Tricuspid dysplasia

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Right-sided cardiomegaly associated with tricuspid dysplasia in a dog[1]
Abnormal attachment of papillary muscle to the notched, thickened leaflet of the tricuspid valve with no intervening cordae tendoneae[1]

Tricuspid valve dysplasia is an autosomal-dominant (partial penetrance) congenital heart disease of dogs characterized by malformation of the tricuspid valve complex, systolic regurgitation and right-sided congestive heart failure.

This defect, which primarily affects large purebred dogs such as the Labrador Retriever and German Shepherd, results in tricuspid insufficiency and systolic regurgitation of blood into the right atrium.

A variant of this disease is Ebstein's anomaly, characterized by downward displacement of the tricuspid valve leaflets (parietal and septal leaflets) into the right ventricle.

Concurrent mitral valve dysplasia[2], ventricular septal defects, subaortic stenosis, pulmonic stenosis or Situs inversus totalis[3] have been observed.

Although rare in dogs, the basal attachments of tricuspid valve may be ventrally displaced into the right ventricle (right ventricular atrialization), resulting in a further malformation named Ebstein's anomaly[4].

Clinical signs are normally seen in young dogs (1 - 2 years of age) but can present at an older age with symptoms of generalized weakness, exercise intolerance, syncope, ascites and pale mucus membranes. A cough may be present intermittently[5].

A tentative diagnosis can be established by auscultation of a harsh holosystolic ejection murmur at the right cardiac apex with radiographic evidence of cardiomegaly. Radiographs which show massive right atrium enlargement in a young animal with right apical systolic murmur is generally pathognomonic[4]. Cardiogenic pulmonary edema may also be present and the caudal vena cava may be significantly enlarged.

Definitive diagnosis requires use of M-mode and Doppler echocardiography. Echocardiography demonstrates malformation of the tricuspid valve and usually severe right atrial and ventricular dilatation. Also, the left heart is often smaller than normal. Tricuspid leaflets may have little movement, appear to be very large, or be adhered to the interventricular septum or to the papillary muscles[6]. Doppler echocardiography demonstrates severe tricuspid regurgitation.

A differential diagnosis would include subaortic stenosis, ventricular septal defect[7], double-chambered right ventricle[8], hyperthyroidism, cardiomyopathy, Duchenne muscular dystrophy, endocarditis, pulmonic stenosis, mitral valve endocardiosis and infections with Dirofilaria spp.

The prognosis for animals with clinical signs of congestive heart failuree is poor, but mildly affected animals may remain free of clinical signs for several years.

Medical therapy is currently the recommended treatment option, consisting of exercise restriction, atenolol, pimobendan[9] and taurine supplementation.

Surgical intervention can be employed in severe cases where financing is not a prohibitive issue. Techniques such as mitral valvular replacement have been employed successfully[10].

References

  1. 1.0 1.1 Sousa, MG et al (2006) Tricuspid valve dysplasia and Ebstein's anomaly in dogs: case report. Arq Bras Med Vet Zootec 58(5):October
  2. Domanjko-Petric A (2004) What is your diagnosis? Mitral and tricuspid dysplasia. J Small Anim Pract 45(2):83-84
  3. Piantedosi D et al (2011) Situs inversus totalis associated with subaortic stenosis, restrictive ventricular septal defect, and tricuspid dysplasia in an adult dog. Can Vet J 52(11):1237-1242
  4. 4.0 4.1 Kittleson, MD (1998) Congenital abnormalities of the atrioventricular valves. In: Kittleson, MD & Kienle, RD Small animal cardiovascular medicine. Saint Louis: Mosby. pp:273-281
  5. Hoffmann, G et al (2000) Tricuspid valve dysplasia in fifteen dogs. Schweiz Arch Tierheilkd 142:268-277
  6. Hirschklau, MJ et al (1977) Cross-sectional echocardiographic features of Ebstein's anomaly of the tricuspid valve. Am J Cardiol 40:400
  7. Guglielmini C et al (2002) Atrial septal defect in five dogs. J Small Anim Pract 43(7):317-322
  8. Fukushima R et al (2011) Epidemiological and morphological studies of double-chambered right ventricle in dogs. J Vet Med Sci 73(10):1287-1293
  9. Boswood A (2010) Current use of pimobendan in canine patients with heart disease. Vet Clin North Am Small Anim Pract 40:571–580
  10. Behr L et al (2007) Beating heart mitral valve replacement with a bovine pericardial bioprosthesis for treatment of mitral valve dysplasia in a Bull Terrier. Vet Surg 36(3):190-198