Canine Heart Disease Stages and the Role of Radiographs in Long-Term Management

Canine Heart Disease Stages and the Role of Radiographs in Long-Term Management

Thoracic radiographs are not a replacement for echocardiography, but they are often the first imaging modality available in GP practice. They allow evaluation of cardiac silhouette size, chamber enlargement patterns, pulmonary vessels, lung parenchyma, pleural space, airways, mediastinum, and thoracic skeletal structures.

For dogs with a newly detected murmur, baseline radiographs can help determine whether radiographic cardiomegaly is present and whether the lungs are clear. The ACVIM consensus recommends thoracic radiography in Stage B patients to assess the hemodynamic relevance of valve disease and obtain baseline thoracic radiographs while the dog is asymptomatic. It also notes that baseline radiographs can help differentiate cardiac from non-cardiac causes of cough later, especially because dogs with MMVD often have concurrent tracheal or bronchial disease.

Differentiating Cardiomegaly From Respiratory Disease

One of the most common GP dilemmas is the older small-breed dog with both a murmur and a cough. The presence of a murmur does not prove that cough is caused by congestive heart failure. Thoracic radiographs help separate cardiac enlargement and pulmonary edema from airway disease, bronchial pattern, tracheal collapse, lower airway inflammation, pulmonary masses, pneumonia, or mixed disease.

This distinction matters because management pathways diverge. A dog with bronchomalacia and stable Stage B1 MMVD should not automatically receive aggressive diuresis. Conversely, a dog with pulmonary venous congestion and an alveolar pattern compatible with cardiogenic edema should not be managed as simple bronchitis.

Detecting Progression From Stage B1 to Stage B2

Radiographs are useful for detecting progression of cardiac size over time. A single VHS slightly above a generic reference interval may be difficult to interpret in a breed with a higher normal VHS. However, a consistent increase in VHS or VLAS over serial studies, especially in a dog with a worsening murmur and supportive echocardiographic findings, is more clinically meaningful.

Radiographic cardiomegaly can support Stage B2 classification when considered with the rest of the case. In many practices, thoracic radiographs serve as the trigger for referral echocardiography or for deeper discussion of pimobendan Stage B2 dog criteria.

Monitoring Pulmonary Edema and Treatment Response

In Stage C dogs, thoracic radiographs help confirm or support the diagnosis of pulmonary edema and provide a baseline for response to therapy. If the dog improves clinically after diuresis, repeat radiographs are not always necessary. They can be helpful when respiratory signs persist, when the initial diagnosis was uncertain, or when the patient worsens despite treatment.

For recurrent canine CHF stages, comparison with prior images helps determine whether the current episode is similar, more severe, or complicated by another thoracic disease. Serial imaging is also useful when clients report increased home respiratory rates but the dog appears stable in the exam room.

What Pulmonary Edema Can Look Like on a Dog X-Ray

A pulmonary edema dog x-ray may show cardiomegaly, left atrial enlargement, pulmonary venous congestion, and an interstitial-to-alveolar pulmonary pattern. In many dogs with left-sided CHF, the distribution is commonly perihilar to caudodorsal, though patient positioning, disease severity, concurrent disease, and radiographic technique can influence appearance.

The clinical question should not be “Is there one radiographic sign of CHF?” It should be: Do the cardiac, pulmonary vascular, and lung pattern findings fit the patient’s clinical presentation?

VHS and VLAS in Dogs: Why These Measurements Matter

What Is VHS in Dogs?

Vertebral heart score, or VHS, is a radiographic method for estimating cardiac size on lateral thoracic radiographs. The long and short axes of the cardiac silhouette are measured, then transposed onto the thoracic vertebrae beginning at T4. The sum is expressed in vertebral units. Buchanan’s vertebral scale method describes this approach, and the original canine reference population had a VHS of 9.7 ± 0.5 vertebrae.

A commonly cited general upper reference is approximately 10.5 vertebrae, but this should not be treated as universal. Breed conformation, thoracic shape, vertebral anomalies, positioning, respiratory phase, and measurement technique can all influence VHS. The ACVIM consensus specifically cautions that breed differences and thoracic conformation matter when using radiographic measurements to refine Stage B.

