Subaortic stenosis in dogs: Doppler gradient and severity
7-month-old male Golden Retriever with a grade 4/6 systolic ejection murmur at the left base radiating to the thoracic inlet and weak femoral pulses. Asymptomatic. Echocardiography shows a fibrous subaortic ridge and concentric left ventricular hypertrophy. Continuous-wave Doppler (unsedated):
| Parameter | Result | Reference |
|---|---|---|
| Peak aortic velocity | 5.0 m/s | < 1.7–2.0 |
| Interventricular septum in diastole | Increased | — |
| Aortic regurgitation | Mild | Absent |
How do you classify the stenosis?
chevron_right Show answer and explanation
A. Mild: the gradient is about 25 mmHg and needs no follow-up
This is a common calculation error: you cannot simply multiply velocity by 5. The simplified Bernoulli equation squares the velocity (4 × 5² = 100 mmHg).
B. Moderate: the gradient is between 50 and 80 mmHg
A velocity of 5 m/s corresponds to about 100 mmHg, above the 80 mmHg limit that separates moderate from severe stenosis.
C. Severe: gradient of about 100 mmHg, with risk of sudden death, ventricular arrhythmias and endocarditis
Correct. Gradient = 4 × v² = 4 × 25 = 100 mmHg. Above 80 mmHg subaortic stenosis is considered severe, and these are the dogs in which sudden death, syncope and heart failure concentrate.
D. It cannot be graded: the gradient can only be measured by catheterisation
Continuous-wave Doppler reliably estimates the gradient using the Bernoulli equation and is the practical standard. Catheterisation is now rarely used for this.
lightbulb Key takeaway
Gradient (mmHg) = 4 × velocity² (m/s). As a guide: mild < 40–50 mmHg, moderate 50–80, severe > 80. Measure unsedated if possible: sedation and anaesthesia lower the gradient and underestimate severity. SAS is common in Newfoundlands, Golden Retrievers, Rottweilers, Boxers and German Shepherds.
Test yourself with 10 random questions
Cardiology · 100 questions, a different test every time
Related questions
Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.