Species ECG Comparison
A side-by-side comparison of ECG parameters, normal values, and clinical interpretation principles across canine and feline species. Understanding species-specific differences is essential for accurate veterinary ECG interpretation and avoidance of diagnostic errors from cross-applying inappropriate reference values.
Also known as: Dog vs Cat ECG, Canine vs Feline ECG, Veterinary Species ECG Differences, Comparative ECG
| Topic Type | Comparison |
| Species | canine, feline |
Key Differences from Human ECG
- Canine normal HR: 60–180 bpm (size-dependent); Feline normal HR: 140–240 bpm
- Canine normal axis: +40° to +100°; Feline normal axis: approximately +0° to +160°
- Respiratory sinus arrhythmia: normal and expected in dogs, not expected in cats
- ECG complex amplitude: larger in dogs (R wave up to 2.5–3.0 mV in large breeds); smaller in cats (R wave ≤0.9 mV)
- Most common cardiac disease: dilated cardiomyopathy and mitral valve disease in dogs; hypertrophic cardiomyopathy in cats
- ECG sensitivity for cardiac disease: moderate-good in dogs; low in cats (HCM frequently has normal ECG)
- AFib prevalence: common and clinically dominant arrhythmia in large breed dogs; less common in cats, typically seen only in advanced HCM
- PR interval: dogs 0.06–0.13 seconds; cats 0.05–0.09 seconds
- QRS duration: dogs <0.06–0.08 seconds (size-dependent); cats <0.04 seconds
Clinical Pearls
- Never apply canine normal values to a feline ECG or vice versa — a heart rate of 180 bpm is high-normal in a cat but sinus tachycardia requiring investigation in a large breed dog
- The absence of respiratory sinus arrhythmia in a cat is normal; the presence of RSA in a cat should prompt consideration of increased vagal tone or unusual physiology
- ECG is a more useful screening tool in dogs than in cats — a normal feline ECG does not exclude significant cardiac disease, while a normal canine ECG is relatively reassuring
- Body position for recording is the same convention for both species in North American practice: right lateral recumbency
- Both species tolerate lead II as the primary rhythm monitoring lead; 12-lead recordings are uncommon in cats due to small complex amplitudes making interpretation more difficult
- P wave duration norms: dogs ≤0.05 seconds; cats ≤0.04 seconds — P mitrale (broad notched P waves) in cats always indicates atrial pathology, unlike in dogs where it can be a normal variant
Frequently Asked Questions
What are the key ECG differences between dogs and cats?
The most important ECG differences between dogs and cats are: (1) Heart rate — cats are physiologically faster (140–240 bpm) than dogs (60–180 bpm, size dependent). (2) Complex amplitude — feline complexes are much smaller due to smaller heart size and thoracic conformation. (3) Electrical axis — cats have a more rightward axis (+0° to +160°) than dogs (+40° to +100°). (4) Respiratory sinus arrhythmia — normal in dogs, not expected in cats. (5) P wave visibility — often difficult to resolve in cats at high rates. (6) QRS duration — shorter in cats (<0.04 s) than in large dogs (<0.08 s). (7) Disease patterns — HCM dominates feline disease; DCM and MVD dominate canine disease.
Why is ECG less useful for detecting cardiac disease in cats than in dogs?
The dominant feline cardiac disease — hypertrophic cardiomyopathy — frequently produces no ECG abnormalities even in severe cases. The thickened but non-dilated left ventricle of HCM does not reliably generate the amplitude or axis changes that would be visible on ECG. Additionally, feline complexes are inherently small, making subtle changes harder to detect. In dogs, dilated cardiomyopathy (the most common myocardial disease) and chronic mitral valve disease (the most common overall cardiac disease) more frequently produce arrhythmias and measurable ECG changes. For cats, echocardiography is the essential diagnostic tool for cardiac assessment; ECG plays a secondary role focused on arrhythmia detection.
Do dogs and cats use the same recording position for ECG?
Yes. Both dogs and cats are recorded in right lateral recumbency in standard veterinary practice. Limb electrodes are placed at the elbows and stifles (or flanks) in both species. This standardized position forms the basis for all published normal values for both species. Cats may be more difficult to maintain in lateral recumbency due to anxiety or respiratory distress; in critically ill dyspneic cats, a brief rhythm strip in sternal recumbency may be necessary with the understanding that axis and amplitude measurements will be unreliable.
How do PR and QRS interval normals compare between dogs and cats?
Dogs have a PR interval of 0.06–0.13 seconds and a QRS duration of less than 0.06 seconds in small breeds and less than 0.08 seconds in large breeds. Cats have a shorter PR interval of 0.05–0.09 seconds and a shorter QRS duration of less than 0.04 seconds. These differences reflect the smaller cardiac dimensions and faster intrinsic conduction velocity in cats. A QRS duration exceeding 0.04 seconds in a cat is considered abnormal and suggests bundle branch block or other intraventricular conduction abnormality, whereas the same duration would be completely normal in a large breed dog.
What is the most common serious arrhythmia in cats versus dogs?
In dogs, atrial fibrillation is the most common serious sustained arrhythmia encountered clinically, particularly in large and giant breed dogs with dilated cardiomyopathy. Ventricular premature contractions and ventricular tachycardia are also clinically important in dogs, especially in Boxers and Dobermans with breed-specific cardiomyopathies. In cats, the most commonly detected significant arrhythmia is ventricular premature contractions associated with HCM. Atrial fibrillation in cats is less common overall but clinically significant when present, typically indicating advanced HCM with severe atrial enlargement. Complete AV block requiring pacemaker implantation is seen in both species.
See It in Action
Explore ECG rhythms interactively with our simulator and 3D heart visualization. Study normal and abnormal rhythms, adjust parameters, and deepen your understanding.
