Clinical History
The cat presented for a chronic history of intermittent lethargy, episodic gait abnormalities (Go to video clip), muscle spasm and heart murmur.  Calicivirus infection was diagnosed as a kitten.  Episodes of lethargy were present throughout life, occurring every 2-6 weeks and lasting about 2 days, with the cat normal between episodes. During the episodes the cat is alert and responsive. Screening blood work was normal including serum creatine kinase and T4 concentrations.  Antibody titers for FeLV and FIV infection were negative.

Physical and Neurological Examination
The cat was bright and alert with no significant neurological abnormalities. A grade 2-3/6 right sided murmur with regular rhythm and fair quality synchronous femoral pulses was noted.  Given the episodic nature of the clinical signs, it was suspected that the gait changes and muscle spasms were secondary to hypertrophic cardiomyopathy and ventricular arrhythmias. A cardiac ultrasound examination was scheduled.

Diagnostic Testing
A cardiac ultrasound examination was performed and showed increased septal and left ventricular free wall thickness (Fig. A,B). The left ventricle was reduced in size in both systole and diastole. The valves were structurally normal although systolic anterior motion of the mitral valve was detected. The ECG on the ultrasound images shows the ventricular tachycardia the cat was experiencing (on image B most of the complexes are ventricular and the fewer smaller complexes are sinus beats).

Diagnosis and Outcome
A diagnosis of hypertrophic cardiomyopathy with ventricular tachycardia was made.  Treatment was initiated and included atenolol (12.5 mg PO once daily) and enalapril (2.5 mg PO once daily).  On recheck examination 1 month following initiation of therapy the cat was doing well and was normal according to the owner.  No episodes of gait abnormalities or muscle spasms had been noted by 3 months following initiation of  treatment, which was the longest the cat had gone without an episode.