1. The Challenge of Cardiac Assessment
Heart disease remains one of the most common and consequential conditions encountered in small animal practice. In dogs, particularly, degenerative valvular disease and cardiomyopathies represent a significant clinical burden. Epidemiological studies suggest that up to 35% of senior dogs show evidence of clinically relevant heart disease, with myxomatous mitral valve disease (MMVD) accounting for the majority of cases. Early identification and accurate staging are critical, yet cardiac assessment has historically been fraught with challenges.
Traditional diagnostic approaches—auscultation, thoracic radiography, and echocardiography—each play an important role, but none are without limitations. Auscultation is subjective and heavily dependent on clinician experience. Echocardiography, while considered the gold standard, is not universally available due to cost, equipment, and training constraints. Thoracic radiographs, therefore, have long served as a cornerstone of cardiac evaluation in general practice.
However, radiographic interpretation of cardiac size has traditionally been subjective. Descriptions such as “mild,” “moderate,” or “severe” cardiomegaly vary widely between observers, even among experienced clinicians. Factors such as patient positioning, breed conformation, respiratory phase, and image quality further complicate interpretation. This variability can lead to inconsistent diagnoses, delayed intervention, or unnecessary treatment.
The need for standardized, repeatable, and objective measurements became increasingly apparent as veterinary cardiology evolved toward evidence-based medicine. Clinicians required tools that could reduce observer bias, improve longitudinal monitoring, and support clearer clinical decision-making. This need laid the groundwork for the development of vertebral-based measurement systems—approaches that would fundamentally change how cardiac size is assessed on thoracic radiographs and usher in a new era of precision in veterinary cardiology.
2. The Birth of VHS: A Brief History
The Vertebral Heart Score (VHS) represents one of the most influential advancements in veterinary diagnostic imaging. Developed in the late 1990s at the University of Pennsylvania, VHS was introduced by Dr. James Buchanan and Dr. Anne Bücheler as a solution to the long-standing problem of subjective cardiac size assessment on radiographs.
Their landmark 1995 publication described a novel method: measuring the long and short axes of the cardiac silhouette on a right lateral thoracic radiograph and comparing those measurements to the length of thoracic vertebrae starting at T4. By expressing heart size in vertebral units, clinicians could normalize measurements across dogs of different sizes and breeds.
The brilliance of this approach lay in its simplicity and anatomical logic. Vertebrae are consistent, easily identifiable structures that scale proportionally with body size. Unlike external measurements or absolute dimensions, vertebral references provided an internal standard that minimized variability related to patient size, magnification, and positioning.
Initial validation studies demonstrated strong correlations between VHS values and clinical assessments of cardiomegaly. A normal VHS of approximately 9.7 ± 0.5 vertebrae was established for most breeds, with recognition that certain breeds (such as Dachshunds or Bulldogs) required breed-specific considerations.
The veterinary community rapidly embraced VHS. It became widely taught in veterinary curricula, incorporated into radiology reports, and adopted as a routine component of thoracic radiograph interpretation. Over time, VHS transitioned from a novel concept to a global standard, forming the foundation upon which further radiographic cardiac measurements would be built.
For a deeper dive, see our dedicated guide on Vertebral Heart Score (VHS).
3. VLAS: The Essential Companion Measurement
While VHS significantly improved the objectivity of cardiac size assessment, clinical experience soon revealed an important limitation: VHS alone does not fully capture all clinically relevant cardiac changes. In particular, diseases characterized by early or predominant left atrial enlargement—most notably MMVD—may progress significantly before total heart size increases enough to elevate the VHS.
Left atrial enlargement is not merely an anatomical change; it is a key prognostic and therapeutic marker. Enlargement of the left atrium reflects chronic volume overload and correlates strongly with disease severity, risk of congestive heart failure, and survival time. Recognizing this, veterinary cardiologists sought a radiographic method to specifically quantify left atrial size.
The result was the Vertebral Left Atrial Size (VLAS) measurement. VLAS focuses on a single linear dimension: the distance from the ventral aspect of the carina to the most caudal border of the left atrium on a lateral thoracic radiograph, again transposed onto vertebral bodies starting at T4. Like VHS, the measurement is expressed in vertebral units, allowing for standardized interpretation.
