18 Apr Atrial and Ventricular Septal Defects in Dogs
Atrial Septal Defect (ASD) in Dogs
What is ASD?
Atrial septal defects (ASD) in dogs are abnormal openings in the septum that separates the left and right atria. This allows oxygen-rich blood (from the left atrium) to mix with oxygen-poor blood (in the right atrium), increasing blood volume in the right heart and lungs.
Types of ASD
- Ostium Secundum ASD (Most Common Type): A defect in the middle of the atrial septum (fossa ovalis), often small and well tolerated.
- Ostium Primum ASD: A defect in the lower atrial septum, often associated with other defects like atrioventricular valve abnormalities. More severe than secundum ASDs.
- Sinus Venosus ASD: A defect near the entry of the vena cava, sometimes affecting pulmonary vein connections. Often requires surgical correction.
How ASD Affects the Heart
- Left-to-right shunting – Blood flows abnormally from the left atrium to the right atrium, increasing right-sided heart volume.
- Increased pulmonary circulation – More blood is pushed into the lungs, leading to overloading.
- Right heart dilation – Over time, the right atrium and right ventricle enlarge.
- Pulmonary hypertension risk – Chronic excessive lung blood flow can lead to high blood pressure in the lungs, causing Eisenmenger’s syndrome (reversal of blood flow, resulting in cyanosis).
Breeds Predisposed to ASD
Boxers
Doberman Pinschers
Standard Poodles
Samoyeds
Golden Retrievers
Symptoms of Artial Septal Defects in Dogs
Mild ASD – No symptoms; may go undiagnosed.
Moderate ASD – Mild exercise intolerance or fainting due to inefficient oxygen delivery.
Severe ASD – Signs of right-sided heart failure, including abdominal fluid accumulation (ascites) and difficulty breathing.
Diagnosis of ASD
Auscultation (Listening to the Heart) – Soft murmur or split second heart sound due to abnormal blood flow.
Chest X-rays – May show right heart enlargement and increased pulmonary vascularity.
Echocardiography (Gold Standard) – Confirms the presence of the septal defect and blood flow direction.
Treatment of ASD
Small ASDs – No treatment needed, as they may not impact lifespan.
Large ASDs – Interventional closure or open-heart surgery (rarely performed in dogs).
Medical management – For symptomatic dogs, diuretics, beta-blockers, and pulmonary hypertension medications can help.
Prognosis for ASD
Small ASDs – Normal lifespan.
Moderate/Large ASDs – Risk of right-sided heart failure and pulmonary hypertension over time.
If Eisenmenger’s syndrome develops, the prognosis is poor since reversal of shunting is irreversible.
Ventricular Septal Defect (VSD) for dogs
What is VSD?
Ventricular septal defects (VSD) in dogs are holes in the wall separating the left and right ventricles. Most VSDs occur high in the septum, just below the aortic valve.
How VSD Affects the Heart
- Left-to-right shunting – High-pressure oxygen-rich blood from the left ventricle leaks into the lower-pressure right ventricle, leading to volume overload in the lungs and left heart.
- Lung congestion – Too much blood flow into the lungs can cause pulmonary overcirculation and congestion.
- Left heart enlargement – Over time, the left atrium and left ventricle dilate, increasing the risk of heart failure.
- Pulmonary hypertension risk – If left untreated, high lung pressure can cause shunting reversal (Eisenmenger’s syndrome), leading to cyanosis and oxygen deprivation.
Breeds Predisposed to VSD
English Bulldogs
Springer Spaniels
West Highland White Terriers
Doberman Pinschers
Keeshonds
Symptoms of Ventricular Septal Defects in Dogs
Small VSDs – No symptoms, often detected incidentally.
Moderate VSDs – Exercise intolerance, rapid breathing, or coughing.
Large VSDs – Severe respiratory distress, heart failure, or cyanosis.
Diagnosis of VSD
Auscultation (Listening to the Heart) – Harsh systolic murmur heard on the right side of the chest.
Chest X-rays – Show left heart enlargement and pulmonary congestion.
Echocardiography (Gold Standard) – Confirms VSD size, shunting direction, and pulmonary pressures.
Treatment of VSD
Small VSDs: No treatment required, often well tolerated.
Moderate/Large VSDs:
- Medical therapy (diuretics, ACE inhibitors, pulmonary hypertension meds).
- Interventional closure (rare in veterinary medicine but possible).
- Surgery (patch closure) (high-risk, rarely performed).
Prognosis for VSD
Small VSDs – Excellent prognosis; may even close spontaneously.
Moderate/Large VSDs – Variable prognosis, depends on heart function and pulmonary pressures.
Eisenmenger’s syndrome (right-to-left shunting) – Poor prognosis; palliative care only.
Key Takeaways
- Septal defects allow abnormal communication between heart chambers, leading to inefficient circulation.
- Atrial septal defects (ASDs) affect the atria and may cause right-sided heart overload.
- Ventricular septal defects (VSDs) affect the ventricles and can lead to left-sided heart overload.
- Small defects often cause no problems, but large defects can lead to heart failure and pulmonary hypertension.
- Echocardiography is the gold standard for diagnosis.
- Some defects require treatment, while others remain well tolerated for life.
If you are concerned about your dog’s heart, contact us today to schedule an appointment.
Images used under creative commons license – commercial use (04/18/2025) Image by Yama Zsuzsanna Márkus from Pixabay