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Doctoral thesis, 2000

Canine idiopathic dilated cardiomyopathy : epidemiology, histopathology and pathophysiology

Tidholm, Anna


Dilated cardiomyopathy (DCM), one of the most common heart diseases in dogs, is a disease of unknown etiology characterized by chamber dilatation and myocardial systolic and diastolic dysfunction, ultimately leading to congestive heart failure (CHF). Since the advent of echocardiography, myocardial hypokinesis and severe left atrial and ventricular dilatation without other detectable cardiac abnormalities have been regarded as diagnostic criteria for DCM. Canine DCM is often referred to as being breed specific. Reports on histologic characterization of DCM are scant in breeds other than the Doberman pinscher.

The aims of the studies presented here were (1) to characterize the clinical, electrocardiographic, radiographic, echocardiographic, and pathologic findings in a homogeneous (Newfoundlands) population and in a large, and with respect to breed heterogeneous, (comprising 38 breeds) population of dogs with DCM, (2) to estimate survival times and identify prognostic indicators for dogs presenting with CHF caused by DCM, (3) to determine the prevalence of attenuated wavy fibers in the myocardium of dogs and the sensitivity and specificity of this finding for DCM, (4) to determine the sensitivity of standard clinical-echocardiographic criteria for DCM, using post mortem findings for final diagnosis, (5) to determine the sequence of events regarding the development of attenuated wavy fibers in relation to echocardiographic evidence of chamber dilatation and myocardial hypokinesis in DCM, (6) to investigate the activity of the renin-angiotensin-aldosterone system (RAAS) and atrial natriuretic peptide (ANP) in dogs with asymptomatic and symptomatic DCM, and (7) to determine concentrations of circulating thyroid hormones in DCM, and whether the expression of mRNA coding for thyroid hormone receptors was altered in dogs with CHF due to DCM in comparison to dogs in CHF due to chronic valvular disease (CVD).

There were no major differences concerning clinical, electrocardiographic, radiographic, echocardiographic and histopathologic characteristics between the homogeneous group, i.e. Newfoundlands, and the heterogeneous group of dogs. DCM carries a poor prognosis in dogs, and only age at time of diagnosis and the presence of dyspnea or ascites can be used as prognostic markers. Young age at onset of clinical signs was the most significantrisk factor identified.

The histologic finding of attenuated wavy fibers has a very high sensitivity (99%) and specificity (100%) for canine idiopathic DCM. Attenuated wavy fibers may develop before any clinical or echocardiographic signs of heart disease are evident, thus indicating an early stage of DCM, which may be denoted “occult DCM”. Sensitivity of standard clinical and echocardiographic criteria for the diagnosis of DCM is 93%, when the final diagnosis is based on post mortem findings.

The RAAS and ANP concentrations were significantly increased in dogs with clinical signs of DCM, but not in dogs with subclinical DCM. Total thyroxine and triiodothyronine concentrations were not decreased in a majority of dogs with CHF caused by DCM. However, free thyroxine concentrations were significantly decreased in dogs with symptomatic DCM, compared to dogs with asymptomatic DCM and to normal control dogs. Messenger RNA for thyroid hormone receptor subtypes Bl and B2 was upregulated in dogs with CHF attributable to DCM or CVD.


dog; heart disease; dilated cardiomyopathy; asymptomatic dilated cardiomyopathy; epidemiology; histopathology; attenuated wavy fibers; thyroid hormone receptor; renin; angiotensin II; aldosterone; atrial natriuretic peptide.

Published in

Acta Universitatis Agriculturae Sueciae. Veterinaria
2000, number: 81
ISBN: 91-576-5932-X
Publisher: Swedish University of Agricultural Sciences

Authors' information

Swedish University of Agricultural Sciences, Department of Small Animal Clinical Sciences
Swedish University of Agricultural Sciences, Department of Animal Physiology
Karolinska Institute

UKÄ Subject classification

Clinical Science

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