Feline Hypertrophic Cardiomyopathy Treatment

Good work on the echo. Your findings are classic for hypertrophic obstructive cardiomyopathy (HOCM). This cat is in ACVIM Stage B2 (structural disease with chamber enlargement, but no clinical signs of failure). My recommendations are as follows.

Treatment Plan:

Atenolol: I agree with starting atenolol. The goal is to alleviate the dynamic left ventricular outflow tract (LVOT) obstruction caused by the SAM. By reducing heart rate and contractility, atenolol lessens the Venturi effect pulling the mitral leaflet into the outflow tract. A typical starting dose is 6.25 mg per cat PO q12h. We can titrate this based on resting heart rate, aiming for 140-160 bpm in the clinic, but the primary goal is clinical stability.

Clopidogrel: Given the left atrial enlargement, thromboprophylaxis is indicated to reduce the risk of aortic thromboembolism (ATE). The standard dose from the FAT CAT study is 18.75 mg (one-quarter of a 75 mg tablet) PO q24h.

Contraindicated Medications: It is critical to avoid positive inotropes like pimobendan in this patient. By increasing contractility, pimobendan would worsen the LVOT obstruction and could precipitate hemodynamic collapse.

Monitoring:

* Home Monitoring: The most important tool is the sleeping respiratory rate (SRR). Instruct the owner to count breaths per minute while the cat is in a deep sleep. A sustained rate >30 breaths/min is the earliest sign of impending congestive heart failure (CHF) and should prompt an immediate recheck.
* Recheck Schedule: I would recommend a brief recheck in 10-14 days to assess tolerance to the atenolol and check blood pressure. Assuming the cat is stable, a full re-evaluation including echocardiogram in 6 months is appropriate to assess for disease progression.

Prognosis Discussion:

The prognosis for cats with subclinical HCM is highly variable. Some cats remain stable in Stage B2 for many years, while others can progress to CHF or experience an ATE event. The presence of LA enlargement is a negative prognostic indicator, but initiating therapy now is the correct approach to mitigate these risks. The key is diligent home monitoring by the owner to catch any transition into Stage C early.

Let me know if you encounter any issues with therapy or if the clinical picture changes.