Ultrasound studies of dilated cardiomyopathy in Dobermanns and English cocker spaniels

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 prognosisThe 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 groupsIn 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.