The application of pulsed wave Doppler tissue imaging in the evaluation of cardiac function in cats with primary cardiomyopathy and disease states linked to specific cardiomyopathies in human-beings

Abstract

Cardiac dysfunction is commonly identified in geriatric cats. Disease may be primary, typically hypertrophic cardiomyopathy (HCM), or may occur in association with a number of specific diseases, such as hyperthyroidism or hypertension.

Doppler Tissue Imaging (DTI) techniques allow for the non-invasive assessment of myocardial dynamics. These techniques have previously demonstrated regional and global diastolic impairment in various forms of human cardiomyopathy and in cats with HCM.

The aim of this study was to characterise the echocardiographic findings in healthy geriatric cats and to compare these to the changes seen in geriatric cats with primary cardiomyopathy and disease states linked to specific cardiomyopathies in human beings. It was predicted that from this it might be possible to derive disease specific cardiac changes. In addition, it may be possible to elucidate the affect of medication on disease processes.

A total of 134 cats, aged eight years or above, were studied. Each cat underwent a conventional echocardiographic examination (two-dimensional, spectral Doppler, and M-mode) and a more advanced assessment of diastolic function (pulsed-wave Doppler tissue imaging [pw-DTI], colour M-mode propagation velocity and spectral Doppler assessment of the isovolumetric relaxation time). The cats were grouped according to either the disease process, or the diastolic filling pattern, and groups were then compared.

Pulsed-wave DTI tracings (of both radial and longitudinal velocity) were successfully recorded from the feline myocardium. The repeatability of these measurements was assessed, and generally found to be comparable to the variability reported in human beings. There was no evidence that pw-DTI velocities are affected by age in a normal geriatric cat population. Furthermore, there was no significant difference in the relationship between pw-DTI velocities and age in cats within any of the disease groups studied, although there was some variation with heart rate (as assessed by the R-R interval). In addition, it was demonstrated that when grouped according to the transmitral diastolic flow pattern and the ratio of transmitral A-wave duration to pulmonary venous atrial reversal duration, the pwDTI flow pattern recorded from the apical four chamber view (at either the lateral aspect of the mitral annulus, or mid-lateral wall) was able to differentiate normal from impaired relaxation and pseudonormal flow patterns.

Analysis of echocardiographic data demonstrated that there was an increase in the thickness of the basilar interventricular septum in the majority of cats studied. Compared to unaffected cats, cats with HCM had a decrease in the E' velocity (recorded by pw-DTI at the interventricular septum) and a tendency towards a decrease at the lateral aspect of the mitral annulus (recorded from the left apical fourchamber view). A similar decrease in the E' velocity in cats and people with HCM has been reported previously, and is thought to suggest diastolic dysfunction in affected individuals. Cats with chronic renal failure demonstrated some mild 2- dimensional and spectral Doppler abnormalities; however, no pw-DTI changes were detected in this group. The hyperthyroid cats demonstrated increased S' velocities, suggesting an increased inotropic state. In addition, the hyperthyroid cats demonstrated increased A' velocities, the cause of which was undetermined, but which may suggest mild diastolic dysfunction or an increase in atrial systolic function. A comparison of treated and untreated hyperthyroid cats was performed. This found that the treated hyperthyroid cats generally demonstrated less variation from the normal cats, compared to the untreated hyperthyroid cats, this may suggest that the use of carbimazole improves the function of the feline myocardium in thyrotoxic cardiomyopathy.

This work, for the first time, uses novel ultrasound techniques to investigate the myocardial dynamics in normal geriatric cats, cats with primary hypertrophy and cats with a range of disease states linked to specific cardiomypathies in human beings. The use of these techniques has provided us with a new insight into these disease processes and has evaluated the use of this clinically applicable tool for the evaluation of feline myocardial dynamics.