Abstract
The basic hypothesis tested in this study was that dogs with dilated
cardiomyopathy have abnormal ventricular function, and that this can be detected
noninvasively using M-mode, two-dimensional (2D), and Doppler echocardiography, and
also by measuring myocardial ultrasonic integrated backscatter. An additional hypothesis
was that different breeds of dogs affected with DCM have a different clinical course, and
that differences in ventricular function between these breeds can be detected by
echocardiography or integrated backscatter measurements that might account for the
different prognosis
The aims of this study therefore were (1) to identify echocardiographic variables
that distinguished normal dogs from dogs with DCM; (2) to identify differences in
ventricular function using echocardiography between Dobermanns and English cocker
spaniels with DCM; and (3) to measure ultrasonic integrated backscatter in normal dogs and
in Dobermanns and Cocker spaniels with DCM.
In this group of Dobermanns, median survival time was 98 days (range 16 - 508
days), whereas median survival in the cocker spaniels was 512 days (range 51 to >1388
days), with 6/11 still alive at the time of writing (p < 0.002). All the measured M-mode
variables differed significantly between the normal dogs and the dogs with DCM. Compared
with the Dobermanns, the cocker spaniels had significantly increased LV free wall
thickening and increased LV diastolic diameter when indexed to body surface area. All the
2D echocardiographic variables were significantly different between the normal dogs and
dogs with DCM when corrected for body size, but there were no significant differences
between Dobermanns and cocker spaniels. Significant differences were found between
normal and DCM dogs in some but not all of the Doppler echocardiographic variables.
Cocker spaniels had higher mitral A wave velocities than the normal dogs, and decreased
mitral E/A ratios compared with both the other groups. Dobermanns had shorter isovolumic
relaxation times than the other groups
In the second part of this study, measurements were made of ultrasonic integrated
backscatter in selected regions of the left ventricle in normal dogs and dogs with DCM.
Ultrasonic integrated backscatter is a measurement of the power of the ultrasound signal
returned from the myocardium to the transducer. This backscattered signal reflects basic
tissue properties, and exhibits dynamic variation with contractile function that may represent
fundamental alterations in the shape, size and distribution of scatterers within the
myocardium. Consistent cyclic variation in integrated backscatter was observed in the LV
free wall and septum of the normal dogs, but this pattern was not consistently seen in the
DCM dogs. Differences were not seen between the Dobermanns and cocker spaniels,
although the number of cocker spaniels measured was small.
In conclusion, the DCM dogs had evidence of markedly reduced systolic function
compared with the normal dogs. The affected dogs had left atrial and left ventricular dilation
with thinner left ventricular walls. Although there was little evidence of any difference in
systolic function between the two affected breeds, there was evidence of different diastolic
function, with a tendency for Dobermanns to show a restrictive pattern of transmitral filling,
and cocker spaniels to show evidence of delayed relaxation. The different pattern of
diastolic dysfunction in the two breeds is consistent with the prognostic value ascribed to
transmitral flow patterns in human DCM patients: delayed relaxation patterns have been
associated with improved survival times in man. Reduced cyclic variation of ultrasonic
integrated backscatter was also seen in the dogs affected with DCM, although no differences
were found between the two affected breeds.