Hypertrophic cardiomyopathy

From Dog
Characteristic ventricular hypertrophy visible on cross-section of the heart[1]

Hypertrophic cardiomyopathy (HCM) is a rare congenital heart disease of dogs characterized by occult heart disease and sudden death[2][3].

Hypertrophic cardiomyopathy, defined as inappropriate myocardial hypertrophy of a nondilated left ventricle, may occur in the absence of an identifiable stimulus for the hypertrophy (congenital) or secondary to other cardiac abnormalities such as mitral valve dysplasia[4].

Functionally, HCM results in dynamic left ventricular outflow tract obstruction and reduced diastolic filling[5].

This disease has been more commonly observed in older Rottweiler and Dalmatian breeds[6], although a wide range of ages and breeds are affected[7], where anesthetic risks with this condition are considered high due to development of intraoperative hypotension[8].

Clinical signs are often absent, but a systolic heart murmur or arrhythmia may be detected on auscultation.

A tentative diagnosis can be established by radiographic evidence of cardiomegaly and pulmonary edema[9].

Echocardiography in older dogs with chronic hypertrophic cardiomyopathy usually show signs of thickened mitral valve, left atrial enlargement, excess motions of the left ventricular free wall and the ventricular septum, and tricuspid, mitral and aortic valve regurgitation[10].

ECGS may show sinus bradycardia, atrial fibrillation, atrial premature complexes and ventricular premature complexes.

A definitive diagnosis unfortunately requires postmortem examination of the heart, which usually shows left ventricular and interventricular septal hypertrophy of equal magnitude, with impact lesion and plaques on the interventricular septum. The mitral valve has often migrated into the left ventricular outflow tract.

Histologically, one usually observes intimal hyperplasia, hypertrophy, and smooth muscle hyaline degeneration of coronary arteries[11] as well as focal myocardial necrosis, fibrosis, and dystrophic calcification.

A differential diagnosis would include ventricular septal defect[12], double-chambered right ventricle[13], hyperthyroidism, arrythmogenic right ventricular cardiomyopathy, endocardial amyloidosis, endocarditis, mitral valve endocardiosis, other causes of congestive heart failure and infections with Dirofilaria spp.

A possible association with canine parvovirus infection has been postulated by not proven[14], and seems unlikely due to the absence of any microscopic inflammatory disease associated with this condition.

Treatment is usually conservative, with management of the secondary congestive heart failure using furosemide and pimobendan.

Surgical correction can be performed at specialty referral centers via balloon valvuloplasty.

References

  1. Quizlet
  2. Sisson D et al (1999) Myocardial diseases of dogs. In: Fox PR, Sisson D, Moise NS, eds. Textbook of Canine and Feline Cardiology. 2nd ed. Philadelphia: WB Saunders. pp:601–606
  3. Baumgartner C & Glaus TM (2004) Acquired cardiac diseases in the dog: a retrospective analysis. Schweiz Arch Tierheilkd 146(9):423-430
  4. De Majo M et al (2003) Hypertrophic obstructive cardiomyopathy associated to mitral valve dysplasia in the Dalmatian dog: two cases. Vet Res Commun 27(1):391-393
  5. Pang D et al (2005) Sudden cardiac death associated with occult hypertrophic cardiomyopathy in a dog under anesthesia. Can Vet J 46(12):1122-1125
  6. Washizu M et al (2003) Hypertrophic cardiomyopathy in an aged dog. J Vet Med Sci 65:753–756
  7. Liu SK et al (1979) Canine hypertrophic cardiomyopathy. J Am Vet Med Assoc 174:708–713
  8. Gaynor JA et al (1999) Complications and mortality associated with anesthesia in dogs and cats. J Am Anim Hosp Assoc 35:13–17
  9. Larsson MH et al (1997) Endocardial fibroelastosis in a dog. J Small Anim Pract 38(4):168-170
  10. Washizu M et al (2003) Hypertrophic cardiomyopathy in an aged dog. J Vet Med Sci 65(6):753-756
  11. Liu SK et al (1993) Comparison of morphologic findings in spontaneously occurring hypertrophic cardiomyopathy in humans, cats and dogs. Am J Cardiol 72:944–951
  12. Guglielmini C et al (2002) Atrial septal defect in five dogs. J Small Anim Pract 43(7):317-322
  13. Fukushima R et al (2011) Epidemiological and morphological studies of double-chambered right ventricle in dogs. J Vet Med Sci 73(10):1287-1293
  14. Levin S (1980) Parvovirus: a possible etiologic agent in cardiomyopathy and endocardial fibroelastosis. Hum Pathol 11(5):404-405