Why VHS Matters

VHS matters because cardiac enlargement is a key marker of disease progression in MMVD and other cardiac diseases. In the ACVIM framework, the B1 to B2 distinction depends on whether structural disease has produced clinically meaningful remodeling. Radiographic cardiomegaly is therefore not only a descriptive finding; it can influence staging, monitoring frequency, referral recommendations, and treatment consideration.

VHS should not be interpreted in isolation. It is strongest when trended over time, interpreted with breed context, and combined with murmur grade, respiratory signs, echocardiographic findings when available, and the patient’s full clinical picture.

What Is VLAS in Dogs?

Vertebral left atrial size, or VLAS, is a radiographic estimate of left atrial size. It is measured on a lateral thoracic radiograph and indexed to vertebral length, similar in concept to VHS. VLAS is clinically useful in MMVD because left atrial enlargement is a central marker of chronic mitral regurgitation and volume overload.

A 2025 literature review summarizes VLAS as a method described in 2018, measured from the ventral aspect of the carina to the caudal aspect of the left atrium where it intersects the dorsal border of the caudal vena cava, then transposed to the vertebral column. The same review reports proposed healthy-dog values around 2.1 vertebrae, with an interquartile range of 1.8 to 2.3 vertebrae in the initial study population.

The ACVIM consensus notes that VLAS provides a quantitative method of estimating left atrial size and that, when echocardiography is unavailable, VLAS values of 3 or higher likely identify Stage B2 MMVD.

How Serial VHS and VLAS Guide Decisions

For long-term monitoring, serial VHS and VLAS are often more informative than a single measurement. A Cavalier King Charles Spaniel with a VHS of 10.8 may not mean the same thing as a mixed-breed dog whose VHS increased from 9.8 to 10.8 over 12 months, especially if the murmur is louder and left atrial prominence is more apparent.

In practice, serial VHS and VLAS help GP teams:

• Document objective progression
• Support B1 versus B2 classification
• Identify patients that warrant echocardiography or cardiology consultation
• Monitor response after CHF therapy
• Communicate progression clearly to clients and the care team
• Reduce subjective disagreement between clinicians reviewing the same case

For suspected Stage B2 MMVD, radiographic cardiomegaly can support treatment decisions, but the strongest classification usually combines thoracic radiographs with echocardiography. The ACVIM and EPIC criteria emphasize cardiac enlargement, including radiographic and echocardiographic evidence, when identifying dogs likely to benefit from pimobendan before CHF develops.

Long-Term Monitoring Workflow by Stage

Stage A Monitoring Workflow

For Stage A dogs, monitoring is primarily preventive and observational. Annual wellness exams with careful auscultation are appropriate for many at-risk patients. In predisposed breeds, clinicians may consider baseline diagnostics if a murmur develops, anesthesia is planned, or respiratory signs appear.

Radiographs are not mandatory in every at-risk dog, but they become useful when the clinical picture changes. A coughing dog with no murmur still deserves a respiratory workup; a predisposed breed with a new murmur deserves staging.

Stage B1 Monitoring Workflow

For Stage B1 dogs, establish a baseline when possible. This may include physical exam, murmur grade, body weight, home resting or sleeping respiratory rate history, blood pressure when indicated, thoracic radiographs if clinically justified, and echocardiography when available.

The ACVIM consensus suggests reevaluation by echocardiography, or radiography if echocardiography is unavailable, in 6 to 12 months depending on imaging results.

Radiographs may be repeated sooner if the murmur increases, respiratory signs develop, resting respiratory rate trends upward, or the clinician needs objective comparison before anesthesia or medication changes. The goal is not to over-image every asymptomatic dog. The goal is to avoid missing the transition from mild structural disease to clinically important remodeling.

Stage B2 Monitoring Workflow

Stage B2 dogs warrant closer monitoring because they have asymptomatic disease with cardiac enlargement. Many clinicians reassess these patients every 6 to 12 months, with shorter intervals when progression is suspected, medication is initiated, or comorbidities complicate interpretation.

