ACVIM staging of canine congestive heart failure

Doses on this pageEvery dose below is quoted from the cited source. Verify against the current label/formulary and the patient's full clinical picture.

What the staging covers and who is affected

The panel describes MMVD as a progressive change in the mitral valve leaflets and chordae. Over time the valve can no longer close, so blood leaks back into the left atrium [1].

The consensus reports the following about who is affected [1]:

• The tricuspid valve is also involved in at least 30% of cases.
• The disease is about 1.5 times more common in males.
• It is more prevalent in dogs under 20 kg.
• In small breeds, up to 85% show the valve lesion by 13 years of age. Having the lesion does not necessarily mean a dog will develop heart failure.
• Larger dogs are affected less often but tend to progress faster and carry a more guarded prognosis.

The panel lists several factors as at least moderately predictive of progression [1]:

• age
• progressive left atrial and ventricular enlargement
• higher transmitral E wave velocity
• higher NT-proBNP (a biomarker released from stretched heart muscle cells, per Merck [2])
• higher resting heart rate

It also notes that development of truly predictive risk schemes "awaits further refinement" [1].

The consensus grades each recommendation by class (I is strongest, IV means likely harmful) and by level of evidence, from strong down to expert opinion [1]. Many recommendations below rest on expert opinion. All ten panelists declared consulting relationships with pharmaceutical or diagnostics companies [1].

Stages A and B1

The consensus defines Stage A as "dogs at high risk for developing heart disease but that currently have no identifiable structural disorder of the heart." It gives any Cavalier King Charles Spaniel without a murmur as an example [1]. For Stage A the panel recommends [1]:

• yearly auscultation for small and predisposed breeds
• no drug or dietary treatment
• that breeding animals found to have a murmur or echocardiographic mitral regurgitation before 6 to 8 years of age should no longer be bred

Stage B dogs have structural disease but have never shown signs of heart failure [1]. For all Stage B dogs the panel recommends thoracic radiographs, partly as a baseline for later telling cardiac from airway causes of cough. It also recommends blood pressure measurement and echocardiography by an experienced operator [1].

Stage B1 covers dogs with normal heart size and dogs whose enlargement falls short of the B2 criteria [1]. The panel recommends no drug or diet treatment at this stage. Its reasoning is that heart failure is unlikely within the recheck interval and that no medication has shown benefit at this point. It suggests repeat imaging in 6 to 12 months [1].

Stage B2

Stage B2 dogs have no clinical signs but have enough left atrial and ventricular enlargement to meet the clinical trial criteria for starting treatment [1]. The panel's criteria, rated Class I with strong evidence, are [1]:

The panel says all four should ideally be met "because treatment represents a lifelong commitment." It considers echocardiographic measurement the most reliable way to identify these dogs [1].

Where echocardiography is unavailable, the consensus accepts either of the following as substitutes [1]:

• clear radiographic cardiomegaly, such as a general breed vertebral heart score of 11.5 or more
• accelerating enlargement over time

It also says a vertebral left atrial size of 3 or more likely identifies B2 [1].

The panel recommends pimobendan, an inodilator that strengthens contraction and dilates vessels, "at a dosage of 0.25-0.3 mg/kg PO q12h" [1][2]. The Merck drug table lists a different figure for delaying heart failure in stage 2 MMVD, 0.5 mg/kg PO q 12 h, so the two sources do not match [3]. The panel also recommends mild sodium restriction with a palatable diet that maintains body condition (Class IIa, weak evidence) [1].

On ACE inhibitors at this stage the panel split: 5 of 10 panelists recommended them, and trial results were described as mixed [1]. The Merck Veterinary Manual cites a 2022 systematic review and meta-analysis that concluded ACE inhibitors gave little to no benefit in delaying heart failure in dogs with mitral regurgitation [2]. The panel does not recommend routine beta blockers or spironolactone in B2 [1].

