Case 21 — Case Discussion

Freckles was a 10-year-old cat that presented with signs of caudal aortic thromboembolism (rear limb paralysis, cold limbs, cyanotic nail beds and pads, lack of femoral pulses). He was in left heart failure producing pulmonary edema (visible caudal to the heart, ventral to the caudal vena cava) and a small amount of pleural effusion. The left auricle was so large it touched the lateral chest wall and stood out as a denser structure on the lateral radiograph.

Because the left atrium was massively enlarged, blood flow velocity was severely slowed, causing red cells to clump (spontaneous contrast/echocardiographic smoke). It was presumed that Freckles had previously formed a left atrial thrombus that broke loose and was carried to his terminal aorta.

Freckles had hypertrophic cardiomyopathy (HCM) evident only in his free wall and papillary muscles — a relatively common variant. The increased stiffness of the left ventricular chamber increased diastolic pressure, transmitted to the left atrium (open mitral valve in diastole), causing the atrium to enlarge like a balloon. This same pressure caused pulmonary edema and pleural effusion.

The ECG revealed atrial fibrillation (~240 bpm, fast, irregular, supraventricular, no P waves). Only cats with severe left atrial enlargement develop atrial fibrillation. PVCs were also present due to severe left ventricular disease.

Freckles also had pericardial effusion and a mass in the pericardial space, most likely a thrombus from left atrial rupture into the pericardial space — rare in cats but plausible given the association with the left auricle.

Freckles was started on Lasix (10 mg IV then 10 mg IM q6h) and heparin (1400 U SQ TID).

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