Congenital heart disease is not all that common in dogs; in fact, studies estimate that fewer than 1% of dogs are affected by congenital heart disease.1 Although these conditions are uncommon, they can have a significant impact on affected dogs. Therefore, it’s important for you to keep these conditions on your radar when seeing young puppies for new pet exams and wellness visits.
The five most common congenital heart defects in dogs, in order of decreasing frequency, are patent ductus arteriosus, pulmonic stenosis, aortic stenosis, persistent right aortic arch, and ventricular septal defect. You are likely to see at least some of these conditions over the course of your career; having a basic understanding of clinical signs and diagnostic workup can help you diagnose and treat these puppies as quickly as possible.
1. Patent Ductus Arteriosus
The clinical signs of patent ductus arteriosus (PDA) can vary significantly. Some affected dogs are completely asymptomatic, while others may present for coughing, exercise intolerance, or even exercise-induced collapse. On exam, a dog with a left-to-right shunt will often have a continuous left-sided machinery murmur with or without a palpable thrill. A right-to-left shunt typically does not produce a murmur, but you may observe cyanosis (especially differential cyanosis, with pink mucous membranes anteriorly and cyanosis posteriorly). Signs of congestive heart failure (CHF) may also be observed with either type of PDA.
Thoracic radiographic findings vary, depending on the type of shunt. Findings consistent with a left-to-right shunt include cardiomegaly, left atrial and ventricular enlargement, descending aortic dilation, visualization of the main pulmonary artery, and a bulge at the pulmonary trunk. Dogs with a right-to-left shunt may have biventricular or right ventricular enlargement, dilation of the main pulmonary artery, and enlargement or tortuosity of other pulmonary arteries. Echocardiography is used to confirm the diagnosis.
2. Pulmonic Stenosis
Most dogs with pulmonic stenosis (PS) are asymptomatic. In severe cases, dogs may develop exercise intolerance, syncope, congestive heart failure, or even sudden death. On exam, you may note a left-sided systolic murmur over the pulmonic valve. Many describe this murmur as having a crescendo-decrescendo nature, which is suggestive of an ejection murmur. (Regurgitation murmurs are often described as holosystolic.) You might also note prominent jugular pulses or signs of CHF on your exam.
On thoracic radiographs, common findings include right ventricular enlargement and a bulge at the main pulmonary artery. You may also see evidence of pulmonary hypoperfusion and vena cava enlargement. Echocardiography is used to confirm the diagnosis.
3. Subaortic Stenosis
The majority of dogs with subaortic stenosis (SAS) are asymptomatic. In severe cases, lethargy, exercise intolerance, syncope, signs of CHF, and even sudden death may be observed. On exam, affected dogs have a left-sided systolic ejection murmur that is loudest over the aortic valve. This murmur can be loud and may be associated with a palpable thrill.
Radiographic findings vary in dogs with SAS, depending on the severity of the disease. In mild cases, the heart may appear radiographically normal. In some cases, dilation of the aortic arch may be visible. If there is concurrent mitral regurgitation (which often develops in SAS), left ventricular and left atrial enlargement may also be observed. Echocardiography is required to confirm the diagnosis.
4. Persistent Right Aortic Arch
Persistent right aortic arch (PRAA) causes very different clinical signs than other common congenital cardiac diseases. While the other conditions are associated with cardiovascular signs, vascular ring anomalies cause clinical signs by constricting the esophagus. Affected dogs often begin to regurgitate with the introduction of solid food, leading to slow growth in comparison to their littermates. A heart murmur is not typically auscultated on exam, but you may be able to palpate a distended esophagus and/or see signs of aspiration pneumonia (such as fever and abnormal lung sounds).
On thoracic radiographs, you may notice an abnormal curvature or deviation of the trachea. The esophagus may also be visibly distended cranial to the heart and signs of aspiration pneumonia may be apparent. Contrast radiography (using barium), fluoroscopy, and/or computed tomography (CT) can confirm the diagnosis.
5. Ventricular Septal Defect
Clinical signs depend on the size of the ventricular septal defect (VSD). Dogs with small defects may be completely asymptomatic, while dogs with a larger VSD may exhibit signs of CHF. On exam, you’re likely to hear a systolic murmur near the right side of the sternum, with or without a palpable thrill. If there is right-to-left shunting through the defect, cyanosis may be seen.
Thoracic radiographs typically show enlargement of the left atrium and left ventricle, with prominent pulmonary vasculature. Signs of CHF may also be seen. Echocardiography is used to confirm the diagnosis.
Don’t Try to Remember Everything!
When it comes to uncommon congenital cardiac diseases (and all uncommon conditions, for that matter), you don’t need to remember everything. I’ve been in practice for 14 years and I’ve only seen a couple of PDAs and one case of subaortic stenosis… these aren’t everyday conditions!
Once you get past the boards, there’s no reason to stay current on every detail of managing these conditions… unless you go into cardiology! Instead, focus on remembering a) that these conditions exist and b) roughly what they look like. You can always look up the details if you have a case that looks suspicious.
References
- Tou SP. 2018. Congenital and Inherited Disorders of the Cardiovascular System in Dogs. Merck Veterinary Manual. Retrieved from: https://www.merckvetmanual.com/dog-owners/heart-and-blood-vessel-disorders-of-dogs/congenital-and-inherited-disorders-of-the-cardiovascular-system-in-dogs
