Dilated cardiomyopathy (DCM) is common in pedigree dog breeds including
Newfoundlands. The breed predisposition and the familial prevalence within breeds support
a genetic basis to the disease. Familial occurrence of DCM has only recently been
recognised in man, and echocardiography abnormalities are common in relatives of DCM
Echocardiography is the method of choice for confirming the diagnosis of DCM.
Echocardiographic/Doppler data are presented from 223 scans from 165 individual
Newfoundland dogs. The scans were categorised into six groups based on the clinical
presentation, M-mode echocardiography results and the Doppler derived aortic velocity.
The Normal group showed no abnormalities (n=86). The DCM (overt or occult) group had
a rounded left ventricle and fractional shortening (FS) <22% (n=35). There were two
depressed fractional shortening groups, without other abnormalities; one with FS less than
18% (dFS<18%) (n=29) and the other with FS 18-20% (dFS18-20%) (n=24). The left
ventricular enlargement (LVE) group was defined as a LV diastolic dimension greater than
55mm (males) or >50 mm (females), without any M-mode evidence of systolic dysfunction
(n=8). Dogs with an aortic velocity exceeding 1.7 m/s were defined as showing evidence of
subaortic stenosis (SAS group) (n=40).
Data from complete echocardiographic/Doppler analysis of the Normal group were assessed
for dependence on the gender, age and size of dog (weight or body surface area (BSA)) and
the heart rate (mean R-R interval) by linear regression analyses. LV volumes and M-mode
measurements were positively correlated with size. Gender was not an important predictor
of most echo measurements once data was normalised for BSA. Advancing age was a
significant negative predictor of LV volumes and dimensions although influence on wall
thickness was not significant. Age also showed a significant influence on diastolic function,
assessed by mitral inflow and pulmonary venous flow, similar to changes described in man.
The Newfoundland groups were compared. The DCM group had significantly increased LV
volume and dimensions and decreased systolic function than other groups. There were few
significant differences between the groups for diastolic function parameters. There was
considerable overlap between groups for all dimensions and the parameters of systolic
function, although the pre-ejection period: ejection time (PEP:ET) ratio appeared to be most
sensitive for distinguishing normal from DCM dogs. In both dFS groups and the LVE group,
this ratio was intermediate between the Normal and DCM groups, in contrast to other
parameters of systolic function. Left atrial dysfunction was also identified in the DCM
group, but was less marked in both dFS and the LVE groups. Some dogs in the LVE and
dFS groups progressed to develop DCM but a longer duration of study would be required
before firm conclusions can be drawn about progression.
Most of the dogs in this study were related. Pedigree and segregation analyses were
supportive but not conclusive for an autosomal dominant mode of inheritance for DCM. A
simulated linkage analysis indicated that this family was sufficiently informative for a
genetic linkage analysis study. A pilot study assessing a number of anonymous canine
microsatellites confirmed that there was sufficient heterozygosity and polymorphism,
despite significant inbreeding, to permit a genetic linkage analysis study. No significant
LOD score was achieved for the twelve microsatellites assessed. However, the available
data indicate that a genome-wide linkage analysis is likely to be successful, with
phenotyping based on the echocardiography data.