Stage C

The consensus places in Stage C "dogs with either current or past clinical signs of heart failure caused by MMVD." A dog stays in Stage C even after its signs resolve [1]. The panel notes one exception: successful surgical valve repair justifies reclassification to Stage B [1].

For hospital treatment, the panel recommends furosemide "2 mg/kg administered IV (or intramuscularly [IM])." The dose is repeated hourly until breathing improves or a total of 8 mg/kg has been given over 4 hours [1]. The panel also lists [1]:

• pimobendan
• oxygen
• drainage of significant effusions
• sedation for distress
• free water once diuresis begins

It reserves dobutamine, nitroprusside and other arterial dilators for dogs that respond poorly [1].

For home care, the Class I recommendations are [1]:

• oral furosemide (or torsemide in selected dogs)
• an ACE inhibitor such as enalapril or benazepril
• spironolactone
• continued pimobendan

The panel's monitoring advice is [1]:

• check creatinine, urea nitrogen and electrolytes 3 to 14 days after starting furosemide
• check creatinine and electrolytes 3 to 14 days after starting an ACE inhibitor
• treat a creatinine rise of 30% or more from baseline as a concern for acute kidney injury

The panel advises against starting a beta blocker while active congestive signs are present (Class IV) [1].

Later evidence on spironolactone includes the BESST trial, published in 2021. A 2022 narrative review in Animals describes BESST as a multicenter double-blind study. It found that benazepril plus spironolactone outperformed benazepril alone when given with furosemide [4]. That review covered 384 studies from 1970 to 2020, and its authors acknowledge that narrative reviews can carry bias from subjective study selection [4]. The same review reports that in one study, adding ramipril to pimobendan and furosemide did not improve survival [4].

On diet, the panel [1]:

• describes cardiac cachexia as easier to prevent than to treat
• recommends maintenance calorie intake of approximately 60 kcal/kg body weight
• advises against low-protein renal diets unless severe kidney failure is present
• recommends modest sodium restriction

Stage D

The consensus defines this stage in its own words: "Patients have clinical signs of failure refractory to standard treatment for Stage C heart failure from MMVD" [1]. Options the panel describes include [1]:

• torsemide in place of furosemide
• more aggressive afterload reduction with hydralazine or amlodipine, under close blood pressure monitoring
• an off-label third daily pimobendan dose
• sildenafil when pulmonary hypertension is present
• hydrochlorothiazide as an adjunct, with warnings about kidney injury and electrolyte shifts

The panel acknowledges that few clinical trials address this group, which made consensus difficult [1]. It describes surgical valve repair at Stage D as possible but tied to higher perioperative mortality [1].

Diagnostic pitfalls the sources flag

Both the consensus and the Merck Veterinary Manual stress that a murmur plus a cough does not establish heart failure. Chronic airway disease is common in the same small older dogs [1][2]. The Merck authors also note that [2]:

• murmur loudness tracks poorly with severity, except when the murmur is soft
• echocardiography cannot detect pulmonary edema
• loud crackles in a coughing small dog without dyspnea point toward chronic bronchitis
• furosemide is a bronchodilator, so a cough that improves on it does not prove cardiogenic edema

The panel writes that a normal or near normal NT-proBNP in a dog with cough, dyspnea or exercise intolerance "strongly suggests that heart failure is not the cause of the clinical signs" [1]. Merck describes a normal sleeping respiratory rate in dogs as under 30 breaths per minute. It suggests owners count it at home when exam room rates are unreliable [2].

Monitoring and client communication

The panel encourages a structured home program covering body weight, appetite, respiratory and heart rate monitoring, and help with medication adherence [1]. Merck suggests that owners of dogs approaching heart failure count sleeping respiratory rate daily to weekly and bring a log to rechecks [2]. The panel describes starting treatment at Stage B2 as a lifelong commitment [1]. The sources reviewed here do not give survival times by stage.

Before using any dose aboveVerify against the current label/formulary and the patient's full clinical picture.