In this lecture, we compare human and feline cardiomyopathy and discuss controversies in current thinking and how to classify feline cardiomyopathy.

Diagnosis of Feline Cardiomyopathy

The classification system for feline cardiomyopathy requires updating, and there is poor agreement between cardiologists using the current system. One problem is that the current system does not account for the changes seen as heart disease progresses over time. For example, a cat may start being classified as hypertrophic cardiomyopathy (HCM), but as the myocardium becomes ischaemic and myocardial function deteriorates with time, the same individual may be classified as restrictive cardiomyopathy and then dilated cardiomyopathy over the coming years. Since many cats do not undergo serial echocardiography, and most patients have a single echo at the time of diagnosis, it is likely that many individuals are misclassified (“misdiagnosed”) at the outset, when they are in fact a case of advanced HCM.

Hypertrophic cardiomyopathy:

• Left ventricular myocardium measures ³6 mm in any 2D view, long or short axis
• No identifiable cause of LV hypertrophy; i.e., exclude hyperthyroidism, hypertension, infiltration (if possible), acromegaly, Cushing’s disease

Restrictive cardiomyopathy:

• Non-hypertrophic, nondilated LV
• Normal systolic function
• Left or bi-atrial dilation
• Restrictive inflow pattern on Doppler interrogation of mitral valve (can be present in any advanced heart disease with increased left atrial pressure)
• Bridging scar across the left ventricle (classified as endomyocardial form of RCM)

Dilated cardiomyopathy:

• Dilated, non-hypertrophic LV
• Subnormal systolic function

Arrhythmogenic right ventricular cardiomyopathy:

• Disproportionate right heart dilation
• Normal appearing LV
• Arrhythmias—usually ventricular—detected on ECG

Unclassified cardiomyopathy:

• Case which does not fit into any of the above classifications