The benefits of the ABCD classification system for heart disease

dvm360dvm360 December 2021
Volume 52

The importance of diagnosing pets in the pre-clinical phase of heart disease, plus the advantages of the classification system.

mtrlin /

mtrlin /

Although veterinarians are often skilled at diagnosing pets with clinical heart failure, it is critical they are skilled at diagnosing those with pre-clinical heart disease as well, according to Amara Estrada, DVM, DACVIM(Cardiology), professor of cardiology at the University of Florida. This proactive approach positively impacts patients by enhancing their quality of life and ultimately helping to delay the disease's development.

At the 2021 New York Vet Show in New York, New York, Estrada shared the various benefits of the “ABCD” classification system, plus she outlined each stage.

The benefits of the ABCD classification system

Classifying each stage of heart disease in pets helps with the following:

  • Development of screening programs for at-risk breeds
  • Implementation of an intervention that decreases the diseases’ risk of development or progression
  • Early identification of asymptomatic patients
  • Quicker, more confident identification of symptomatic patients
  • Communication among veterinarians and with clients as you gain an understanding of where in the timeline the patient is

The ABCD classification system

Although the first several stages (A-B2) consist of preclinical heart disease and are when it is key to step in and take initiative, the final 2 stages (C-D) include the clinical phases of heart failure.

Stage A

During this first stage, the pet appears healthy and there is no structural disease, but they are at high risk for developing heart disease because of their breed—some at-risk dog and cat breeds Estrada noted include Doberman pinschers, cavalier King Charles spaniels, and Maine coons.

“Stage A, this is pets that have nothing wrong with them, you don’t find anything on the physical exam, but they’re kind of the poster child for heart disease in the veterinary world,” she explained.

There are genetic tests available for heart disease that allow pets to be tested as early as in puppyhood which Estrada said is a great time to begin. Although this will likely not change the course of the disease, you can confirm if mutations are present and establish with the owner that earlier screenings are advised for their predisposed pet.

Stage B1 and B2

Stage B1 is classified by asymptomatic disease with none to minimal remodeling present yet something abnormal appears on the physical exam, which then should prompt you to stage the disease, according to Estrada.

“The reason I have to stage it is because I’m trying to decide: is [the dog] very, very early in the course of his disease where [it’s] a B1 and [it] doesn’t have any structural remodeling, or is [the dog] at the phase where he’s a B2 and I now have clinical trial evidence that tells me if I start to treat X at this stage B2, I will make an extreme difference in that dog’s long term survival and quality of life,” she emphasized.

Meanwhile in the B2 stage, the disease is asymptomatic as well, however it is established that significant remodeling is apparent, so the pet is ready for therapy.

“B2s, these are the dogs or cats, where you heard something on your physical exam, you now looked at some kind of imaging modality and found that there is structural remodeling, so you are going to classify that patient and he is ready for therapy,” Estrada said.

Stage C

Stage C is when the clinical signs of heart disease the pet has been screening for begin to appear, therefore specific therapy and follow up are now required.

Some shared clinical signs of heart disease in dogs and cats include1,2,3:

  • Weakness/collapse
  • Lethargy
  • Increased respiratory rate and effort
  • Coughing
  • Abdominal swelling

Stage D

According to Estrada, the main priority of this last stage is to best retain the pet’s quality of life and discuss end-of-life care considerations with the pet parent. Symptom-specific therapy and follow up are required as well.

“Stage D is where I kind of shift my brain and I’m no longer just thinking about heart failure, I’m thinking about quality of life…those are those pets that are refractory to standard treatment, they’re requiring frequent visits to the hospital…but my brain starts to switch to quality of life and hospice care,” she explained.


  1. Diagnosis of cardiovascular disease in dogs. Merck manual veterinary manual. Accessed Novmeber 4, 2021.
  2. Llera R, Ward E. Heart disease in cats. Veterinary Centers of America, Inc. Accessed November 4, 2021.
  3. Ruotsalo K, Tant MS. Testing for abdominal enlargement in cats. Veterinary Centers of America, Inc. Accessed November 4, 2021.
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