Monitoring typically includes history, resting respiratory rate trends, physical exam, renal values and electrolytes when medications require it, blood pressure when relevant, thoracic radiographs for serial comparison, and echocardiography when available. For dogs started on pimobendan after meeting Stage B2 criteria, follow-up should confirm clinical stability and ensure that new respiratory signs are not developing.

Radiographs in B2 are especially helpful if the dog later presents in crisis. Having pre-CHF images allows the clinician to determine whether pulmonary findings are new and whether the cardiac silhouette has changed significantly.

Stage C Monitoring Workflow

Stage C monitoring is more individualized. During acute CHF, thoracic radiographs are often used to support diagnosis, assess severity, and guide initial treatment. Once stabilized, follow-up depends on clinical response, respiratory rate, renal values, electrolyte status, appetite, hydration, medication tolerance, and owner observations.

Repeat radiographs are indicated when signs recur, response is incomplete, diagnostic uncertainty remains, or a new respiratory problem is suspected. In stable dogs, imaging frequency should be based on clinical need rather than routine repetition alone.

Home sleeping respiratory rate is particularly useful in Stage C. A rising trend may precede overt distress and can help determine when reassessment is needed.

Stage D Monitoring Workflow

Stage D patients require highly individualized monitoring. These dogs may have narrow therapeutic margins, especially when higher diuretic doses are required. Thoracic radiographs should be obtained when the result is likely to change management and when the patient can tolerate imaging safely.

In these cases, radiographs help answer a high-stakes question: Is this truly recurrent pulmonary edema, or is another process driving the respiratory signs? That distinction can affect diuretic escalation, oxygen support, antimicrobial consideration, bronchodilator or anti-inflammatory decisions, referral, and end-of-life planning.

How AI-Assisted Radiograph Interpretation Supports GP Teams

AI-assisted radiograph interpretation is increasingly entering veterinary practice, including tools designed to estimate VHS, VLAS, cardiothoracic ratio, or broader thoracic findings. Used responsibly, these systems may support GP teams by improving consistency, reducing some measurement variability, flagging meaningful changes between studies, and giving clinicians an additional review layer during busy workflows.

This is particularly relevant for VHS and VLAS because small differences in measurement technique can affect interpretation. Recent research has evaluated deep learning approaches for automated VHS and cardiothoracic ratio estimation from canine and feline thoracic radiographs, with one 2025 study reporting strong agreement between automated and manual evaluations. The same study also notes that integration into clinical practice remains limited by issues such as interpretability and workflow alignment.

The responsible framing is important. AI should be treated as decision support, not as a replacement for clinical judgment, radiologist review, or full patient assessment. Veterinary imaging research has emphasized that radiograph interpretation can be challenging and error-prone, and that computer-aided diagnostic tools may support clinicians, but results should be confirmed with appropriate clinical review before decisions are made.

In a GP setting, AI-assisted interpretation may be most useful when it helps the team ask better questions:

• Has VHS increased compared with the prior study?
• Is VLAS above the clinic’s threshold for concern?
• Are there findings compatible with pulmonary edema?
• Does this case need echocardiography, cardiology referral, or radiologist review?
• Is there a discrepancy between the AI output and the clinician’s interpretation?

The clinician remains responsible for integrating imaging with respiratory effort, auscultation, pulse quality, perfusion, renal values, blood pressure, medications, prior history, and the patient’s condition in the exam room. AI can provide a second set of eyes, but it cannot determine the full clinical context of a dyspneic dog on its own.

REFERENCES:
Bruce W. Keene, Clarke E. Atkins, John D. Bonagura, Philip R. Fox, Jens Häggström, Virginia Luis Fuentes, Mark A. Oyama, John E. Rush, Rebecca Stepien, Masami Uechi, ACVIM consensus guidelines for the diagnosis and treatment of myxomatous mitral valve disease in dogs, Journal of Veterinary Internal Medicine, Volume 33, Issue 3, May-June 2019, Pages 1127–1140, https://doi.org/10.1111/jvim.15488

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