Boxer arrhythmogenic cardiomyopathy: Holter and diagnosis
7-year-old Boxer with episodes of syncope during exercise. Echocardiography is normal. 24-hour Holter:
| Parameter | Result | Reference |
|---|---|---|
| Ventricular premature complexes | 5,200 / 24 h | < 100 |
| Ectopic QRS morphology | Positive in II, III and aVF | — |
| Complexity | Couplets and runs of ventricular tachycardia | — |
What is the most likely diagnosis?
chevron_right Show answer and explanation
A. Arrhythmogenic right ventricular cardiomyopathy (ARVC)
Correct. Ventricular premature complexes with positive QRS in the inferior leads (left bundle branch block morphology) indicate a right ventricular origin. With syncope and runs of ventricular tachycardia, antiarrhythmic treatment (sotalol or mexiletine) is indicated.
B. Sick sinus syndrome
It causes bradyarrhythmias and long sinus pauses, mainly in Miniature Schnauzers and West Highland Terriers, and often needs a pacemaker. It does not explain thousands of ventricular premature complexes.
C. Vasovagal syncope without heart disease
Vasovagal syncope can occur in Boxers, but it does not explain the heavy ventricular arrhythmia burden on the Holter.
D. Hypertrophic cardiomyopathy
It is very rare in dogs and would show on echocardiography as wall thickening. Here echocardiography is normal.
lightbulb Key takeaway
In ARVC echocardiography is usually normal: Holter is the key test. More than 300 ventricular premature complexes in 24 h in an adult Boxer is considered abnormal. There is a genetic basis (striatin mutation), so screening breeding dogs is advisable.
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Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.