New Murmur in a Cavalier — When to Start Treatment

This is an interesting case, particularly given the breed, as Cavaliers are so predisposed to myxomatous mitral valve disease. The owner's proactive approach regarding pimobendan is also very common in these situations.

However, I need to be transparent: this case falls completely outside my area of expertise. As a feline-exclusive practitioner, my entire practice is dedicated solely to cats. I do not see canine patients, and therefore, canine cardiology, including the staging and treatment protocols for MMVD, is not something I actively manage or stay current on. My focus is entirely on feline-specific conditions and the unique physiology and responses of cats.

For a detailed workup, differentiation between Stage B1 and B2 MMVD, and the decision tree for starting pimobendan in a Cavalier King Charles Spaniel, I would strongly recommend consulting with a board-certified veterinary cardiologist. They will be able to provide the most current, evidence-based guidelines and specific recommendations based on the echocardiographic findings once available. They'll also be best equipped to discuss the EPIC study and current ACVIM consensus guidelines relevant to this specific scenario.

For an asymptomatic 6-year-old CKCS with a murmur, you absolutely wait on pimobendan until you have a proper workup. The echo is essential.

Here’s my approach:

Immediate Priority: Echocardiogram.

* You can't differentiate Stage B1 from Stage B2 without a good quality echocardiogram. This is non-negotiable for this breed with this murmur.
* The echo must assess left atrial and left ventricular size and function, quantify mitral regurgitation, and measure pulmonary pressures. Specific measurements (e.g., LA:Ao ratio, LVIDdN) are key.
* If you can get a specialist to do it, great. If not, get the best images you can, measure meticulously, and consider a telemedicine cardiology consult for interpretation if you're unsure.

Supporting Diagnostics:

* Thoracic Radiographs (2-3 views): Critical for assessing cardiomegaly (VHS, specific chamber enlargement) and ruling out early pulmonary edema or other lung pathology. This is a baseline. My clients can afford films, and they give you a lot of information.
* Blood Pressure: Baseline systemic blood pressure.
* Full Bloodwork (CBC/Chem/UA): Assess overall health, kidney function before considering long-term medication.

Decision Tree for Stage B1 vs. B2 (Based on ACVIM Consensus):

* Stage B1:
Definition: MVD present (murmur), but no* echocardiographic or radiographic evidence of cardiac remodeling (i.e., no left atrial or left ventricular enlargement).
* Action: Do NOT start pimobendan. It provides no benefit at this stage and adds cost.
* Monitoring: Recheck annually with radiographs and physical exam. Consider repeat echo every 12-18 months, or sooner if clinical signs develop (e.g., cough, decreased exercise tolerance).

* Stage B2:
Definition: MVD present (murmur), with* echocardiographic and/or radiographic evidence of significant cardiac remodeling (left atrial and/or left ventricular enlargement), but the dog is still asymptomatic.
* Specific Criteria (Echo-based, these are what you need from the echo):
* Left atrial-to-aortic root ratio (LA:Ao) ≥ 1.6
* Left ventricular internal diameter in diastole, normalized for body weight (LVIDdN) ≥ 1.7
* Mitral regurgitation velocity (Vmax) typically > 5.0-5.5 m/s.
* Action: Start pimobendan. The EPIC study clearly demonstrated that starting pimobendan at this stage significantly delays the onset of clinical congestive heart failure and prolongs survival. This is a game changer for these dogs.
* Pimobendan Dose: 0.25-0.3 mg/kg orally BID. I usually recommend giving it on an empty stomach (30-60 minutes before food) for optimal absorption.
* Monitoring: Recheck physical exam and radiographs every 3-6 months. Monitor for any signs of progression to CHF.

In summary: Get the echo. Without it, you cannot accurately stage the disease. Do not start pimobendan until you confirm Stage B2 criteria.

This is a classic presentation in a breed highly predisposed to myxomatous mitral valve disease (MMVD), so it's excellent that you've scheduled an echocardiogram. That's the critical next step, and frankly, without it, any decision on pimobendan would be purely speculative and potentially counterproductive.

My primary advice is to wait for the echocardiogram results before initiating pimobendan.

Here's how I approach this decision tree for Stage B1 vs. B2 MMVD:

Understand the Stages:

* ACVIM Stage B1: Patients with a murmur but no evidence of cardiac enlargement on radiographs or echocardiography. These dogs are truly asymptomatic.
* ACVIM Stage B2: Patients with a murmur and evidence of cardiomegaly (left atrial and/or left ventricular enlargement) consistent with MMVD, but are still asymptomatic. This is the stage where the EPIC study demonstrated a significant benefit for pimobendan.

The Essential Diagnostic Workup:

* Echocardiogram (Primary): This is non-negotiable for staging. It directly assesses chamber sizes, valve morphology, and blood flow dynamics. For this 6-year-old CKCS, we're specifically looking for:
* Left atrial-to-aortic root ratio (LA:Ao) > 1.6
* Left ventricular internal diameter in diastole normalized to body weight (LVIDdN) > 1.7
* Mitral valve regurgitation velocity > 2.2 m/s (indicates significant regurgitation)
* Presence of ruptured chordae tendineae (though less likely in B2)
These criteria, especially the LA:Ao and LVIDdN, are what distinguish B1 from B2.
* Thoracic Radiographs (Secondary/Baseline): While the echo is paramount for precise chamber measurement, radiographs can provide a valuable baseline for overall heart size (Vertebral Heart Scale – VHS) and rule out pulmonary edema (which would place the dog in Stage C). I always get them.
* Bloodwork: A baseline CBC, biochemistry panel, and urinalysis are important before starting any long-term medication, especially to assess renal function.
* Blood Pressure: Good practice for any geriatric or cardiac patient.

Decision on Pimobendan:

* If the echocardiogram confirms Stage B1: Do NOT start pimobendan. The EPIC study specifically showed no benefit, and potentially a detriment, to starting pimobendan in Stage B1 MMVD. It adds unnecessary cost, potential side effects, and can accelerate disease progression in some cases where it's not indicated. We would monitor this patient with annual physical exams, recheck radiographs, and potentially echocardiograms every 12-18 months.
* If the echocardiogram confirms Stage B2: Yes, initiate pimobendan. The evidence from the EPIC study is compelling. Pimobendan significantly prolongs the pre-clinical period (time to onset of congestive heart failure or cardiac death) by an average of 15 months. The standard dose is 0.25-0.3 mg/kg PO BID. I start at 0.25 mg/kg BID, ideally on an empty stomach about an hour before meals, though some owners find it easier to dose with a small amount of food.

Fear Free Integration for the Echocardiogram:
An echocardiogram requires the patient to lie still for an extended period, which can be incredibly stressful. Even in an otherwise 'calm' dog, the unfamiliarity, noise, and restraint can trigger anxiety that elevates heart rate and can even impact diagnostic accuracy.

For this CKCS, I would absolutely recommend pre-visit pharmaceuticals:
* Trazodone: 5-7 mg/kg PO 2 hours prior to the appointment.
* Gabapentin: 10-20 mg/kg PO 2-3 hours prior to the appointment.
* I often send both home, instructing the owner to administer them together. This combination provides excellent anxiolysis, allowing for a much calmer and more accurate study. Ensure the echo suite is quiet, has non-slip mats, and allow the dog to relax into position with positive reinforcement (high-value treats, lick mats) rather than force.

Clinical Pearl: While a murmur is concerning in a CKCS, remember that not all murmurs are created equal. The echo is our guide to understanding the severity and progression, and ensuring we intervene with the right medication at the right time. Rushing to treat without a definitive diagnosis can be as detrimental as waiting too long.