What is the current monitoring and treatment protocol for MMVD in Cavalier King Charles Spaniels by ACVIM stage?

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Stage B1 CKCS require no treatment and monitoring every 12 months, with the goal of detecting progression to B2 before clinical signs develop. 3 Stage B2 is defined by cardiac enlargement and warrants pimobendan initiation. The 2019 ACVIM consensus guidelines form the basis of current treatment recommendations, and 67% of surveyed practitioners correctly initiate pimobendan as monotherapy at the B2 stage. 3 The ACVIM guidelines recommend breed-specific radiographic reference values when available — for CKCS, the breed-specific vertebral heart score reference is 10.6 ± 0.5 vertebrae, which is higher than the non-breed-specific reference of 9.7 ± 0.5, making breed-specific thresholds essential to avoid over-staging. 4 Echocardiographic staging in CKCS should incorporate LA/Ao ratio, left atrial anteroposterior diameter normalized to body weight (LADn), and left atrial volumes. CKCS in ACVIM B1 already demonstrate increased LADn and increased left atrial volumes compared to stage A dogs, indicating atrial remodelling begins at the earliest detectable stage of disease. 1 LA enlargement is an adverse prognostic factor, and B1 dogs with LA enlargement have poorer outcomes than B1 dogs without it. 10 Both active and passive left atrial emptying fractions are useful indexes for detecting atrial dysfunction, which becomes particularly evident in symptomatic (stage C) dogs. 1 Pulmonary hypertension (PH) screening is warranted in CKCS with MMVD, as CKCS are more likely to develop PH from MMVD than dogs of other breeds. ACVIM stage, LA/Ao ratio, and mitral E wave velocity are all independently associated with PH development, and PH development is associated with worse MMVD severity by ACVIM stage. 2 Stage C treatment requires a loop diuretic combined with pimobendan as the only evidence-based drug combination. Only 48% of surveyed practitioners prescribed this correct combination for chronic stage C management; 19% of practitioners prescribed two loop diuretics simultaneously,