Validation studies demonstrated that VLAS correlates well with echocardiographic indicators of left atrial enlargement, such as the LA:Ao ratio. Importantly, VLAS has shown strong diagnostic utility in distinguishing preclinical MMVD stages and identifying dogs at higher risk of progression.
Rather than replacing VHS, VLAS complements it. Together, these measurements provide a more nuanced and complete picture of cardiac remodeling—global heart size through VHS and chamber-specific enlargement through VLAS. This dual-measurement approach has become increasingly recognized as best practice in radiographic cardiac assessment. Learn more in our comprehensive overview of Vertebral Left Atrial Size (VLAS).
4. Clinical Impact: The EPIC Study and Beyond
The true clinical value of accurate VHS and VLAS measurements is best illustrated through their role in evidence-based treatment decisions, most notably highlighted by the EPIC (Evaluation of Pimobendan In Cardiomegaly) study.
The EPIC study was a large, multicenter, randomized, placebo-controlled trial that evaluated the effect of pimobendan in dogs with preclinical MMVD and cardiomegaly. A critical inclusion criterion was the presence of radiographic and echocardiographic evidence of cardiac enlargement—specifically defined using VHS thresholds (≥10.5) and left atrial enlargement.
Results from the EPIC study were practice-changing. Dogs treated with pimobendan before the onset of congestive heart failure experienced a significant delay (approximately 15 months) in the development of clinical signs and improved overall survival. These findings established the now-familiar ACVIM Stage B2 category and firmly linked radiographic measurements to therapeutic decision-making.
In this context, accurate and reproducible VHS and VLAS measurements are not academic exercises—they directly influence when life-prolonging therapy begins. Overestimation may lead to unnecessary medication, while underestimation can delay treatment during a critical window where intervention is most beneficial.
Beyond MMVD, these measurements support longitudinal monitoring, allowing clinicians to track disease progression objectively over time. Subtle increases in VHS or VLAS can prompt earlier re-evaluation, echocardiography referral, or client discussions about prognosis and monitoring strategies.
As clinical guidelines continue to emphasize objective criteria, the importance of precise radiographic measurements only grows. VHS and VLAS have become essential tools that bridge the gap between imaging findings and real-world patient outcomes.
5. The Technology Evolution
Despite their proven value, manual VHS and VLAS measurements are not without challenges. Accurate placement of measurement lines requires training and experience, and studies have consistently demonstrated inter- and intra-observer variability. In busy clinical settings, time constraints may further limit consistency.
The evolution from manual measurement to AI-assisted radiographic analysis represents the next major leap forward. Advanced algorithms can now identify anatomical landmarks, place measurement axes, and calculate VHS and VLAS with remarkable speed and consistency. By standardizing technique, these tools dramatically reduce observer-dependent variability.
AI-assisted platforms also improve accessibility. General practitioners who may be less confident in manual measurements can rely on validated automated systems, ensuring that objective data informs every case—regardless of clinician experience level.
RadAnalyzer exemplifies this new generation of technology. By integrating AI-driven measurement tools directly into the radiographic workflow, RadAnalyzer delivers rapid, repeatable VHS and VLAS assessments from routine thoracic images. The result is greater efficiency, enhanced diagnostic confidence, and more consistent patient care across practices.
As technology continues to evolve, the focus is shifting from whether measurements can be performed to how accurately, consistently, and efficiently they can be integrated into everyday clinical decision-making.
6. What This Means for Your Practice
For veterinary practices, the implications are clear. Implementing accurate VHS and VLAS measurements elevates the standard of cardiac care you provide. Objective data supports clearer staging, more confident treatment decisions, and improved monitoring of disease progression.
These measurements also enhance client communication. Numerical values and trend graphs help pet owners understand their animal’s condition, the rationale behind treatment recommendations, and the importance of follow-up. Transparency builds trust—and trust improves compliance.
With AI-assisted tools, incorporating these measurements no longer requires additional time or specialized expertise. Instead, they become a seamless part of your diagnostic workflow.
If you’re ready to bring the next era of veterinary cardiac assessment into your practice, now is the time to explore RadAnalyzer. Experience how precision, technology, and evidence-based medicine come together to improve outcomes—for both you and your patients.