Moving Beyond the Textbook: Your Guide to Breed-Specific ECG Normals

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Estimated reading time: 3.53 minutes

To the dedicated veterinarians on the front lines of care,

For decades, ECG interpretation has relied on a simplified framework: cat, small dog, large dog. While this was a useful starting point, advancing evidence now allows us to refine our interpretations for greater precision. At CardioBird, we are pioneering the future of ECG analysis with AI models trained on data from over 269 breeds. While our current diagnostic reports remain aligned with the widely accepted veterinary consensus guidelines to ensure consistency and clear communication, our research is actively building the breed-specific benchmarks of tomorrow.

This newsletter will equip you with practical knowledge to refine your interpretations and understand the future of precision ECG diagnosis.

Key Canine Variations: What’s Normal vs. What’s Not

  1. The Sighthound (Greyhound, Whippet, Saluki): This is the most critical example. Normal for them is abnormal for almost anyone else.
    • Normal: Profound sinus bradycardia (40-60 bpm) and marked sinus arrhythmia are signs of a superior athlete. Most strikingly, R-waves in Lead II frequently exceed 3.0 mV. This is a normal consequence of a large, muscular left ventricle and is not a sign of left ventricular enlargement (LVE) in this group.
    • Not Normal: A consistently high resting heart rate can be a more concerning sign than bradycardia. While tall R-waves are normal, the development of a left anterior fascicular block pattern can be an early indicator of underlying cardiomyopathy in some sighthounds.
  2. The Brachycephalic (Bulldog, Pug, Boston Terrier): Their unique anatomy and high vagal tone create a distinct ECG picture.
    • Normal: Pronounced respiratory sinus arrhythmia and a shifting P-wave morphology (wandering atrial pacemaker) are extremely common and benign. A degree of right axis deviation can also be a normal variant due to their heart’s position and potential for underlying pulmonary changes.
    • Not Normal: Sustained tachyarrhythmias are almost always abnormal. Severe right axis deviation, especially when paired with clinical signs like exercise intolerance, should prompt investigation for pulmonary hypertension.
  1. The At-Risk Giant Breed (Newfoundland, Leonberger, Irish Wolfhound): These breeds are predisposed to dilated cardiomyopathy (DCM), and the ECG can provide early clues.
    • Normal: Their large size means larger complexes, but not to the extreme of the sighthound.
    • Not Normal: Take note! Even occasional ventricular premature complexes (VPCs) in a giant breed dog should raise a major red flag for underlying arrhythmogenic DCM and warrant further investigation with echocardiography and Holter monitoring.

 

Feline Breed-Specific Concerns

Cats may have less breed diversity in size and conformation than dogs, yet breed-specific risks like Hypertrophic Cardiomyopathy (HCM) demand a different interpretive approach. In predisposed breeds, ECG findings that might be dismissed in others warrant serious investigation.

  • The High-Risk Breeds (Maine Coon, Ragdoll, Sphynx, Bengal): These breeds have a well-documented genetic predisposition to HCM.
    • Normal: Standard feline parameters apply.
    • Not Normal: Left Axis Deviation (mean electrical axis < 0°) is one of the most consistent ECG indicators of left ventricular hypertrophy in cats. Tall R-waves (>0.9 mV in Lead II) or any evidence of arrhythmias (APCs, VPCs) in these breeds should never be dismissed as “normal variant” and justify an echocardiogram.

Your Practical Guide to Adjusting Interpretation

  1. Think Breed First: Before you look at the ECG trace, ask: “What is normal for this specific patient’s breed?”
  2. Correlate Clinically: An ECG finding could be a “normal variant” if the patient is otherwise healthy. The same finding in a dog with syncope or a cat with a murmur is a pathological clue.
  3. Use Your Tools: The CardioBird AI analysis is built on a deep understanding of these complexities. While our reports use consensus guidelines for the final diagnosis, they are informed by one of the most comprehensive breed-aware dataset in the world.
  4. Escalate Appropriately: The ECG is a superb screening tool. When it suggests enlargement or arrhythmia—especially in an at-risk breed—your next step is clear: echocardiography for function and structure, and Holter monitoring for arrhythmia burden.

 

Conclusion: Embrace a Smarter Normal

By moving beyond the generic textbook approach, you elevate your diagnostic accuracy. You avoid misdiagnosing a healthy Greyhound with LVE and become adept at catching the first subtle signs of disease in a predisposed breed.

 

Our commitment at CardioBird is to provide you with the most sophisticated tools available today, while we build the even more precise, breed-specific standards of tomorrow. Always remember to pair your CardioBird report with your invaluable clinical judgment.

— The CardioBird Team