Arrythmogenic right ventricular cardiomyopathy (ARVC) is a relatively rare condition in cats. It is more common in some canine breeds, particularly Boxers (MacDonald, 2008). It is caused by fibrofatty infiltration of the right ventricle (Fuentes, 2002). Its hallmarks are:
- Dilated right heart (typically both the right ventricle and right atrium)
- Significant tricuspid regurgitation, secondary to annular dilatation
- The right ventricular wall may be thin and aneurysmal (Fox et al., 2000)
- Right-sided congestive heart failure – pleural effusions and ascites are common.
There may be varying degrees of left-sided involvement. The video clip below is of a six year old Burmese cat who presented with dyspnoea, ascites and a large pleural effusion. The vet drained the majority of the pleural effusion prior to echo. The echo was performed with the cat in the sitting position, so as not to cause her any distress.
Even without ECG, tachyarrythmia is evident. The ventricles are barely contracting. The right heart is severely dilated – particularly the right atrium. The left atrium also looks prominent.
There is severe (torrential) tricuspid regurgitation shown on colour Doppler below, arising centrally. The valve leaflets themselves appear normal, and there is clearly severe annular dilatation (look at the size of the right atrium!), so we can be confident that the severe regurgitation is not due to primary valve disease; it is due to a complete failure of leaflet coaptation.
The Continuous Wave Doppler trace
The density of the Continuous Wave Doppler trace can provide us qualitative information about the severity of tricuspid regurgitation. Most importantly, the Bernoulli equation (4v2) can be applied to the peak TR velocity to estimate right ventricular systolic pressure. A peak tricuspid regurgitation velocity of 3m/s, for example, would correspond to an estimated right ventricular systolic pressure of 36mmHg + an estimation of right atrial pressure.
In cats and dogs, due to the difficulties in estimating right atrial pressure, a good rule of thumb is that a TR velocity of 3m/s or greater is an indicator of elevated right ventricular systolic pressure (RVSP).
In the absence of pulmonary stenosis, RVSP = PASP (pulmonary artery systolic pressure). For this reason, obtaining the peak TR velocity allows us to estimate PASP.
The above CW Doppler trace, with the regurgitant jet shown below the baseline, is certainly dense – the same density as the forward flow above the baseline, in fact. As well as severe regurgitation, this cat almost certainly has elevated pulmonary pressures, but when regurgitation is almost free-flow in this way then the gradient obtained from the CW trace is not particularly helpful. The lack of coaptation means that there is almost equalisation of pressure between the right ventricle and right atrium; the pressure gradient between the two chambers is, therefore, unimpressive. In this cat, the peak is only 0.8m/s.
Beginners often confuse the velocity of the tricuspid regurgitant (TR) jet with the severity of the TR. It is possible to have elevated pulmonary pressures and therefore a high peak TR velocity on continuous wave Doppler with only trivial or mild tricuspid regurgitation; equally, this case demonstrates how it is possible to have severe TR without a high velocity on continuous wave Doppler.
ARVC in cats is often a diagnosis of exclusion. Unfortunately, it carries a very poor prognosis, and this particular cat had to be put down due to kidney failure before a definitive diagnosis could be made by a cardiologist.
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Fox, P., Maron, B., Basso, C., et al. (2000). Spontaneously Occurring Arrhythmogenic Right Ventricular Cardiomyopathy in the Domestic Cat. Circulation, 102:1863-1870.
Fuentes, V. (2002). Feline Cardiomyopathy – Establishing a Diagnosis. The Ohio State University.
MacDonald, K. (2008). Essential tools for diagnosis of feline heart disease and heart failure. Proceedings of the International SCIVAC Congress.