Pimobendan Dosing for MMVD Stage B2

Excellent workup and accurate staging. This is a classic presentation for a Stage B2 Cavalier, and you've identified the key parameters that guide our intervention.

Yes, you should absolutely start pimobendan now. This dog meets the EPIC trial criteria perfectly: a characteristic murmur (grade ≥III/VI), echocardiographic evidence of significant cardiomegaly (LA:Ao ≥1.6 and LVIDdN ≥1.7), and is a breed predisposed to MMVD. Starting pimobendan at this stage has been definitively shown to delay the onset of congestive heart failure by an average of 15 months.

Here is the protocol I would recommend:

Pimobendan: Start at 0.25-0.3 mg/kg PO q12h. Counsel the owner to give it on an empty stomach (ideally one hour before meals) to maximize absorption. This is the cornerstone of therapy for this stage.

ACE Inhibitor (Enalapril/Benazepril): The evidence for ACE inhibitors in Stage B2 is less robust than for pimobendan. However, given the significant atrial enlargement (LA:Ao 2.1), it is a reasonable addition to mitigate RAAS activation. I would start enalapril at 0.5 mg/kg PO q12-24h. Be sure to check a baseline renal panel and blood pressure, then recheck renal values and electrolytes 5-7 days after initiation.

Furosemide: Do not start furosemide. This is critical. This patient has heart disease, but not heart failure. There is no evidence of fluid retention (congestion) to treat. Initiating a diuretic now will needlessly activate the RAAS, risk dehydration and azotemia, and provides no clinical benefit. Furosemide is reserved for Stage C (active or historical CHF).

Monitoring Plan:

* At Home: The single most important tool for the owner is monitoring the sleeping respiratory rate (SRR). Have them count breaths per minute while the dog is sound asleep. A consistent SRR of <30 breaths/min is our goal and indicates stability. An increase of >20% from baseline or a consistent rate >30-35 breaths/min is the earliest warning sign of impending CHF and should trigger a recheck.
* In Clinic: I would schedule a re-evaluation in 6 months. This should include a brief physical exam, blood pressure, and a repeat echocardiogram to assess disease progression. A renal panel should be checked every 6-12 months while on an ACE inhibitor.

This protocol is designed to prolong the asymptomatic period and maintain an excellent quality of life for as long as possible. Great job catching this at the ideal time for intervention.