador Retriever[6], Beagle[7] and Boxer breeds[8].

Clinically affected dogs usually present with severe ascites, cyanosis, respiratory distress and exercise intolerance[8]. On auscultation, there is usually an audible systolic murmur in the tricuspid area, and radiographic imaging usually shows cardiac enlargement, particularly of the right atrium[9].

A presumptive diagnosis can be made on clinical history and radiography, supported with an ECG finding of supraventricular tachycardia and bundle branch block with giant P waves[10].

A definitive diagnosis requires echocardiography and cardiac catheterization with intracardiac ECG studies. The echocardiographic features include apical displacement of the septal leaflet of the tricuspid valve, abnormalities in the morphology, or absence, of the septal or parietal tricuspid leaflets, eccentric leaflet coaptation, a markedly dilated right atrium, atrialized right ventricle, moderate-to-severe tricuspid regurgitation, and a dilated right ventricle, with decreased contractile performance[1].

Cardiac catheterization with intracardiac ECG studies often provides a definitive finding by measuring right ventricular electrical activity on the intracardiac ECG results with simultaneous right atrial pressure and waveform.

Treatment includes enalapril, pimobendan and furosemide together with anti-arrhythmic medication or catheter ablation for paroxysmal tachyarrhythmias, and oxygen support and phlebotomy for cyanosis.

Sildenafil may also be effective in dogs with secondary pulmonary hypertension[11].

The prognosis is dependent on the severity of right side heart failure and concurrent conduction disturbances, but some dogs may live for years with this condition.

References

  1. 1.0 1.1 Choi R et al (2009) Ebstein's anomaly with an atrial septal defect in a jindo dog. Can Vet J 50(4):405-410
  2. Hyun C & Park IC (2006) Congenital heart diseases in small animals: Part II. Potential genetic aetiologies based on human genetic studies. Vet J 171:256–262
  3. Shaughhnessy R (2004) Ebstein’s anomaly. In: Crawford MH, DiMarco JP, Paulus WJ, editors. Cardiology. 2nd ed. Tokyo: Mosby. pp:1335–1342
  4. Cohen LS et al (1994) A reevaluation of risk of in utero exposure to lithium. J Am Med Assoc 271:146–150
  5. Tobias AH et al (1993) Cor triatriatum dexter in two dogs. J Am Vet Med Assoc 202(2):285-290
  6. Andelfinger G et al (2003) Canine tricuspid valve malformation, a model of human Ebstein anomaly, maps to dog chromosome 9. J Med Genet 40(5):320-324
  7. Takemura N et al (2003) Ebstein's anomaly in a beagle dog. J Vet Med Sci 65(4):531-533
  8. 8.0 8.1 Chetboul V et al (2004) Congenital malformations of the tricuspid valve in domestic carnivores: A retrospective study of 50 cases. Schweiz Arch Tierheilkd 146:265–275
  9. Eyster GE et al (1977) Ebstein's anomaly: a report of 3 cases in the dog. J Am Vet Med Assoc 170(7):709-713
  10. Tilley LP & Liu SK (1977) Ebstein’s anomaly. J Am Vet Med Assoc 171:798-802
  11. Bach JF et al (2006) Retrospective evaluation of sildenafil citrate as a therapy for pulmonary hypertension in dogs. J Vet Intern Med 20:1132–1135